Title of article :
Sources and biogeochemical behavior of nitrate and sulfate in an alluvial aquifer: Hydrochemical and stable isotope approaches
Choi، نويسنده , , Byoung-Young and Yun، نويسنده , , Seong-Taek and Mayer، نويسنده , , Bernhard and Kim، نويسنده , , Kyoung-Ho، نويسنده ,
Issue Information :
روزنامه با شماره پیاپی سال 2011
Based on hydrochemical and environmental isotope data (δ15N and δ18O of NO 3 - , and δ34S of SO 4 2 - ) of depth-specific groundwater samples from multi-level samplers, the source(s) and biogeochemical behavior of NO 3 - and SO 4 2 - in a shallow (<25 m below ground level) sandy alluvial aquifer underneath a riverside agricultural area in South Korea were evaluated. The groundwater in the study area was characterized by a large variability in the concentrations of NO 3 - (0.02 to ∼35 mg/L NO 3 N) and SO 4 2 - (0.14 to ∼130 mg/L). A distinct vertical redox zoning was observed sub-dividing an oxic groundwater at shallow depths (<8–10 m below ground surface) from sub-oxic groundwater at greater depths. The δ15N and δ18O values indicated that elevated NO 3 - concentrations in the oxic groundwater are due to manure-derived NO 3 - and nitrification of urea- and ammonia-containing fertilizers used on agricultural fields. Chemical and isotopic data also revealed that groundwater NO 3 - concentrations significantly decrease due to denitrification in the lower oxic and sub-oxic groundwater. The δ34Ssulfate values of the oxic groundwater ranged from −14.4‰ to +2.4‰. The relationship between δ34Ssulfate values and SO 4 2 - concentrations with depth showed that increasing SO 4 2 - concentrations were caused by S-bearing fertilizers, not pyrite oxidation. Bacterial (dissimilatory) SO 4 2 - reduction occurred locally in the sub-oxic groundwater, as indicated by increasing δ34Ssulfate values (up to 64.1‰) with concomitant decreases of SO 4 2 - concentrations. This study shows that isotope data are very effective for discriminating different sources for the waters with high SO 4 2 - and low NO 3 - concentrations in the lower oxic zone. It is also suggested that the use of N- and S-containing fertilizers should be better controlled to limit nitrate and SO 4 2 - contamination of shallow groundwater.
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