Characterisation of domestic and industrial sewage in Southern California coastal sediments using nitrogen,carbon, sulphur and uranium tracers |
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| Authors: | RE Sweeney EK Kalil IR Kaplan |
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| Institution: | 1. Institute of Geophysics and Planetary Physics. University of California, Los Angeles, California 90024, USA;7. Department of Earth and Space Sciences. University of California, Los Angeles, California 90024, USA |
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| Abstract: | A degradation-mixing model has been developed to aid in the interpretation of geochemical processes occurring in sewage-contaminated marine sediment near San Pedro, California. The nitrogen isotope ratio () is shown to be an effective tracer of sewage discharge-on the San Pedro Shelf. Isotopic fractionation of during release of amino compounds or ammonia (as a consequence of bacterial degradation of organic detritus) appears to be negligible. The nitrogen isotope ratio, therefore, may be considered a conservative component for tracing the source of organic matter deposited in marine sediment.Uranium enrichment from seawater is shown not to occur in the highly reducing sewage-contaminated sediments. The content of uranium in the effluent particulates (18 ppm) is large compared with the content in the uncontaminated sediment (3 to 5 ppm). This allows the content of uranium to also be used as a tool for tracing the deposition of sewage particles in marine sediment. Uranium and nitrogen are shown to be incorporated in the organic fraction of sewage effluent and are released during bacterial degradation of the organic matter. Cadmium and sulphur are shown not to be mobilised during sewage deposition and degradation. The stable isotope ratio of sulphur () is used to demonstrate that sulphur enrichment occurs in the sediment by in situ reduction of seawater sulphate. The data summarised by Morel et al. (1975) are presented and discussed in accordance with the above model. |
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