News Release

Madison, WI, February 23, 2009 | Tiny sediment grains are covered with a very fine-grained, complex mixture of minerals in an open fabric that results in a large surface area in contact with water between the grains. Scientists at the U.S. Geological Survey (USGS) are studying this microscopic layer and finding that the mineral composition of these coatings on sediment grains in the unsaturated zone (i.e., between land surface and the water table) can have a substantial effect on the retention of nitrate and sulfate. Their findings are particularly important for evaluating the long-term effects of agriculture on water quality, as the storage of these common components of fertilizer in the unsaturated zone can affect the quality of shallow groundwater for many years after fertilizer application ceases.

Nitrate and sulfate are important plant nutrients. Farmers and soil scientists routinely monitor the nutrient content of the soil in farm fields so that fertilizer application can be managed to maintain profitability and to minimize runoff or infiltration. Loss of excess nutrients can elevate levels in streams and shallow groundwater. Understanding the mechanisms of nutrient storage in the unsaturated zone is critical to protecting groundwater resources.

Timothy Reilly, the lead author of the study, stated â