Northeastern Section - 53rd Annual Meeting - 2018

Paper No. 48-2
Presentation Time: 8:25 AM


BARCLAY, Janet Rice1, HELTON, Ashley M.2, BRIGGS, Martin A.3, STARN, J. Jeffrey4 and HUNT, Ann3, (1)Natural Resources and the Environment, University of Connecticut, 1376 Storrs Road, Unit 4087, Storrs, CT 06269-4087, (2)Center for Environmental Sciences and Engineering, University of Connecticut, 3107 Horsebarn Hill Rd., Unit 4210, Storrs, CT 06269-4210, (3)Office of Groundwater, Branch of Geophysics, U.S. Geological Survey, Storrs, CT 06279, (4)US Geological Survey, 101 Pitkin Street, East Hartford, CT 06108

Despite years of management, excess nitrogen (N) is a pervasive problem in many aquatic ecosystems. More than half of surface water in the United States is derived from groundwater, and widespread N contamination in aquifers from decades of watershed N inputs suggest legacy N discharging from groundwater may contribute to contemporary N pollution problems in surface waters. Legacy N loads to streams and rivers are controlled by both regional scale flow paths and fine-scale processes that drive N transformations, such as groundwater-surface water exchange across steep redox gradients that occur at stream bed interfaces. Adequately incorporating these disparate scales is a challenge, but it is essential to understanding legacy N transport and making informed management decisions. We developed a regional groundwater flow model for the Farmington River, a HUC-8 basin that drains to the Long Island Sound, a coastal estuary that suffers from elevated N loads despite decades of management, to understand broad patterns of regional transport. To evaluate and refine the regional model, we used thermal infrared imagery along 36 km of stream reaches paired with vertical temperature profiling (n=25) to estimate groundwater discharge at the streambed interface. We also analyzed discharging groundwater (n=54) for multiple N species and dissolved organic carbon to quantify fine scale patterns of N loading and transformation via denitrification at the streambed interface. Integrating regional and local estimates of groundwater discharge of legacy N to river networks should improve our ability to predict spatiotemporal patterns of legacy N loading to and transformation within surface waters.