These findings, published in a new USGS report, further refine the LIS nitrogen budget, or the inputs and outputs of nitrogen into the Sound. With a comprehensive understanding of how, where and when nitrogen enters LIS, natural resource managers can reduce nutrient loading by implementing strategies specific to their area. 

For decades, excess nitrogen in LIS has caused harmful algal blooms that lower dissolved oxygen too much to support fish and shellfish. It has been widely known that most of the nitrogen entering LIS comes from wastewater treatment plants, septic systems, and fertilizers. Managers have made concerted efforts to reduce nitrogen from wastewater treatment plants and these nitrogen sources have been carefully researched. However, dispersed sources of nitrogen from fertilizers and septic systems were not as well defined even though it is estimated to be the major contributor of nitrogen into LIS from Connecticut. 

“This study fills in that key gap that has been missing” said hydrologist and lead study author Janet Barclay. “Analyzing monthly groundwater-transported nitrogen from the north shore of Long Island Sound is a vital piece of the puzzle.”

In cooperation with the U.S. Environmental Protection Agency’s Long Island Sound Study and the Connecticut Department of Energy and Environmental Protection, USGS developed models and created a simulation to determine how nitrogen from the atmosphere, septic systems, and fertilizer moves through groundwater into LIS in southern Connecticut. They developed a soil-water-balance model and a monthly MODFLOW groundwater-flow model coupled with a nitrogen transport simulation to calculate where the nitrogen comes from, how quickly it moves over time, and when and where it enters streams, rivers, or coastal waters from the groundwater system. 

“While most of the nitrogen that enters Long Island Sound comes from rivers and streams, the amount of nitrogen that enters those water bodies from groundwater was never fully characterized,” Barclay said. “With this information, managers can implement changes in their watershed based on the major nitrogen inputs, know how quickly management action will show results, and decide whether or not additional modeling or monitoring is needed.”

The USGS study also included different management scenarios on the groundwater-transported nitrogen to show what would happen if septic systems were upgraded or if less turf-grass fertilizers were used in the various watersheds. 

Natural resource managers can also use the outputs from these models individually to answer specific management questions by inputting new hydrology or nitrogen loading information as that information changes over time.

Learn more about this project here.

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