Climatic influences on dissolved nutrients in an agribusiness-dominated eutrophic estuary

Recent outbreaks of toxic dinoflagellates, phytoplankton and macroalgae have brought the eutrophic condition of coastal waters to national attention. These organisms are fueled by increased levels of nutrients, particularly nitrogen and phosphorus. There is little knowledge of the environmental factors that lead to fluctuations of these materials, but it is quite clear that large variations exist both seasonally and from one week to the next. Marine biologists have speculated that fluctuations in precipitation and temperature may be responsible for variations in nutrient concentrations. The specific goal of this study is to determine how meteorological factors, as expressed by a water budget, affect variations in dissolved nutrient concentrations.

Model development began with production of a climatic water budget for Delaware's Rehoboth and Indian River Bays. Climatic variables were analyzed using statistical and correlative procedures against six years collection of bi-monthly nutrient samples. From this analysis an algorithm was developed for each subbasin of the Rehoboth/Indian River watershed, describing weather-nutrient relationships. GIS-based analysis isolated physical and cultural differences between each site's watershed that explained algorithm discrepancies. For example, sites located in more urban watersheds with greater area under impervious surfaces were more impacted by runoff conditions, leading to spikes in nutrient concentrations.