The Effects of Urbanization on Nitrate Removal Capacity of Urban Wetlands
Abstract
Wetlands are increasingly being used 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. Wetland functions are frequently assessed based on hydrogeomorphic (HGM) setting, because processes such as nitrogen cycling should reflect sources and flow patterns of water. However, HGM assessment may not be applicable in urban environments because urbanization alters wetland hydrology, thus causing wetlands to function differently than their natural HGM setting would suggest. We tested the ability of HGM classification to explain variations in nitrogen cycling rates in a sample of wetlands in northeastern New Jersey, a heavily developed metropolitan area. Fourteen palustrine, forested wetlands, representing three HGM classes and including "reference" sites in less heavily-developed landscapes, were sampled for hydrology and rates of nitrogen cycling processes. One autowell in each site recorded water table measurements four times daily. In situ rates of net nitrogen mineralization and nitrification were measured monthly during the same time period using the static core technique. Potential denitrification rates were measured monthly in laboratory incubations using the acetylene block technique. Hydrographs demonstrated that many sites have water table depths below 30 cm (i.e., below the biologically active zone) for long periods of time. Many wetlands display uncharacteristically flashy hydrographs. In some cases our selected reference wetlands showed more symptoms of altered hydrology than more urban sites. In this region it is therefore necessary to identify reference wetlands based on hydrology monitoring data. There were no differences in nitrification rates among HGM classes. There appeared to be seasonal differences in denitrification rates, but there were no trends relating to HGM class. However, wetlands with dry or flashy hydrographs did have higher nitrification and lower denitrification rates than wetlands with more normal hydrology. This suggests that urbanization is a better predictor of nitrogen cycling functions than HGM class.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2006
- Bibcode:
- 2006AGUSM.B23A..06S
- Keywords:
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- 0469 Nitrogen cycling;
- 0493 Urban systems;
- 0497 Wetlands (1890);
- 1834 Human impacts