Assessing Mississippi embayment and coastal lowlands aquifer systems by groundwater stress index and regional groundwater model

Abstract

The Mississippi embayment aquifer system (MEAS) and the coastal lowlands aquifer system (CLAS) provide substantial freshwater for human activities in the U.S. Gulf Coastal Plain. However, anthropogenic impacts on groundwater in both aquifer systems remain poorly understood, hindering effective groundwater management. This study presents a significant advancement in the groundwater stress assessment for the MEAS and the CLAS in the Louisiana and southwestern Mississippi region, focusing on groundwater availability and sustainability in response to natural and human dynamics at various spatial and temporal scales. To achieve these, a novel groundwater stress index (GSI) was introduced to quantify the influence of groundwater use on groundwater availability. This metric was rigorously compared with the widely recognized groundwater footprint index (GFI). The assessment employed a regional groundwater model, which was contrasted with the assessment based on the Gravity Recovery and Climate Experiment (GRACE)-derived groundwater storage data. The modeling assessment reveals net groundwater storage gain in the study region from 2004 to 2021. Nevertheless, critical groundwater stress levels were identified in specific aquifers of the MEAS and CLAS, indicating localized groundwater depletion and unsustainable groundwater use. The model highlights the impacts of river-aquifer interactions on seasonal variations of groundwater availability and stress. The long-term trend of simulated groundwater storage aligns with GRACE-derived data. Moreover, the model-based assessment suggests similar groundwater stress to the GRACE-based assessment on a regional scale. The comparison between GSI and GFI suggests that the GSI is an effective approach to quantifying groundwater stresses across various scales.