National Wetlands Inventory Maps Research Articles

Fusion of Lidar and Aerial Imagery to Map Wetlands and Channels via Deep Convolutional Neural Network

Wetlands and channels provide significant ecological and societal services. Mapping their locations and types at high resolution remains a challenge for scientific communities and regulatory agencies. In the U.S.A., the National Wetland Inventory (NWI) provides the best nationwide wetland maps, but the NWI for some locations has not been updated for up to four decades and includes omission errors. To address these problems, we developed a deep learning framework for identifying wetlands and channels from lidar point clouds and 1 m aerial images. Both deep learning and terrain analysis were applied to classify wetlands and identify channels. The deep learning classifier was a convolutional neural network that utilized both image color information and lidar-derived canopy height. When tested on a 94 km2 Ohio watershed, the method achieved a classification accuracy of 85.6%. Compared with the NWI maps, the results included 76% more forested wetlands by area and 168% more channels by length. It was also found that only leaf-off images were useful for detecting forested wetlands and typical commission errors (i.e., false positives) were attributed to tree shadows. The study demonstrates the advantages of combining lidar structural and aerial spectral information over the use of each alone and exemplifies the utility of deep learning as an effective means to leverage open-source data for high resolution mapping of wetlands.

Comparison of USACE Three-Factor Wetland Delineations to National Wetland Inventory Maps

Wetlands are mapped across the USA for compliance with §404 of the Clean Water Act using field-collected data and protocols in the 1987 Federal Wetlands Delineation Manual (3-factor method). The National Wetlands Inventory (NWI) maps wetlands and deepwater habitats for management and policy-making using aerial image analysis with limited field verification. There have been few comparisons of maps other than for limited geographic areas or wetland types. We compared 3-factor wetland delineations to NWI maps for 1751 assessment areas (AA) in different regions. We did not assess the accuracy of either product, but instead compared mapped area and polygon count for existing data at sites, then aggregated results to broader scales and compared with ancillary data to identify factors correlated with map differences. In a subset of NWI polygons eliminating non-wetland Cowardin types, 74% of NWI polygons were mapped in common with 3-factor polygons. NWI identified greater area in 33% of AA and greater total area across all sites. Approximately 27% of AA had 3-factor but no NWI polygons, while 6.7% of AA had features mapped only by NWI. Multiple factors likely contributed to differences including polygon size and temporal mismatches between maps, suggesting caution be used when comparing products.

Field Verification of Original and Updated National Wetlands Inventory Maps in three Metropolitan Areas in Illinois, USA

National Wetland Inventory (NWI) maps are the most comprehensive wetland maps in the U.S., but NWI maps are now outdated in many regions. A consortium led by Ducks Unlimited is updating the NWI for the Great Lakes/Atlantic Region. Updates are complete for several states but have not been verified extensively with field data. We used wetland maps from 129 on-site wetland delineation projects in three Illinois regions to assess accuracy of original and updated NWI maps. We used ancillary spatial data to characterize areas that were incorrectly classified and identify potential sources of error. Across the three regions, the original NWI omitted 49 % of total wetland area for wetlands greater than 0.2 ha, and 57 % of the area mapped by the NWI was non-wetland. The updated NWI omitted less wetland area (40 % omitted for wetlands larger than 0.2 ha), but only slightly improved errors of commission (55 % of mapped area was non-wetland). Polygons mapped as forested wetlands were less likely to be truly wetlands. Small (<0.06 ha) wetlands were often omitted. Errors reflect ambiguity in the definition of wetlands and technical limitations of the NWI methodology. Due to the high error rates, we recommend further refinement of regional wetland inventories.

