Historical analysis of wetlands and their functions for the Nanticoke River Watershed: A comparison between pre-settlement and 1998 conditions

              Historical Analysis of Wetlands and Their Functions
For the Nanticoke River Watershed:
A Comparison between
Pre-settlement and 1998 Conditions
U.S. Fish and Wildlife Service
National Wetlands Inventory
Northeast Region
Hadley, MA 01035
November 2003
Historical Analysis of Wetlands and Their Functions for the Nanticoke River
Watershed: A Comparison between Pre-settlement and 1998 Conditions
by
R.W. Tiner and H.C. Bergquist
U.S. Fish and Wildlife Service
Northeast Region
National Wetlands Inventory Program
300 Westgate Center Drive
Hadley, MA 01035
Prepared for:
Kent Conservation District
3500 S. DuPont Highway
Dover, DE 19901
and
Maryland Eastern Shore Resource Conservation & Development Council
8133 Elliot Road, Suite 201
Easton, MD 21601-7131
November 2003
This report should be cited as:
Tiner, R.W. and H.C. Bergquist. 2003. Historical Analysis of Wetlands and Their Functions for
the Nanticoke River Watershed: A Comparison Between Pre-settlement and 1998 Conditions.
U.S. Fish & Wildlife Service, National Wetlands Inventory (NWI) Program, Northeast Region,
Hadley, MA. NWI technical report. 41 pp. plus appendices and maps.
Table of Contents
Page
Introduction 1
Study Purpose 1
Organization of Report 1
Study Area 2
Methods 3
Pre-settlement Wetland Inventory 3
1998 Wetland Inventory 8
Enhanced Wetland Classification 8
Preliminary Assessment of Wetland Functions 10
Extent of Natural Habitat 11
Function Comparison: Pre-settlement vs. 1998 11
General Scope and Limitations of the Study 12
Pre-settlement Wetland Inventory 12
1998 Wetland Inventory and Digital Database 12
Preliminary Assessment of Wetland Functions 12
Rationale for Preliminary Functional Assessment 14
Appropriate Use of this Report 15
Results 16
Maps 16
Pre-settlement Conditions 17
Wetlands by NWI Types 17
Wetlands by LLWW Types 18
Preliminary Functional Assessment 20
Contemporary Conditions (1998) 21
Wetlands by NWI Types 21
Wetlands by LLWW Types 23
Preliminary Functional Assessment 25
Comparison: Pre-settlement Conditions vs. 1998 Conditions 27
Wetland Extent 27
Wetland Functions 27
Natural Habitat Extent 29
Discussion 30
Conclusions 37
Acknowledgments 38
References 39
Appendices
A. Dichotomous Keys and Mapping Codes for Wetland Landscape Position, Landform, Water Flow
Path, and Waterbody Type Descriptors (Tiner 2003a)
B. Correlating Enhanced NWI Data with Wetland Functions for Watershed Assessments: A
Rationale for Northeastern U.S. Wetlands (Tiner 2003b)
Thematic Maps in separate folder on the CD
1
Introduction
The states of Delaware and Maryland are cooperating to investigate and evaluate wetlands of the
Nanticoke River watershed. They are collecting data on reference wetlands to gain information
on wetland functions and levels of performance for evaluating impacts to presentday wetlands
and to develop a watershed-based strategy for wetland conservation and restoration. The U.S.
Fish and Wildlife Service is assisting the states in several ways. Roughly two years ago, the
states provided funds to the U.S. Fish and Wildlife Service to expand the current National
Wetlands Inventory (NWI) digital data to include hydrogeomorphic-type descriptors (i.e.,
landscape position, landform, and water flow path) to all mapped wetlands and to use these data
to produce a preliminary assessment of wetland functions for the watershed. The results of this
analysis were published in two watershed-based reports on the Nanticoke wetlands, one for
Maryland and the other for Delaware (Tiner et al. 2000, 2001).
Upon receipt of this information, the states became interested in gaining a historical perspective
on wetlands and the impact of estimated losses on wetland functions. In 2002 and 2003, funding
was provided to the Service by the Kent Conservation District and Maryland Eastern Shore
Resource Conservation & Development Council to design and conduct a historical assessment of
wetlands in the Nanticoke River watershed.
Study Purpose
The purpose of the project was to produce a historical perspective of wetlands and their functions
for the Nanticoke River watershed and compare these findings to previous work done for
contemporary wetlands in this watershed. The specific objectives were: 1) to produce a map
showing the general extent of wetlands prior to European colonization, 2) to use this information
to prepare a preliminary functional assessment of pre-settlement wetlands, 3) to create a
consistent database of contemporary wetlands for the entire watershed from existing enhanced
NWI data, 4) to prepare a preliminary functional assessment for the watershed for contemporary
wetlands, and 5) to compare the changes in wetland functions and extent based on the pre-settlement
and contemporary wetland assessments. This information will assist wetland
managers in wetland planning and evaluation at the watershed level. This report describes study
methods and presents the results.
Organization of Report
The report is organized into the following sections: Study Area, Methods, General Scope and
Limitations of the Study, Results, Discussion, Conclusions, Acknowledgments, and References.
Two appendices provide keys to hydrogeomorphic wetland classification and the rationale for
correlating wetland characteristics with wetland functions. Thematic maps are contained in a
separate folder on the CD version of this report with linkages provided.
2
Study Area
The study area is the Nanticoke River watershed which begins in western Delaware and drains in
a southwesterly direction into Maryland and ultimately into Chesapeake Bay (Figure 1). This
watershed is roughly 800-square miles in size and includes about 25 percent of the state of
Delaware. Major tributaries include five in Delaware (Broad Creek, Deep Creek, Gravelly
Branch, Gum Branch, and Marshyhope Creek) and four in Maryland (Marshyhope Creek,
Rewastico Creek, Quantico Creek, and Wetipquin Creek).
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Figure 1. Locus map showing Nanticoke River watershed.
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Methods
Pre-settlement Wetland Inventory
The distribution and extent of pre-settlement wetlands were determined from two sources: 1) soil
survey data from the U.S.D.A. Natural Resource Conservation Service (NRCS) and the
Delaware Department of Natural Resources and Environmental Control (DNREC) and 2) U.S.
Geological Survey topographic maps. The former source was the primary source and most
historic wetlands were identified from this material. The latter source was used to "lost"
estuarine wetlands that are now open water.
Hydric soil map units from soil survey data were identified as historic wetlands. A digital
database of hydric soil map units was created for the Nanticoke watershed from existing digital
soil survey data and from soil map unit data in published soil surveys. Two counties had digital
soils data available: Dorchester (SSURGO data from NRCS based on Brewer et al. 1998) and
Sussex (from DNREC). For other counties (Caroline, Wicomico, and Kent), hydric soil digital
data were created by scanning individual soil survey maps from county soil survey reports
(Matthews 1964; Hall 1970; Matthews and Ireland 1971, respectively). Scanning was done at
300 dots per inch (dpi) and saved as TIFF images. The black color band (all linework) was
selected in each image and copied to form a composite image (mosaic) for the county. Mosaics
were georeferenced in ARCGIS 8.0 using the georeferencing extension, with a 1:24,000 digital
raster graphics (DRG) serving as the base. These mosaics were then converted to georeferenced
GRIDS and then to linear coverages which were converted to polygonal coverages and finally to
shapes. The shapes were edited and hydric soil map units labeled using the georeferencing
image to code ID in the background in ARCGIS 8.3.
Certain soil map units were identified as historic wetlands. These units were represented by
hydric soil series or land types that are equated with wetlands (e.g., Swamp, Tidal Marsh, and
Muck). Table 1 presents a list of the soil map units that were considered wetlands.
The soil-based historic wetland data were compared with existing NWI data to identify possible
large wetland complexes (typically forested wetlands) that were not recorded as historic wetlands
by soils data. When one overlays digital data sets derived from different sources and using
different bases, there are usually many “slivers” that are detected due to problems matching the
two data sets (i.e., alignment problems). By establishing a 12-acre threshold for identifying
significant NWI omissions, the sliver issue was resolved. The remaining NWI wetlands not
included in the hydric soil coverage were added to the historic data base. This process allowed
for a more consistent comparison between wetland data for the two eras.
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Table 1. Hydric soil series that were considered historic wetlands in the general study area.
Note: Some of these soils may occur outside the Nanticoke River watershed.
Soil Series/Land
Type County
Bayboro Caroline, Wicomico, and Kent
Beaches Wicomico and Dorchester
Berryland Sussex
Bestpitch and Transquaking Dorchester
Bibb Caroline
Chicone Dorchester
Coastal Beach/Dune Land* Sussex and Kent
Elkton Caroline, Wicomico, Dorchester, Sussex, and Kent
Fallsington Caroline, Wicomico, Dorchester, Sussex, and Kent
Fill Land Sussex
Fluvaquents Dorchester
Honga peat Dorchester
Hurlock Dorchester
Johnston Caroline, Sussex, and Kent
Leon Wicomico
Made Land Caroline and Wicomico
Mixed Alluvial Land Caroline, Wicomico, and Sussex
Muck Caroline, Wicomico, and Sussex
Nanticoke Dorchester
Osier Sussex
Othello Caroline, Wicomico, Dorchester, and Kent
Othello and Kentuck Dorchester
Plummer Caroline, Wicomico, and Sussex
Pocomoke Caroline, Wicomico, Sussex, and Kent
Pone Dorchester
Portsmouth Caroline, Wicomico
Puckum Dorchester
Rutlege Wicomico and Sussex
St. Johns Wicomico
Swamp Caroline, Wicomico, Sussex, and Kent
Sunken Dorchester
Tidal Marsh Caroline, Wicomico, Sussex, and Kent
*Includes both wetland (beach) and upland (dune).
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We recognized that over the past 500 years estuarine wetlands have migrated landward (upriver)
and permanent inundation of low-lying estuarine marshes has occurred due to rising sea level.
We therefore had to: 1) relocate the pre-settlement estuarine-riverine break further downriver
than its current location and 2) add "lost" estuarine wetlands. For the former, we used the
presence of soils recognized as submerged uplands and the appearance of salt-stressed forests to
help establish this break at the mouth of the Baron Creek. Understandably, this is a conservative
demarcation as it is likely that freshwater forested wetlands also occurred downstream along the
edges of estuarine wetlands. The Honga and Sunken series (submerged “uplands,” now brackish
tidal wetlands) both represent former “uplands” (likely low-lying wet flatwoods similar to those
growing today on Othello and Elkton soils) that became estuarine wetlands with rising sea level
over the past few hundred years. The former soil is an organic soil (Terric Sulfihemists) with
more than 16 inches of organic matter overlying mineral soil (Brewer et al. 1998). In contrast,
the Sunken series is a mucky silt loam soil (Typic Ochraquults) with only 2-8 inches of organic
matter forming a surface layer. This soil is typified by salt-stressed (dying or dead) stands of
loblolly pine (Pinus taeda), while some areas have converted to salt/brackish marshes (Figure 2).
While both series represent former “uplands,” for purposes of this study, we identified only the
Sunken series as a former freshwater forested wetlands that may have existed prior to European
settlement. By the thickness of its organic horizon, the Honga series most likely represents
former “upland” that became estuarine wetland longer than 300 years ago (e.g., wood found in
the organic and mineral horizons was carbon-dated at less than 700 years before present; Brewer
et al. 1998). Our interpretation is therefore conservative; others might consider all Honga soils
to be freshwater wetland prior to settlement. For our study, the approximation used is
satisfactory. Moreover, it is also possible that some areas of Othello and Elkton soils, for
example, were upland soils (Mattapex, Mattapeake, or Keyport) at that time (Jim Brewer, pers.
comm. 2003). Pone soils are drier than Puckham soils and were designated as temporarily
flooded-tidal forested wetlands when they were contiguous with tidal marsh soils. In other
places, they were designated as nontidal temporarily flooded forested wetlands. Muck soils
(referenced in other soil surveys) and contiguous soils that are now classified as estuarine
wetlands were also identified as historic tidal forested wetlands. Elsewhere, muck soil map units
were regarded as nontidal forested wetlands. The Nanticoke series and the tidal marsh map units
from the soil surveys were considered freshwater tidal marsh for the pre-settlement era. The pre-settlement
limits of estuarine and freshwater tidal reaches therefore represent approximate
boundaries (educated guess), mainly used to indicate a significant ecological and hydrological
change in this watershed over time. We also recognized that the upstream limit of tidal influence
was probably downstream from its current location, but lacked information to aid in redefining
this limit.
To identify "lost" estuarine wetlands due to sea level rise over the past few hundred years, we
referred to U.S. Geological Survey 1:24,000 topographic maps (Deal Island 1972, Mardela
Springs 1982, Nanticoke 1983, and Wetipquin 1983) and located shallow water areas less than 6
feet (2 meters) deep (i.e., the shallowest depth recorded as a depth contour on the maps). These
shallow water areas were predicted to be former estuarine wetlands (probably some combination
of tidal marshes and flats) at some time prior to European colonization. Since the 6-foot (or 2m)
depth was shown as a bottom contour line on the topographic maps, it served as a practical mark
for identifying the lower boundary of pre-settlement intertidal wetlands for our study. Again,
this is an approximate, not absolute, boundary.
6
Impounded sections of rivers (i.e., artificial in-stream ponds and lakes) shown on the soil surveys
needed to be classified as some type of pre-settlement wetland. They were predicted to have
been forested wetlands on hydric soils similar to contiguous wetlands above and below the
impoundment. Some minor acreage of open water was probably included in the wetland acreage
following this interpretation.
After pre-settlement wetlands were identified, they were classified according to NWI types
(Cowardin et al. 1979; Table 2). We considered all inland wetlands to be palustrine forested
wetlands1, recognizing that periodic wildfires would have created a succession of types from
emergent wetlands through shrub swamps to forested wetlands, much like we observe today after
timber harvest. The condition of the historic landscape is therefore much simplified. We did not
separate forested wetlands into different types at the subclass level according to Cowardin et al.
(1979) since this was impossible to predict. Water regimes were assigned to pre-settlement
wetlands based on descriptions of seasonal high water tables for individual hydric soils (soil map
unit) from the published soil survey reports.
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Figure 2. Area of Honga soil showing salt-stressed pines along marsh edge. (Brewer et al. 2003)
1According to the 1920s soil surveys, most of the soils were forested in their original state (e.g.,
Wicomico County was “practically” all forested until “reclaimed for agricultural purposes” -
Snyder and Gillett 1925).
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Table 2. Hydric soil map unit acreage for the Nanticoke River watershed and expected NWI
type. Note: The total hydric soil acreage is less than the estimated pre-settlement wetland
acreage because palustrine forested wetlands occurring on nonhydric soil map units were added;
also dammed rivers and impoundments (“water”) were classified as a vegetated wetland type
equivalent to that predicted for adjacent hydric soil map units.
