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Groundwater Makes Measuring Bay Nutrient Levels Difficult

Shortly after manure or fertilizer is spread on the land, a portion of the nitrogen that goes unused by crops takes a turn that could affect the course of nutrient trading in the watershed.

Instead of being flushed downhill and into a stream during a rainstorm, some of the excess slowly leaches through the soil until it reaches slow-moving groundwater.

The groundwater will also carry the nitrogen to a stream-and ultimately the Bay-but at a more leisurely pace: It often takes years, and sometimes decades, to complete the journey.

How much nitrogen takes the slow road to the Bay varies by a host of site-specific factors such as soil type. On average, U.S. Geological Survey studies in the Bay region estimate that 48 percent of the nitrogen reaching streams from nonpoint sources, such as farming or lawn fertilizer application, travels through groundwater. 

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