Discovery of the Oregon Spotted Frog in the Northern Puget Sound Basin, Washington State

The Oregon Spotted Frog (Rana pretiosa), a federally threatened species also listed as endangered in Washington State, has a historical distribution that extends from southwestern British Columbia to northeastern California, yet their current range appears highly fragmented. This pattern may reflect this species' distinctive aquatic habitat requirements or simply be a function of the limited historical survey effort in selected areas. Hence, in an attempt to determine whether any additional populations of Oregon Spotted Frogs existed in the northern Puget Sound basin of Washington State, we conducted surveys at a large number of sites (n = 131) across this region in 2011–2013. To increase the likelihood of detecting this species, we created a Geographic Information System screening tool to identify areas of appropriate habitat (low stature emergent marsh ≥4 ha) based on National Wetlands Inventory maps. We also concentrated survey efforts on the headwater portions of lowland streams because non-headwater areas within the study area are highly altered and more likely to harbor exotic aquatic predators (American Bullfrogs [Lithobates catesbeianus] and warmwater fish species), which reduce the likelihood of Oregon Spotted Frog occupancy. We visually documented breeding activity of Oregon Spotted Frogs at 13 previously unrecognized sites in the Samish (n = 8), Nooksack (n = 4), and Sumas (n = 1) watersheds. We located a total of 1359 Oregon Spotted Frog egg masses at the 13 occupied sites over the three survey seasons. We genetically verified the species identification at 4 of these sites. In the course of these surveys, we also documented breeding chronology and provided information on habitat. Vegetation changes due to cessation of grazing and recent woody plantings may have decreased habitat suitability in at least 5 of the 13 occupied sites. Despite time and land-ownership constraints, our discovery of new breeding sites suggests that additional surveys for Oregon Spotted Frogs are needed to fully understand the species' distribution. Although Oregon Spotted Frogs are still rare, their current distribution is more widespread than previously recognized.

Mapping Geographically Isolated Wetlands in the Dougherty Plain, Georgia, USA

Increasing interest in isolated wetlands requires an understanding of the location, spatial extent, and configuration of the resource. The National Wetlands Inventory (NWI) is the most commonly used data source for this information; however, the accuracy is limited in some contexts, e.g., agricultural, seasonally-ponded, or forested wetlands. This study sought to improve isolated wetland mapping accuracy by integrating currently available NWI maps with other geospatial data sources (i.e., Soil Survey Geographic Database [SSURGO], Digital Raster Graphics [DRGs], and Digital Elevation Models [DEMs]). Relative to NWI, the optimal model (combining data derived from NWI, SSURGO, and DRGs) identified 1,874 additional isolated wetlands and 19,737-ha of additional isolated wetland area. A remote accuracy assessment indicated a high degree of accuracy for the optimal model (Kappa = 0.88, Sensitivity = 90%, and Specificity = 98%), as compared to NWI maps (Kappa = 0.70, Sensitivity = 68%, and Specificity = 99%). Small wetlands (< 4-ha) dominated the wetland population and reduced nearest neighbor distances between wetlands. Isolated wetlands were clustered and clustering was strongest among larger wetlands. This study identified a framework for improving the accuracy of wetland maps and serves as a foundation for ongoing wetland studies within the Dougherty Plain.

Wetland hydrologic class change from prior to European settlement to present on the Des Moines Lobe, Iowa

It has been hypothesized that wetland restoration policies have favored the restoration of the wettest classes of wetlands on the Des Moines Lobe of the prairie pothole region. To test this hypothesis we compared pre-drainage wetland distributions based on soils data and National Wetland Inventory (NWI) estimates of contemporary wetland distributions on the Des Moines Lobe. Based on the NWI data, the Des Moines Lobe today has only 3–4% of the wetland area that it had prior to the onset of drainage. On the basis of their soils, pre-drainage wetlands were predominantly temporarily flooded to saturated wetlands (84%), with only about 6% of the wetlands with water regimes classified as semi-permanently to permanently flooded. Depending on the interpretation of wetland modifiers on NWI maps, wetlands classified by the NWI as semi-permanent to permanently flooded make up more than 41% of the wetland area while wetlands with temporarily flooded to saturated water regimes account for 45–58% of the Lobe’s wetland area. The water regimes of contemporary wetlands when compared to their historic regimes suggest that many of today’s wetlands have different water regimes than they did prior to the onset of drainage. Because of the regional lowering of the groundwater table, many of today’s wetlands have drier water regimes, but some have wetter water regimes because they receive drainage tile inputs. Our results indicate that restoration has favored the wettest classes of wetlands and that temporarily to saturated wetland classes have not been restored in proportion to their relative abundance in the pre-drainage landscape.

