Impact of land use and land cover change on groundwater recharge and quality in the southwestern US

Abstract

Humans have exerted large-scale changes on the terrestrial biosphere, primarily through agriculture; however, the impacts of such changes on the hydrologic cycle are poorly understood. The purpose of this study was to test the hypothesis that the conversion of natural rangeland ecosystems to agricultural ecosystems impacts the subsurface portion of the hydrologic cycle by changing groundwater recharge and flushing salts to underlying aquifers. The hypothesis was examined through point and areal studies investigating the effects of land use/land cover (LU/LC) changes on groundwater recharge and solute transport in the Amargosa Desert (AD) in Nevada and in the High Plains (HP) in Texas, US. Studies use the fact that matric (pore-water-pressure) potential and environmental-tracer profiles in thick unsaturated zones archive past changes in recharging fluxes. Results show that recharge is related to LU/LC as follows: discharge through evapotranspiration (i.e., no recharge; upward fluxes o0.1 mm yr À1 ) in natural rangeland ecosystems (low matric potentials; high chloride and nitrate concentrations); moderate-to-high recharge in irrigated agricultural ecosystems (high matric potentials; lowto-moderate chloride and nitrate concentrations) (AD recharge: $ 130-640 mm yr À1 ); and moderate recharge in nonirrigated (dryland) agricultural ecosystems (high matric potentials; low chloride and nitrate concentrations, and increasing groundwater levels) (HP recharge: $ 9-32 mm yr À1 ). Replacement of rangeland with agriculture changed flow directions from upward (discharge) to downward (recharge). Recent replacement of rangeland with irrigated ecosystems was documented through downward displacement of chloride and nitrate fronts. Thick unsaturated zones contain a reservoir of salts that are readily mobilized under increased recharge related to LU/LC changes, potentially degrading groundwater quality. Sustainable land use requires quantitative knowledge of the linkages between ecosystem change, recharge, and groundwater quality.

Mountain ecohydrology: quantifying the role of vegetation in the water balance of montane catchments

“…Not surprisingly then, ecohydrological research originally focused on areas that experience either seasonal water limitation (Rodriguez-Iturbe, 2000;Porporato et al, 2003;Huxman et al, 2004Huxman et al, , 2005Scott et al, 2006) or rapidly changing vegetation (e.g. due to agriculture, logging or disturbance) Scanlon et al, 2005). The semiarid southwestern United States is an example of a water-limited region where climate change is altering the amount, timing and form of precipitation (Mote et al, 2005) and model projections suggest a much drier future (Seager et al, 2007).…”

Potential climate change effects on groundwater recharge in the High Plains Aquifer, USA

“…[11] Agricultural development has resulted in increased deep drainage rates (water flux below the root zone as opposed to recharge at the water table) across the High Plains and has recharged the aquifer in parts of the central and southern High Plains, as shown by rising groundwater levels by up to 23 m [Luckey and Becker, 1999;Scanlon et al, 2005]. Increases in recharge on some other areas may be masked by depletion related to groundwater-based irrigation.…”

Application of chloride profile and water balance methods in estimating groundwater recharge in Luanjing Irrigation Area, Inner Mongolia / Application des méthodes du profil de chlorure et du bilan hydrique pour l'estimation de la recharge hydrogéologique dans le Périmètre Irrigué de Luanjing, Mongolie Intérieure

“…Gee & Hillel (1988) and Allison et al (1994) have listed several approaches for estimating groundwater recharge from natural rainfall and irrigation, and summarized the relative merits. The chloride ion, which is characterized by its conservation, low cost and being pollution-free, has been widely applied in groundwater recharge studies in arid and semi-arid regions (Bazuhair & Wood, 1996;Bromley et al, 1997;Scanlon et al, 2005). Previous studies have shown that many arid regions have experienced little or no direct recharge for millennia (Allison et al, 1990;Scanlon et al, 2003).…”