Does groundwater contribute nutrients to streams?
Groundwater contributions of nutrients to streams can be significant—particularly for nitrate. Specifically, at least a third of the total annual load of nitrate in two-thirds of 148 small streams studied across the Nation was derived from base flow, consisting mostly of groundwater (Spahr and others, 2010; http://pubs.usgs.gov/sir/2009/5199/). The generally low concentrations of phosphorus in groundwater suggest that input of phosphorus to streams from groundwater is modest. However, geologic sources of phosphorus in an aquifer, coupled with chemical conditions favorable to phosphorus transport, can result in high groundwater inputs of phosphorus to streams during low flow conditions such as was found in the Coastal Plains of North Carolina (Spruill and others, 1998; http://pubs.usgs.gov/circ/circ1157/). Similarly, groundwater contributes phosphorus to the Tualatin River, Oregon, during summer low-flow conditions. In this case, the primary source of high phosphorus in groundwater was
