Human actions have profoundly altered the natural input and cycling of nutrients in the environment and greatly changed the amount of nutrients transported to our streams, rivers, and estuaries. Impacts to aquatic health include nuisance and toxic algal blooms, oxygen depletion, alteration of instream habitat, and shifts in aquatic food resources and community composition. Excess nitrogen in streams also can increase drinking water treatment costs. Excess nutrients have a major economic impact—causing an estimated $2.2 billion per year in recreational water usage, waterfront real estate, and drinking water treatment. This presentation will provide an overview of our present understanding in stream nutrient ecology, along with future research needs. Although research on nutrients has been extensive, this presentation will draw upon studies from the USGS National Water Quality Assessment Program and existing literature.
Results/Conclusions
It is well established that headwater streams are critical for nutrient processing, and therefore any activities that decrease retention time, as in channelization, reduces the natural capacity of a stream’s natural ability to remove nutrients. This problem can be exacerbated by high nutrient input from land application as well as by groundwater legacy nutrients that can continue to enter streams over long periods of time. Therefore, nutrient reductions would have to be substantial before any improvements in stream health are observed. Trends data indicate that although some sites show a decrease in nutrients, many show no change or an increase in concentrations. Studies often indicate that excessive nutrients can result in increased primary production, a consequent shift in food resources, and a change in community composition. Addressing nutrient effects alone are common; however, recent multi-stressor studies have reported that biota are influenced by various stressors, including nutrients, contaminants, and physical habitat. The shifts in algal assemblages may include increased frequency and extent of harmful algal blooms, resulting in the release of toxins into stream environments and receiving waters. Although our knowledge of nutrients in streams has increased substantially, additional research is required in several areas. Examples of future research include, but are not limited to, understanding drivers of toxic algal blooms, controlled studies of Best Management Practices, strategies for prioritizing streams for nutrient management, use of high-frequency nutrient sensors for assessing temporal changes in nutrients, and regional-based predictive models to facilitate these and other issues surrounding nutrients.