Denitrification in urban brownfield wetlands.

摘要

Wetland processes are highly spatially and temporally heterogeneous, and managers lack models relating important wetland processes to specific combinations of biological communities, flooding, and soils. Wetlands in urban settings, while having the potential to deliver ecosystem services (nutrient removal) to urban areas, pose a particular challenge in linking ecosystem processes with their environmental drivers, because urban wetlands have been little studied, and each urban system has its own unique set of altered conditions. These issues are especially true of wetlands that develop on brownfield sites, on highly modified soil materials.;My research questions were the following: (1) Where and when do the highest rates of nitrate removal occur in urban brownfield wetlands, and what are the spatio-temporal dimensions of these high rates?; (2) What are the environmental drivers of nitrate removal rates (via denitrification) in urban brownfield wetlands?; and (3) How can the spatial and temporal dimensions of nitrate removal rates be modeled and predicted to aid in restoration and management at the watershed scale?.;I utilized a combination of lab- and field-based studies to construct models designed to isolate and explain the relationship between environmental variables and soil denitrification in urban wetland environments. Whole-wetland denitrification potential was estimated through spatial interpolation of the variables mediating the highest rates of denitrification at the scale of a couple square meters. I also measured components of the nitrogen and hydrologic cycle in wetlands to construct budgets estimating the role of denitrification in removing nitrate under wet and dry conditions.;My research shows that brownfield wetlands in northern New Jersey support active populations of denitrifying bacteria and are potential sinks for nitrate in urban landscapes. Rates of nitrate consumption in the soils equaled or exceeded the rate of nitrate loading, at least from the atmosphere. Soil structure and texture, water table levels, and landscape position appear to be primary determinants of whether brownfield soils are sinks for nitrate. Modifications to hydrology that promote (1) endogenous nitrate production, particularly in low-oxygen waterlogged areas, and (2) contact between stormwater and soils with high macroporosity may augment levels of nitrate removal from brownfield wetlands.