Effects of Nutrient Enrichment on Stream Ecosystems (Upper Snake River Basin NAWQA)

Science Center Objects

Nutrient enrichment can affect the ecological health of a stream. For example, excessive aquatic plant growth caused by increased nutrients can reduce dissolved oxygen necessary for other aquatic life. Topics of particular interest in this study area include:

seasonal patterns among nutrients, flows, algae and plants in streams

rooted aquatic plant vs. algae growth

stream metabolism and nutrient transport processes

field sample technique improvement

Beginning in 2006, we collected and analyzed aquatic chemical, physical, and biological samples to evaluate relationships between nutrients in streams and levels of aquatic plant growth. These analyses helped us to understand the role of nutrient concentrations and eutrophication in agricultural streams nationally and how conditions in the irrigated agricultural settings in the arid west differ from those in the Midwest or Eastern regions of the country.

  • While many freshwater nutrient management strategies such as total maximum daily load plans (TMDLs) target phosphorus concentrations in water, growth of algae in streams was more commonly limited by nitrogen concentrations than by phosphorus.
  • This implies that nutrient management plans based on reducing phosphorus may have uncertain connections to reducing undesired plant growth in streams.
  • Phosphorous in water was not correlated with abundance of rooted aquatic plants or benthic algae in streams, but phosphorus in sediments was correlated with both.
  • Other important factors limiting excessive growth of rooted aquatic plants in streams include flow histories, shading from riparian plants, and water clarity.
  • Sampling designs to evaluate nutrient enrichment that ignore rooted plants may lead to misleading impressions of aquatic productivity in streams.
  • Sampling designs that only target one-time, mid-summer conditions may lead to misleading impressions of nutrient concentrations in streams.

Stalker Creek (see photos below), a spring-fed stream in Idaho, acquires excessive plant growth during spring and summer because of low velocities, ample sunlight, clear water, and ample nutrients from groundwater. This condition can lead to undesirably low dissolved oxygen levels that may negatively affect fish and recreational uses such as fishing or swimming.