Combining HGM and EMAP procedures to assess wetlands at the watershed scale — status of flats and non-tidal riverine wetlands in the Nanticoke River watershed, Delaware and Maryland (USA)

Abstract

The hydrogeomorphic (HGM) approach to wetland assessment was combined with the Environmental Monitoring and Assessment Program (EMAP) survey design procedures to evaluate the condition of non-tidal riverine and flats wetlands in the Nanticoke River watershed (Delaware and Maryland, USA). We found degradation of wetland functions below reference standard levels for the majority of wetlands in both classes. Wetland condition was also related to the level of disturbance in both wetland classes. In flats, the most common disturbances were associated with hydrologic and vegetation modifications. Flat wetlands with low HGM function scores for the Plant Community and Habitat functions had almost all been converted from hardwood forest to Loblolly pine plantations. Most modifications associated with riverine wetlands were associated with stream channelization. Results of this study demonstrate that a site-specific and reference-based approach to assessment (i.e., the HGM method) can successfully be applied at the scale of an entire watershed if it is combined with a sampling approach that allows sites to be selected without geographic bias. The approach can also be used to determine if wetland functions vary from one sub-basin to another, and results of this project can be used by managers to begin to develop strategies for restoration of wetland functions at the watershed scale.