Geochemistry of shallow ground water in coastal plain environments in the southeastern United States: implications for aquifer susceptibility |
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| Institution: | 1. College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China;2. Nansi Lake Water Quality Monitoring Center of Shandong Province, Jining 272100, China;1. College of Water Resources and Architecture Engineering, Northwest A&F University, Yangling 712100, Shaanxi, China;2. School of Hydraulic, Energy and Power Engineering, Yangzhou University, Yangzhou, 225009, Jiangsu, China;3. Pearl River Hydraulic Research Institute, Pearl River Water Resources Commission of the Ministry of Water Resources, 510611 Guangzhou, China;4. Soil and Water Conservation Monitoring Center of Pearl River Basin, Pearl River Water Resources Commission of the Ministry of Water Resources, Guangzhou 510611, China;5. Institute of Soil and Water Conservation, Northwest A & F University, Yangling 712100, Shaanxi, China;6. Institute of Soil and Water Conservation, Chinese Academy of Sciences & Ministry of Water Resources, Yangling 712100, Shaanxi, China;7. Department of Land, Air, and Water Resources, University of California Davis, Davis, CA 95616, USA;8. Department of Soil Science, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada |
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| Abstract: | Ground-water chemistry data from coastal plain environments have been examined to determine the geochemical conditions and processes that occur in these areas and assess their implications for aquifer susceptibility. Two distinct geochemical environments were studied to represent a range of conditions: an inner coastal plain setting having more well-drained soils and lower organic carbon (C) content and an outer coastal plain environment that has more poorly drained soils and high organic C content. Higher concentrations of most major ions and dissolved inorganic and organic C in the outer coastal plain setting indicate a greater degree of mineral dissolution and organic matter oxidation. Accordingly, outer coastal plain waters are more reducing than inner coastal plain waters. Low dissolved oxygen (O2) and nitrate (NO3?) concentrations and high iron (Fe) concentrations indicate that ferric iron (Fe (III)) is an important electron acceptor in this setting, while dissolved O2 is the most common terminal electron acceptor in the inner coastal plain setting.The presence of a wide range of redox conditions in the shallow aquifer system examined here underscores the importance of providing a detailed geochemical characterization of ground water when assessing the intrinsic susceptibility of coastal plain settings. The greater prevalence of aerobic conditions in the inner coastal plain setting makes this region more susceptible to contamination by constituents that are more stable under these conditions and is consistent with the significantly (p<0.05) higher concentrations of NO3? found in this setting. Herbicides and their transformation products were frequently detected (36% of wells sampled), however concentrations were typically low (<0.1 μg/L). Shallow water table depths often found in coastal plain settings may result in an increased risk of the detection of pesticides (e.g., alachlor) that degrade rapidly in the unsaturated zone. |
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