Groundwater/Surface-Water Interaction

Featured publication: The value of high-frequency nitrate data

Featured publication: The value of high-frequency nitrate data

Learn about how continuous data on nitrate concentrations tells us about the role of groundwater in contributing nitrate to surface water.

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Key influences on nitrate concentrations in Chesapeake Bay

Key influences on nitrate concentrations in Chesapeake Bay

Land use, organic carbon in soils and geology are among the most important factors affecting high nitrate in base flow in streams that flow into Chesapeake Bay, reports a new USGS study. Much of that nitrate is from groundwater.

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Water and the chemicals it contains are constantly being exchanged between the land surface and the subsurface. Surface water seeps into the ground and recharges the underlying aquifer—groundwater discharges to the surface and supplies the stream with baseflow. USGS Integrated Watershed Studies assess these exchanges and their effect on surface-water and groundwater quality and quantity.

Groundwater and surface water physically overlap at the groundwater/surface water interface through the exchange of water and chemicals. This exchange is a critical part of the hydrologic cycle. Surface water supplies recharge to the underlying aquifer, where the groundwater can remain in storage for days, months, years, centuries, or even millennia. Eventually the groundwater discharges back into the stream. Depending on how much time the water spends underground, and the geochemical conditions within the aquifer, the quality of the original recharge water can undergo profound changes before it discharges at the surface.

USGS Integrated Watershed Studies seek to better understand and quantify the exchanges at the surface water/groundwater interface. This understanding is used to forecast how the chemical quality of water will change in response to changes in climate, land use, or management practices. Integrated Watershed Studies develop methods to quantify the movement of water and chemicals between the watershed, stream, and groundwater to estimate past and forecast future water-quality conditions at regional scales. The USGS also develops new methods to interpret high-frequency water-quality monitoring data to inform and develop watershed models.

Interested in surface-water quality? Find out more here.

Interested in groundwater quality? Find out more here.