%AGilmore, Troy [Now at Conservation and Survey Division and Department of Biological Systems Engineering University of Nebraska Lincoln Nebraska USA, Department of Marine Earth, and Atmospheric Sciences, North Carolina State University Raleigh North Carolina USA]%AGilmore, Troy [Now at Conservation and Survey Division and Department of Biological Systems Engineering; University of Nebraska; Lincoln Nebraska USA; Department of Marine; Earth, and Atmospheric Sciences, North Carolina State University; Raleigh North Carolina USA]%AGenereux, David [Department of Marine Earth, and Atmospheric Sciences, North Carolina State University Raleigh North Carolina USA]%AGenereux, David [Department of Marine; Earth, and Atmospheric Sciences, North Carolina State University; Raleigh North Carolina USA]%ASolomon, D. [Department of Geology and Geophysics University of Utah Salt Lake City Utah USA]%ASolomon, D. [Department of Geology and Geophysics; University of Utah; Salt Lake City Utah USA]%AFarrell, Kathleen [North Carolina Geological Survey, Coastal Plain Field Office and Core Repository; Raleigh North Carolina USA]%AFarrell, Kathleen [North Carolina Geological Survey, Coastal Plain Field Office and Core Repository Raleigh North Carolina USA]%AMitasova, Helena [Department of Marine Earth, and Atmospheric Sciences, North Carolina State University Raleigh North Carolina USA]%AMitasova, Helena [Department of Marine; Earth, and Atmospheric Sciences, North Carolina State University; Raleigh North Carolina USA]%BJournal Name: Water Resources Research; Journal Volume: 52; Journal Issue: 11; Related Information: CHORUS Timestamp: 2023-08-21 08:43:18 %D2016%IDOI PREFIX: 10.1029 %JJournal Name: Water Resources Research; Journal Volume: 52; Journal Issue: 11; Related Information: CHORUS Timestamp: 2023-08-21 08:43:18 %K %MOSTI ID: 10031428 %PMedium: X %TQuantifying an aquifer nitrate budget and future nitrate discharge using field data from streambeds and well nests %XAbstract

Novel groundwater sampling (age, flux, and nitrate) carried out beneath a streambed and in wells was used to estimate (1) the current rate of change of nitrate storage,/dt, in a contaminated unconfined aquifer, and (2) future []FWM(the flow‐weighted mean nitrate concentration in groundwater discharge) and(the nitrate flux from aquifer to stream). Estimates of/dtsuggested that at the time of sampling (2013) the nitrate storage in the aquifer was decreasing at an annual rate (mean = −9 mmol/m2yr) equal to about one‐tenth the rate of nitrate input by recharge. This is consistent with data showing a slow decrease in the [] of groundwater recharge in recent years. Regarding future []FWMand, predictions based on well data show an immediate decrease that becomes more rapid after ∼5 years before leveling out in the early 2040s. Predictions based on streambed data generally show an increase in future []FWManduntil the late 2020s, followed by a decrease before leveling out in the 2040s. Differences show the potential value of using information directly from the groundwater—surface water interface to quantify the future impact of groundwater nitrate on surface water quality. The choice of denitrification kinetics was similarly important; compared to zero‐order kinetics, a first‐order rate law levels out estimates of future []FWMand(lower peak, higher minimum) as legacy nitrate is flushed from the aquifer. Major fundamental questions about nonpoint‐source aquifer contamination can be answered without a complex numerical model or long‐term monitoring program.

%0Journal Article