Soil Series/Land Type Acreage % of Total Predicted NWI Type
Bayboro 145.3 <1 PFO_E
Beaches* 157.6 <1 E2EM, PFO_E
Berryland 108.9 <1 PFO_E
Bestpitch 3,100.0 1.4 E2EM
Chicone 313.3 <1 PFO_E, PFO_R
Elkton 6,186.8 2.9 PFO_A
Fallsington 102,356.3 47.7 PFO_A, PFO_S
Fill Land 60.2 <1 PFO_A, PFO_S
Fluvaquents 1,095.8 <1 PFO_E, PFO_R
Honga peat 4,671.1 2.2 E2EM
Hurlock 5,490.0 2.6 PEM_R, PFO_E, PFO_R
Johnston 11,200.8 5.2 PFO_E, PFO_R
Kentuck 761.2 <1 PFO_A
Leon 280.7 <1 PFO_A
Made Land 46.1 <1 E2EM, PEM_R, PFO_E
Mixed Alluvial Land 1,542.1 <1 PEMR, PFO_E, PFO_S, PFO_A
Muck 1,572.1 <1 E2EM, PFO_E, PFO_R
Nanticoke 998.6 <1 PEM_R, PFO_E
Osier 2,984.1 1.4 PFO_A, PFO_S
Othello 10,565.4 4.9 PFO_A
Plummer 3,338.4 1.6 PFO_A, PFO_S
Pocomoke 36,988.3 17.3 PFO_E, PFO_R
Pone 3,464.6 1.6 PFO_E, PFO_S
Portsmouth 682.5 <1 PFO_E
Puckum 4,196.6 2.0 PFO_E, PFO_R
Rutlege 1,747.2 <1 E2EM, PFO_E, PFO_R
St. Johns 65.2 <1 PFO_E
Sunken 675.0 <1 E2EM
Swamp 1,266.5 <1 PFO_E, PFO_R
Tidal Marsh 8,312.2 3.9 E2EM, PEM_R, PEM_F, PFO_E,
PFO_R
------------------------ -------------
Total 214,372.9
*Beaches on the soil survey report were actually vegetated wetlands.
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1998 Wetland Inventory
The foundation of this project was a fairly comprehensive, geospatial wetland database created
by the Service’s NWI Program. Basic NWI data included both geospatial data from standard
NWI maps with wetlands classified according to Cowardin et al. (1979). NWI data for the
Nanticoke watershed were recently updated using spring 1998-1:40,000 black and white
photography (see Tiner et al. 2001, 2000 for details).
Enhanced Wetland Classification
Through our previous work (Tiner et al. 2001, 2000), the NWI database was expanded to include
hydrogeomorphic-type properties for mapped wetlands. Landscape position, landform, water
flow path, and waterbody types (LLWW descriptors) were applied to all wetlands in the NWI
digital database by merging NWI data with on-line U.S. Geological Survey topographic maps
(digital raster graphics) and consulting aerial photography where necessary (see Tiner et al.
2001, 2000). Appendix A of this report contains dichotomous keys for applying these
descriptors. Previous work was reviewed and revised based on these keys.
Landscape position defines the relationship between a wetland and an adjacent waterbody, if
present. Four landscape positions are relevant to the Nanticoke watershed: 1) lotic - along
freshwater rivers and streams and periodically flooded at least during high discharge periods, 2)
lentic - in lakes, reservoirs, and their basins with water levels significantly affected by the
presence of these waterbodies, 3) terrene - isolated or headwater wetlands, fragments of former
isolated or headwater wetlands that are now connected to downslope wetlands via drainage
ditches, and wetlands on broad, flat terrain cut through by stream but where overbank flooding
does not occur, and 4) estuarine - associated with tidal brackish waters (estuaries). Lotic
wetlands are further separated by river and stream sections (based on watercourse width -
polygon = river vs. linear = stream at a scale of 1:24,000) and then divided into one of five
gradients: 1) high (e.g., shallow mountain streams on steep slopes - not present in the study
areas), 2) middle (e.g., streams with moderate slopes - not present in the study areas), 3) low
(e.g., mainstem rivers with considerable floodplain development and slow-moving streams), 4)
intermittent (i.e., periodic flows), and 5) tidal (i.e., under the influence of the tides).
Landform is the physical form of a wetland or the predominant land mass on which it occurs
(e.g., floodplain or interfluve). Six types are recognized in the Nanticoke watershed: basin,
interfluve, flat, floodplain, fringe, and island (see Table 3 for definitions); no slope wetlands
were identified due to the flat terrain of the coastal plain.
Additional modifiers were assigned to indicate water flow paths associated with wetlands:
bidirectional, throughflow, inflow, outflow, or isolated. Surface water connections are
emphasized because they are more readily identified than groundwater linkages. Bidirectional
flow is two-way flow either related to tidal influence (bidirectional-tidal) or water level
fluctuations in lakes and impoundments (bidirectional-nontidal). Throughflow wetlands have
either a watercourse or another type of wetland above and below them, so water flows through
these wetlands. All lotic wetlands are throughflow types. Inflow wetlands are sinks where no
surface water outlets exist, yet water is entering via a stream or river (often intermittent) or an
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Table 3. Definitions and examples of landform types (Tiner 2003a). Map codes in parentheses.
Landform Type General Definition Examples
Basin* (BA) a depressional (concave) landform lakefill bogs; wetlands in the
(including tidal wetlands with restricted saddle between two hills;
flow) wetlands in closed or open
depressions, including
narrow stream valleys; tidal
marshes with restricted flow
Slope (SL) a landform extending uphill (on a slope) seepage wetlands on
hillsides; wetlands along
drainageways or mountain
streams on slopes
Flat* (FL) a relatively level landform, often on wetlands on flat areas
broad level landscapes with high seasonal ground-water
levels; wetlands on
terraces along rivers/streams;
wetlands on hillside benches;
wetlands at toes of slopes
Floodplain (FP) a broad, generally flat landform wetlands on alluvium;
occurring on a landscape shaped by bottomland swamps
fluvial or riverine processes
Interfluve (IF) a broad, level to imperceptibly flatwood wetlands on coastal
depressional poorly drained landform or glaciolacustrine plains
occurring between two drainage systems
(i.e., on interstream divides)
Fringe (FR) a landform occurring within the banks of a buttonbush swamps; aquatic
river or stream or along the shores of a beds; salt and brackish
waterbody (estuary, river, stream, pond, marshes with unrestricted
lake, or ocean) that is either: vegetated and tidal flow; cobble-gravel
semipermanently flooded or wetter, or beds and bars in and along
permanently saturated due to this location, streams
or irregularly flooded (tidal wetlands with
unrestricted flow) or a nonvegetated bank
or shore that is seasonally flooded or
temporarily flooded
Island (IL) a landform completely surrounded by deltaic and insular wetlands;
water (including deltas) floating bog islands
*May be applied as sub-landforms within the Interfluve (IFba, IFfl) and Floodplain (FPba, FPfl).
10
upslope wetland. Outflow wetlands have water leaving them and moving downstream via a
watercourse or a slope wetland; they are often sources of streams. Isolated wetlands are
essentially closed (“geographically isolated”) depressions or flats where water comes from direct
precipitation, localized surface water runoff, and/or ground water discharge. From the surface
water perspective, these wetlands are “isolated” from other wetlands since they lack an apparent
surface water connection, however it must be recognized that they may be hydrologically linked
to other wetlands and waterbodies via groundwater.
Other descriptors applied to mapped wetlands include headwater, drainage-divide, fragmented,
partly drained, human-induced outflow, and human-impacted. Headwater wetlands are sources
of streams or wetlands along first-order (perennial) streams. They include wetlands connected to
first-order streams by ditches; they were labeled with a partly drained modifier as were other
wetlands with ditches draining them. Many such wetlands are remnants of once larger interfluve
wetlands that naturally drained into streams. A complex of such remnants when in close
proximity to one another was typically treated as a single unit for water flow path classification
purposes. Wetlands occurring in more than one watershed or subbasin or straddling the defined
watershed boundary line between a watershed or subbasin and a neighboring one, were classified
as drainage-divide wetlands. We identified pieces of wetlands separated by major highways
(federal and state roads) as fragmented wetlands. This is a first step in addressing the issue of
fragmentation which is quite complex and beyond the scope of our work. For example, we did
not apply the descriptor to wetlands that were simply reduced in size due to land use practices.
The listing of fragmented wetlands is therefore extremely conservative. Human-induced outflow
wetlands were identified in the Delaware portion of the watershed only based on previous work.
They are wetlands where outflow is now through the drainage ditch network. Human-impacted
wetlands are those significantly altered by excavation or impoundment.
For open water habitats such as the ocean, estuaries, lakes, and ponds, additional descriptors
following Tiner (2003a) were applied.
Note: There may be minor discrepancies between the 1998 classification and the historic
wetland classification due to source data and how the datasets were compiled. The former is
more detailed than the latter as more lotic stream wetlands were identified. These wetlands are
the remnants of once larger wetlands (identified as terrene interfluve types) that have been
essentially reduced in size to follow the narrow stream. These wetlands might have always been
lotic stream wetlands but fell within large wetland complexes (hydric soil mapping unit)
characterized as terrene interfluve wetlands.
Preliminary Assessment of Wetland Functions
After improving and enhancing the NWI digital database, analyses were performed to produce a
preliminary assessment of wetland functions for the watershed. Ten wetland functions were
evaluated: 1) surface water detention, 2) streamflow maintenance, 3) nutrient transformation, 4)
sediment and other particulate retention, 5) coastal storm surge detention, 6) shoreline
stabilization, 7) provision of fish and shellfish habitat, 8) provision of waterfowl and waterbird
habitat, 9) provision of other wildlife habitat, and 10) conservation of biodiversity. The latter
function was not evaluated for the pre-settlement era since source data were limited.
11
This study employed a watershed assessment approach that may be called "Watershed-based
Preliminary Assessment of Wetland Functions" (W-PAWF). W-PAWF applies general
knowledge about wetlands and their functions to develop a watershed overview that highlights
possible wetlands of significance in terms of performance of various functions. The rationale for
correlating wetland characteristics with wetland functions is described in a separate report
included as Appendix B (Tiner 2003b).
After running the analyses, a series of maps for watershed were generated to highlight wetland
types that may perform these functions at high or other significant levels. Statistics (acreage
summaries) were generated from Microsoft's Access program, whereas topical maps were
generated by ArcView software. (Note: Recompilation of statistics from the database may
produce slightly different acreage totals than reported herein due to format conversions and
computer round-off procedures. Any difference should be minor, amounting to less than 1% of
the reported value.)
Extent of Natural Habitat
Maps showing the extent of natural habitat in the Nanticoke watershed were prepared. The pre-settlement
map was based largely on interpretation of soil map units, while the 1998 map came
from previous work in the watershed (Tiner et al. 2001, 2000).
Function Comparison: Pre-settlement vs. 1998
To assess the cumulative loss of wetlands on specific functions, one can simply examine the
change in acreage of specific wetland types. This was done, but the acreage difference alone
may not adequately convey the cumulative impact of the lost acreage on wetland function. To
address the latter, the senior author devised a simple weighting scale for wetlands of potential
significance for each function. A “high” potential was given a weight of 2, while a “moderate”
potential and other significant wetlands were assigned a weight of 1. By multiplying the wetland
acreage listed as high, moderate, or other potential by the weighting factor, a total number of
functional units was calculated for each function at pre-settlement and 1998. This would allow
comparison between pre-settlement functional capacity (total functional units for time one) and
the 1998 capacity (total functional units for time two) and could demonstrate a percent loss of
pre-settlement function. This provides an interesting perspective on the current conditions from
a functional capacity standpoint and perhaps gives a better sense of the relative magnitude of the
functional loss than wetland acreage loss alone.
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General Scope and Limitations of the Study
Pre-settlement Wetland Inventory
Historic wetland data compiled from contemporary soil surveys produced the most accurate
depiction of pre-settlement wetlands for the Nanticoke River watershed prepared to date.
Translating this information to historic wetland extent required making certain assumptions:
1) hydric soil mapping units represent historic wetlands, 2) areas of the Sunken series were
freshwater forested wetlands at pre-settlement, 3) areas of typical freshwater wetland soils that
are now mapped as estuarine wetlands were also freshwater forested wetlands at pre-settlement,
4) areas of Honga series were estuarine wetlands at this time, although they were forested
wetlands at least 700 years ago (Brewer et al. 1998), and 5) areas within nonhydric soil map
units that were mapped as forested wetlands in 1998 were forested wetlands at pre-settlement.
1998 Wetland Inventory and Digital Database
Despite being five years "old," the 1998 database should reasonably reflect contemporary
conditions. One must, however, recognize the limitations of any wetland mapping effort
derived mainly through photointerpretation techniques (see Tiner 1997, 1999 for details). For
example, use of spring aerial photography for wetland mapping precludes identification of
freshwater aquatic beds. Such areas are included within areas mapped as open water (e.g.,
lacustrine and palustrine unconsolidated bottom) because vegetation is not developed so they
appear as water on the aerial photographs. Also drier-end wetlands such as seasonally saturated
and temporarily flooded palustrine wetlands are often difficult to separate from nonwetlands
through photointerpretation.
Preliminary Assessment of Wetland Functions
At the outset, it is important to emphasize that this functional assessment is a preliminary one
based on wetland characteristics interpreted through remote sensing and using the best
professional judgment of the senior author and other wetland specialists (including specialists
working in the Nanticoke River watershed). Wetlands believed to be providing potentially high
or other significant levels of performance for a particular function were highlighted. As the
focus of this report is on wetlands, an assessment of deepwater habitats (e.g., lakes, rivers, and
estuaries) and linear features such as perennial and intermittent streams for providing the listed
functions was not done. The importance of permanently flooded habitats to fish, for example,
should be obvious and the beneficial functions of small streams (even intermittent ones) to water
quality and sediment retention should also be recognized (Meyer et al. 2003). Also, no attempt
was made to produce a more qualitative ranking for each function or for each wetland based on
multiple functions as this would require more input from others and more data, well beyond the
scope of this study. For a technical review of wetland functions, see Mitsch and Gosselink
(2000) and for a broad overview, see Tiner (1985; 1998) and Tiner and Burke (1995).
Functional assessment of wetlands can involve many parameters. Typically such assessments
have been done in the field on a case-by-case basis, considering observed features relative to
13
those required to perform certain functions or by actual measurement of performance. The
present study does not seek to replace the need for such evaluations as they are the ultimate
assessment of the functions for individual wetlands. Yet, for a watershed analysis, basin-wide
field-based assessments are not practical or cost-effective or even possible given access
considerations. For watershed planning purposes, a more generalized assessment is worthwhile
for targeting wetlands that may provide certain functions, especially for those functions
dependent on landscape position, landform, vegetation life form, and other photointerpretable
features. Subsequently, these results can be field-verified when it comes to actually evaluating
particular wetlands for acquisition purposes, e.g., for conservation of biodiversity or for
preserving flood storage capacity. Current aerial photography may also be examined to aid in
further evaluations (e.g., condition of wetland/stream buffers or adjacent land use) that can
supplement this preliminary assessment.
