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.

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