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Interactions between point and non-point source nitrate pollution and aquifer complexity present many land and water resource management issues; specifically managing anthropogenic nitrogen loads to springs under changing hydrologic conditions and in light of numeric nutrient criteria. Increased nitrogen loading in the Upper Floridan Aquifer (UFA) has contributed to observed ecological shifts in aquatic flora and fauna in many spring systems. The hydrogeologically complex UFA includes well-developed karst conduits, highly permeable limestone, and varying degrees of aquifer confinement. This complexity leads to heterogeneous aquifer properties, groundwater residence times, geochemistry, and hydraulic connectivity with the land surface that complicate management of nitrate pollution, interpretation of geochemical data, and estimates of nitrate attenuation in the aquifer. Significant differences between the estimated nitrogen loads in springsheds and observed nitrogen export from spring vents have been identified, suggesting that denitrification is mitigating the effects of nitrogen loading.
The objective of this study is to characterize denitrification in UFA springsheds near point and non-point sources of nitrate and examine factors that contribute to enhanced denitrification, using spatially distributed measurements of aquifer geochemistry, nitrate isotopes (δ15N and δ18O), dissolved noble gases, and dissolved organic carbon. North Florida springsheds of the UFA provide an ideal test bed for examining how the degree of UFA land-surface connectivity, heterogenous aquifer properties, and spatial variability in nitrogen loads to the aquifer influence the occurrence or magnitude of denitrification. Information about nitrate transformations along groundwater flow paths is key to predicting the attenuation of nitrate in the aquifer and minimizing aquifer pollution in vulnerable areas. Future work will focus on improving water supply management decisions by combining information about nitrate transformations with potential changes in groundwater residence times due to groundwater extraction and climate change.
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