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Rapid assessment of urban wetlands: Do hydrogeomorpic classification and reference criteria work?
STANDER, E. K. AND J. G. Ehrenfeld. Rapid assessment of urban wetlands: Do hydrogeomorpic classification and reference criteria work? ENVIRONMENTAL MANAGEMENT. Springer-Verlag, New York, NY, 43(4):725-742, (2009).
to inform the public
The Hydrogeomorphic (HGM) functional assessment method is predicated on the ability of a wetland classification method based on hydrology (HGM classification) and a visual assessment of disturbance and alteration to provide reference standards against which functions in individual wetlands can be evaluated. The effectiveness of this approach was tested by measuring nitrogen cycling functions in a sample of forested wetlands in an urbanized region in New Jersey, USA. Fourteen sites were chosen to represent three HGM classes and were characterized as ‘least disturbed reference’ or ‘non-reference’ based on an initial visual assessment. Water table levels and in situ rates of net nitrogen mineralization, net nitrification, and denitrification were measured over a one year period in each site. Hydrological alterations, resulting in consistently low or flashy water table levels, were not correlated with a priori designations as reference and non-reference. Although the flat-riverine wetland class had lower net nitrification and higher denitrification rates than either riverine or mineral flat wetland classes, this difference was attributable to the lack of hydrologically-altered wetlands in the flat-riverine class, and thus more consistently wet conditions. Within all HGM classes a classification based on the long-term hydrological record that separated sites with ‘normal’ hydrology, defined as slowly changing water levels and long periods of saturation, from those with ‘altered’ hydrology, defined as predominantly dry surface soils and/or rapid, frequent and large water table fluctuations, clearly distinguished sites with different nitrogen cycling function. Based on these findings, current practices for designating reference standard sites to judge wetland functions, at least in urbanized regions, are ineffective and potentially misleading. At least one year of hydrological monitoring data is suggested to classify wetlands into groups that have different nutrient cycling functions, particularly in urban landscapes.