Indicators for evaluating the influence of diverted Mississippi River water on Louisiana coastal marsh

Mississippi River water containing elevated nitrate levels is being introduced into Louisiana coastal marsh to slow or reverse marsh deterioration due to salt water intrusion and subsidence. We evaluated the stable nitrogen isotope composition (delta N-15,) of marsh vegetation and extractable sodium content marsh soils as potential indicators for delta marsh area influenced by the diverted Mississippi River water. The N-15 content of plant material was highest at marsh sites near freshwater input. The N-15 content was positively correlated with reduction in soil extractable sodium. Results suggested that soil extractable sodium and 15N content of marsh vegetation may serve as indicators for assessing area impacted by the freshwater input.