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

Abstract

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.

A Paleoecological Perspective on Wetland Restoration

“…However, as noted by Cairns and Heckman (1996) this immediately raises the question as to what frame of reference or benchmark does one use to establish the pre-disturbance condition? Moreover, others have demonstrated that restoring an ecosystem to a prescribed composition is difficult because the assumption of predictable community assembly is often not valid and restoration can result in unpredictable outcomes (Gwin et al 1999;Magee et al 1999;Zedler 2000;Magee and Kentula 2005). Such results led Hilderbrand et al (2005) to go so far as to declare such prescriptive restoration approaches to be a so-called restoration myth (i.e., their "Carbon Copy" myth) in that creating or restoring an ecosystem that is a copy of an idealized state with a single endpoint is at odds with the dynamic nature of ecosystems.…”

Wetlands as natural assets

“…Thus, as a wetland landscape varies in scale, due perhaps to conversion, draining or other human-induced disturbances, the impact on the provision of and synergies between wetland services can be substantial. Such a landscape approach is being used increasingly for assessing the cumulative effects of wetland loss and degradation, characterizing wetland boundaries and identifying restoration or mitigation opportunities (NRC 1995, Bedford 1996, 1999, Gwin et al 1999, Mitsch and Gosselink 2000, Simenstad et al 2006. It follows that the various goods and services provided by a wetland will also be tied to, and thus defined by, its landscape extent; i.e.…”

“…Increasingly, a hydrologybased landscape approach is being used to assess the cumulative effects of wetland loss and degradation, characterizing wetland boundaries and identifying restoration or mitigation opportunities (Bedford 1996, 1999, Gwin et al 1999, Mitsch and Gosselink 2000, NRC 1995, Simenstad et al 2006. As emphasized in this paper, such an approach is consistent with the view of wetlands as natural assets that generate multiple ecosystem services.…”

Characterization of wetland hydrology using hydrogeomorphic classification

“…As management activities change the numbers, types, and positions of wetlands on the landscape, especially in urban areas (e.g., Kentula et al 1992a, b, Holland et al 1995, Bedford 1996, Gwin et al 1999, maintaining the diversity of hydrologic regimes will be essential to preserving the diversity of wetland functions. Bedford (1996) has recommended landscape-level analyses of wetlands to assess the cumulative effects of past management decisions and to guide future management decisions toward preserving and restoring the natural mosaic.…”