Journal
SCIENCE OF THE TOTAL ENVIRONMENT
Volume 538, Issue -, Pages 539-554Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.scitotenv.2015.08.036
Keywords
Coastal carbonate aquifer; Seawater intrusion; Groundwater mean residence time; Nitrate transport; Anthropogenic contamination
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Funding
- strategic science and technology project of the Exploring Advanced Discipline in the Institute of Geographic Sciences and Natural Resources Research [2012QY007]
- National High Technology Research and Development Program of China (863 Program) [2012AA062603]
- groundwater survey project entitled Assessment of Vulnerability and Investigation of Environmental Geology in the Key Section of Circum-Bohai-Sea Region [1212010540501]
- Tianjin Institute of Geology and Mineral Resources
- Liaoning Hydrological and Engineering Geological Prospecting Academy, Dalian
- Chinese Academy of Sciences
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Groundwater within the coastal aquifer systems of the Daweijia area in northeastern China is characterized by a large of variations (33-521 mg/L) in NO3- concentrations. Elevated nitrate concentrations, in addition to seawater intrusion in the Daweijia well field, both attributable to anthropogenic activities, may impact future water-management practices. Chemical and stable isotopic (delta O-18, delta H-2 ) analysis, H-3 and CFCs methods were applied to provide a better understanding of the relationship between the distribution of groundwater mean residence time (MRT) and nitrate transport, and to identify sources of nitrate concentrations in the complex coastal aquifer systems. There is a relatively narrow range of isotopic composition (ranging from -8.5 to -7.0%.) in most groundwater. Generally higher tritium contents observed in the wet season relative to the dry season may result from rapid groundwater circulation in response to the rainfall through the preferential flow paths. In the well field, the relatively increased nitrate concentrations of groundwater, accompanied by the higher tritium contents in the wet season, indicate the nitrate pollution can be attributed to domestic wastes. The binary exponential and piston-flow mixing model (BEP) yielded feasible age distributions based on the conceptual model. The good inverse relationship between groundwater MRTs (92-467 years) and the NO3- concentrations in the shallow Quaternary aquifers indicates that elevated nitrate concentrations are attributable to more recent recharge for shallow groundwater. However, there is no significant relationship between the MRTs (8-411 years) and the NO concentrations existing in the carbonate aquifer system, due to the complex hydrogeological conditions, groundwater age distributions and the range of contaminant source areas. Nitrate in the groundwater system without denitrification effects could accumulate and be transported for tens of years, through the complex carbonate aquifer matrix and the successive inputs of nitrogen from various sources. (C) 2015 Elsevier B.V. All rights reserved.
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