Nutrient movement into estuaries and the resulting effects on primary productivity, the depletion of oxygen, habitat structure, and trophic changes in coastal waters have dominated estuarine research for decades. Another, and neglected, linkage between land and coastal waters is the input of dissolved and particulate organic carbon and organic nitrogen. Organic nitrogen inputs are frequently greater than inorganic nitrogen inputs and in many cases the input of organic carbon from land is greater than the in situ production of organic carbon. Despite the quantitative importance of organic matter inputs from land, there is little data on its actual use in coastal waters and even less data on effects of organic matter loading on coastal ecosystem structure and function. Recent developments in the chemical analysis of dissolved organic C and N and stable isotope tracer technology now make it possible to refine the input-output budgets and also address the fate and importance of organic matter entering coastal waters from land. Two broad questions addressed in this project are: (1) What is the importance to estuarine ecosystems of organic carbon and organic nitrogen inputs from watersheds with various land covers and uses? and (2) Does the interaction of inorganic nutrients with the quantity and quality of organic carbon and organic nitrogen play an important role in determining the trophic structure, production, and trophic efficiency in estuaries? This project will attempt to answer these questions through measurements of the quantity of dissolved and particulate organic carbon and organic nitrogen entering coastal waters from land, through experiments to determine the effects of various nutrient and organic matter inputs and interactions on the flow and recycling of C and N through pelagic and benthic food webs including higher trophic levels, and through modeling of food chain transformations and the effects of changes in land use and land cover. The proposed research integrates estuarine biogeochemistry with studies of food webs and population biology of higher trophic levels. Site-specific research will be focused in the Plum Island Sound System of the cold-water Acadian Biogeographic Province in northern New England. This projects seeks conclusions and models that are applicable across a wide range of coastal waters; hypothesis testing of specific questions across ecosystems is the most effective way to achieve this goal. This project will combine experimental studies in the Plum Island Sound Ecosystem with comparative studies at different coastal sites (LMER/LTER) chosen to represent end-members in an analysis of interactions between organic matter and inorganic nutrient loading.
