T87 Achieving Groundwater Security across Local-to-Regional Scales in the Anthropocene

Monday, 16 October 2023
8:00 AM - 12:00 PM
319

DATA-DRIVEN APPROACHES DEMONSTRATE LEGACY N ACCUMULATION IN UPPER MISSISSIPPI RIVER BASIN GROUNDWATER

Paper number: T87-7
Program: Technical Sessions
Time: 9:25 AM – 9:40 AM

Authors

Abstract

Increases in nitrogen (N) fertilizer application, livestock densities, and human population over the last century have led to substantial increases in nitrate contamination. While increases in riverine N loads are well-documented, the total magnitude of N accumulation in groundwater remains unknown. Here we provide a first data-driven estimate of N mass accumulation in groundwater within the Upper Mississippi River Basin (UMRB), an area of intensive row-crop agriculture and the primary contributor to Gulf of Mexico hypoxia. Using approximately 49,000 groundwater nitrate well concentration values and a suite of geospatial predictors, we developed a Random Forest model to produce gridded predictions of depth-varying nitrate concentrations. Our results suggest that approximately 15 Tg of N (328 ± 167 kg-N ha-1) is currently stored in UMRB groundwater recharged over the last 50 years. For context, we compare these predictions to those from a lumped statistical model, which predicts accumulation of 387 ± 133 kg-N ha-1, as well as to a simple N mass balance model of the UMRB, which puts an upper bound on accumulation of approximately 1,000 kg-N ha-1 (1967-2017). These findings highlight the importance of considering legacy N when forecasting future water quality, as N in the subsurface will continue to impair drinking water quality and elevate surface water N concentrations for decades to come.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-391442

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