Spatial variability in the sources of groundwater salinity in the Rio Grande Valley of the Mesilla Basin, New Mexico and West Texas, USA
Abstract
Spatial variability in sources of groundwater salinity may exist due to stratigraphic, geochemical, and hydrologic processes even in an integrated and relatively homogeneous aquifer system. For this reason, characterization methods are needed to determine salinity sources, flow, and transport in alluvial/fluvial groundwater basins. Geochemical tracers analyzed from groundwater samples were used to determine the sources of salt contributing to groundwater beneath the Rio Grande flood plain of the Mesilla Basin located in southern New Mexico and West Texas. Groundwater flow is dominantly from north to south beneath the Rio Grande flood plain, so an interpretation of mixing between endmembers is appropriate. Results from central Mesilla Basin groundwaters show relatively lower concentrations of total dissolved solids (291-2,040 mg/L) and δ34S signatures (+2.28 to +5.76‰) that are slightly greater than SO4 of local fertilizers (-2.1 to +1.6 ‰) suggesting some contributions of salt other than irrigation. Southern Mesilla Basin groundwaters have substantially higher total dissolved solid concentrations (16,300-29,700 mg/L) and δ34S signatures (+12.36 to +12.46‰) that are comparable to that of Paleozoic evaporites (+7.6 to +12.9 ‰). The lower δ34S signatures and lower total dissolved solid concentrations in deep central Mesilla Basin groundwaters ( 400 m) suggest evaporite minerals do not contribute significant amounts of salt to groundwater in the central Mesilla Basin even at depth. Instead, evaporate mineral sources of groundwater salinity appear to be localized at the southern end of the Mesilla Basin within the Middle Santa Fe Group. This study illustrates how nested well clusters and geochemical tracers can be used to indicate salinity sources and processes in basin-wide geochemical investigations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H53H1690K
- Keywords:
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- 1040 Radiogenic isotope geochemistry;
- GEOCHEMISTRYDE: 1041 Stable isotope geochemistry;
- GEOCHEMISTRYDE: 1832 Groundwater transport;
- HYDROLOGYDE: 1843 Land/atmosphere interactions;
- HYDROLOGY