| Autor: |
Magdalena Modelska, Rogelio Monreal, Anna Szynkiewicz, Miguel Rangel Medina, Lisa M. Pratt |
| Rok vydání: |
2008 |
| Předmět: |
|
| Zdroj: |
Applied Geochemistry. 23:2539-2558 |
| ISSN: |
0883-2927 |
| Popis: |
Groundwater from the Costa de Hermosillo aquifer has been used extensively for irrigation over the past 60 a in the Sonora region of northwestern Mexico resulting in salinization of fresh groundwater resources. Salinization of groundwater is most pronounced on the western/coastal side of the aquifer, with an aerial extent of 26.7 km2, where maximum values are reported for conductivity (31 mS/cm) and Cl− concentrations (16,271 mg/L). Salinization is likely to increase if groundwater pumping continues at levels comparable to the present time. Upward incursion of marine water into the aquifer is inferred from δ2H (−7.2 ‰) and δ18O (+1.6‰) compositions of groundwater samples with the highest conductivity. Compared to modern seawater in the Gulf of California, ratios of SO4/Cl and Cl/Br are small (0.01 and 33, respectively) and the S isotopic composition of SO 4 2 - is high (+32.7%) in the most saline portions of the Costa de Hermosillo. This saline groundwater is inferred to result from an earlier phase of dissimilatory bacterial SO 4 2 - reduction coupled to decomposition of organic matter in marine blue clays deposited during the Miocene/Pliocene transgression. The isotopic composition of present-day surface discharge from agricultural fields is substantially enriched in 32S due to widespread application of (NH4)2SO4 fertilizers and potential mobilization of S from mineral resources. Surface water discharging from irrigated fields has δ34S values ranging from −2.1 to 3.3 ‰ which are distinctly different from groundwater and surface water in adjacent non-agricultural areas with δ34S values ranging from 5.2 to 13.5 ‰. Prolonged irrigation pumping that promotes the incursion of air to the subsurface could enhance the weathering of S-bearing minerals such as magmatic sulfides, producing 32S-enriched SO 4 2 - . |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
|
Full Text from ScienceDirect