254 A New Approach in Studying the Sources of Salinization in the Rio Grande

Thursday, November 5, 2009: 2:00 PM
Kohlberg (Camino Real Hotel)
Anna A. Szynkiewicz , Geological Sciences, University of Texas at El Paso, El Paso, TX
David Borrok , Department of Geological Sciences, University of Texas at El Paso, El Paso, TX
James Witcher , Witcher and Associate, Las Cruces, NM
Lisa M. Pratt , Geological Sciences, Indiana University, Bloomington, IN
The Rio Grande River is located in an arid climate zone and it is used mainly as a municipal water supply and for agriculture. High evaporation rates and groundwater recharge associated with salt-rich sedimentary rocks increase the solute content of the river.  Irrigation likely contributes additional constituents into the Rio Grande; however, no information has been acquired on the potential role of fertilizers in salinization. In 2007 and 2008, we determined the chemistry and sulfur isotope composition (d34S of sulfate) for the Rio Grande and for several commonly used fertilizers to evaluate potential impact on the Rio Grande from Espanola to El Paso. The d34S of sulfate ranged from -4.2 to +2.0 ‰ over this ~500 km distance and was significantly lighter compared to natural sulfate inputs of geologic origin (ranging from +6.1 to +12.9 ‰). The d34S of commonly used liquid and solid fertilizers varied over similar range to the river, -2.1 to +4.8 ‰, suggesting that fertilizers contribute to the Rio Grande sulfate ions.  Other potential sources of lower d34S of sulfate may include municipal waste streams into the river and biogenic processes in soils and shallow groundwater.