Geochemical Tracers to Evaluate Hydrogeologic Controls on River Salinization

Abstract

The salinization of rivers, as indicated by salinity increases in the downstream direction, is characteristic of arid and semiarid regions throughout the world. Historically, salinity increases have been attributed to various mechanisms, including (1) evaporation and concentration during reservoir storage, irrigation, and subsequent reuse; (2) displacement of shallow saline ground water during irrigation; (3) erosion and dissolution of natural deposits; and/or (4) inflow of deep saline and/or geothermal ground water (ground water with elevated water temperature). In this study, investigation of salinity issues focused on identification of relative salinity contributions from anthropogenic and natural sources in the Lower Rio Grande in the New Mexico-Texas border region. Based on the conceptual model of the system, the various sources of water and, therefore, salinity to the Lower Rio Grande were identified, and a sampling plan was designed to characterize these sources. Analysis results for boron (delta(11)B), sulfur (delta(34)S), oxygen (delta(18)O), hydrogen (delta(2)H), and strontium ((87)Sr/(86)Sr) isotopes, as well as basic chemical data, confirmed the hypothesis that the dominant salinity contributions are from deep ground water inflow to the Rio Grande. The stable isotopic ratios identified the deep ground water inflow as distinctive, with characteristic isotopic signatures. These analyses indicate that it is not possible to reproduce the observed salinization by evapotranspiration and agricultural processes alone. This investigation further confirms that proper application of multiple isotopic and geochemical tracers can be used to identify and constrain multiple sources of solutes in complex river systems.

Acidification of salinised waterways by saline groundwater discharge in south-western Australia

“…In contrast, previous investigations of stream and land salinity problems across the globe typically report the groundwater as being circum-neutral to alkaline (Farber et al, 2004;Moore et al, 2008;Salama et al, 1999). Interaction of saline groundwater containing acidity with surface waterways and lakes at basin scales has not been previously investigated.…”

“…While acidity in saline groundwater is known to occur across southern Australia (Dickson and Giblin, 2009), the influence of this on surface waters was reported as being limited to primary saline lakes (Bowen and Benison, 2009) and some lakes salinised after land clearing (Shand and Degens, 2008). Furthermore, investigations of stream and land salinity problems associated with rising saline groundwater across the globe typically report the groundwater as being circum-neutral to alkaline (Farber et al, 2004;Moore et al, 2008;Salama et al, 1999). In contrast, we have found that rising saline ground water in inland parts of south-western Australia is carrying acidity that also results in increasing discharge of acidity (along with salt) to water-ways and wetlands.…”

Water quantity and quality challenges from Elephant Butte to Amistad

“…While these low flow periods result in elevated Cl concentration, solute loads (the mass flux of solutes over a period of time) are significantly lower indicating salinity storage within the groundwater system. This particularly occurred during the 1950s drought when loads were less at El Paso than at Elephant Butte indicating salt storage likely within the shallow groundwater system as demonstrated by graph from Moore et al 2008. Conversely high flow periods have low concentrations with high loads.…”

“…Conversely high flow periods have low concentrations with high loads. A final note on the historical solute record is that, irrespective of climate, the solute loads during the early part of the 1900s loads were higher (Bastien 2009), particularly in the lower portion of the basin (Moore et al 2008). This period of time coincides with EBID and the Middle Rio Grande Conservancy District (irrigation district near Albuquerque) began construction of the agricultural drains which potentially flushed 800 years worth of agricultural salt accumulation from the vadose zone and shallow groundwater.…”

Water, climate, and social change in a fragile landscape

“…The negative economic impact of excessive salt v www.esajournals.org concentrations in the Rio Grande was recently estimated by the Rio Grande Project Salinity Management Coalition (RGPSMC, a group that brings together the Colorado, New Mexico, and Texas Rio Grande compact commissioners with interested federal, state, local, and university partners) at ; $11,000,000/year, with municipalities like El Paso, TX, shouldering the largest fractions of these costs (Michelsen et al 2009). In addition to the possible impact from agricultural sources, previous investigations have demonstrated that salt loads in the Rio Grande increase in part because of (1) the increasing annual temperatures southward which leads to higher evaporation and evapotranspiration rates in the irrigated fields, (2) the high geothermal gradient of the Rio Grande Rift, which may enhance upwelling of highly mineralized groundwater from deeper parts of basins, and (3) the dissolution of salt-rich sedimentary rocks in the central and southern parts of the Rio Grande Valley (Eastoe et al 2008, Phillips et al 2003, Hibbs and Merino 2006, Hogan et al 2007, Witcher et al 2004, Moore et al 2008. These complexities are highlighted in Fig.…”