Nitrate transport in a karst aquifer: Numerical model development and source evaluation
Abstract
Protecting karst aquifers from nitrate contamination is an issue of global concern due to the inherent vulnerability of karst aquifers to contamination and the negative health effects of elevated nitrate levels. Hydrological and transport models were developed to assess nitrate transport within a karstic aquifer located in an area with both semi-arid and sub-humid climate conditions. Groundwater flow through the aquifer matrix and conduits was simulated with CFPv2, an experimental version of the Conduit Flow Process (CFP) version of the MODular FLOW (MODFLOW) groundwater model. Nitrate transport was simulated with the experimental Conduit Mass Transport Three-Dimensional Model (CMT3D). The hydrologic calibration of the steady-state model was successful based on a scaled Root Mean Squared Error (RMSE) of 4.9% for hydraulic heads and percent errors of 3.0% and 6.6% for the two major springs in the area. Performance of the transient hydrologic model exceeded the performance of the existing Equivalent Porous Media (EPM) model with a scaled RMSE of 2.2% and springflow errors of 1.5% and 2.8% for the major springs. Similarly, nitrate calibration was successful with all Percent Bias (PBIAS) values between ±25%. Additional calibration statistics including a two-tailed t-test indicated successful calibration. The CMT3D model corroborates prior research findings that anthropogenic sources as well as biogenic wastes are important sources of nitrate to the aquifer. The methodology used in this study represents an additional tool for watershed managers to address nitrate contamination within karst aquifers.
- Publication:
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Journal of Hydrology
- Pub Date:
- June 2019
- DOI:
- 10.1016/j.jhydrol.2019.03.078
- Bibcode:
- 2019JHyd..573..432S
- Keywords:
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- Karst hydrology;
- Conduit Flow Process;
- Conduit Mass Transport Three-Dimensional;
- Groundwater transport modeling;
- Nitrate