This study employs a watershed assessment approach that may be called "Watershed-based
Preliminary Assessment of Wetland Functions" (W-PAWF). W-PAWF applies general
knowledge about wetlands and their functions to develop a watershed overview that highlights
possible wetlands of significance in terms of performance of various functions. To accomplish
this objective, the relationships between wetlands and various functions must be simplified into a
set of practical criteria or observable characteristics. Such assessments could also be further
expanded to consider the condition of the associated waterbody and the neighboring upland or to
evaluate the opportunity a wetland has to perform a particular function or service to society, for
example.
W-PAWF usually does not account for the opportunity that a wetland has to provide a function
resulting from a certain land-use practice upstream or the presence of certain structures or land-uses
downstream. For example, two wetlands of equal size and like vegetation may be in the
right landscape position to retain sediments. One, however, may be downstream of a land-clearing
operation that has generated considerable suspended sediments in the water column,
while the other is downstream from an undisturbed forest. The former should be actively
performing sediment trapping in a major way, while the latter is not. Yet if land-clearing takes
place upstream of the latter area, the second wetland will likely trap sediments as well as the first
wetland. The entire analysis typically tends to ignore opportunity since such opportunity may
have occurred in the past or may occur in the future and the wetland is awaiting a call to perform
this service at higher levels than presently.
W-PAWF also does not consider the condition of the adjacent upland (e.g., level of disturbance)
or the actual water quality of the associated waterbody which may be regarded as important
metrics for assessing the health of individual wetlands (not part of this study). Collection and
analysis of these data were done as another part of prior studies (Tiner et al. 2000, 2001) and
were not part of the present study.
We further emphasize that the preliminary assessment does not obviate the need for more
detailed assessments of the various functions. This assessment should be viewed as a starting
point for more rigorous assessments, as it attempts to cull out wetlands that may likely provide
significant functions based on generally accepted principles and the source information used for
this analysis. This type of assessment is most useful for regional or watershed planning
14
purposes. For site-specific evaluations, additional work will be required, especially field
verification and collection of site-specific data for potential functions (e.g., following the HGM
assessment approach as described by Brinson 1993 and other onsite evaluation procedures). This
is particularly true for assessments of fish and wildlife habitats and biodiversity. Other sources
of data may exist to help refine some of the findings of this report. Additional modeling could
be done, for example, to identify habitats of likely significance to individual species of animals
(based on their specific life history requirements).
Field checking of seasonally flooded and seasonally flooded/saturated emergent wetlands should
be done to determine if they are marshes or wet meadows. If the former, they will likely have
high potential as both fish and shellfish habitat and waterfowl habitat rather than the moderate
rating given in this report.
Rationale for Preliminary Functional Assessments
Correlations were established between wetland characteristics in the wetland database and ten
functions: 1) surface water detention, 2) streamflow maintenance, 3) nutrient transformation, 4)
sediment and other particulate retention, 5) coastal storm surge detention, 6) shoreline
stabilization, 7) provision of fish and wildlife habitat, 8) provision of waterfowl and waterbird
habitat, 9) provision of other wildlife habitat, and 10) conservation of biodiversity. These
correlations were based on a general review of the scientific literature and professional judgment
of the senior author and other wetland specialists throughout the Northeast. The rationale for
these correlations are presented in a separate report “Correlating Enhanced National Wetlands
Inventory Data with Wetland Functions for Watershed Assessments: A Rationale for
Northeastern U.S. Wetlands” (Tiner 2003b) which is included as Appendix B of this report.
The conservation of biodiversity function was only evaluated for the 1998 period. In the context
of this report, the term "biodiversity" is used to identify certain wetland types that appear to be
scarce or relatively uncommon in the watershed, or complexes of large wetlands. Schroeder
(1996) noted that to conserve regional biodiversity, maintenance of large-area habitats for forest
interior birds is essential. Robbins et al. (1989) suggested a minimum forest size of 7,410 acres
to retain all species of the forest-breeding avifauna in the Mid-Atlantic region. For the
Nanticoke watershed, we attempted to highlight uncommon wetlands, wetlands of potential high
diversity, and areas that may be important for forest-breeding birds in the Mid-Atlantic region
(i.e., forested areas 7,410 acres and larger containing contiguous palustrine forested wetlands and
upland forests). All riverine tidal wetlands, palustrine tidal emergent wetlands, and oligohaline
wetlands were identified as significant for this function because they are often colonized by a
diverse assemblage of plants and are among the most diverse plant communities in the Mid-
Atlantic region. Other wetlands deemed important for this function included Atlantic white cedar
swamps and bald cypress swamps. We also identified wetlands that were uncommon types
based on mapping classification (not on Natural Heritage Program data) including palustrine
tidal evergreen forested wetlands, palustrine tidal scrub-shrub wetlands, and palustrine
seasonally flooded and wetter emergent wetlands.
Use of Natural Heritage Program data and GAP data has been suggested, but these data were not
provided for our use and to incorporate such data is beyond the scope of W-PAWF. It is
15
expected that such information will be utilized at a later date by state agencies and others for
more detailed planning and evaluation. The wetlands designated as potentially significant for
biodiversity are simply a foundation to build upon. Local knowledge of significant wetlands will
further refine the list of wetlands important for this function. For information on rare and
endangered species, contact the Natural Heritage Program office.
Appropriate Use of this Report
The report provides a basic characterization of wetlands in the Nanticoke watershed including a
preliminary assessment of wetland functions and historic changes since pre-colonial times.
Keeping in mind the limitations mentioned above, the results are a first-cut or initial screening of
the watershed's wetlands to designate wetlands that may have a significant potential to perform
different functions. The targeted wetlands have been predicted to perform a given function at a
significant level presumably important to the watershed's ability to provide that function.
"Significance" is a relative term and is used in this analysis to identify wetlands that are likely to
perform a given function at a level above that of wetlands not designated. Review of these
preliminary findings and consideration of additional information not available to us may identify
the need to modify some of the criteria used to identify wetlands of potential significance for
certain functions.
While the results are useful for gaining an overall perspective of the watershed's wetlands and
their relative importance in performing certain functions, the report does not identify differences
among wetlands of similar type and function. The latter information is often critical for making
decisions about wetland acquisition and designating certain wetlands as more important for
preservation versus others with the same categorization. Additional information may be gained
through consulting with agencies having specific expertise in a subject area and by conducting
field investigations to verify the preliminary assessments. When it comes to actually acquiring
wetlands for preservation, other factors must be considered. Such factors may include: 1) the
condition of the surrounding area, 2) the ownership of the surrounding area and the wetland
itself, 3) site-specific assessment of wetland characteristics and functions, 4) more detailed
comparison with similar wetlands based on field data, and 5) advice from other agencies (federal,
state, and local) with special expertise on priority resources (e.g., for wildlife habitat, contact
appropriate federal and state biologists). The latter agencies may have site-specific information
or field-based assessment methods that can aid in further narrowing the choices to help insure
that the best wetlands are acquired for the desired purpose.
The report is a watershed-based wetland characterization for the Nanticoke watershed and a
historical assessment of changes in wetland extent and function. The report does not make
comparisons with other watersheds.
The report is useful for natural resource planning as an initial screening for considering
prioritization of wetlands (for acquisition, restoration, or strengthened protection), as an
educational tool (e.g., helping people better understand wetland functions and the relationships
between wetland characteristics and performance of individual functions), for characterizing the
differences among wetlands (both form and function), and for gaining perspective on how
wetlands in the watershed have changed over time and how this has affected wetland functions.
16
Results
The wetland database created for this project allowed production of wetland maps and statistics
on wetland extent and predicted functions for two time periods (pre-settlement and 1998). Study
findings are presented in four subsections. The first subsection contains a list of the maps
prepared for this project, while the next two subsections present the acreage summary findings
for each era. The last subsection of the Results contains a comparative analysis of changes in
wetland conditions and functions from pre-settlement to 1998. The report and accompanying
maps may be posted on the NWI homepage (http://wetlands.fws.gov) under “reports and
publications” in the near future.
Maps
Due to their size, the maps are included in a separate file on the compact disk (CD) containing
this report. Two sets of maps were produced at a scale of 1:110,000 to profile the Nanticoke’s
wetlands - one set showing estimated pre-settlement conditions and predicted wetlands of
significance for nine functions (excluding conservation of biodiversity) and the other set showing
1998 conditions and predicted wetlands of significance for ten functions.
A list of the maps follows:
Pre-settlement Maps
Map 1NW pre-settlement - Wetlands and Deepwater Habitats Classified by NWI Types
Map 2NW pre-settlement- Wetlands Classified by Landscape Position
Map 3NW pre-settlement - Wetlands Classified by Landform
Map 4NW pre-settlement - Wetlands Classified by Water Flow Path
Map 5NW pre-settlement - Potential Wetlands of Significance for Surface Water Detention
Map 6NW pre-settlement - Potential Wetlands of Significance for Streamflow Maintenance
Map 7NW pre-settlement - Potential Wetlands of Significance for Nutrient Transformation
Map 8NW pre-settlement - Potential Wetlands of Significance for Sediment and Other
Particulate Retention
Map 9NW pre-settlement - Potential Wetlands of Significance for Coastal Storm Surge
Detention
Map 10NW pre-settlement - Potential Wetlands of Significance for Shoreline Stabilization
Map 11NW pre-settlement - Potential Wetlands of Significance for Fish and Shellfish Habitat
Map 12NW pre-settlement - Potential Wetlands of Significance for Waterfowl and Waterbird
Habitat
Map 13NW pre-settlement - Potential Wetlands of Significance for Other Wildlife Habitat
Map 14NW pre-settlement - Extent of Natural Habitat in the Nanticoke Watershed
1998 Maps
Map 1NW 1998 - Wetlands and Deepwater Habitats Classified by NWI Types
Map 2NW 1998 - Wetlands Classified by Landscape Position
Map 3NW 1998 - Wetlands Classified by Landform
17
Map 4NW 1998 - Wetlands Classified by Water Flow Path
Map 5NW 1998 - Potential Wetlands of Significance for Surface Water Detention
Map 6NW 1998 - Potential Wetlands of Significance for Streamflow Maintenance
Map 7NW 1998 - Potential Wetlands of Significance for Nutrient Transformation
Map 8NW 1998 - Potential Wetlands of Significance for Sediment and Other Particulate
Retention
Map 9NW 1998 - Potential Wetlands of Significance for Coastal Storm Surge Detention
Map 10NW 1998 - Potential Wetlands of Significance for Shoreline Stabilization
Map 11NW 1998 - Potential Wetlands of Significance for Fish and Shellfish Habitat
Map 12NW 1998 - Potential Wetlands of Significance for Waterfowl and Waterbird Habitat
Map 13NW 1998 - Potential Wetlands of Significance for Other Wildlife Habitat
Map 14NW 1998 - Potential Wetlands of Significance for Biodiversity
Map 15NW 1998 - Extent of Natural Habitat in the Nanticoke Watershed
Pre-settlement Conditions
Historic wetlands were classified according to the U.S. Fish and Wildlife Service's official
wetland classification system (Cowardin et al. 1979) and by landscape position, landform, and
water flow path descriptors following Tiner (2003a). Wetland acreage summaries for the
Nanticoke watershed are given in Tables 4 and 5 and wetland distribution illustrated on Pre-settlement
Maps 1NW through 4NW. Table 4 summarizes acreage of wetland types through the
subclass level of the Service’s classification ("NWI types"), while Table 5 tabulates statistical
data on wetlands by landscape position, landform, and water flow path ("LLWW types").
Wetlands by NWI Types
The predicted acreage of Nanticoke wetlands at pre-settlement was roughly 230,000 acres (Table
4) which represented about 45 percent of the watershed. The distribution of these wetlands by
major type is shown on Map 1NW pre-settlement.
Most (88.5%) of the wetlands were forested, with the rest being listed as emergent (10.3% as
estuarine and 1.2% as palustrine). Wild fires or fires set by Native Americans probably had a
substantial impact on plant composition of wetlands. The actual acreage of palustrine emergent
wetlands was undoubtedly greater than our estimate, but we had no reasonable means to predict
this effect. We also realize that these changes would be quite dynamic over time (related to fire
frequency and intensity). Our estimates also do not include acreage for palustrine scrub-shrub
wetlands, yet it is also likely that these successional communities were also present due to fire
impacts. There was no reasonable way to estimate their extent and distribution.
18
Table 4. Pre-settlement wetland acreage based on interpretation on soil survey data and
U.S.G.S. topographic maps. Note: Totals may not sum exactly due to computer round-off.
Wetland Type Acreage % of Total Acreage
Estuarine Emergent* 23,636.8 10.3
Palustrine Emergent
Seasonally Flooded-Tidal 2,696.5 1.2
Semipermanently Flooded 63.5 <0.1
------------------------------- ---------- -------
Total 2,760.0 1.2
Palustrine Forested
Seasonally Flooded-Tidal 6,459.1 2.8
Temporarily Flooded-Tidal 769.2 <0.1
Seasonally Flooded 63,498.1 27.6
Temporarily Flooded 132,896.1 57.8
--------------------------------- ------------- -------
Total 203,622.5 88.5
---------------------------------------------------------------------------------------------
GRAND TOTAL 230,019.3
*Includes an undetermined amount of estuarine unconsolidated shore (tidal flat).
Wetlands by LLWW Types
Prior to European settlement, the Nanticoke watershed had an estimated 2,809 wetlands
occupying about 230,000 acres (Table 5). Seventy-eight percent of the acreage was terrene (e.g.,
wetlands at the head of the watershed or isolated forms) (Map 2NW pre-settlement). Wetlands
associated with rivers and streams (lotic) accounted for about 12 percent of the acreage, while
the remaining 10 percent was in the estuary. From the landform perspective, almost 77 percent
of the acreage was represented by interfluve types occupying broad flat interstream divides
between streams and other watersheds (Map 3NW pre-settlement). Most of the remaining
acreage was either floodplain (10.4%) or fringe (11.2%). Nearly three-quarters (73.0%;
168,042.4 acres) of the acreage experienced outflow. Bidirectional-tidal flow affected 14.6
percent of the acreage (33,561.6 acres), while throughflow and geographically isolated acreage
accounted for 7.4 percent (17,013.2 acres) and 5.0 percent (11,401.9 acres), respectively (Map
4NW pre-settlement).
19
Table 5. Pre-settlement wetland acreage classified by landscape position, landform, and water
flow path. Note: Some totals may differ slightly due to round-off procedures; number of
wetlands is approximate due to GIS processing.
