Ground Water Flow Rate

Ground water flow rates can be a slow process. USGS hydrologic researchers, for example, have found that the movement of nitrate through groundwater to streams can take decades to occur. This long lag time means that changes in the use of nitrogen-based fertilizer (the typical source of nitrate) — whether the change is initiation, adjustment, or cessation — may take decades to be fully observed in their effect on streams, according to a recent study published in the journal Environmental Science and Technology. Water quality experts have been noting in recent years that nitrate trends in streams and rivers do not match their expectations based on reduced regional use of nitrogen-based fertilizer. The long travel times of groundwater discharge, like those documented in this study, is the likely cause.