Organic contaminants in sediments of the Newport Submarine Canyon, California and the adjacent shelf
Abstract:Organic contaminants in sediment were measured in samples collected from five stations in the Newport Submarine Canyon, Calif., and six nominal 60-m shelf stations (1985–1991); the 60-m stations included one at the terminus of an ocean outfall. Two hypotheses were tested: there is no increase in sediment contaminant concentration with water depth in Newport Canyon and there is no difference in contaminant concentration between the canyon and adjacent shelf. Based on analyses herein, hypothesis one was accepted and hypothesis two was rejected. Mean DDE, tDDT, and Aroclor 1254 were higher in the canyon (Station C2) and tPCB was higher at the ocean outfall (Station 0). The results presented here show that the canyon serves as a sediment trap for elevated concentrations of both trace metals and organic compounds.
Due to the highly seasonal nature of rainfall and surface runoff in southern California we anticipated finding quantitative seasonal patterns (e.g., high concentrations during the wet season and low concentrations during the dry season). The present analyses do not support this trend. Remission of the 7-yr drought with heavy rainfall from December 1992 through February 1993, and in January–March 1995, may provide the opportunity to document this relationship. Comparison of canyon data with other regional studies suggests multiple sources of contaminants (e.g., Santa Ana River, Newport Bay, offshore dredge disposal, storm runoff, atmospheric fallout) rather than a single source (e.g., ocean outfall).
Normalization of contaminant concentrations with TOC was done to compensate for grain size differences between the canyon and the shelf. In a few comparisons, TOC normalized data yielded different results than nonnormalized data. While normalization may become a conventional practice in sediment geochemistry, we urge further study of this practice before unreservedly applying it to develop state and federal guidelines of permissible sediment levels of sediment contaminants.
Document Type: Research Article
Publication date: September 1, 1996
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