Nutrient Indicator Research
Nutrients are an important indicator of ecosystem health because the presence or absence of nutrients can cause serious changes to an aquatic ecosystem. Some of the most common nutrients, or chemical elements, found in aquatic systems are phosphorous, nitrogen, and potassium. Nutrients are found naturally in aquatic systems but excess nutrients can make their way into water systems from land and human activities in and around the water and affect aquatic communities.
On this page:
- Nutrient Levels in the Great Lakes
- More Comprehensive Sampling and Experimentation
- Nutrient Indicators and Environmental Management
- Related Research
Nutrient Levels in the Great Lakes
EPA researchers work to create a nutrient uptake indicator to assess conditions that cause algal blooms and, possibly, conditions that cause algal in blooms to produce harmful toxins.
Although phosphorous is an essential nutrient for algae, levels that are too high or too low can cause harmful algal blooms or starve aquatic species. Algal blooms can occur as a result of nutrient enrichment, or eutrophication. The growth may impede water clarity and oxygen levels, which can eventually lead to dead zones in lakes where typical organisms aren’t able to thrive.
Some algal blooms can produce toxins that can harm wildlife and humans. National Coastal Condition Assessments (NCCAs) in the Great Lakes use total phosphorus concentration as a metric of water quality and as part of the water quality indicator. (could link to something here). High phosphorous concentrations, relative to what is expected, suggest poor conditions.
Thresholds vary by lake. Lake Superior conditions are assessed as poor when concentrations exceed 10 micrograms per liter (ug/L). In western Lake Erie, which is naturally more nutrient-rich due to its watershed characteristics and shallow depth, poor conditions are not assessed until concentrations exceed 32 ug/L.
Research has found that phosphorous concentrations may not tell the whole story of eutrophication or the formation of harmful algal blooms in the Great Lakes. It is likely that the differential uptake of phosphorous and nitrogen by algae is important to consider.
Nutrient uptake is the process of nutrients being consumed by plants, like algae, therefore changing the concentration available in the surrounding environment.
More Comprehensive Sampling and Experimentation
Traditionally, EPA researchers monitor water bodies for nutrients based on discrete water samples, or grab samples. Discrete water samples also provide valuable information about the types and population sizes of phytoplankton species present at a single instance in time. These samples do not tell researchers if primary producers, like algae, have too many or too few nutrients available to them. To gain an understanding of nutrient dynamics in water bodies prone to algal blooms, EPA researchers develop tools using in-situ nutrient uptake experiments.
These experiments allow researchers to assess a water sample at time intervals which provides more data. Once the data from these experiments are analyzed, the researchers will know more accurately how “productive” the water at that site is, or how nutrients cycle through the aquatic system.
These experiments measure the amount of nutrients that a community of primary producers use and the ratio of carbon to nitrogen to silicon to phosphorous (C:N:Si:P) that a community needs to thrive. Researchers are then able to identify how close a body of water is to saturation for a nutrient; which nutrients are in limited supply; and the preferred form of limited nutrients (i.e., is nitrogen in the compound NO3 or NH4 more useful to the algae community).
Nutrient Indicators and Environmental Management
EPA researchers develop tools and indicators to help environmental managers prioritize watershed protection and restoration. They are also looking at the physical stream characteristics that increase nutrient retention in order to make more informed decisions when restoring streams.
The management of aquatic systems must consider all elements of a watershed, including channels and embankments. It is also important to understand the retention, transport and fate of nutrients in the streams and rivers feeding larger bodies of water.
Using nutrient uptake methods, researchers can determine whether a stream is retaining nutrients or if those nutrients travel to a larger waterbody.