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Ecological Effects of Excess Nutrients
Background and Goal
Human activities have dramatically changed the quantity, distribution, and movement of nutrients (e.g., nitrogen, phosphorus, silica) entering coastal environments. This has affected both human health and the environment. For example, increased algal levels due to nutrient enrichment are principally responsible for: (1) changes in basic food webs including altered algal communities (e.g., harmful or nuisance algal blooms), which can lead to loss of both commercially important fisheries and overall aquatic biodiversity; (2) loss of natural submerged aquatic vegetation (SAV) habitats, which are important to fish and other biota; and (3) hypoxia (or anoxia) leading to fish kills and/or degraded benthic (bottom) habitats that affect shellfish and other biota.
Existing models that describe relationships between nutrient loading and environmental effects are available for only a few well-studied systems. There is a need to develop models that predict the adverse effects of nutrient enrichment on systems with limited data. Together with EPA's Gulf, Mid- Continent, and Western Ecology Divisions, the Atlantic Ecology Division (AED) is participating in a multi-year National Aquatic Stressors Research Program to develop regional nutrient loading-response models for estuarine and Great Lakes coastal systems. These models will be available to states and tribes and EPA's Office of Water and Regional Offices to help translate biological response data such as chlorophyll a, SAV extent, and hypoxia extent, into the appropriate level of nutrient loading.
Approach
Using a comparative systems approach, AED is developing empirical nitrogen loading-response models that will allow environmental managers to formulate regional nitrogen input limits for small embayments in southern New England. Novel, efficient methods are being developed and applied to measure aquatic response to different nitrogen loadings (estimated from land use models, etc.). The methods focus on evaluating the effects of nitrogen enrichment on water column, SAV, and benthic habitats. Remotely-sensed chlorophyll-a data are being measured by aircraft to quantify water column algal (phytoplankton) responses. Aircraft derived digital photography is being used to 
measure SAV extent. A sediment profile camera is being used to assess benthic habitat quality due to low dissolved oxygen.
Further Information
For further information, please contact Jim Latimer (401) 782-3167 latimer.jim@epa.gov at the Atlantic Ecology Division of the National Health and Environmental Effects Research Laboratory; Matt Liebman (617) 918-1626 liebman.matt@epa.gov at the EPA Region 1 Office; or Ifeyinwa Davis (202) 566-1096 davis.ifeyinwa@epa.gov at the EPA Office of Water.