The Effects of Urbanization on the Nitrate Removal Capacity of Urban WetlandsEPA Grant Number: FP916337
Title: The Effects of Urbanization on the Nitrate Removal Capacity of Urban Wetlands
Investigators: Stander, Emilie K.
Institution: Rutgers University - New Brunswick
EPA Project Officer: Graham, Karen
Project Period: January 1, 2004 through December 31, 2004
Project Amount: $94,157
RFA: STAR Graduate Fellowships (2004) RFA Text | Recipients Lists
Research Category: Fellowship - Terrestrial Ecology and Ecosystems , Academic Fellowships , Ecological Indicators/Assessment/Restoration
Wetlands are being viewed and used increasingly as management tools to combat the widespread problem of excess nitrogen in surface waters of the United States. This is particularly true in urban or urbanizing watersheds. To better serve managers, models have been created that use hydrogeomorphic (HGM) class to predict biological functions such as soil nitrogen cycling. These models may not be applicable, however, in urban environments because urbanization may alter wetland hydrology, thus causing wetlands to function differently than their natural HGM setting would suggest. In addition, it is more difficult to identify a reference domain in an urban region. The objective of this research project is to determine if HGM class can be used effectively in the functional assessment of urban wetlands.
Fifteen palustrine, forested wetlands in urban northeastern New Jersey were sampled for hydrology and rates of in situ nitrogen cycling processes to determine the usefulness of the HGM approach. Three HGM classes, riverine, mineral flat, and flat-riverine, were represented by five wetlands, two of which served as reference (less urban) sites. Sites were designated as reference on the basis of three criteria: lower surrounding population density, larger size, and longer history of protection. Three clusters of nested piezometers in each site were sampled between October 2002 and November 2003. One autowell in each site recorded water table measurements four times daily. In situ rates of net ammonification, net nitrogen mineralization, and net nitrification were measured monthly during the same time period using the static core technique. Hydrographs demonstrated that many of the wetlands have water table depths below 30 centimeters (i.e., below the biologically active rooting zone) for long periods of time. Many wetlands also display uncharacteristically flashy hydrographs. In some cases, reference wetlands showed more symptoms of altered hydrology than more urban sites, suggesting that the criteria used to choose reference sites were not effective. In this region, it is necessary to identify reference wetlands based on hydrology data. The nitrogen cycling data were not conclusive on the question of whether urbanization or HGM setting is a better predictor of nitrogen cycling dynamics. On some sampling dates, there were marked differences in net nitrification rates between reference and nonreference sites. On other sampling dates, there were marked differences in net ammonification rates among sites of different HGM classes. Further analysis of a more complete data set will be needed to fully assess the validity of the HGM functional assessment approach in the urban setting.