Wetland change mapping for the U.S. mid-Atlantic region using an outlier detection technique

Although the impacts of wetland loss are often felt at regional scales, effective planning and management require a comparative assessment of local needs, costs, and benefits. Satellite remote sensing can provide spatially explicit, synoptic land cover change information to support such an assessment. However, a common challenge in conventional remote sensing change detection is the difficulty of obtaining phenologically and radiometrically comparable data from the start and end of the time period of interest. An alternative approach is to use a prior land cover classification as a surrogate for historic satellite data and to examine the self-consistency of class spectral reflectances in recent imagery. We produced a 30-meter resolution wetland change probability map for the U.S. mid-Atlantic region by applying an outlier detection technique to a base classification provided by the National Wetlands Inventory (NWI). Outlier-resistant measures – the median and median absolute deviation – were used to represent spectral reflectance characteristics of wetland class populations, and formed the basis for the calculation of a pixel change likelihood index. The individual scene index values were merged into a consistent region-wide map and converted to pixel change probability using a logistic regression calibrated through interpretation of historic and recent aerial photography. The accuracy of a regional change/no-change map produced from the change probabilities was estimated at 89.6%, with a Kappa of 0.779. The change probabilities identify areas for closer inspection of change cause, impact, and mitigation potential. With additional work to resolve confusion resulting from natural spatial heterogeneity and variations in land use, automated updating of NWI maps and estimates of areal rates of wetland change may be possible. We also discuss extensions of the technique to address specific applications such as monitoring marsh degradation due to sea level rise and mapping of invasive species.

Assessment of C-band synthetic aperture radar data for mapping and monitoring Coastal Plain forested wetlands in the Mid-Atlantic Region, U.S.A.

Multi-temporal C-band SAR data (C-HH and C-VV), collected by ERS-2 and ENVISAT satellite systems, are compared with field observations of hydrology (i.e., inundation and soil moisture) and National Wetland Inventory maps (U.S. Fish and Wildlife Service) of a large forested wetland complex adjacent to the Patuxent and Middle Patuxent Rivers, tributaries of the Chesapeake Bay. Multi-temporal C-band SAR data were shown to be capable of mapping forested wetlands and monitoring hydroperiod (i.e., temporal fluctuations in inundation and soil moisture) at the study site, and the discrimination of wetland from upland was improved with 10 m digital elevation data. Principal component analysis was used to summarize the multi-temporal SAR data sets and to isolate the dominant temporal trend in inundation and soil moisture (i.e., relative hydroperiod). Significant positive, linear correlations were found between the first principal component and percent area flooded and soil moisture. The correlation ( r 2) between the first principal component (PC1) of multi-temporal C-HH SAR data and average soil moisture was 0.88 ( p = < .0001) during the leaf-off season and 0.87 ( p = < .0001) during the leaf-on season, while the correlation between PC1 and average percent area inundated was 0.82 ( p = < .0001) and 0.47 ( p = .0016) during the leaf-off and leaf-on seasons, respectively. When compared to field data, the SAR forested wetland maps identified areas that were flooded for 25% of the time with 63–96% agreement and areas flooded for 5% of the time with 44–89% agreement, depending on polarization and time of year. The results are encouraging and justify further studies to attempt to quantify the relative SAR-derived hydroperiod classes in terms of physical variables and also to test the application of SAR data to more diverse landscapes at a broader scale. The present evidence suggests that the SAR data will significantly improve routine wooded wetland mapping.