Landscape Position Landform Water Flow Path Approx. # Pre-settlemt Acreage
of Wetlands (% of Grand Total)
Estuarine Fringe Bidirectional-tidal 83 22,793.6 (10.0)
Island Bidirectional-tidal 1 843.1 (0.3)_
Total 84 23,636.7 (10.3)
Lotic River Floodplain Bidirectional-tidal 102 7,181.0 (3.1)
Throughflow 10 164.2 (<0.1)
------------------------ ------- -----------
Subtotal 112 7,345.2 (3.2)
Fringe Bidirectional-tidal 105 2,696.5 (1.2)
Throughflow 2 63.5 (<0.1)
------------------------ ------- -----------
Subtotal 107 2,760.0 _ (1.2)__
Total 219 10,105.2 (4.4)
Lotic Stream Floodplain Bidirectional-tidal 2 47.3 (<0.1)
Throughflow 130 16,476.5 (7.2)
----------------------- ------ -----------
Subtotal 132 16,523.8 (7.2)
Basin Throughflow 12 73.2 (<0.1)
Flat Throughflow 13 168.5 (<0.1)_
Total 157 16,765.5 (7.3)
Terrene Interfluve Isolated 1723 11,401.9 (5.0)
Outflow 380 164,638.7 (71.6)
Throughflow 5 67.3 (<0.1)
------------------- -------- -------------
Subtotal 2,108 176,107.9 (76.6)
Basin Outflow 79 815.6 (0.4)
Flat Outflow 162 2,588.2 (1.1)_
Total 2,349 179,511.7 (78.0)
______________________________________________________________________________
GRAND TOTAL 2,809 230,019.1
20
Preliminary Functional Assessment
Most of the historic wetlands were predicted to perform four functions at significant levels:
surface water detention (97.9% of all wetlands), streamflow maintenance (79.0%), nutrient
transformation (100%), and provision of other wildlife habitat (100%) (Table 6). A significant
level of sediment and other particulate retention was projected for nearly 44 percent of the
wetlands. Other functions were estimated to be performed at significant levels by less than 25
percent of the wetlands: shoreline stabilization (22.0%), coastal storm surge detention (14.6%),
provision of fish and shellfish habitat (18.8%), and provision of waterfowl and waterbird habitat
(20.1%). Since it was not possible to identify the existence of Atlantic white cedar swamps, bald
cypress swamps, and other uncommon wetland types, the function addressing the conservation of
biodiversity could not be examined. Click on maps in Table 6 to see the extent and distribution
of wetlands of potential significance for nine functions.
---------------------------------------------------------------------------------------------------------------------
Table 6. Preliminary functional assessment results for Nanticoke wetlands at pre-settlement.
Pre-settlement % of Total
Function (Map) Potential Significance Acreage Wetland Acreage
Surface Water Detention High Potential 50,339.9 21.9
(Map 5NW pre-settlement) Moderate Potential 174,911.7 76.0
Streamflow Maintenance High Potential 180,238.8 78.4
(Map 6NW pre-settlement) Moderate Potential 1,349.5 0.6
Nutrient Transformation High Potential 96,353.9 41.9
(Map 7NW pre-settlement) Moderate Potential 133,665.3 58.1
Retention of Sediments
and Inorganic Particulates High Potential 50,338.9 21.9
(Map 8NW pre-settlement) Moderate Potential 50,302.0 21.9
Coastal Storm Surge Detention High Potential 33,561.6 14.6
(Map 9NW pre-settlement)
Shoreline Stabilization High Potential 50,507.4 22.0
(Map 10NW pre-settlement)
Fish/Shellfish Habitat* High Potential 26,354.9 11.5
(Map 11NW pre-settlement) Shading Potential 16,765.4 7.3
Waterfowl/Waterbird Habitat High Potential 26,396.7 11.5
(Map 12NW pre-settlement) Wood Duck Potential 19,823.6 8.6
Other Wildlife Habitat High Potential 223,681.7 97.2
(Map 13NW pre-settlement) Moderate Potential 6,337.5 2.8
-------------------------------------------------------------------------------------------------------------------------------
*Wetlands important for streamflow maintenance should also be recognized as vital to
maintaining fish and shellfish habitat.
21
Contemporary Conditions (1998)
Wetlands were classified according to the U.S. Fish and Wildlife Service's official wetland
classification system (Cowardin et al. 1979) and by landscape position, landform, and water flow
path (LLWW) descriptors following Tiner (2003a). Wetland acreage summaries for the
Nanticoke watershed are given in Tables 7 and 8 and wetland distribution is illustrated on 1998
Maps 1NW through 4NW. Table 7 summarizes wetland types through the subclass level of the
Service’s classification ("NWI types"), while Table 8 tabulates statistical data on wetlands by
landscape position, landform , and water flow path ("LLWW types").
Wetlands by NWI Types
According to the NWI, in 1998 the Nanticoke watershed had 142,005 acres of wetlands,
excluding linear features (Table 7; Map 1NW 1998). Eighty-eight percent of wetlands were
palustrine wetlands. Palustrine forested wetlands accounted for nearly 85,000 acres or 68
percent of the palustrine wetlands. This figure excludes mixed forested/scrub-shrub and
forested/emergent types and many of the other palustrine types (e.g., scrub-shrub/emergent
wetlands) that represent forested wetlands in post-harvest succession. The overwhelming
majority (93%) of palustrine wetlands was nontidal (beyond the influence of the tides); only 7
percent of the palustrine wetlands were subjected to periodic tidal flooding. Nearly 400 acres of
other freshwater wetlands were tidally influenced; they were classified as riverine tidal wetlands
(emergent and unconsolidated shore types). These wetlands represented only 0.2 percent of the
Nanticoke’s wetlands. Estuarine wetlands accounted for 12 percent of the watershed’s wetlands.
Irregularly flooded emergent wetlands predominated, occupying over 15,000 acres and
representing about 91 percent of the Nanticoke’s estuarine wetlands.
Note: The watershed also had 19,708 acres of deepwater habitats: 116,703 acres of estuarine
waters, 1,832 acres of tidal rivers, 138 acres of nontidal rivers, and 1,035 acres of lacustrine
waters (impounded lakes), excluding linear streams.
22
Table 7. Wetlands in the Nanticoke watershed in 1998 classified by NWI wetland type to the
class level (Cowardin et al. 1979).
NWI Wetland Type 1998 Acreage
Estuarine Wetlands
Emergent (Regularly Flooded) 640.2 (239.3 = oligohaline)
Emergent (Irregularly Flooded) 15,323.5 (6,100.2 = oligohaline)
Scrub-Shrub (Irregularly Flooded) 139.3 (85.3 = oligohaline)
Forested (Irregularly Flooded) 241.1
Unconsolidated Shore (Irregularly Exposed) 38.8
Unconsolidated Shore (Regularly Flooded) 535.2 (274.4 = oligohaline)
------------------------------------------------------------------------------------------------------------
Total 16,918.1 (6,699.2 = oligohaline)
Palustrine Wetlands (nontidal, except where noted)
Aquatic Bed 0.8
Emergent 1,457.9 (8.5 = Emergent/Forested)
Emergent (Tidal) 296.2
Mixed Emergent/Scrub-Shrub (Deciduous) 3,113.7
Mixed Emergent/Scrub-Shrub (Evergreen) 785.8
Farmed 3,527.8
Needle-leaved Deciduous Forested 79.9
Evergreen Forested 8,274.6 (67.1 = Atlantic White Cedar)
Evergreen Forested (Tidal) 107.9
Scrub-Shrub/Emergent 2,550.5
Broad-leaved Deciduous Forested 38,502.1 (187.8 = w/Bald Cypress)
Broad-leaved Deciduous Forested (Tidal) 7,169.8 (26.0 = w/Bald Cypress)
Mixed Forested 30,204.7
Mixed Forested (Tidal) 572.5
Deciduous Forested/Emergent 410.3 (23.4 = tidal)
Forested/Scrub-Shrub and Forested/Scrub-Shrub 13,992.5 (107.5 = tidal)
Deciduous Scrub-Shrub 2,115.6
Evergreen Scrub-Shrub 6,115.5
Mixed Scrub-Shrub 4,034.8
Scrub-Shrub (Tidal) 189.5
Unconsolidated Bottom/Vegetated 40.4 (34.8 = w/Bald Cypress)
Unconsolidated Bottom 1,157.0
Unconsolidated Shore 7.9
---------------------------------------------------------------------------------------------------------------------
Total 124,707.7
Riverine Wetlands
Emergent (Tidal) 332.0
Unconsolidated Shore (Tidal) 46.7
---------------------------------------------------------------------------------------------------------------------
Total 378.7
_____________________________________________________________________________________
GRAND TOTAL 142,004.5
_____________________________________________________________________________________
23
Wetlands by LLWW Types2
Roughly 4,900 wetlands (excluding ponds) were inventoried in the Nanticoke River watershed
and classified by their hydrogeomorphic features (Table 8). Terrene wetlands were the
predominant type, comprising 78 percent of these wetlands (excluding ponds) and 72 percent of
the watershed’s wetland acreage (Map 2NW 1998). Lotic wetlands were second-ranked in
number (17.5% of the wetlands) and were third-ranked in acreage (12.0% of the total acreage).
Estuarine wetlands were second-ranked in acreage (16.1%) and third-ranked in number (2.9%).
Lentic wetlands made up 1 percent of the wetland number and only 0.2 percent of the wetland
acreage.
From the landform standpoint, interfluve wetlands accounted for 71 percent of the wetland
acreage, followed by fringe wetlands (16.6%) and floodplain wetlands (10.6%) (Map 3NW
1998). Other wetland landforms accounted for less than two percent of the acreage (flats - 1.1%;
basins - 0.5%, and islands - 0.2%).
Outflow wetlands were the predominant water flow path type, totaling 95,190 acres (67.6% of
the wetland acreage; Map 4NW 1998). Bidirectional-tidal wetlands were second-ranked with
25,772 acres (18.3% of the total acreage), followed by throughflow wetlands with 10,532 acres
(10.4%). Isolated wetlands accounted for 5,011 acres (3.6%) and bidirectional water flow
wetlands associated with impoundments totaled only 260 acres (0.2%).
A total of 910 ponds were identified, occupying 1,289 acres. The average size of a pond was 1.4
acres. Over half of the pond acreage (51.1%) and nearly 40 percent of the number of ponds were
represented by outflow ponds (658.8 acres for 335 ponds). Isolated ponds were most numerous
(458 ponds, 443.1 acres), accounting for half of the ponds and slightly more than one-third of the
pond acreage. The 117 throughflow ponds identified occupied almost 187 acres (14.5% of the
pond acreage and 12.9% of the number of ponds). (Note: Pond acreage re: LLWW types is
higher than based on NWI types because large sewage treatment lagoons were treated as ponds
in the former and as lacustrine in the latter.)
The lakes present in the Nanticoke watershed were artificially created by damming rivers and
streams or by excavation and diking activities. A total of 19 “lakes” covering nearly 904 acres
were inventoried. The average size of a lake was 47.6 acres. Most (88.4%) of the lakes were
throughflow lakes, while the rest were outflow lakes.
2 All wetlands, except palustrine unconsolidated bottoms, were characterized by LLWW
descriptors. These exceptions were classified as pond or lake types and are not reflected in the
wetland summary statistics.
24
Table 8. Wetlands (excluding ponds) in the Nanticoke watershed in 1998 classified by
landscape position, landform, and water flow path (Tiner 2003a). Note: Number of wetlands is
approximate due to GIS processing.
Landscape Landform Water Flow Approx. # of 1998 Acreage
Position Wetlands (% of Grand Total)
Estuarine Fringe* Bidirectional-tidal 143 22,384.5 (15.9)
Island Bidirectional-tidal 2 248.5____ (0.2)__
Total 145 22,633.0 (16.1)
Lentic Basin Bidirectional 26 109.6 (0.1)
Flat Bidirectional 8 21.4 (<0.1)
Fringe Bidirectional 14 123.5 (0.1)
Island Bidirectional 4 5.0________ (<0.1)_
Total 52 259.5 (0.2)
Lotic River Floodplain Bidirectional-tidal 151 2,364.3 (1.7)
Throughflow 6 28.0 (<0.1)
Fringe Bidirectional-tidal 104 614.2 (0.4)
Island Bidirectional-tidal 1 0.3_______ (<0.1)
Total 262 3,006.8 (2.1)
Lotic Stream
Basin Throughflow 52 351.8 (0.2)
Flat Throughflow 95 779.6 (0.6)
Floodplain Throughflow 385 12,396.0 (8.8)
Bidirectional-tidal 25 138.7 (0.1)
Fringe Throughflow 29 245.8 (0.2)
_____________ Bidirectional-tidal 13 21.0_________ (<0.1)_
Total 599 13,932.9 (9.9)
Terrene Basin Isolated 7 14.8 (<0.1)
Outflow 14 251.3 (0.2)
Flat Isolated 10 82.7 (0.1)
Outflow 47 721.6 (0.5)
Throughflow 1 1.0 (<0.1)
Fringe Outflow 1 1.0 (<0.1)
Interfluve Isolated 1551 4,913.4 (3.5)
Outflow 2120 94,216.3 (66.9)
_____________ Throughflow 111 813.2________ (0.6)__
Total 3,862 101,015.3 (71.7)
-------------------------------------------------------------------------------------------------------------------------------
GRAND TOTAL 4,920 140,847.5
-------------------------------------------------------------------------------------------------------------------------------
*Includes tidal freshwater wetlands contiguous with estuarine wetlands and along estuarine waters.
25
Preliminary Functional Assessment
Most of the wetlands in the Nanticoke watershed performed four functions at significant levels
(Table 9): surface water detention (96.9% of the wetland acreage), nutrient transformation
(96.2%), provision of other wildlife habitat (96.2%), and streamflow maintenance (74.6%).
About 30 percent of the wetland acreage was predicted to provide significant retention of
sediments and other particulates and shoreline stabilization. One fourth of the acreage was
estimated to be significant for the conservation of biodiversity in the watershed. Nearly three-quarters
of this acreage was represented by two large predominantly forested areas that are
probably important for forest-breeding birds of the Mid-Atlantic Region. About 23-24 percent of
the total wetland acreage was predicted to provide important habitat for fish, shellfish, waterfowl
and waterbirds. Click on maps in Table 9 to see the extent and distribution of wetlands of
potential significance for each of the ten functions.
---------------------------------------------------------------------------------------------------------------------
Table 9. Preliminary functional assessment results for Nanticoke wetlands in 1998. Ponds are
included in this assessment.
