Understanding local groundwater hydrology and geochemistry is critical for evaluating the effectiveness of wetlands at mitigating agricultural impacts on surface waters. The effectiveness of depressional wetlands at mitigating nitrate (NO 3 ) transport from fertilized row crops, through groundwater, to local streams was examined in the watershed of the upper Choptank River, a tributary of Chesapeake Bay on the Atlantic Coastal Plain. Hydrologic, geochemical, and water quality data were collected from January of 2008 through December of 2009 from surface waters and networks of piezometers installed in and around current or former depressional wetlands of three major types along a gradient of anthropogenic alteration: (1) natural wetlands with native vegetation (i.e., forested); (2) prior-converted croplands, which are former wetlands located in cultivated fields; and (3) hydrologically restored wetlands, including one wetland restoration and one shallow water management area. These data were collected to estimate the orientation of groundwater flow paths and likely interactions of groundwater containing NO 3 from agricultural sources with reducing conditions associated with wetlands of different types. Natural wetlands were found to have longer periods of soil saturation and reducing conditions conducive to denitrification compared to the other wetland types studied. Because natural wetlands are typically located in groundwater recharge areas along watershed divides, nitrogen (N) from nearby agriculture was not intercepted. However, these wetlands likely improve water quality in adjacent streams via dilution. Soil and geochemical conditions conducive to denitrification were also present in restored wetlands and prior-converted croplands, and substantial losses of agricultural NO 3 were observed in groundwater flowing through these wetland sediments. However, delivery of NO 3 from agricultural areas through groundwater to these wetlands resulting in opportunities for denitrification were limited, particularly where reducing conditions did not extend throughout the entire thickness of the surficial aquifer allowing NO 3 to pass conservatively beneath a wetland along deeper groundwater flow paths. The complexity of N fate and transport associated with depressional wetlands complicates the understanding of their importance to water quality in adjacent streams. Although depressional wetlands often contribute low NO 3 water to local streams, their effectiveness as landscape sinks, for N from adjacent agriculture varies with natural conditions, such as the thickness of the aquifer and the extent of reducing conditions. Measurement of such natural geologic, hydrologic, and geochemical conditions are therefore fundamental to understanding N mitigation in individual wetlands.Key words: agriculture-Chesapeake Bay-denitrification-depressional wetlandsgroundwater-wetland conservation practices Local hydrologic and geochemical conditions control the movement of nitrate (NO 3 ) through and around depressional wetlands...

For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit http://www.usgs.gov or call 1-888-ASK-USGS.For an overview of USGS information products, including maps, imagery, and publications, visit http://store.usgs.gov.Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. AcknowledgmentsFunding for this study was provided by the U.S. Geological Survey (USGS) Ecosystems Mission Area as part of the Priority Ecosystem Science (PES) Program. Sincere appreciation is extended to the many landowners in all four study watersheds who provided us with access to many of the study sites. Cooperation from the U.S. Department of Agriculture, Natural Resources Conservation Service, as well as the Soil and Water Conservation Service, was instrumental for better understanding each basin and for gaining access to study sites. Additional contributions of data and information were made by the Virginia Department of Environmental Quality, Pennsylvania Department of Environmental Protection, the Maryland Department of Natural Resources, and the U.S. Environmental Protection Agency. Appreciation is extended to the Stormwater Planning Division of the Fairfax County Department of Public Works and Environmental Services for supporting elements of water-quality monitoring in Difficult Run that were incorporated into this report and for providing data on the implementation of best management practices throughout Difficult Run.We are indebted to the many USGS field technicians and hydrologists who have contributed to the collection of field samples and other technical content throughout the report. Technical reviews by Doug Burns of the USGS New York Water Science Center and Angie Crain of the USGS Indiana-Kentucky Water Science Center strengthened this report and are sincerely appreciated. AbstractDespite widespread and ongoing implementation of conservation practices throughout the Chesapeake Bay watershed, water quality continues to be degraded by excess sediment and nutrient inputs. While the Chesapeake Bay Program has developed and maintains a large-scale and long-term monitoring network to detect improvements in water quality throughout the watershed, fewer resources have been allocated for monitoring smaller watersheds, even though water-quality improvements that may result from the implementation of conservation practices are likely to be first detected at smaller watershed scales.In 2010, the U.S. Geological Survey partnered with the U.S. Environmental Protection Agency and the U.S. Department of Agriculture to initiate water-quality monitoring in four selected small watersheds that were targeted for increased implementation of con...

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Graphs showing major ion contributions to specific conductance (SC) for 72 groundwater samples from Bradford County, Pennsylvania, 2016: A, comparison of estimated ionic conductivity contributions by sodium, calcium, magnesium, chloride, bicarbonate, and sulfate to measured SC for all 72 samples; and B, relative contributions by major ion species to computed SC and selected groundwater samples of representative water types, expressed in percent, in order of increasing SC .

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). Elevation, as used in this report, refers to distance above the vertical datum.