9805928 McGlathery Estuaries and shallow lagoons are the link between terrestrial and oceanic ecosystems and receive considerable external inputs of nutrients and organic matter. Excess inorganic nutrient loading from coastal watersheds has been directly related to increases in primary production and to changes in habitat structure and trophic dynamics in receiving waters. By comparison, little is known about the cycling and bioavailability of organic nutrients in nearshore systems, even though organic nutrient inputs to these systems can sometimes be higher than inorganic loadings. This POWRE award focuses on dissolved organic nitrogen (DON) as a potentially important component of the nitrogen cycle in shallow coastal waters. Coastal lagoons and bays constitute a major type of land margin ecosystem on most continents, but the retention and transport of nutrients through these systems have received far less attention than in large estuaries. A major difference in the nitrogen cycling processes between these systems is the large influence that benthic primary producers have on nutrient transformations in shallow coastal lagoons and bays. Exchanges across the sediment-water interface play a key role in nutrient cycling in lagoonal systems because the water column is well-mixed and small in volume relative to the large sediment surface area. A combination of field observations, laboratory experiments and numerical modeling will be used to test hypotheses regarding interactions between and among organic matter load, flux of DON, and benthic plants. The results will aid our ability to predict both the consequences of different loading regimes to coastal lagoonal systems and the effectiveness of possible mitigation efforts to reduce the effects of eutrophication in shallow coastal systems.