1998 % of Total
Function (Map) Potential Significance Acreage Wetland Acreage
(total) (total)
Surface Water Detention High Potential 39,200.7 27.6
(Map 5NW 1998) Moderate Potential 98,423.7 69.3
(137,624.4) (96.9)
Streamflow Maintenance High Potential 23,678.0 16.7
(Map 6NW 1998) Moderate Potential 82,331.3 57.9
(106,009.3) (74.6)
Nutrient Transformation High Potential 35,756.1 25.2
(Map 7NW 1998) Moderate Potential 100,934.9 71.0
(136,691.0) (96.2)
Retention of Sediments
and Other Particulates High Potential 38,599.3 27.2
(Map 8NW 1998) Moderate Potential 4,742.6 3.3
(43,341.9) (30.5)
Coastal Storm Surge
Detention High Potential 25,725.2 18.1
(Map 9NW 1998)
Shoreline Stabilization High Potential 39,021.2 27.5
(Map 10NW 1998) Moderate Potential 0.9 -
(39,022.1) (27.5)
26
Table 9. (cont'd)
Fish/Shellfish Habitat* High Potential 17,619.4 12.4
(Map 11NW 1998) Moderate Potential 1,413.5 1.0
Shading Potential 13,161.8 9.3
(32,194.7) (22.7)
Waterfowl/Waterbird High Potential 18,122.4 12.8
Habitat Moderate Potential 1,201.5 0.8
(Map 12NW 1998) Wood Duck Potential 14,739.6 10.4
(34,063.5) (24.0)
Other Wildlife Habitat High Potential 130,041.8 91.5
(Map 13NW 1998) Moderate Potential 6,666.8 4.7
(136,708.6) (96.2)
Biodiversity Atlantic White Cedar 119.6 0.1
(Map 14NW 1998) Bald Cypress 354.0 0.2
Estuarine Oligohaline 6683.6 4.7
Riverine Tidal 378.5 0.3
Palustrine Tidal Emergent 373.5 0.3
Palustrine Tidal Evergreen
Forested 627.9 0.4
Palustrine Tidal Scrub-Shrub 243.1 0.2
Estuarine Forested 242.1 0.2
Estuarine Scrub-Shrub 69.5 <0.1
Palustrine Aquatic Bed** 0.8 <0.1
Palustrine Emergent
Seasonally Flooded 289.6 0.2
Palustrine Semipermanently
Flooded 317.1 0.2
Palustrine Scrub-Shrub
Seasonally Flooded 134.1 0.1
Palustrine Evergreen Forested
Seasonally Flooded 102.4 0.1
Palustrine Forested/Emergent
Seasonally Flooded 125.8 0.1
Palustrine Forested/Broad-leaved
Evergreen
Seasonally Flooded 189.2 0.1
Forested Complex #1 15,324.7 10.8
Forested Complex #2 10,188.4 7.2
(35,763.9) (25.2)
*Wetlands important for streamflow maintenance are also vital for maintaining this habitat.
**Probably more extensive but not detected by this inventory due to source imagery.
27
Comparison: Pre-settlement Conditions vs. 1998 Conditions
Wetland Extent
The estimated acreage of wetlands in pre-settlement times was 230,019 acres (approximately
45% of the watershed). By 1998, wetland acreage declined to only 62 percent of the original
acreage and many of these wetlands were altered (e.g., ditched, excavated, or impounded). In
1998, only 28 percent of the watershed was occupied by wetlands. Acreage of palustrine
wetlands decreased by nearly 40 percent, while acreage of estuarine wetlands dropped by 28
percent due to sea level rise effects. Some of the loss of palustrine forested wetlands was also
attributed to sea level rise and subsequent coastal subsidence that converted these forests to
estuarine wetlands. This process is still occurring as witnessed by the presence of salt marsh
vegetated growing with salt-stressed loblolly pines and the remains of woody plants in estuarine
marshes. Most of the loss of palustrine wetlands, however, was due to conversion to agriculture,
the predominant land use in the watershed today. Besides the outright elimination of wetlands,
this conversion also caused fragmentation of the remaining wetlands. For example, at pre-settlement,
there was an estimated 380 terrene interfluve outflow wetlands accounting for 72
percent of the wetlands; these wetlands had an average size of 433 acres. By 1998, this type had
increased in number by nearly 6 times (to 2120) and decreased in acreage by 43 percent (to
94,216.3 acres), resulting in a reduction in the average size to 44 acres (just one tenth of its
original average size).
Wetland Functions
Two comparisons of changes in functions were made, one showing changes in acres providing
functions at significant levels (Table 10) and the other depicting changes in functional units
(Table 11). From an acreage standpoint, substantial losses in wetlands providing all functions
ranging from over 50 percent acreage loss in wetlands performing sediment retention to about 20
percent loss of wetlands stabilizing shorelines and providing coastal storm surge detention.
Thirty percent of the wetland acreage performing most functions was lost. The streamflow
maintenance function experienced the greatest change in performance. Ditching of terrene
interfluve wetlands effectively drained many headwater wetlands converting them to cropland
(upland) or significantly altered the hydrology of many remaining wetlands, thereby lowering
their streamflow maintenance function from high to moderate. Eighty-seven percent of high-functioning
streamflow maintenance acreage was lost, with 48 percent of this acreage converted
to upland and 52 percent reduced to moderate potential.
When functional units were evaluated, the change in “functional capacity” can be better seen
(Table 11). Roughly 64 percent of the functional capacity of wetlands contributing to
streamflow maintenance was lost. This means that the watershed may be operating at only 36
percent of its pre-settlement capacity. The watershed's capacity for providing six other functions
decreased by more than 25 percent (i.e., surface water detention, nutrient transformation,
sediment and other particulate retention, fish and shellfish habitat, waterfowl and waterbird
habitat, and other wildlife habitat). The two remaining functions (shoreline stabilization and
coastal storm surge detention) were reduced by approximately 23 percent of their pre-settlement
capacity. No function experienced an increase in capacity.
28
Table 10. Comparison of preliminary functional assessment results for Nanticoke wetlands at
pre-settlement versus 1998. Acreage of function and percentage of the wetland total are given
for each function.
Pre-settlement 1998 %
Function Potential Acreage Acreage Change
Significance (% of total acreage) (% of total) in Acres
Surface Water Detention High 50,339.9 (21.9) 39,200.7 (27.6) -22.1
Moderate 174,911.7 (76.0) 98,423.7 (69.3) -43.7
Streamflow Maintenance High 180,238.8 (78.4) 23,678.0 (16.7) -86.9
Moderate 1,349.5 (0.6) 82,331.3 (57.9) +600.1%
Nutrient Transformation High 96,353.9 (41.9) 35,756.1 (25.2) -62.9
Moderate 133,665.3 (58.1) 100,934.9 (71.0) -24.5
Retention of Sediments
and Other Particulates High 50,338.9 (21.9) 38,599.3 (27.2) -23.3
Moderate 50,302.0 (21.9) 4,742.6 (3.3) -90.6
Shoreline Stabilization High 50,507.4 (22.0) 39,021.2 (27.5) -22.7
Moderate - 0.9 (-) +neglible
Coastal Storm Surge
Detention High 33,561.6 (14.6) 25,725.2 (18.1) -23.3
Fish/Shellfish Habitat High 26,354.9 (11.5) 17,619.4 (12.4) -33.1
Moderate - 1,413.5 (1.0) +signif
Shading 16,765.4 (7.3) 13,161.8 (9.3) -21.5
Waterfowl/Waterbird Habitat High 26,396.7 (11.5) 18,122.4 (12.8) -31.3
Moderate - 1,201.5 (0.8) +signif
Wood Duck 19,823.6 (8.6) 14,739.6 (10.4) -25.6
Other Wildlife Habitat High 223,681.7 (97.2) 130,041.8 (91.5) -41.9
Moderate 6,337.5 (2.8) 6,666.8 (4.7) +5.2
29
Table 11. Predicted change in the Nanticoke watershed's capacity to perform nine wetland
functions from pre-settlement to 1998. Functional units were derived from predictive values for
each time period by applying a weighting scheme (2 for high; 1 for moderate; and 1 for other
significant features, e.g., stream shading). The conservation of biodiversity function was not
compared since original data lacked sufficient detail for such comparison.
Pre-settlement 1998 Predicted % Change
Function Functional Units Functional Units in Functional
Capacity
Surface Water Detention 275,591.5 176,825.1 -35.8
Streamflow Maintenance 361,827.1 129,687.3 -64.2
Nutrient Transformation 326,373.1 172,447.1 -47.2
Sediment and Other
Particulate Retention 150,979.8 81,941.2 -45.7
Shoreline Stabilization 101,014.8 78,043.3 -22.7
Coastal Storm Surge
Detention 67,123.2 51,450.4 -23.3
Fish and Shellfish Habitat 69,475.2 49,814.1 -28.3
Waterfowl and Waterbird
Habitat 72,617.0 52,185.9 -28.1
Other Wildlife Habitat 453,700.9 266,750.4 -41.2
---------------------------------------------------------------------------------------------------------------------
Natural Habitat Extent
At pre-settlement, the entire watershed (excluding river and stream bottoms) was in natural
vegetation (Map 14NW pre-settlement). European settlement and the rise in human population
led to the conversion of much of this natural habitat to land for human uses like farming,
housing, and commercial/industrial facilities. By 1998, over half of the "natural" habitat (e.g.,
forests, thickets, vegetated wetlands, and non-agricultural fields) had been converted to
agricultural land (235,000 acres or 46.5% of the watershed) and developed land (38,000 acres or
7.5%) (Map 15NW 1998).
30
Discussion
Extensive wetlands have always been recognized on the Delmarva Peninsula. Interpretation of
the 1920s soil surveys predicted that the percent of the county represented by wetlands ranged
from 32 percent for Caroline County to a high of 75 percent for Dorchester County (Table 12).
The latter county had extensive tidal wetlands bordering Chesapeake Bay and much acreage of
flatwood soils (e.g., Elkton). If the former are discounted, the extent of wetlands in the five-county
area was between 40-50 percent. In the Nanticoke River watershed, an estimated 44
percent of the watershed was occupied by wetlands in the pre-settlement era. Today, only 28
percent of the watershed is wetland. Similarly, land use has converted much of the natural
habitat of the watershed to agricultural land and to a lesser degree, developed (urban/suburban)
land (see Map 15NW 1998). As of 1998 only 46 percent of the watershed was in “natural
habitat” and that figure includes commercial forests as “natural habitat."
The pre-settlement estimate of estuarine wetlands is probably an overestimate since the rate of
sea level rise appears to have only accelerated substantially over the past 100 years. Prior to this
time, the rate of sea level rise was minimal or at least, low enough for marsh accretion to keep
pace with the rising tides. The U.S.G.S. topographic maps displayed a 6-foot (2 m) depth
contour as the shallowest depth line that could be used to approximate the lower limit of former
estuarine wetlands (including tidal flats). Perhaps navigation charts may provide more detailed
depth contours, but electronic versions were not available for the study area. Consulting historic
maps might be beneficial but was not part of this study. Kearney et al. (1988) examined marsh
loss in the Nanticoke River estuary and reported an average marsh loss of 0.5 percent (122.5
acres) annually since 1938, with higher rates in the lower estuary. Widening of tidal channels
within the marshes also increased with channel width doubling in many creeks. Marsh loss
appears to originate in the marsh interior with a merging of ponds and waterlogging of
substrates. Today, only the upstream tidal marshes appear to be keeping pace with or exceeding
the rate of sea level rise; downstream there seems to be little allochthonous sediment input,
thereby creating an accretionary deficit relative to sea level. These marshes are in jeopardy and
many acres may be converted to open water during the next 50-100 years.
For historic vegetation patterns, information comes from two sources: 1) The Plant Life of
Maryland (Shreve et al. 1910) and 2) 1920s soil survey reports. Table 13 summarizes data from
Shreve (1910), while Table 14 presents a list of plants associated with various soil types. For the
latter, the list comes directly from the soil survey reports and one can usually determine what
genus or species they are referring to; in a few cases, the common names are no longer used, so
one would have to make a best guess, without doing more investigation. These reports also
support our interpretation that essentially all of the soils were forested in their original state,
except for tidal marsh.
More recent descriptions of wetland plant communities typical of the Nanticoke River watershed
have been reported in NWI state reports for Delaware and Maryland (see Tiner 1985, Tiner and
Burke 1995, respectively). Dominant trees of tidal swamps include red maple (Acer rubrum) and
green ash (Fraxinus pennsylvanica var. subintergerrima). Black willow (Salix nigra) and black
gum (Nyssa sylvatica) may co-dominate in places and large areas of tidal loblolly pine swamp
(Pinus taeda) are common in Dorchester and Somerset Counties, Maryland (Tiner and Burke
31
1995). Seasonally flooded nontidal forested wetlands are usually represented by one or more of
the following species: red maple, sweet gum (Liquidambar styraciflua), willow oak (Quercus
phellos), pin oak (Q. palustris), basket or swamp chestnut oak (Q. michauxii), and loblolly pine.
Temporarily flooded3 or seasonally saturated wetland forests (“winter wet woods”) are largely
characterized by loblolly pine with various hardwoods including white oak (Q. alba), American
beech (Fagus grandifolia), tulip or yellow poplar (Liriodendron tulipifera), American holly (Ilex
opaca), red maple, and black gum. Red oak (Q. rubra) and southern red oak (Q. falcata) may
also occur in significant numbers. Other seasonally saturated wetlands are wet deciduous forests
dominated by red maple. black gum, and sweet gum. Associated trees include loblolly pine,
American holly, sweet bay (Magnolia virginiana), willow oak, southern red oak, red oak, water
oak (Q. nigra), and basket oak.
3Temporarily flooded wetlands noted in Tiner (1985) and Tiner and Burke (1995) are mostly
represented by seasonally saturated types (a term not widely used until the mid-1990s - see
footnote 2 page 91 in Tiner and Burke 1995).
32
Table 12. Acreage of wetlands in each county in the study area in the early 21st Century based on 1920s county soil
surveys (Snyder et al. 1924, Dunn et al. 1920, Winant and Bacon 1929, Snyder and Gillett 1925, and Snyder et al.
1926). Note statistics are for the entire county not just the area within the Nanticoke River watershed.
