USGS Develops Finer-Scale Approach to Find Areas of High Nitrogen Input to Groundwater
A recent study by the U.S. Geological Survey demonstrates that measuring nitrogen in stream reaches can identify areas where decreasing nitrogen inputs may improve the water quality of downstream receiving waters.
Human-caused nitrogen pollution degrades the quality of surface water and groundwater, particularly in areas of New England where there are many homes using septic systems. Traditional onsite wastewater treatment systems remove bacteria from wastewater, but do not effectively remove nitrogen – sending treated wastewater containing nitrogen back into the soil and groundwater. Understanding where the highest levels of nitrogen pollution originate can help guide effective nutrient management efforts.
The new study measured nitrogen loads, or the amount of nitrogen delivered into the surface water over time, along 63 stream reaches on Cape Cod. Led by hydrologist Tim McCobb of the USGS New England Water Science Center, scientists used a regional groundwater model to map 'reachsheds'— land areas where groundwater recharge, or the water that percolates through the soil to the aquifer, contributes to specific stream reaches.
“This approach provides an alternative to identify potential areas of high nitrogen input at a more focused scale than the entire groundwater watershed by using observations at the receiving streams and existing groundwater flow models,” said McCobb.
The researchers found that groundwater nitrogen is a significant contributor to the nitrogen pollution entering these streams and showed strong correlations between land use and nitrogen levels in the surface water, particularly in areas where there are many septic systems.
Published in the Journal of Hydrology: Regional Studies, the study ranks areas by load, which can help inform where nitrogen mitigation, such as through sewering or installing enhanced septic systems, could most help towns meet water quality standards. This new approach and the study’s findings can help natural resource managers better target nitrogen reduction efforts in communities with high levels of wastewater-derived nitrogen.
The study funding was provided by the U.S. Environmental Protection Agency Southeast New England Program (SNEP) and the U.S. Geological Survey Environmental Health Program. Learn more about this project here.
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Measurement and Modeling of Nitrogen Discharge to Cape Cod Rivers to Identify High-Priority Nitrogen Reduction Areas
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