Stable isotope dynamics of nitrogen sewage effluent uptake in a semi-arid wetland

Our objectives were to determine (1) how much N is transferred into the food web via plants from a wetland receiving not only inputs of treated sewage effluent, but also containing contaminants such as polychlorinated biphenyls (PCBs), (2) how birds, as consumers, utilize exogenous N and uptake PCBs in relation to the food web of the wetlands, (3) the feasibility of using isotopic analysis in estimating trophic levels in a semi-arid system. Our results demonstrate that there is very high spatial variability in the N isotopic composition of primary producers. Birds had lower variability in delta15N, despite feeding at multiple trophic levels. In very high spatial variability in delta15N of primary producers, it is difficult to use N isotope techniques to define trophic levels relevant to the bioaccumulation of organic pollutants, but it is possible to track the flow of exogenous N through the food web.