Coastal lagoon-type estuaries such as the Virginia Coast Reserve are often nitrogen-limited. The availability of nitrogen controls aquatic primary productivity in the estuary. The effects of N-loading on the estuary due to agricultural runoff depends to a large extent upon the N-cycling processes that occur in the intertidal sediments. Processes such as nitrification- denitrification result in losses of N from the sediment, whereas dissimilatory nitrate reduction to ammonium tends to conserve N in the sediment. Efforts to develop models to predict the effects of nitrogen influx to estuaries due to natural or anthropogenic processes have been limited by the difficulties involved in measuring the rates of the various N-cycling processes in wetland sediments. Many of the techniques currently used to measure the rates of these processes are disruptive, utilize inhibitors of questionable effectiveness, or require additions of substrates at higher than ambient concentrations. Such techniques may at best then measure potential rather than in-situ reaction rates. This project will develop the methodologies required to apply 15N isotope pool dilution techniques to intact sediment cores taken from vegetated and unvegetated intertidal wetland ecosystems. These measurements will allow the determination of the relative importance of nitrification, followed by denitrification v.s. dissimilatory nitrate reduction to the overall N-budget. The study will be performed at a Long Term Ecological Research site in the Virginia Coast Reserve. Taken together, this information will improve the accuracy of rate estimates of nitrogen cycling reactions in wetland and near shore sediments and permit an evaluation of the role of these processes in the ecology of coastal marine ecosystems.
