Controls on the spatial and temporal variability of vadose dripwater geochemistry: Edwards Aquifer, central Texas
نویسندگان
چکیده
A 4-yr study of spatial and temporal variability in the geochemistry of vadose groundwaters from caves within the Edwards aquifer region of central Texas offers new insights into controls on vadose groundwater evolution, the relationship between vadose and phreatic groundwaters, and the fundamental influence of soil composition on groundwater geochemistry. Variations in Sr isotopes and trace elements (Mg/Ca and Sr/Ca ratios) of dripwaters and soils from different caves, as well as phreatic groundwaters, provide the potential to distinguish between local variability and regional processes controlling fluid geochemistry, and a framework for understanding the links between climatic and hydrologic processes. The Sr isotope compositions of vadose cave dripwaters (mean Sr/Sr 0.7087) and phreatic groundwaters (mean Sr/Sr 0.7079) generally fall between values for host carbonates (mean Sr/Sr 0.7076) and exchangeable Sr in overlying soils (mean Sr/Sr 0.7088). Dripwaters have lower Mg/Ca and Sr/Ca ratios, and higher Sr/Sr values than phreatic groundwaters. Dripwater Sr/Sr values also inversely correlate with both Mg/Ca and Sr/Ca ratios. Mass-balance modeling combined with these geochemical relationships suggest that variations in fluid compositions are predominantly controlled by groundwater residence times, and water-rock interaction with overlying soils and host aquifer carbonate rocks. Consistent differences in dripwater geochemistry (i.e., Sr/Sr, Mg/Ca, and Sr/Ca) between individual caves are similar to compositional differences in soils above the caves. While these differences appear to exert significant control on local fluid evolution, geochemical and isotopic variations suggest that the controlling processes are regionally extensive. Temporal variations in Sr/Sr values and Mg/Ca ratios of dripwaters from some sites over the 4-yr interval correspond with changes in both aquifer and climatic parameters. These results have important implications for the interpretation of trace element and isotopic variations in speleothems as paleoclimate records, as well as the understanding of controls on water chemistry for both present-day and ancient carbonate aquifers. Copyright © 2004 Elsevier Ltd
منابع مشابه
Springwater geochemistry at Honey Creek State Natural Area, central Texas: Implications for surface water and groundwater interaction in a karst aquifer
0022-1694/$ see front matter Published by Elsevier doi:10.1016/j.jhydrol.2010.04.036 * Corresponding author at: US Geological Survey, 1505 Ferguson Lane, Austin, TX 78754, United States. E-mail address: [email protected] (M. Musgrov A two and a half year study of two adjacent watersheds at the Honey Creek State Natural Area (HCSNA) in central Texas was undertaken to evaluate spatial and tempora...
متن کاملVariability in Terrestrial and Microbial Contributions to Dissolved Organic Matter Fluorescence in the Edwards Aquifer, Central Texas
Most cave and karst ecosystems are believed to be dependent on an influx of allochthonous organic carbon. Although microbes are largely responsible for the fate of dissolved organic matter (DOM) in karst, the role of microbes in chemosynthetic (autochthonous) production and processing of DOM has received limited attention. Chromophoric dissolved organic matter (CDOM) is the fraction of DOM that...
متن کاملFactors Affecting Public-Supply Well Vulnerability in Two Karst Aquifers
Karst aquifers occur in a range of climatic and geologic settings. Nonetheless, they are commonly characterized by their vulnerability to water-quality impairment. Two karst aquifers, the Edwards aquifer in south-central Texas and the Upper Floridan aquifer in western Florida, were investigated to assess factors that control the movement of contaminants to public-supply wells (PSWs). The geoche...
متن کاملTemporal-Spatial Variability of the Severest Dry Spells in the North-West of Iran
The variability of temperature and precipitation is regarded as one of the main characteristics of the climate.Precipitation and its results, especially results such as droughts, vary on different temporal and spatial scales. Thepurpose of this paper is to determine the frequency of the inter-annual variability of the driest month in north-westIran. In order to obtain the best results, we used ...
متن کاملImpact of spatial-temporal variations of climatic variables on summer maize yield in North China Plain
Summer maize (Zea mays L.) is one of the dominant crops in the North China Plain (NCP). Its growth is greatly influenced by the spatial-temporal variation of climatic variables, especially solar radiation, temperature and rainfall. The WOFOST (version 7.1) model was applied to evaluate the impact of climatic variability on summer maize yields using historical meteorological data from 1961 to 20...
متن کامل