County Wetland Soils Acreage % of County Source
Caroline Elkton loam 21,632 10.6
Elkton sandy loam 7,424 3.6
Elkton silt loam 3,584 1.8
Plummer loamy sand 2,304 1.1
Portsmouth loam 7,872 3.9
Portsmouth sandy loam 7,424 3.6
Meadow 10,304 5.0
Tidal marsh 4,416 2.2
------------------------------ ----------- -----
Total 65,010 31.8 Winant and Bacon 1929
Dorchester Elkton silt loam 161,536 43.8
Elkton sandy loam 12,800 3.5
Elkton loam 7,808 2.1
Meadow 5,056 1.4
Portsmouth loam 1.344 0.4
Tidal marsh 88,128 23.9
----------------------------- ------------ --------
Total 276,672 75.1 Snyder et al. 1926
Wicomico Elkton sandy loam 19,648 8.1
Elkton silt loam 18,112 7.5
Elkton fine sandy loam 17,728 7.3
Elkton loam 10,944 4.5
Portsmouth f. sandy loam 18,432 7.6
Portsmouth loam 6,528 2.7
St. Johns sandy loam 6,272 2.6
Meadow 4,416 1.8
Swamp 6,784 2.8
Tidal marsh 15,168 6.3
------------------------------- -------------- ------
Total 124,032 51.2 Snyder and Gillett 1925
Kent Elkton sandy loam 51,392 13.5
Elkton loam 16,128 4.3
Elkton silt loam 12,096 3.2
Portsmouth sandy loam 17,920 4.7
Portsmouth silt loam 14,528 3.8
Portsmouth loam 6,400 1.7
Coastal beach 704 0.2
Meadow 8,512 2.2
Swamp 10,688 2.8
Tidal marsh 45,568 12.0
------------------------------ ---------- -----
Total 183,936 48.4 Dunn et al. 1920
33
Table 12. (Continued)
County Wetland Soils Acreage % of County Source
Sussex Elkton sandy loam 91,712 15.2
Elkton sand 7,488 1.2
Elkton loam 2,496 0.4
Portsmouth sandy loam 52,544 8.7
Portsmouth loam 17,344 3.0
St. Johns sand 960 0.1
Coastal beach 4,224 0.7
Meadow 3,392 0.6
Swamp 26,432 4.4
Tidal marsh 35,136 5.8
-------------------------- ----------- ----
Total 241,728 40.1 Snyder et al. 1924
-------------------------------------------------------------------------------------------------------------------------------------------
Table 13. Vegetation of Eastern Shore swamps and floodplains according to Shreve (1910). Major tree species are
italicized. Common names generally follow Tiner (1988).
Wetland Type Vegetation
Clay Upland Swamps Trees: sweet gum, white oak, black gum, willow oak, red maple, swamp white oak,
loblolly pine, American holly, and basket oak
Shrubs: sweet pepperbush, maleberry, highbush blueberry, swamp azalea, fetterbush,
southern arrowwood, Virginia sweet-spires, black haw, sweet bay, common winterberry,
flowering dogwood, and smooth alder
Herbs: sedges and pale manna grass
Others: peat moss
Sandy Loam Upland
Swamps Trees: loblolly pine, willow oak, white oak, sweet gum, red maple, water oak, basket oak,
black gum, sweet bay, American holly, flowering dogwood, fringe-tree, and river birch
Shrubs: wax myrtle, southern arrowwood, poison sumac, staggerbush, Virginia sweet-spires,
devil’s walking stick, red chokeberry, and American strawberrybush
Herbs: none specified
Others: peat moss
Wetter Floodplain
Forests Trees: red maple, black gum, white ash, and sweet bay
Shrubs: common winterberry, sweet pepperbush, smooth alder, southern arrowwood,
buttonbush, and poison sumac
Herbs: lizard’s tail, cinnamon fern, sensitive fern, golden saxifrage, turtlehead, marsh St.
John’s-wort, jewelweed, sweet white violet, cursed crowfoot, bladder sedge, and sweet-scented
bedstraw
Sandy Floodplains Trees: loblolly pine, water oak, American holly, black gum, sweet bay, white ash, fringe-tree,
flowering dogwood, and ironwood
Shrubs: sweet pepperbush, southern arrowwood, pink azalea, and American
strawberrybush
Herbs: partridgeberry, bladder sedge, Long’s sedge, and sedge
Vines: common greenbrier, Virginia creeper, fox grape, trumpet creeper, and wild yam
34
Table 13. (cont’d)
Drier Floodplain
Forests Trees: tulip poplar, ironwood, sweet gum, white ash, sycamore, American elm, willow
oak, red maple, and black gum
Shrubs: spicebush, southern arrowwood, and American strawberrybush
Herbs: Virginia grape fern, white grass, smooth Solomon’s-seal, jack-in-the-pulpit, sweet
white violet, swamp aster, and wood sorrel
Upland Swamps of the
Wicomico Terrace Trees: black gum, swamp white oak, red maple, sweet gum, willow oak, white oak,
American holly, beech, sweet bay, and swamp cottonwood
Shrubs: Virginia sweet-spires, red chokeberry, and swamp azalea
Herbs: water smartweed, inflated bladderwort, and mermaid-weed
River Swamps Trees: bald cypress, black gum, red maple, sweet gum, swamp black gum, green ash,
sweet bay, tulip poplar, ironwood, swamp cottonwood, water oak, Atlantic white cedar,
loblolly pine, white oak, and American holly
Shrubs: wax myrtle, sweet pepperbush, maleberry, smooth alder, buttonbush, silky
dogwood, southern arrowwood, staggerbush, water-willow, and dangleberry
Vines: trumpet creeper, grapes, common greenbrier, Virginia creeper, poison ivy, and
cross vine
Herbs: dwarf St. John’s-wort, jewelweed, water pennywort, marsh St. John’s-wort, marsh
fern, cardinal flower, three-way sedge, water primrose, mermaid-weed, lizard’s tail, false
nettle, ditch stonecrop, Virginia bugleweed, and hoplike sedge
Stream Swamps Trees (small-sized): red maple, green ash, loblolly pine, Atlantic white cedar, black gum,
sweet bay, sweet gum, black willow, swamp white oak, and river birch
Shrubs: common winterberry, sweet pepperbush, buttonbush, smooth alder, water-willow,
silky dogwood, Virginia sweet-spires, poison sumac, southern arrowwood, and
swamp rose
Herbs: broad-leaved cattail, cinnamon fern, jewelweed, lizard’s tail, royal fern, big-leaved
arrowhead, water hemlock, water dock, arrow arum, pickerelweed, New York
ironweed, water pepper, blue flag, mermaid-weed, tall meadow-rue, marsh blue violet,
and false nettle
35
Table 14. Generalized plant-soil correlations from early 1900s soil survey reports.
County (Source) Soil or Land Type Characteristic Vegetation
Dorchester Elkton sandy loam Loblolly pine, oak, black gum, sweet gum, holly, myrtle,
(Snyder et al. 1926) huckleberry, and bull brier (65-75% of this soil was forested
with second growth)
Elkton loam Pine, oak, maple, gum, myrtle, and huckleberry (50% of this
soil was forested with second growth)
Elkton silt loam Gum, soft maple, loblolly pine, oaks, holly, myrtle,
huckleberry, with other “bushes and shrubs” (75% of this soil
was forested with second growth)
Elkton silt loam,
low phase Loblolly pine, maple, oak, holly, myrtle, huckleberry, grass,
and “shrubs that thrive on a moist soil.” (very little of this soil
was cleared; averages 1.5-2-feet above sea level)
Portsmouth loam Pine, oak, black gum, sweet gum, huckleberry, bullberries,
myrtle, and “other shrubs and grasses.” (only a “very small
part” was cultivated; rest is in forest)
Meadow (“semiswampy
alluvial soils”) Oak, pine, black gum, sweet gum, myrtle bushes, and briers
(when in forest)
Tidal marsh Marsh grasses and a few shrubs or salt-water bushes
Tidal marsh, low phase Stunted pines, myrtle bushes, and marsh grasses
Wicomico Elkton sandy loam White oak, black oak, willow oak, water oak, black gum,
(Snyder and Gillett 1925) sweet gum, pine, beech, maple, dogwood, myrtle, huckleberry,
and other shrubs (a considerable amount of this soil was
cultivated)
Elkton fine sandy loam Pine, white oak, sweet gum, black gum, huckleberry, myrtle,
holly, smilax, and other shrubs and vines (some of this soil is
cleared; most in forest)
Elkton loam White and black oaks, pine, beech, sweet gum, black gum,
myrtle, huckleberry, smilax, and other vines and shrubs
(probably 50% was in forest)
Elkton silt loam White, black, red, and willow oaks, sweet gum, black gum,
loblolly pine, maple, beech, hickory (“white oak land”; a
large part of this soil was forest)
St. Johns sandy loam Pine, oak, gum, holly, maple, myrtle, buckberry, smilax, and
“other shrubs and vines that thrive on a moist soil” (65-75%
was cultivated)
Portsmouth fine sandy
loam Not listed (50% was forested; vegetation similar to “the other
poorly drained soils”)
Portsmouth loam Loblolly pine, hardwoods, myrtle, bay, huckleberry, smilax,
and other vines and shrubs (most of this soil was forested)
Meadow (poorly drained
alluvial soil) In its native state meadow supported a dense forest of “water-loving
species”
Swamp No plants listed
Tidal Marsh Salt grasses and other “marsh-loving plants”
Caroline Elkton loam Not listed (about 40-50% was cultivated)
(Winant and Bacon 1929) Elkton sandy loam Not listed
Elkton silt loam Not listed (only a small portion was cultivated)
Portsmouth loam Not listed (no more than 35% was cultivated)
36
Portsmouth sandy loam Sweet gum, black gum, beech, maple, pine, huckleberry,
gallberry, and other bushes (not more than 33% was cleared)
Meadow Alder, oak, pine, black gum, sweet gum, myrtle, and briers
Tidal Marsh Marsh grasses, numerous sedges, ironweed, cow lily,
arrowhead, water hemp, and wild rice
Kent Elkton sandy loam Oaks (mostly white), black gum, sweet gum, maple, dogwood,
(Dunn et al. 1920) and other trees (used extensively for agriculture but still much
remained in timber)
Elkton loam White oak, willow oak, black gum, sweet gum, maple, and
other deciduous trees (“white oak land”; over 50% forested)
Elkton silt loam White oak, willow oak, sweet gum, black gum, maple,
hickory, red oak, and moss (“white oak land”; considerable
portion was cultivated despite low agricultural value)
Portsmouth sandy loam Willow oak, swamp white oak, black gum, sweet gum, ash,
maple, ironwood, chestnut, willow, azalea, buttonbush, high-bush
huckleberry, and similar plants (large proportion of this
soil was forest)
Portsmouth loam Willow oak, sweet gum, black gum, and alder (much of this
soil was nonagricultural)
Portsmouth silt loam Vegetation like Portsmouth loam with denser underbrush
(most remained in forest)
Meadow Water oak, spotted oak, maple, birch, alder, sweet gum,
willow, ash, cat-brier, wild grape, and poison ivy (original
state was forest)
Swamp Gum, willow, alder, cedar, pine, bay, birch, maple, and
extremely dense undergrowth of brush, vines, and other plants
adapted to swampy conditions
Tidal Marsh Cattails, swordgrass, calamus, and various “salt-loving and
marsh-loving plants”
Sussex Elkton sand Pine, oak, maple, beech, and gum (about 50% was forest)
(Snyder et al. 1924) Elkton sandy loam White oak, black oak, willow oak, water oak, black gum,
sweet gum, pine, beech, maple, dogwood, myrtle, huckleberry,
and other shrubs (large part was farmed; rest was forest)
Elkton loam White oak, willow oak, black gum, sweet gum, maple and
other deciduous trees (“white-oak land”; large part of this soil
was forest)
St. Johns sand Pine, oak, gum, holly, maple, huckleberry, and other shrubs
(“iron-mine land”; about 50% was forest)
Portsmouth sandy loam Loblolly pine, post oak, white oak, willow oak, water oak,
sweet gum, holly, beech, maple, ash, bay, buttonbush,
highbush huckleberry, myrtle, laurel, and smilax; cleared areas
support dense growth of broom sedge (much of this soil was
cleared and cultivated)
Portsmouth loam Pine, sweet gum, oak, maple, some cypress, briers, smilax,
bay, huckleberry, and gallberry (only small areas cultivated)
Meadow Willow oak, white oak, black oak, sweet gum, alder, maple,
birch, loblolly pine, smilax (catbrier or greenbrier), wild
grape, and poison ivy
Swamp Pine, gum, birch, maple, alder, buttonbush, cedar, and dense
growth of vines and shrubs (none of this was cultivated)
Tidal Marsh Swordgrass, calamus, cat-tails, and various “marsh-loving and
salt-water plants”
37
Conclusions
Wetlands in the Nanticoke River watershed have undergone significant changes since pre-settlement.
Prior to European colonization, about 45 percent of the watershed (roughly 230,000
acres) was wetland, with extensive headwater wetlands supporting streamflow. By 1998, only
about 142,000 wetland acres (64% of the original acreage) remained and much of this acreage
has been ditched, excavated, or impounded. Conversion of wetlands to agricultural lands was
the predominant cause of wetland change since by 1998 about 46 percent of the watershed was in
agricultural land use.
Cumulative wetland losses have led to significant reductions in many wetland functions. Since
colonial times, it was estimated that the Nanticoke watershed lost over 60 percent of its predicted
capacity for streamflow maintenance and over 30 percent of its capacity for four other functions:
surface water detention, nutrient transformation, sediment and other particulate retention, and
provision of other wildlife habitat. No function has experienced an increase in capacity.
The findings of this report provide an overview of the predicted changes in wetland extent and
function for the Nanticoke River watershed since European settlement. The comparison of
changes in wetland function watershed-wide should be considered approximate due to the nature
of this type of analysis (e.g., reconstruction of pre-settlement wetland distribution from soils and
topographic data). As with any remotely-sensed analysis, field checking should be conducted to
validate the interpretations regarding functions of individual wetlands since this type of
assessment is a coarse-filter approach and not a fine-filter one. Despite these limitations, the
report serves as a foundation for understanding the extent to which wetlands have changed in
general form and in function. As such, it provides a valuable tool for resource planning to be
used with other tools (derived from field observations and other site-specific data) to help devise
a watershed-wide strategy for wetland conservation and restoration.
38
Acknowledgments
This study was funded by the Kent Conservation District (KCD) and the Maryland Eastern Shore
Resource Conservation and Development Council (ESRC&D). Project officers were Tim Riley
for KCD and Dave Wilson for ESRC&D. Ralph Tiner was principal investigator for the Service
and was responsible for study design, project oversight, analysis, and report preparation.
Herbert Bergquist (FWS) was responsible for digital database construction of historic wetlands,
wetland classification, GIS analyses, and preparation of statistics and maps included in this
report. Bobbi Jo McClain assisted in digital database construction during the early phase of this
work. Correlations between wetland characteristics and wetland functions used to produce the
preliminary assessment of wetland functions were prepared jointly by the Service, wetland
specialists from Maryland and Delaware, and other wetland scientists.
Amy Jacobs (DNREC) and the Nanticoke wetland group she assembled reviewed the draft
protocols for correlating wetland characteristics with wetland functions and provided
recommendations to modify the selection criteria. Participants included David Bleil, Katheleen
Freeman, Cathy Wazniak, Mitch Keiler, and Bill Jenkins (Maryland Department of Natural
Resource); Julie LaBranche (Maryland Department of the Environment); Marcia Snyder, Dennis
Whigham, and Don Weller (Smithsonian Environmental Research Center); Matt Perry and Jon
Willow (U.S. Geological Survey); Mark Biddle (DNREC); and Peter Bowman (Delaware
Natural Heritage Program). Amy Jacobs and David Bleil reviewed the draft report. Abby
Rokosch (DNREC) provided copies of the texts of 1920s soil survey reports for Kent and Sussex
Counties.
