Assessment of Nutrient Loading in Coastal Ecosystems: Assateague Island National Seashore

Principal Investigator: Scott Nixon, Graduate School of Oceanography, University of Rhode Island

Project summary:

This project includes three related elements: 1) Review of the nutrient loading to the Maryland and Virginia portions of Chincoteague Bay, Newport Bay and Sinepuxent Bay, 2) evaluation of the health of specific eelgrass (Zostera marina L) beds within these bays as indicators of general ecosystem health, and 3) statistical analysis of NPS water quality sampling results.

1) This element of the project is currently ongoing as a portion of Luke Cole's M.S. research at the Graduate School of Oceanography. Nutrient loading estimates to the Maryland portion of Chincoteague Bay, Newport Bay and Sinepuxent Bay developed by Coastal Environmental Services in 1990 will be reviewed, updated and expanded. Additional data on the Virginia portion of Chincoteague Bay will also be included. Using existing GIS analysis, an inventory of Nitrogen (N) and Phosphorus (P) loading of individual sub- watersheds of each bay will be generated. Land use – nutrient runoff coefficients will be used to estimate non-point source loading. Sensitivity of overall loading estimates to different assumptions regarding source strength will be applied using a land use – N loading model developed by Valiela et.al. The land use – nutrient data will also be compared with recent USGS estimates of nitrate loading in groundwater. Additionally, atmospheric deposition estimates will be updated.

2) Field testing for a suite of indicators of eelgrass health and anthropogenic nitrogen impact was conducted. Five sampling sites along a longitudinal axis through the bay systems were used. In previous research the common diagnostic assessment tool for eelgrass health has been area coverage of beds; often based on aerial photos. Although this metric can be useful in elucidating dramatic loss of beds; it does not provide sensitive information that would indicate chronic stress or incipient loss of beds. Eelgrass beds were evaluated for vitality and persistence using a set of plant growth parameters; shoot density, biomass, and rate of rhizome, leaf and lateral shoot production, which have been successfully utilized in the field and in shallow water mesocosm experiments during the last 10 years. Preliminary reports indicate that nitrogen-stable isotope signatures (d15 N) in plant leaves and macroalgae provide a sensitive indicator of anthropogenic N impacts. Therefore, we conducted ad15 N analysis of eelgrass leaves and the two major species of macroalgae from each bay.

3) The NPS has been conducting regular water quality monitoring for the last 15 years at 18 stations in the four bays. Employing a statistical approach, trends for water quality parameters (water temperature, salinity, density stratification, chlorophyll, all forms of nutrients measured, extinction coefficients and dissolved oxygen) were evaluated. Results from this study led to the development of a project that will combine the water quality analysis with spatio-temporal statistical modeling of the abundance and distribution of fishes and eelgrass over a twenty year period.

The application of a nitrogen loading model continues as part of Luke Cole's M.S. research with Scott Nixon.

Analysis of the water quality data led to a more rigorous project that will use spatio-temporal statistical modeling to examine the abundance and distribution of fishes and eelgrass in relation to pertinent water quality variables.

Student Involvement

Granger, S., S. Nixon, L. Harris, J. Chaves, R. Fulweiler, C. Mueller, B. Sturgis, and A. Almario. A preliminary assessment of seagrass health and vitality in Assateague National Seashore's coastal bays. Understanding the Role of Macroalgae in Shallow Estuaries. January 10-11, 2002. Linthicum, Maryland.

Nixon, S.W. (Plenary Speaker) Responses of shallow marine ecosystems to nutrient enrichment. Understanding the Role of Macroalgae in Shallow Estuaries Conference. January 10-11, 2002. Linthicum, Maryland.

Nixon, S., B Buckley, S. Granger, J. Bintz. 2001. Responses of very shallow marine ecosystems to nutrient enrichment. Human and Ecological Risk Assessment. 7: 1457-1481.