Wetland types and wetland maps differ in ability to predict dissolved organic carbon concentrations in streams

Three categories of digital wetland maps widely available in the United States were used to develop models relating wetlands to DOC: (1) wetlands mapped by the U.S. National Wetlands Inventory (NWI) (2) wetland vegetation cover mapped by the U.S. National Land Cover Dataset (NLCD), and (3) maps of hydric soils. Data extracted from these maps for 27 headwater catchments of the Ontonagon River in northern Michigan, USA were used with DOC concentrations measured in catchment streams to develop stepwise multiple regressions based on wetland area and type. The catchments of the 27 tributaries ranged in area from 2 to 66 km 2 and wetlands constituted 10 to 53% of their area. Although all three databases provided regressions that were highly significant ( p < 0.001), the variance explained was greater for NWI maps ( R 2 = 0.75) than for NLCD ( R 2 = 0.61) or soil maps ( R 2 = 0.60). Wetland–stream relationships were strongest during September 2002, but were significant for nine out of ten dates sampled during subsequent seasons. The individual wetland type most highly correlated ( r > 0.62) with stream DOC concentrations was conifer peatland, represented on the NWI maps as Palustrine Needle-leaved Forest, the NLCD maps as woody wetland, and the soil maps as organic soils. For the NWI dataset, DOC was negatively correlated with area of palustrine emergent wetlands (i.e., sedge meadows and graminoid fens) and bog shrubs, inferring that these wetland types may be sinks for DOC. Because of the different effects of wetland vegetation types on DOC, a GIS data source such as the NWI which depicts those wetland types is superior for predicting landscape contributions to stream DOC concentrations.

Improved wetland remote sensing in Yellowstone National Park using classification trees to combine TM imagery and ancillary environmental data

The U.S. Fish and Wildlife Service uses the term palustrine wetland to describe vegetated wetlands traditionally identified as marsh, bog, fen, swamp, or wet meadow. Landsat TM imagery was combined with image texture and ancillary environmental data to model probabilities of palustrine wetland occurrence in Yellowstone National Park using classification trees. Model training and test locations were identified from National Wetlands Inventory maps, and classification trees were built for seven years spanning a range of annual precipitation. At a coarse level, palustrine wetland was separated from upland. At a finer level, five palustrine wetland types were discriminated: aquatic bed (PAB), emergent (PEM), forested (PFO), scrub–shrub (PSS), and unconsolidated shore (PUS). TM-derived variables alone were relatively accurate at separating wetland from upland, but model error rates dropped incrementally as image texture, DEM-derived terrain variables, and other ancillary GIS layers were added. For classification trees making use of all available predictors, average overall test error rates were 7.8% for palustrine wetland/upland models and 17.0% for palustrine wetland type models, with consistent accuracies across years. However, models were prone to wetland over-prediction. While the predominant PEM class was classified with omission and commission error rates less than 14%, we had difficulty identifying the PAB and PSS classes. Ancillary vegetation information greatly improved PSS classification and moderately improved PFO discrimination. Association with geothermal areas distinguished PUS wetlands. Wetland over-prediction was exacerbated by class imbalance in likely combination with spatial and spectral limitations of the TM sensor. Wetland probability surfaces may be more informative than hard classification, and appear to respond to climate-driven wetland variability. The developed method is portable, relatively easy to implement, and should be applicable in other settings and over larger extents.

Tracking changes in wetlands with urbanization: Sixteen years of experience in Portland, Oregon, USA

Abstract Long-term studies are essential to understanding the effects of urbanization on wetlands and the effectiveness of management actions. Using data from the National Wetlands Inventory (NWI) in combination with GIS analyses and field surveys, we tracked changes over 16 years (1982–1998) in small (≤2 ha), palustrine emergent/open water wetlands (PEM/POW) in Portland, Oregon, USA. Wetlands identified on NWI maps and that had not been converted to other land uses at the time of the 1992 survey were surveyed in 1998. Data were collected on 164 of the 171 wetlands in the target population. Despite development pressure throughout the 1990s, loss of small PEM/POW wetlands slowed between 1992 and 1998, with only 6% of the sites being destroyed as compared to 40% between 1982 and 1992. Of 11 sites that were not identifiable due to drought in 1992, eight had recovered with the return of typical rainfall; three had been destroyed. Most of the wetlands existing in 1998 were in hydrogeomorphic (HGM) classes atyp...

