Nutrients: Research
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 distribution
1. 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.
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