172-6 Hydro-chemical Investigation of surface water and groundwater interactions in a karst dominated aquifer in south central Texas

Session: Urban Geochemistry

Presenting Author:

Authors:

Abstract:

The Edwards Aquifer, a highly productive karst system, provides essential water supplies, natural habitats, and economic activity throughout south central Texas. Its peculiar hydrogeology, characterized by broken limestone, conduits, and sinkholes, makes it particularly vulnerable to both natural and artificial pollution. Water enters the subsurface quickly through discrete recharge structures, avoiding the lengthy filtration procedures found in less permeable systems. As a result, the aquifer and its accompanying springs and rivers are particularly vulnerable to changes in land use, climate variability, and pollutant loading. In this study, we focused on the occurrence, spatial distribution, and potential sources of trace and major metals—including lead (Pb), arsenic (As), strontium (Sr), and iron (Fe)—in the Edwards Aquifer system of South‐Central Texas. Between 2024 and 2025, samples were collected seasonally from the aquifer’s contributing, recharge, and confined zones, as well as from adjacent river reaches, to quantify metal concentrations and assess their correlations with microbial and physicochemical indicators. Geochemical data showed that groundwater wells have greater median calcium and magnesium concentrations, indicating substantial breakdown of carbonate minerals over protracted aquifer residency. Rivers had lower and more variable cation contents, indicating dilution under high-flow conditions and less time for mineral-water interactions. Groundwater frequently has higher alkalinity and more stable bicarbonate concentrations than other anions, indicating carbonate geology's dominance. Trace metals such as lead, strontium, and arsenic were present at low levels but varied by site, possibly representing both geogenic and periodic anthropogenic inputs. The wells, which are protected by the aquifer matrix, undergo more gradual alterations, with chemical signatures reflecting the cumulative impacts of water-rock interaction and longer flow pathways. However, the study also describes instances in which severe rainfall or high-flow events resulted in quantifiable increases metal concentrations in well samples, suggesting the possibility of rapid pollutant transport across karst conduits. Such instances emphasize the significance of ongoing monitoring and the inherent vulnerability of karst aquifers, where the boundary between surface and subsurface is sometimes more apparent than actual.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9471

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