Executive Summary Journal Article

Environmental Tracers Applied to Quantifying Causes of Salinity in Arid-Region Rivers: Preliminary Results from the Rio Grande, Southwestern USA

URL: https://webapps.usgs.gov/mrgescp/documents/Phillipsetal_2003_EnvironmentalTracersAppliedtoQuantifyingCausesofSalinityinArid-RegionRiversPrelimResultsfromtheRioGrandeSouthwesternUSA.pdf

Date: 2003/01/01

Author(s): Phillips F.M., Hogan J., Mills S., Hendrickx J.M.H.

Publication: Developments in Water Science, v. 50, p. 327-334

Abstract:

The upper Rio Grande extends ∼1,200 km between its headwaters in southern Colorado (USA) and the USA/Mexico border region. Over this distance the total dissolved solids content of the water increases from ∼40 mg L^−1 to over 2,000 mg L^−1. This increase has previously been attributed to evapotranspirative concentration and to flushing by irrigation water of salts accumulated by pre-irrigation evapotranspiration. We employed environmental tracers, including σ¹⁸O, σ²H, Cl−, and the Cl/Br ratio to help identify the causes of salinization. Both σ¹⁸O and σ²H are enriched with flow distance due to evaporation, but not sufficiently to explain most of the salinization as caused by evapotranspiration. The Cl/Br ratio increases from about 50 in the headwaters to over 1,000 at the distal end of the river basin, indicating influx of subsurface saline waters, which are commonly characterized by high Cl/Br ratios. The Cl^− concentration and the Cl/Br ratio increase in a stepwise fashion and are typically localized at the southern ends of the sedimentary basins comprising the Rio Grande Rift, suggesting that the salts are from discharge of deep ground water where it is forced to the surface by bedrock highs, rather than due to flushing by irrigation water.