Relationships between National Wetlands Inventory maps and hydrophytic vegetation in Florida

This paper reports a preliminary investigation about National Wetlands Inventory (NWI) maps to see how they might be used in conjunction with other sources of information to provide offsite wetlands regulatory delineation. A geographic information system was used to overlay and compare NWI maps with ground-based tree species composition data from the US Department of Agriculture Forest Service Forest Inventory and Analysis program (FIA). Ninety plots located in the Apalachicola National Forest in northern Florida were used. The NWI mapped 42 of the 90 plots as wetlands. FIA data was used to calculate Prevalence Index (PI) scores. Twenty-four additional plots had PI < 3.0 and thus had hydrophytic vegetation. These plots may also have been wetlands by the Cowardin definition. The hypothesis that wetland identification did not differ between natural-origin versus planted forests was evaluated. NWI classified 61% of natural stands with PI <3.0 as wetlands, whereas 38% of planted stands with PI < 3.0 were mapped as wetlands. There were statistically significant differences (P < 0.05) in the relationships between hydrophytic vegetation and wetland status for plantations and natural-origin stands. FIA data was used to compare the actual frequency of species found in wetlands with the frequency ranges assigned for the NWI Regional Indicators. The observed frequency of occurrence in NWI-mapped wetlands agreed with the Regional Indicator frequency range for 6 of the 18 species. Most species not in agreement were reasonably close to their assigned frequency range, but some differed substantially. While this was a pilot-scale study, we believe that this technique can ultimately yield valuable new information on the tree characteristics of NWI wetlands, especially at larger spatial scales, such as states or regions.

Evaluation of National Wetland Inventory maps in a heavily forested region in the upper Great Lakes

National Wetland Inventory (NWI) maps are widely used in the United States but have not been independently evaluated in the Great Lakes region nor in forested areas with level topography. Field data from 148 plots in the Hiawatha National Forest ecological classification and inventory program were combined with an additional review to evaluate NWI mapping accuracy. NWI maps were over 90% accurate in identifying uplands and jurisdictional wetlands. All nonforested wetlands were identified correctly. Uplands were correctly identified 96.9% of the time. The lowest level of accuracy, 90.7%, was achieved in identifying forested wetlands. The most common error was the NWI classification of wetlands on the AuGres soil series, a somewhat poorly drained upland soil that often occurs in complexes with wetland soils in the region. Forested wetlands with a cover type similar to adjacent uplands were also a source of error on NWI maps. The already high accuracy of NWI maps could be improved by the mapping of wetland-upland complexes, a development corresponding to the increased mapping of hydric-nonhydric soil complexes in area soil surveys. The continued refinement of regional lists of hydrophytic vegetation is supported by indicator status discrepancies between an extensive Hiawatha National Forest database and the current NWI list for the region.

Penalties Did Not Violate Due Process

Frank Irish is a farmer with property in South Burlington, Vermont. This dispute involved a 26‐acre (10‐ha) parcel of the farm. In the middle of the parcel is a wetland demarcated on the National Wetland Inventory maps. The Irish Development Corp. applied to the city for a 48‐lot subdivision for the property. A state wetlands coordinator visited the site and told the owner that the site contained significant wetlands requiring a conditional use determination by the state agency secretary before any development could occur. Later, Irish hired a contractor to excavate a drainage ditch along two boundaries of the parcel to intercept water draining onto the land from an existing water supply line. On a subsequent visit, the wetlands coordinator found substantial erosion in the ditch that was causing a continual discharge of silt into a nearby brook. Irish received two zoning violation notices from the city. The state also sent a notice of violation. Later, the state issued an order finding Irish violated the Wetland Rules. A court imposed penalties on Irish. He appealed. Irish argued that the Vermont Wetland Rules failed to provide sufficient notice that the portion of his property was a significant wetland. The court said the Wetland Rules were sufficient to put Irish on reasonable notice of the existence of significant wetland areas and the possibility that the planned excavation might require environmental review and approval. Although the Wetland Rules did not define the precise boundaries of the wetland areas, the state clearly put him on notice of the existence of those areas, offered its administrative expertise and advice to clarify the precise boundaries, and delineated methods to identify those areas. Thus, the imposition of civil penalties did not violate due process.

