Cole, C.A., R.P. Brooks, P.W. Shaffer, and M.E. Kentula. 2002. A comparison of the hydrology of wetlands in Pennsylvania and Oregon as an indicator of the transferability of HGM functional models between regions. Environ. Mgt. 30(2)265-278. WED-01-132
The hydrogeomorphic (HGM) approach to wetland classification and functional assessment is becoming more widespread in the U.S., but its use has been limited by the length of time needed to develop appropriate data sets and functional assessment models. One particularly difficult aspect is the transferability among geographic regions of specific models used to assess wetland function. If models could be shared, this could considerably shorten development and implementation of HGM throughout the U.S. As hydrology is the driving force behind wetland functions, we assessed the comparability of hydrologic characteristics of three HGM subclasses (slope, headwater floodplain, mainstem floodplain) using comparable long-term hydrologic data sets from different regions of the U.S. (Ridge and Valley Province in Pennsylvania and the Willamette Valley in Oregon). If hydrology by HGM subclass was similar between different geographic regions, it might be possible to more readily transfer extant models between those regions. We found that slope wetlands (typically groundwater-driven) had similar hydrologic characteristics, even though absolute details (such as depth of water) differed. We did not find the floodplain subclasses to be comparable, likely due to effects of urbanization in Oregon, regional differences in soils and, perhaps, climate. Slight differences in hydrology can to shift wetland functions from those mediated by aerobic processes to those dominated by anaerobic processes. Functions such as nutrient cycling can be noticeably altered as a result. Our data suggest considerable caution in the application of models outside of the region for which they were developed.