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Upstream of a covered bridge along Fishing Creek in Pennsylvania, Hilary Dozier, a USGS hydrologist, measures streamflow as part of a synoptic water quality study to inform nitrogen reduction strategies in a representative agricultural karst setting of the Chesapeake Bay watershed. 

The complex hydrologic network in agricultural carbonate watersheds presents a challenge for targeting and monitoring of conservation practices. Water and excess nitrogen in a karst landscape can travel rapidly underground through a complex network of dissolved pathways in the carbonate rock (e.g., limestone) before departing to streams and springs. To inform management and monitoring efforts of nitrogen, USGS used near simultaneous measurements (synoptic sampling) of water quality across multiple stream and spring locations during seasonal high and low stream baseflow. This study revealed that the main sources of nitrogen include manure, fertilizer, and wastewater with a low potential for denitrification (conversion of nitrate to nitrogen gas). Depending on the season or location in the watershed, the nitrogen load shifted among losing and gaining stream sections. Establishing monitoring at fixed locations without synoptic sampling could be problematic for assessing management progress. Karst areas have the potential to reduce nitrogen rapidly, but inputs, conservation effectiveness, and legacy nutrients confound progress.  

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