39
References
Brewer, J.E., G.P. Demas, and D. Holbrook. 1998. Soil Survey of Dorchester County,
Maryland. U.S.D.A. Natural Resources Conservation Service, Washington, DC.
Brinson, M. M. 1993. A Hydrogeomorphic Classification for Wetlands. U.S. Army Corps of
Engineers, Washington, DC. Wetlands Research Program, Technical Report WRP-DE-4.
Cowardin, L. M., V. Carter, F. C. Golet, and E. T. LaRoe. 1979. Classification of Wetlands and
Deepwater Habitats of the United States. U.S. Fish and Wildlife Service, Washington, DC.
FWS/OBS-79/31.
Dunn, J.E., J.M. Snyder, and E. Hoffecker. 1920. Soil Survey of Kent County, Delaware. U.S.
Department of Agriculture. Government Printing Office, Washington, DC.
Hall, R.L. 1970. Soil Survey Wicomico County, Maryland. U.S.D.A. Soil Conservation
Service, Washington, DC.
Ireland, W., Jr. and E.D. Matthews. 1974. Soil Survey of Sussex County, Delaware. U.S.D.A.
Soil Conservation Service, Washington, DC.
Kearney, M.S., R.E. Grace, and J. C. Stevenson. 1988. Marsh loss in Nanticoke Estuary,
Chesapeake Bay. The Geographical Review 78: 205-220.
Matthews, E.D. 1964. Soil Survey Caroline County, Maryland. U.S.D.A. Soil Conservation
Service, Washington, DC.
Matthews, E.D., and W. Ireland, Jr. 1971. Soil Survey Kent County, Delaware. U.S.D.A. Soil
Conservation Service, Washington, DC.
Meyer, J.L., L.A. Kaplan, D. Newbold, D.L. Strayer, C.J. Woltemade, J.B. Zedler, R. Beilfuss,
Q. Carpenter, R. Semlitsch, M.C. Watzin, and P.H. Zedler. 2003. Where Rivers are Born: The
Scientific Imperative for Defending Small Streams and Wetlands. American Rivers and Sierra
Club, Washington, DC. 23 pp.
Mitsch, W.J. and J.G. Gosselink. 1993. Wetlands. Van Nostrand Reinhold, New York, NY.
Robbins, C.S., D.K. Dawson, and B.A. Dowell. 1989. Habitat area requirements of breeding
forest birds of the Mid-Atlantic states. Wildlife Monogr. 103: 1-34.
Schroeder, R.L. 1996. Wildlife Community Habitat Evaluation Using a Modified Species-Area
Relationship. U.S. Army Corps of Engineers, Waterways Expt. Station, Vicksburg, MS.
Wetlands Research Program Tech. Rep. WRP-DE-12.
40
Shreve, F. 1910. The ecological plant geography of Maryland: Coastal Zone; Eastern Shore
District. In: F. Shreve, M.A. Chrysler, F.H. Blodgett, and F.W. Besley. The Plant Life of
Maryland. The John Hopkins Press, Baltimore, MD. pp. 101-148.
Snyder, J.M., J.H. Barton, J.E. Dunn, J. Gum, and W.A. Gum. 1924. Soil Survey of Sussex
County, Delaware. U.S. Department of Agriculture, Bureau of Soils. Government Printing
Office, Washington, DC.
Snyder, J.M. and R.L. Gillett. 1925. Soil Survey of Wicomico County, Maryland. U.S.
Department of Agriculture, Bureau of Soils. Government Printing Office, Washington, DC.
Snyder, J.M., W.C. Jester, and O.C. Bruce. 1926. Soil Survey of Dorchester County, Maryland.
U.S. Department of Agriculture, Bureau of Soils. Government Printing Office, Washington, DC.
Tiner, R.W. 1985. Wetlands of Delaware. U.S. Fish and Wildlife Service, National Wetlands
Inventory Project, Newton Corner, MA and Delaware Department of Natural Resources and
Environmental Control, Dover, DE. Cooperative publication.
Tiner, R.W. 1988. Field Guide to Nontidal Wetland Identification. Maryland Department of
Natural Resources, Annapolis, MD and U.S. Fish and Wildlife Service, Northeast Region,
Newton Corner, MA.
Tiner, R.W. 1997. NWI Maps: What They Tell Us. National Wetlands Newsletter 19(2): 7-12.
Tiner, R.W. 1998. In Search of Swampland: A Wetland Sourcebook and Field Guide. Rutgers
University Press, New Brunswick, NJ.
Tiner, R.W. 1999. Wetland Indicators: A Guide to Wetland Identification, Delineation,
Classification, and Mapping. Lewis Publishers, CRC Press, Boca Raton, FL.
Tiner, R. W. 2000. Keys to Waterbody Type and Hydrogeomorphic-type Wetland Descriptors
for U.S. Waters and Wetlands (Operational Draft). U.S. Fish and Wildlife Service, Northeast
Region, Hadley, MA.
Tiner, R.W. 2003a. Dichotomous Keys and Mapping Codes for Wetland Landscape Position,
Landform, Water Flow Path, and Waterbody Type Descriptors. U.S. Fish and Wildlife Service,
National Wetlands Inventory Program, Northeast Region, Hadley, MA.
Tiner, R.W. 2003b. Correlating Enhanced National Wetlands Inventory Data with Wetland
Functions for Watershed Assessments: A Rationale for Northeastern U.S. Wetlands. U.S. Fish
and Wildlife Servie, Northeast Region, Hadley, MA.
Tiner, R., M. Starr, H. Bergquist, and J. Swords. 2000. Watershed-based Wetland
Characterization for Maryland’s Nanticoke River and Coastal Bays Watersheds: A Preliminary
Assessment. U.S. Fish and Wildlife Service, Northeast Region, Hadley, MA. NWI report.
41
Tiner, R.W., H.C. Bergquist, J.Q. Swords, and B.J. McClain. 2001. Watershed-based Wetland
Characterization for Delaware’s Nanticoke River Watershed: A Preliminary Assessment Report.
U.S. Fish and Wildlife Service, National Wetlands Inventory Program, Northeast Region,
Hadley, MA. NWI report.
Tiner, R.W. and D.G. Burke. 1995. Wetlands of Maryland. U.S. Fish and Wildlife Service,
Ecological Services, Northeast Region, Hadley, MA and Maryland Department of Natural
Resources, Annapolis, MD. Cooperative National Wetlands Inventory publication.
Winant, H.B. and S.R. Bacon. 1929. Soil Survey of Caroline County, Maryland. U.S.
Department of Agriculture, Bureau of Chemistry and Soils. Government Printing Office,
Washington, DC.
Appendices
Appendix A.
Dichotomous Keys and Mapping Codes for Wetland Landscape Position,
Landform, Water Flow Path, and Waterbody Type Descriptors (Tiner 2003a).
U.S. Fish and Wildlife Service
Dichotomous Keys and Mapping Codes for Wetland
Landscape Position, Landform, Water Flow Path, and
Waterbody Type Descriptors
September 2003
Dichotomous Keys and Mapping Codes for Wetland Landscape Position,
Landform, Water Flow Path, and Waterbody Type Descriptors
Ralph W. Tiner
Regional Wetland Coordinator
U.S. Fish and Wildlife Service
National Wetlands Inventory Project
Northeast Region
300 Westgate Center Drive
Hadley, MA 01035
September 2003
This report should be cited as:
Tiner, R.W. 2003. Dichotomous Keys and Mapping Codes for Wetland Landscape Position,
Landform, Water Flow Path, and Waterbody Type Descriptors. U.S. Fish and Wildlife Service,
National Wetlands Inventory Program, Northeast Region, Hadley, MA. 44 pp. (original version;
this attachment = 43 pp.)
Table of Contents
Page
Section 1. Introduction 1
Need for New Descriptors 1
Background on Development of Keys 2
Use of the Keys 3
Uses of Enhanced Digital Database 3
Organization of this Report 4
Section 2. Wetland Keys 5
Key A-1: Key to Wetland Landscape Position 8
Key B-1: Key to Inland Landforms 11
Key C-1: Key to Coastal Landforms 14
Key D-1: Key to Water Flow Paths 15
Section 3. Waterbody Keys 17
Key A-2: Key to Major Waterbody Type 18
Key B-2: Key to River/Stream Gradient and Other Modifiers Key 19
Key C-2: Key to Lakes 21
Key D-2: Key to Ocean and Marine Embayments 22
Key E-2: Key to Estuaries 22
Key F-2: Key to Water Flow Paths 24
Key G-2: Key to Estuarine Hydrologic Circulation Types 25
Section 4. Coding System for LLWW Descriptors 26
Codes for Wetlands 26
Landscape Position 26
Lotic Gradient 26
Lentic Type 27
Estuary Type 27
Inland Landform 28
Coastal Landform 29
Water Flow Path 30
Other Modifiers 30
Codes for Waterbodies (Deepwater Habitats and Ponds) 31
Waterbody Type 31
Water Flow Path 35
Estuarine Hydrologic Circulation Type 35
Other Modifiers 35
Section 5. Acknowledgments 36
Section 6. References 36
Section 7. Glossary 39
1
Section 1. Introduction
A wide variety of wetlands have formed across the United States. To describe this diversity and
to inventory wetland resources, government agencies and scientists have devised various wetland
classification systems (Tiner 1999). Features used to classify wetlands include vegetation,
hydrology, water chemistry, origin of water, soil types, landscape position, landform
(geomorphology), wetland origin, wetland size, and ecosystem form/energy sources.
The U.S. Fish and Wildlife Service's wetland and deepwater habitat classification (Cowardin et
al. 1979) is the national standard for wetland classification. This classification system
emphasizes vegetation, substrate, hydrology, water chemistry, and certain impacts (e.g., partly
drained, excavated, impounded, and farmed). These properties are important for describing
wetlands and separating them into groups for inventory and mapping purposes and for natural
resource management. They do not, however, include some abiotic properties important for
evaluating wetland functions (Brinson 1993). Moreover, the classification of deepwater habitats
is limited mainly to general aquatic ecosystem (marine, estuarine, lacustrine, and riverine) and
bottom substrate type, with a few subsystems noted for riverine deepwater habitats. The
Service’s classification system would benefit from the application of additional descriptors that
more fully encompass the range of characteristics associated with wetlands and deepwater
habitats.
In the early 1990s, Mark Brinson created a hydrogeomorphic (HGM) classification system to
serve as a foundation for wetland evaluation (Brinson 1993). He described the HGM system as
"a generic approach to classification and not a specific one to be used in practice" (Brinson 1993,
p. 2). This system emphasized the location of a wetland in a watershed (its geomorphic setting),
its sources of water, and its hydrodynamics. The system was designed for evaluating similar
wetlands in a given geographic area and for developing a set of quantifiable characteristics for
“reference wetlands” rather than for inventorying wetland resources (Smith et al. 1995). A series
of geographically focused models or “function profiles” for various wetland types have been
created and are in development for use in functional assessment (e.g., Brinson et al. 1995,
Ainslie et al. 1999, Smith and Klimas 2002).
Need for New Descriptors
The Service’s National Wetlands Inventory (NWI) Program has produced wetland maps for 91
percent of the coterminous United States and 35 percent of Alaska. Digital data are available for
46 percent of the former area and for 18 percent of the latter. Although these data represent a
wealth of information about U.S. wetlands, they lack hydrogeomorphic and other characteristics
needed to perform assessments of wetland functions over broad geographic areas. Using
geographic information system (GIS) technology and geospatial databases, it is now possible to
predict wetland functions for watersheds - a major natural resource planning unit. Watershed
managers could make better use of NWI data if additional descriptors (e.g., hydrogeomorphic-type
attributes) were added to the current NWI database. Watershed-based preliminary
assessments of wetland functions could be performed. This new information would also permit
2
more detailed characterizations of wetlands for reports and for developing scientific studies and
lists of potential reference wetland sites.
Background on Development of Keys
Since the Cowardin et al. wetland classification system (1979) is the national standard and forms
the basis of the most extensive wetland database for the country, it would be desirable to develop
additional modifiers to enhance the current data. This would greatly increase the value of NWI
digital data for natural resource planning, management, and conservation. Unfortunately,
Brinson’s “A Hydrogeomorphic Classification of Wetlands” (1993) was not designed for use
with the Service’s wetland classification. He used some terms from the Cowardin et al. system
but defined them differently (e.g., Lacustrine and Riverine). Consequently, the Service needed
to develop a set of hydrogeomorphic-type descriptors that would be more compatible with its
system. Such descriptors would bridge the gap between these two systems, so that NWI data
could be used to produce preliminary assessments of wetland functions based on characteristics
identified in the NWI digital database. In addition, more descriptive information on deepwater
habitats would also be beneficial. For example, identification of the extent of dammed rivers and
streams in the United States is a valuable statistic, yet according to the Service’s classification
dammed rivers are classified as Lacustrine deepwater habitats with no provision for separating
dammed rivers from dammed lacustrine waters. Differentiation of estuaries by various
properties would also be useful for national or regional inventories.
Recognizing the need to better describe wetlands from the abiotic standpoint in the spirit of the
HGM approach, the Service developed a set of dichotomous keys for use with NWI data (Tiner
1997b). The keys bridge the gap between the Service's wetland classification and the HGM
system by providing descriptors for landscape position, landform, water flow path and waterbody
type (LLWW descriptors) important for producing better characterizations of wetlands and
deepwater habitats. The LLWW descriptors for wetlands can be easily correlated with the HGM
types to make use of HGM profiles when they become available. The LLWW attributes were
designed chiefly as descriptors for the Service’s existing classification system (Cowardin et al.
1979) and to be applied to NWI digital data, but they can be used independently to describe a
wetland or deepwater habitat.
The first set of dichotomous keys was created to improve descriptions of wetlands in the
northeastern United States (Tiner 1995a, b). They were initially used to enhance NWI data for
predicting functions of potential wetland restoration sites in Massachusetts (Tiner 1995a, 1997a).
Later, the keys were modified for use in predicting wetland functions for watersheds nationwide
(Tiner 1997b, 2000). A set of keys for waterbodies was added to improve the Service’s ability to
characterize wetland and aquatic resources for watersheds.
The keys are periodically updated based on application in various physiographic regions. This
version is an update of an earlier set of keys published in 1997 and 2000 (Tiner 1997b, 2000).
Relatively minor changes have been made, including the following: 1) added “drowned river-mouth”
modifier to the Fringe and Basin landforms (for use in areas where rivers empty into
large lakes such as the Great Lakes where lake influences are significant), 2) added “connecting
3
channels” to river type (to address concerns in the Great Lakes to highlight such areas), 3) added
“Throughflow-intermittent” water flow path (to separate throughflow wetlands along intermittent
streams from those along perennial streams), 4) added “Throughflow-artificial” and “Outflow-artificial”
to water flow path (to identify former "isolated" wetlands or fragmented wetlands that
are now throughflow or outflow due to ditch construction), 5) revised the lake key to focus on
permanently flooded deepwater sites (note: shallow and seasonally to intermittently flooded sites
are wetlands) and added “open embayment” modifier, and 6) revised the estuary type key
(consolidated some types). This version also clarifies that a terrene wetland may be associated
with a stream where the stream does not periodically flood the wetland. In this case, the stream
has relatively little effect on the wetland’s hydrology. This is especially true for numerous
flatwood wetlands. It also briefly discusses how the term "isolated" is applied relative to surface
water and ground water interactions. In the near future, illustrations will be added to this
document to aid users in interpretations.
