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Health and Environmental Effects Research

Nutrients

Human activities over the past century have dramatically increased the amount of nutrients (nitrogen and phosphorous, in particular) that is introduced to our Nation's rivers, lakes, and coastal waters. This change has adversely affected the health of the natural environment and, in some cases, poses risks to human health.

The introduction of excess nitrogen and phosphorous promotes the growth of algae which eventually dies and sinks to the sediment. Naturally occurring bacteria subsequently decompose the algae in a process which consumes oxygen. When the bacterial demand for oxygen exceeds supply, oxygen levels in waters become inadequate to support the aquatic life living in that habitat and are described as "hypoxic." In addition to lowering oxygen levels, the increases in algal production that are caused by excess nutrients also adversely affect submerged aquatic vegetation and the populations dependent upon it and can induce changes in aquatic food webs.

EPA's research in this area will support development of nutrient criteria and standards aimed at protecting aquatic life from the adverse effects of nutrient loading. Specific attention will be focused on defining and quantifying the relationships between nutrient loading in coastal areas and three major ecological responses: decreased oxygen levels, loss of submerged aquatic vegetation, and changes in food webs. A long-term objective of this research is to expand scientists' understanding of how aquatic ecosystems function so that predictions can be made for systems about which only limited data exists. This objective will be met by developing classification schemes, standard measurement endpoints, and nutrient load-response models.

To learn more about nutrients, you may wish to visit Water Quality Criteria: Nutrients.

View information about the Implementation Plan for Nutrients Research within the Aquatic Stressors PDF file. (PDF, 197 pp, 3.21 MB, About PDF).

Research

Drinking Water

A frog sitting among submerged vegetation.

Decreased Oxygen Levels

To prevent waters from becoming hypoxic, it is necessary to limit the influx of the nutrients which are responsible for initiating the cascade of events that causes waters to become depleted of oxygen. Part of the process of setting nutrient criteria based on dissolved oxygen (DO) involves determination of the minimum DO requirements of aquatic organisms. EPA scientists are in the process of conducting exposure experiments that will provide risk-assessment managers with the basic information needed to set minimum DO limits for the Nation's waters. Other on-going research aims to reduce the uncertainty associated with setting DO-based nutrient criteria by establishing common methods of measurement and by developing an improved classification scheme.

Loss of Submerged Aquatic Vegetation

Nutrients primarily affect submerged aquatic vegetation (SAV) through their effects on water quality and the associated effects on light availability caused by increased algal biomass. Light availability is generally considered to be the major factor determining SAV survival and distribution1. To protect SAV from loss due to nutrient loading, a set of models will be developed and used to examine how nutrients interact with the physical and biological components of the environment. EPA scientists will rely on field monitoring, direct experimentation, and the large body of literature which already exists to inform their development of models and of an improved classification scheme. Work is currently underway to investigate the relationship between nutrient loading and several quantitative attributes of SAV including percent cover, diversity, abundance, and maximum depth of macrophyte growth and to develop a database of changes in water quality, light availability, and SAV distributions.

Changes in Food Webs

Increases in the concentration or changes in the ratios or timing of nutrient inputs have the potential to adversely affect populations of ecologically and commercially important organisms by affecting the food webs of which these populations are a part. Research in this area will focus on quantifying the amount of nutrient loading that can induce these adverse effects and will begin with efforts to identify pelagic and benthic species that are particularly sensitive to these effects.

1 Dennison, W.C. 1987. Effects of light on seagrass photosynthesis, growth and depth distribution. Aquatic Botany 27: 15-26

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