Assessment of a judgment-based hydrogeomorphic wetland classification using long-term hydrologic data

Hydrogeomorphic (HGM) wetland classifications are becoming increasingly common but lack substantial review of assumptions behind those classifications. In this paper, I compare an HGM classification of wetland sites developed by best professional judgment with a classification developed using long-term hydrologic data over those same sites. Forty-two wetlands, covering five HGM subclasses, were sampled for over a decade in central Pennsylvania. Using median depth to water as the metric, four groups were identified through cluster analysis (created, riparian depression/slope, and two combinations of headwater/mainstem floodplains). The groundwater-fed sites (riparian depressions and toe-of-slopes) were clearly separated by their more consistent source of water, whereas other slopes and floodplain sites were less clearly defined. Long-term assessment of hydrology generally supported an HGM classification scheme developed under less stringent conditions and produced by best professional judgment, but improvements in the assessment of drier sites are needed.