Does Land-Use Modifies the Effect of Climate Variability in Controlling Nitrogen Transport in Urban Water Bodies?.

Nitrogen (N) transport is controlled by complex interactions among land use, climate, and soils. In most coastal water bodies such as the Tampa Bay Estuary, N is the limiting nutrient that drives eutrophication. The key questions on how climate-driven extremes and land-use interactions control N transport in the Tampa Bay are yet unclear. Here, we hypothesize that land-use in the watersheds can modify the effects of the climate-driven extremes in controlling N transport at watershed scales. In this study, we used long-term (1981-2014) monthly concentrations data of N forms (organic, inorganic, and total N) for 15 watersheds that drain to the Tampa Bay Estuary. We determined changes in the pattern of concentrations in the N forms in the wet and dry years across the urban land-use gradient. Key questions that we address are: Identification of watersheds with total N concentration greater than EPA numeric nutrient criteria; how total N transport varied in the wet and dry years in the watersheds; how land use and climatic-driven extremes control organic, inorganic, and total N transport. Our preliminary results showed that N concentration decreased in the wet years in the undeveloped (<5% residential and built up), while either increased or remained similar in the developed (>20% residential and built up). This study will enhance our understanding on interactions between human activities, climatic extremes, and ecosystem services, which can be used to develop management practices to control N transport in the urbanizing watersheds.