Natural and anthropogenic geochemical signatures of floodplain and deltaic sedimentary strata, Sacramento-San Joaquin Delta, California, USA |
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Authors: | Pasternack G B Brown K J |
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Institution: | Department of Land, Air and Water Resources, University of California, 211 Veihmeyer Hall, One Shields Avenue, Davis, CA 95616-8628, USA. gpast@ucdavis.edu |
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Abstract: | The geochemical history of an upper deltaic plain pending tidal wetland restoration was reconstructed to assess remobilization of redox-sensitive constituents in sediment, identify depositional processes promoting geochemical retention, and determine the extent of contamination with Hg, As, Pb, Cu, and Zn. Three 12-14-m sediment cores were analyzed for bulk sediment geochemistry using ICP-AES. Rather than showing similar stratigraphic and geochemical down-core trends, cores had a unique record indicative of strong spatial gradients in deposition processes. Each strata type (e.g. basal clay, sand channel, distal floodplain, and agriculturally impacted surficial horizon) had a unique geochemical "fingerprint". The agriculturally impacted surficial layer showed high Hg], As], and Pb]. The significance is that a restored upper delta will have a complex geomorphology defying conventional criteria of "success" in a restoration framework. Also, there is a significant risk of generating toxic, bio-available CH3Hg+ that would be hazardous to fish. |
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