Evaluating the effects of wetland regulation through hydrogeomorphic classification and landscape profiles

Landscape profiles describing the pattern of the diversity of wetlands in a region can serve as a standard for characterizing the resource and quantifying the effects of management decisions. We used hydrogeomorphic (HGM) classification to generate landscape profiles to evaluate the effects of mitigation in the rapidly urbanizing area of Portland, Oregon, USA. The profiles were produced from information on the types, numbers, and relative abundances of wetlands by HGM class. Using field data, topographic maps, and National Wetland Inventory maps, we classified 45 naturally occurring wetlands (NOWs) into regional HGM classes (depression, riverine, slope, andlacustrine fringe) and developed the corresponding landscape profile (the NOW-Profile). We then classified 51 mitigation wetlands (MWs) and added them to the profile (the All Site-Profile) to examine changes in the regional wetland resource. The classification of MWs required development of new, atypical HGM classes to describe the unique combinations of site morphology and landscape setting found in these wetlands:depression-in-riverine-setting, in-stream-depression, anddepression-in-slope-setting. Comparison of the landscape profiles showed that the structure and settings of NOWs and MWs are very different. Most NOWs fell into the regional HGM classes (91%), but most MWs fit the atypical classes (75%). Most NOWs were riverine wetlands (56%), whereas most MWs were depressions-in-riverine-setting and in-stream-depressions (33% for each class). The All Site-Profile showed an increase in the proportion of wetlands with depressional morphology, comprised mostly of MWs. Results also showed that the majority (71%) of MWs were constructed, at least partially,within existing NOWs through an exchange of wetland types and that most of these MWs (86%) belonged to the atypical classes. The approach used shows that the cumulative effects of wetland management decisions can be discerned effectively through HGM classification and development of landscape profiles. Although our results are important in documenting the landscape changes taking place in a specific region through mitigation, our approach is generally applicable for evaluating wetland management decisions and helping resource managers to make better-informed, broad-based decisions about the wetland resource.

Contiguity and edge characteristics of wetlands in five coastal counties of north Carolina, USA

Wetland contiguity and edge were determined with a geographic information system (GIS) for five coastal counties in North Carolina. USA. The digital database was created from wetlands digitized from U.S. Fish and Wildlife Service National Wetlands Inventory maps. The GIS analysis was based on three classes of information: 1) all wetlands as one class; 2) wetlands separated by dominant vegetative community type (e.g., forest, shrub, or marsh); and 3) forest and shrub wetlands further separated by dominant vegetation (e.g., evergreen, deciduous, or mixed). The contiguity analysis supports the perception that the lower coastal plain counties are dominated by large contiguous wetlands When wetlands were clumped into one class, the number of wetlands >1,000 ha ranged from 2 to 7 and the area accounted for 77 to 96% of the total wetland area. Several of those sites were > 100,000 ha in size. When wetlands were separated into more specific classes, the number of sites < 10 ha ranged from 416 to 3,370, but the wetland area in this size class was < 5% of the total wetland area. The average size of evergreen forest and shrub wetlands was typically much greater than deciduous forest and shrub wetlands a reflection of the configuration of large, block pocosin wetlands. Percent edge was also typically lower for the evergreen forest and shrub wetlands than for deciduous forest and shrub wetlands. The counties with the highest, number of wetland sites in transition to other uses have the most land owned by private timber companies. Contiguity analysis of wetlands with GIS provides landscape-scale information for natural resource management issues such as preserve design, habitat fragmentation, rare species management, and species migration opportunities.

Abstract: Land-use / Land-cover Classification of West Central Alabama using Landsat Thematic Mapper Data

Abstract: Land-use / Land-cover Classification of West Central Alabama using Landsat Thematic Mapper Data

Evaluation of national wetland inventory maps to inventory wetlands in the southern Blue Ridge of Virginia

