Estuaries

Nutrients enter the upper Rhode River estuary from its watershed and are carried in and out of marshes (foreground) with the tides. Our long-term studies have traced nutrient exchanges among these ecosystems.

Human activities have greatly increased the delivery of plant nutrients to estuarine and coastal waters throughout the world. Over abundant nutrients fuel excessive algal growth, which destroys critical habitats for fish and shellfish by depleting oxygen in the water and by blocking light from reaching sea grasses. This is a serious problem in Chesapeake Bay and many other estuaries.
      Research by the nutrient lab and collaborators investigates the fates and effects of nutrients discharged from watersheds into estuaries. The Rhode River watershed and estuary have served as model systems these studies. The Rhode River watershed includes agricultural lands, upland forests, riparian forests, and freshwater wetlands. Water flow connects these systems to the shallow estuarine waters and tidal marshes of the Rhode River. We have measured nutrient exchanges between the tidal marshes and the estuary (Jordan et al. 1983; Jordan and Correll 1991), transport of nutrients in marsh groundwater (Jordan and Correll 1985), and fluxes of particulate matter in the upper estuary (Jordan et al. 1986, Estuaries). We also constructed a salinity based model of mixing

Sediment traps are deployed in a study of the transport and transformation of nutrients along the salinity gradient of the Patuxent River estuary.

to determine rates of nutrient uptake and release in segments of the upper Rhode River estuary (Jordan et al. 1991, Limnol. Oceanogr.). By comparing flows of N and P through the watershed, marshes and estuary, we identified the most important sites of nutrient transformation and the factors that may limit nutrient availability in the different ecosystems (Jordan et al. 1986, in Watershed Research Perspectives; Jordan et al. 1991). By correlating long-term interannual variations in watershed discharges with variations in nutrient and chlorophyll concentrations in the estuary, we resolved separate effects of the local Rhode River watershed and the distant Susquehanna River watershed on phytoplankton biomass within the Rhode River estuary (Jordan et al. 1991, Mar. Ecol. Prog. Ser.; Gallegos and Jordan 1997; Gallegos et al. 1997). We have also analyzed long-term trends and short-term variation in delivery of nutrients via atmospheric deposition at the Rhode River (Jordan et al. 1995).
     For unknown reasons, phosphorus (P) enrichment generally has the greatest impact in freshwater while nitrogen (N) enrichment has the greatest impact in saltwater. A new study by SERC's nutrient lab in collaboration with researchers at the University of Maryland seeks to understand how the biogeochemistry of N and P changes along the transition from freshwater to saltwater in an estuary. This project measures inputs and removals of N and P along the salinity transition of the Patuxent River estuary, to investigate the importance of watershed-derived particulate P, and to test hypotheses about interactions of N, P, iron and sulfur cycles. Transformations and releases of N and P are measured by incubating sediment cores from along the salinity gradient. The mechanisms of salinity effects are investigated by experimentally altering concentrations of seawater, sea salts, sulfate, and nitrate over incubated cores. We hope that the results will help guide nutrient management in coastal ecosystems.

Click here for more information on current research along the salinity gradient of the Patuxent River estuary.