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Nutrients such as nitrogen, phosphorus, and silica are essential to life on Earth.  However, in high enough concentrations, they become harmful environmental contaminants.  Important examples of nutrient contamination in water include the hypoxic zone in the Gulf of Mexico and toxic algal blooms in places like Lake Erie.  At the NWQL, nutrients are analyzed in both filtered and unfiltered water samples to better understand the health of aquatic systems and to pinpoint potential sources of contamination such as agricultural runoff.  For more information on USGS research into the fate and effects of nutrients in the environment please visit:  

Each year, the NWQL analyzes tens of thousands of water samples to help monitor nutrients concentrations throughout the United States and United States territories.  When discussing water quality, nutrients most commonly refers to nitrogen and phosphorus.  At the NWQL, nitrogen and phosphorus, along with silica and iodide, are analyzed using colorimetric analysis or colorimetry.  The NWQL uses both Automated Segmented Flow Analyzers and Automated Discrete Analyzers to measure nutrients by colorimetry.  Other essential nutrients such as minerals (e.g. cations and trace metals) are analyzed using inductively coupled plasma (ICP) analyzers (i.e. ICP-OES and ICP-MS).  Colorimetric and ICP analyzers typically allow for detection of nutrients down to a few micrograms per liter (parts-per-billion) and sometimes allow for detection as low as a few nanogram per liter (parts-per-trillion) in groundwater and surface water as well as wastewater and drinking water. 

Nutrients results from the NWQL are an essential part of various local, regional and nation studies including the USGS National Water-Quality Assessment (NAWQA) Project.  For more information of the NAWQA project please visit:    

Links for Nutrients section:

Hypoxic zone:

Toxic algal bloom: