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 (I) document changes in the wetland resource since the National Wetlands Inventory tNWI) 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 Inost 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 quickty in rapidly urbaniLing 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 conjunclion wiih information on patterns in wetland loss to identify and prioritize areas for wetland protection before development takes place.
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, and lacustrine .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, and depression-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 depressionsin-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 betterinformed, broad-based decisions about the wetland resource.
Hydrologic data are essential for understanding relationships between wetland morphology and function and for characterizing landscapeTscale patterns of wetland occurrence. We monitored water levels in 45 wetlands for three years to characterize the hydrology of wetlands in the vicinity of Portland, Oregon, USA and classified wetlands by hydrogeomorphic (HGM) class to determine whether hydrologic regimes differed in wetlands in different HGM classes. We also compared hydrologic regimes in naturally occurring wetlands (NOWs) and nutigation wetlands (MWs) and in wetlands with/without a human-made water-retention structure to determine whether and how human modifications are changing the hydrology of wetlands. We found no relationship between hydrologic attributes and land use, soil association, or wetland area. We did find significant differences related to presence of a water-retention structure and to wetland type (NOW or MW). Water levels were higher and had less temporal variability and more extensive inundation ~as % wetland area) in MWs and in wetlands modified to include a retention structure. HGM class was very effective for characterizing wetland hydrology, with significant differences among HGM classes for water level and for extent and duration of inundation. For three regional classes, we found the lowest water levels and lowest extent/duration of inundation in slope wetlands, intermediate conditions in riverine wetlands, and the highest water levels and greatest extent and duration of inundation in depressions. In "'atypical" classes tGwin et al. 1999), average water level and extent of inundation were similar to conditions in depressions, but the within-site variability in water levels in depressions-in-slope-setting and in-stream-depressions was significantly smaller than in the regional classes
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