Use of the Keys
Two sets of dichotomous keys (composed of pairs of contrasting statements) are provided - one
for wetlands and one for waterbodies. Vegetated wetlands (e.g., marshes, swamps, bogs,
flatwoods, and wet meadows) and periodically exposed nonvegetated wetlands (e.g., mudflats,
beaches, and other exposed shorelines) should be classified using the wetland keys, while the
waterbody keys should be used for permanent deep open water habitats (subtidal or >6.6 feet
deep for nontidal waters). Some sites may qualify as both wetlands and waterbodies. A good
example is a pond. Shallow ponds less than 20 acres in size meet the Service’s definition of
wetland, but they are also waterbodies. Such areas can be classified as both wetland and
waterbody, if desirable. However, we recommend that ponds be classified using the waterbody
keys. Another example would be permanently flooded aquatic beds in the shallow water zone of
a lake. We have classified them using wetland hydrogeomorphic descriptors, yet they also
clearly represent a section of the lake (waterbody). This approach has worked well for us in
producing watershed-based wetland characterizations and preliminary assessments of wetland
functions.
Uses of Enhanced Digital Database
Once they are added to existing NWI digital data, the LLWW characteristics (e.g., landscape
position, landform, water flow path, and waterbody type) may be used to produce a more
complete description of wetland and deepwater habitat characteristics for watersheds. The
enhanced NWI digital data may then be used to predict the likely functions of individual
wetlands or to estimate the capacity of an entire suite of wetlands to perform certain functions in
a watershed. Such work has been done for several watersheds including Maine’s Casco Bay
watershed and the Nanticoke River and Coastal Bays watersheds in Maryland, the Delaware
portion of the Nanticoke River, and numerous small watersheds in New York (see Tiner et al.
1999, 2000, 2001; Machung and Forgione 2002; Tiner 2002; see sample reports on the NWI
website:http://wetlands.fws.gov for application of the LLWW descriptors). These
characterizations are based on our current knowledge of wetland functions for specific types
(Tiner 2003) and may be refined in the future, as needed, based on the applicable HGM profiles
4
and other information. The new terms can also be used to describe wetlands for reports of
various kinds including wetland permit reviews, wetland trend reports, and other reports
requiring more comprehensive descriptions of individual wetlands.
Organization of this Report
The report is organized into seven sections: 1) Introduction, 2) Wetland Keys, 3) Waterbody
Keys, 4) Coding System for LLWW Descriptors (codes used for classifying and mapping
wetlands), 5) Acknowledgments, 6) References, and 7) Glossary.
5
Section 2. Wetland Keys
Three keys are provided to identify wetland landscape position and landform for individual
wetlands: Key A for classifying the former and Keys B and C for the latter (for inland wetlands
and coastal wetlands, respectively). A fourth key - Key D - addresses the flow of water
associated with wetlands. Table 1 lists the LLWW descriptors. It gives readers a good idea of
what the various combinations may be. Also see wetland codes in one of the following sections.
Users should first identify the landscape position associated with the subject wetland following
Key A-1. Afterwards, using Key B-1 for inland wetlands and Key C-1 for salt and brackish
wetlands, users will determine the associated landform. The landform keys include provisions
for identifying specific regional wetland types such as Carolina bays, pocosins, flatwoods,
cypress domes, prairie potholes, playas, woodland vernal pools, West Coast vernal pools,
interdunal swales, and salt flats. Key D-1 addresses water flow path descriptors. Various other
modifiers may also be applied to better describe wetlands, such as headwater areas; these are
included in the four main keys.
Besides the keys provided, there are numerous other attributes that can be used to describe the
condition of wetlands. Some examples are other descriptors that address resource condition
could be ones that emphasize human modification, (e.g., natural vs. altered, with further
subdivisions of the latter descriptor possible), the condition of wetland buffers, or levels of
pollution (e.g., no pollution [pristine], low pollution, moderate pollution, and high pollution).
Addressing wetland condition, however, was beyond our immediate goal of describing wetlands
from a hydrogeomorphic standpoint.
6
Table 1. List of landscape position, landform, water flow path, and waterbody type (LLWW) descriptors. Note that more detailed
categorization of landforms and pond types are possible through the use of modifiers, but they have not been shown here.
Landscape
Position Landform Water Flow Path Waterbody Type
Marine Fringe Bidirectional-tidal Open Ocean
Island Reef-protected Waters
Atoll Lagoon
Fjord
Semi-protected Oceanic Bay
Estuarine Fringe Bidirectional-tidal Fjord
Basin Island Protected Rocky Headland Bay
Basin (tidally restricted) Rocky Headland Bay
Island Tectonic Estuary
River-dominated Estuary
Drowned River Valley Estuary
Bar-built Estuary
Bar-built Estuary (Coastal Pond)
Bar-built Esturay (Hypersaline Lagoon)
Island-protected Estuary
Shoreline Bay Estuary
Lotic Floodplain Throughflow River (Gradients: Tidal, Dammed, High,
Basin Throughflow-intermittent Middle, Low, and Intermittent)
Flat Throughflow-entrenched Stream (Gradients: Tidal, Dammed, High,
Fringe Bidirectional-tidal Middle, Low, and Intermittent)
Island
7
Lentic Fringe Bidirectional-nontidal Natural Lake (Main body, Open Embayment,
Basin Bidirectional-tidal Semi-enclosed Embayment, Barrier Beach
Flat Throughflow Lagoon)
Island Dammed River Valley Lake (Reservoir)
Dammed River Valley Lake (Hydropower)
Dammed River Valley Lake (Other)
Other Dammed Lake (Former Natural Lake)
Other Dammed Lake (Artificial Lake)
Terrene Fringe (pond) Outflow Pond (numerous types)
Basin Outflow-artificial
Basin (former floodplain) Inflow
Flat Throughflow
Flat (former floodplain) Throughflow-artificial
Interfluve Throughflow-entrenched
Slope Isolated
Paludified
8
Key A-1: Key to Wetland Landscape Position
This key characterizes wetlands based on their location in or along a waterbody, in a
drainageway, or in isolation.
1. Wetland is located in or along tidal salt or brackish waters (i.e., an estuary or ocean) including
its periodically inundated shoreline (excluding areas formerly under tidal influence)...................2
1. Wetland is not located in or along these waters...........................................................................3
2. Wetland is located along shores of the cean....................................................................Marine
Go to Key C-1 for coastal landform
2. Wetland is located in or along an estuary (e.g., typically a semi-enclosed basin or tidal river
where fresh water mixes with sea water)..........................................................................Estuarine
Go to Key E-2 for Estuary Type, then to Key C-1 for coastal landform
Note: If area was formerly connected to estuary but now is completely cut-off from tidal
flow, consider as one of inland landscape positions - Terrene, Lentic, or Lotic, depending
on current site characteristics. Such areas should be designated with a modifier to
identify such wetlands as “former estuarine wetland.” Lands overflowed infrequently by
tides such as overwash areas on barrier islands are considered an Estuarine. Tidal
freshwater wetlands contiguous to salt/brackish/oligohaline tidal marshes are also
considered Estuarine, whereas similar wetlands just upstream along strictly fresh tidal
waters are considered Lotic.
3. Wetland is located in or along a lake or reservoir (permanent waterbody where standing water
is typically much deeper than 6.6 feet at low water), including streamside wetlands in the lake
basin and wetlands behind barrier islands and beaches with open access to the lake............Lentic
Go to Key C-2 for Lake Type
Then Go to Key B-1 for inland landform
Note: Lentic wetlands consist of all wetlands in a lake basin, including those bordering
streams that empty into the lake. The upstream limit of lentic wetlands is defined by the
upstream influence of the lake which is usually approximated by the limits of the basin
within which the lake occurs. The streamside lentic wetlands are designated as
“Throughflow,” thereby emphasizing the stream flow through these wetlands. Other
lentic wetlands are typically classified as “Bidirectional Flow” since water tables rise and
fall with lake levels during the year. Tidally-influenced freshwater lakes have
“Bidirectional Tidal” flow.
Modifiers: Natural, Dammed River Valley, Other Dammed - see Key C-2 for others.
3. Wetland does not occur along this type of waterbody.................................................................4
4. Wetland is located in or along a river or stream (flowing water), including in-stream ponds and
wetlands on the active floodplain and it is subjected to periodic flooding......................................5
9
4. Wetland occurs on a slope or flat, or in a depression (including ponds, potholes, and playas)
lacking a stream or is situated on a historic (inactive) floodplain; may be connected to other
wetlands or waters through ditches; also includes flatwoods with streams but streams do not
periodically inundate the wetland........................................................................................Terrene
Go to Key B-1 for inland landform
Modifiers may include Headwater (for first-order streams, possibly second-order streams
also; including large wetlands in upper portion of watershed believed to be significant
groundwater discharge sites important to streamflow) and for terrene wetlands whose
outflow goes directly to an estuary or the ocean: Estuarine Outflow or Marine Outflow,
respectively.
5. Wetland is the source of a river or stream but this waterbody does not extend through the
wetland................................................................................................................................Terrene
5. Wetland is in or along a river or stream, or on its active floodplain...........................................6
6. Wetland is in or along a river (a broad channel mapped as a polygon or 2-lined watercourse on
a 1:24,000 U.S. Geological Survey topographic map), or on its active floodplain........Lotic River
6. Wetland is in or along a stream (a.linear or single line watercourse on a 1:24,000 U.S.
Geological Survey topographic map), or on its active floodplain...............................Lotic Stream
Go to Couplet "a" below
(Also see note under first couplet #3 - Lentic re: streamside wetlands in lake basins)
Note: Artificial drainageways--ditches--are not considered part of the Lotic classification,
whereas channelized streams are part of the Lotic landscape position.
Modifiers: Headwater (first order streams, possibly second order streams and large
wetlands in upper portion of watershed believed to be significant groundwater discharge
sites) and Channelized (excavated and/or stream course modified).
a. Water flow is under tidal influence (freshwater tidal areas)....................Tidal Gradient
Go to Key B-1 for inland landform
a. Water flow is not under tidal influence (nontidal)..........................................................b
b. Water flow is dammed, yet still flowing downstream, at least seasonally......................
....................................................................................................................Dammed Reach
Go to Key B-1 for inland landform
Modifiers: Lock and Dammed, Run-of-River Dam, Beaver Dam, and Other Dam
(see Waterbody Key B-2 for further information).
b. Water flow is unrestricted................................................................................................c
c. Water flow is intermittent during the year...................................Intermittent Gradient
Go to Key B-1 for inland landform
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c. Water flow is perennial (year-round)..............................................................................d
d. Water flow is generally rapid due to steep gradient; typically little or no floodplain
development; watercourse is generally shallow with rock, cobbles, or gravel bottoms;
first and second order "streams"; part of Cowardin's Upper Perennial and Intermittent
subsystems....................................................................................................High Gradient
Go to Key B-1 for inland landform
d. Watercourse characteristics are not so; "stream" order greater than 2............................e
e. Water flow is generally slow; typically with extensive floodplain; water course shallow
or deep with mud or sand bottoms; typically fifth and higher order "streams", but
includes lower order streams in nearly level landscapes such as the Great Lakes Plain
(former glacial lakebed) and the Coastal Plain (the latter streams may lack significant
floodplain development) and ditches; Cowardin's Lower Perennial subsystem............Low
Gradient
Go to Key B-1 for inland landform
e. Water flow is fast to moderate; with little to some floodplain; usually third and fourth
order "streams"; part of Cowardin's Upper Perennial subsystem.............Middle Gradient
Go to Key B-1 for inland landform
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Key B-1: Key to Inland Landforms
1. Wetland occurs on a noticeable slope (e.g., greater than a 2 percent slope)........Slope Wetland
Go to Key D-1 for water flow path
Modifiers can be applied to Slope Wetlands to designate the type of inflow or outflow as
Channelized Inflow or Outflow (intermittent or perennial, stream or river),
Nonchannelized Inflow or Outflow (wetland lacking stream, but connected by observable
surface seepage flow), or Nonchannelized-Subsurface Inflow or Outflow (suspected
subsurface flow from or to a neighboring wetland upslope or downslope, respectively).
1. Wetland does not occur on a distinct slope..................................................................................2
2. Wetland forms an island......................................................................................Island Wetland
(Go to Key D-1 for water flow path)
Note: Can designate an island formed in a delta at the mouth of a river or stream as a
Delta Island Wetland; other islands are associated with landscape positions (e.g., lotic
river island wetland, lotic stream island wetland, lentic island wetland, or terrene island
pond wetland). Vegetation class and subclass from Cowardin et al. 1979 should be
applied to characterize the vegetation of these wetland islands; vegetation is assumed to
be rooted unless designated by a modifier – “Floating Mat” to indicate a floating island.
2. Wetland does not form an island.................................................................................................3
3. Wetland occurs within the banks of a river or stream or along the shores of a pond, lake, or
island, or behind a barrier beach or island, and is either: (1) vegetated and typically permanently
inundated, semipermanently flooded (including their tidal freshwater equivalents plus seasonally
flooded-tidal palustrine emergent wetlands which tend to be flooded frequently by the tides) or
otherwise flooded for most of the growing season, or permanently saturated due to this location
or (2) a nonvegetated bank or shore that is temporarily or seasonally flooded .....Fringe Wetland
Go to Couplet “a” below for Types of Fringe Wetlands
Then Go to Key D-1 for water flow path
Attention: Seasonally to temporarily flooded vegetated wetlands along rivers and streams
(including tidal freshwater reaches) are classified as either Floodplain, Basin, or Flat landforms
- see applicable categories.
a. Wetland forms along the shores of an upland island within a lake, pond, river, or
stream.......................................................................................................................b
a. Wetland does not form along the shores of an island......................................................d
b. Wetland forms behind a barrier island or beach spit along a lake..............Lentic Barrier
Island Fringe Wetland or Lentic Barrier Beach Fringe Wetland
Modifier: Drowned River-mouth
b. Wetland forms along another type of island....................................................................c
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c. Wetland forms along an upland island in a river or stream..................Lotic River Island
Fringe Wetland or Lotic Stream Island Fringe Wetland
c. Wetland forms along an upland island in a lake or pond..................Lentic Island Fringe
Wetland or Terrene Pond Island Fringe Wetland
d. Wetland forms in or along a river or stream..........................Lotic River Fringe Wetland
or Lotic Stream Fringe Wetland
d. Wetl