Salinization of Surface Water and Groundwater, Hueco Bolson and Mesilla Valley, New Mexico, Texas and Chihuahua: Sources of Sulfate as Indicated by Stable O, H and S Isotopes.
Abstract
Salinity and δ34S values in Rio Grande surface water increase downstream within the Hueco Bolson, with sharp increases detected in El Paso and near Fabens at times of low flow. Fluctuations at El Paso reflect variations in relative input of high-δ34S salty groundwater discharging from the Mesilla Valley upstream. Near Fabens, further addition of water with δ34S > 9 ‰, [SO4] > 300 mg/L and Cl/SO4 near 1 is required. Such water can be derived from Hueco Bolson groundwater north of the river or from salty sediment beneath the flood plain, but not from urban effluent or agricultural drainage. Sulfate δ34S and δ18O values are consistent with Hueco Bolson groundwater as the source of high-δ34S sulfate. The origin of flood-plain groundwater is identified as pre-dam (pre-1916) or post-dam river water according to degree of evaporation as expressed in O and H isotope content. Sulfate geochemistry and salinization mechanisms differ in the two types of groundwater. Pre-dam groundwater in Hueco Bolson and Mesilla Valley has increased in salinity relative to contemporaneous river water as a result of addition of salty basin water with δ34S > 9 ‰; and Cl/SO4 > 1 in the Hueco Bolson where interaction with salty sediment below the flood plain is likely. Post -dam groundwater salinity in the Hueco Bolson has increased by addition of sulfate with δ34S commonly lower than values in present-day river water, and can be explained by oxidation of sulfide in alluvium, but not by addition of urban wastewater, or of gypsum and sulfuric acid as agricultural amendments. Post-dam groundwater salinity in the Mesilla Valley most commonly results from addition of salty basin water with δ34S > 8 ‰, [SO4] > 200 mg/L and Cl/SO4 >2.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2005
- Bibcode:
- 2005AGUSM.H21B..05E
- Keywords:
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- 1040 Isotopic composition/chemistry;
- 1806 Chemistry of fresh water;
- 1829 Groundwater hydrology;
- 1831 Groundwater quality;
- 1871 Surface water quality