The area of wetlands in the U.S. is being estimated as part of the National Wetlands Inventory (NWI). Minimal information is available to verify the effectiveness of NWI maps to inventory wetlands or delineate jurisdictional wetlands. We evaluated the use of NWI maps (1∶24,000 scale) to inventory and delineate jurisdictional wetlands in the Virginia Blue Ridge. Each wetland identified in the Woolwine and Meadows of Dan NWI maps was field-checked to determine if the areas met the criteria as a jurisdictional wetland. Of the 171 palustrine wetlands identified, 91% met the criteria. Jurisdictional wetlands were delineated in four 2.5-minute study areas. Two study areas, located in the Blue Ridge Highlands region, contain 91.8 and 109.3 hectares of jurisdictional wetlands. The NWI maps indicated 2.5 and 17.4 hectares of wetlands in these two study areas. A similar but smaller discrepancy occurred in the areas mapped in the Blue Ridge Escarpment region. We concluded, because of the small scale that photo interpreters must work with and the number of wetlands located in dense woodlands, that NWI maps may not adequately inventory wetlands in the Blue Ridge. This conclusion was based on a detailed study of 22% (6888 ha) of the area covered on the NWI maps. Predominant plant species in the forested, scrub-shrub, and emergent wetlands were red maple (Acer rubrum), speckled alder (Alnus rugosa), and yellow nutsedge (Cyperus esculentus), respectively, Wetland soils were classified as Typic Humaquents and Humaqueptic Fluvaquents.

Wetland degradation and loss in the rapidly urbanizing area of Portland, Oregon

An inventory was conducted of small (≤2 ha) freshwater wetlands composed of some combination of open water and emergent marsh in the metropolitan area of Portland, Oregon to (1) document changes in the wetland resource since the National Wetlands Inventory (NWI) was conducted (1981/1982 aerial photograph dates) and (2) identify patterns in wetland loss and degradation over a 10-year period in a rapidly urbanizing area. Wetlands identified on NWI maps were visited during summer 1992, and data on the location, wetland type, and surrounding land use or the cause of loss were collected. Of the 233 wetlands identified by NWI in 1981/1982, approximately 40% had been destroyed by human activities or were missing due to drought. Although conversion to urban land uses was the predominant cause of wetland loss from human activities, agricultural conversion accounted for about 31%. Drier-end wetlands (e.g., seasonally flooded) were missing from the landscape most frequently. Of the 141 wetlands still existing, 25% were severely degraded by human activities. Approximately half of those wetlands not severely degraded were affected by noise, and about 40% were disturbed, primarily by grazing and littering. We suggest that because land uses change quickly in rapidly urbanizing areas, leading to increased pressures to convert wetlands, resource agencies and urban planners should conduct similar inventories in other metropolitan areas. Then, demographic projections could be used in conjunction with information on patterns in wetland loss to identify and prioritize areas for wetland protection before development takes place.

Response of Wetlands to Rising Sea Level in the Lower Coastal Plain of North Carolina

Most of the coastal wetlands of the South Atlantic region of the United States are expected to diminish in size in response to the opposing forces of increasing human population growth and accelerating rates of rising sea level. We evaluated several models that project the response of coastal wetlands to rising sea level and concluded that current models appear unsuited for wetlands of the Albemarle-Pamlico peninsula of North Carolina. We came to this conclusion after we examined the distribution of wetlands, elevation contours, estimates of surface slope, soil types, and peat deposits on the peninsula. Most of the data were obtained from U.S. Geological Survey topographic quadrangle maps, U.S. Fish and Wildlife Service National Wetlands Inventory maps, U.S. Soil Conservation Service soil surveys, and inventories of peat deposits. Some unusual features of this pen- insula are low elevation (56% of total area <1.5 m), extensive coverage by wetlands (53%) and hydric soils (90%), negligible slopes of the land surface, virtual absence of tides, and lack of abundant sources of sediment. In the process of reconstructing how past rises in sea level most likely led to present conditions, it became apparent that vertical accretion of peat in situ is largely responsible for landscape features in areas where elevations are lowest. Were it not for these deposits, the land surface area of the peninsula would be decreasing relative to sea level. This situation contrasts sharply with areas in the eastern United States fringed by tidal marshes, which are undergoing overland migration at a rate dictated by landward slope and the rate of rising sea level. If the rate of sea level rise accelerates, it is doubtful if vertical accretion rates of peat can prevent submergence of extensive areas of wetlands in the Albemarle-Pamlico peninsula. Land use and drainage in the lowest elevations of the peninsula are currently being affected by sea level. Future land management of the peninsula will be constrained by potential landscape changes as a result of rising sea level.