Sediment-Water Interactions Affecting Dissolved-Mercury Distributions in Camp Far West Reservoir, California

By James S. Kuwabara1, Charles N. Alpers2, Mark Marvin-Dipasquale3, Brent R.Topping4, James L. Carter5, A. Robin Stewart6, Steven V. Fend7, Francis Parchaso8, Gerald E. Moon9 and David P. Krabbenhoft10

U.S. Geological Survey Water Resources Investigations Report 03-4140

This report is also available in PDF format.


Field and laboratory studies were conducted in April and November 2002 to provide the first direct measurements of the benthic flux of dissolved (0.2-micrometer filtered) mercury species (total and methylated forms) between the bottom sediment and water column at three sampling locations within Camp Far West Reservoir, California: one near the Bear River inlet to the reservoir, a second at a mid-reservoir site of comparable depth to the inlet site, and the third at the deepest position in the reservoir near the dam (herein referred to as the inlet, midreservoir and near-dam sites, respectively; Background, Fig. 1). Because of interest in the effects of historic hydraulic mining and ore processing in the Sierra Nevada foothills just upstream of the reservoir, dissolved-mercury species and predominant ligands that often control the mercury speciation (represented by dissolved organic carbon, and sulfides) were the solutes of primary interest. Benthic flux, sometimes referred to as internal recycling, represents the transport of dissolved chemical species between the water column and the underlying sediment.  Because of the affinity of mercury to adsorb onto particle surfaces and to form insoluble precipitates (particularly with sulfides), the mass transport of mercury in mining-affected watersheds is typically particle dominated. As these enriched particles accumulate at depositional sites such as reservoirs, benthic processes facilitate the repartitioning, transformation, and transport of mercury in dissolved, biologically reactive forms (dissolved methylmercury being the most bioavailable for trophic transfer). These are the forms of mercury examined in this study.


In contrast to typical scientific manuscripts, this report is formatted in a pyramid-like structure to serve the needs of diverse groups who may be interested in reviewing or acquiring information at various levels of technical detail (Appendix 1). The report enables quick transitions between the initial summary information (figuratively at the top of the pyramid) and the later details of methods or results (figuratively towards the base of the pyramid) using hyperlinks to supporting figures and tables, and an electronically linked Table of Contents.


During two sampling events, two replicate sediment cores (Coring methods; Fig. 2) from each of three reservoir locations (Fig. 1) were used in incubation experiments to provide flux estimates and benthic biological characterizations. Incubation of these cores provided “snapshots” of solute flux across the sediment-water interface in the reservoir, under benthic, environmental conditions representative of the time and place of collection.  Ancillary data, including nutrient and ligand fluxes, were gathered to provide a water-quality framework from which to compare the results for mercury. The following major observations from interdependent physical, biological, and chemical data were made:

Table of Contents

Executive Summary

Physical and Biological Characterizations

Chemical Characterizations

Remedial Implications


Results and Discussion

Physical Data

Biological Data

Chemical Data

Study Design and Methods

Coring Operation

Core Incubations

Physical Data

Biological Data

Chemical Parameters

References Cited


Appendix 1: Comments on the Report Structure

Appendix 2: List of Figures

Appendix 3: List of Tables


For additional information write to:


James S. Kuwabara

U.S. Geological Survey

345 Middlefield Road, MS 439

Menlo Park, CA 94025


Copies of this report may be obtained from the authors or:


U.S. Geological Survey Information Center

Box 25286, MS 517

Denver Federal Center

Denver, CO 80225

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