Mercury Accumulation by Lower Trophic-level Organisms in Lentic Systems within the Guadalupe River Watershed, California

By James S. Kuwabara1, Brent R. Topping2, Gerald E. Moon3, Peter Husby4, Andrew Lincoff5, James L. Carter6, and Marie-Noële Croteau7


U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2005-5037—ONLINE ONLY, U.S. Geological Survey, Menlo Park, CA, U.S. Geological Survey, Menlo Park, CA, U.S. Geological Survey, Menlo Park, CA, U.S. Environmental Protection Agency, Richmond, CA, U.S. Environmental Protection Agency, Richmond, CA, U.S. Geological Survey, Menlo Park, CA, U.S. Geological Survey, Menlo Park, CA


A pdf is available for this report


The water columns of four reservoirs (Almaden, Calero, Guadalupe and Lexington Reservoirs) and an abandoned quarry pit filled by Alamitos Creek drainage for recreational purposes (Lake Almaden) were sampled on September 14 and 15, 2004 to provide the first measurements of mercury accumulation by phytoplankton and zooplankton in lentic systems (bodies of standing water, as in lakes and reservoirs) within the Guadalupe River watershed, California. Because of widespread interest in ecosystem effects associated with historic mercury mining within and downgradient of the Guadalupe Riverwatershed, transfer of mercury to lower trophic-level organisms was examined. The propensity of mercury to bioaccumulate, particularly in phytoplankton and zooplankton at the base of the food web, motivated this attempt to provide information in support of developing trophic-transfer and solute-transport models for the watershed, and hence in support of subsequent evaluation of load-allocation strategies. Both total mercury and methylmercury were examined in these organisms.

During a single sampling event, replicate samples from the reservoir water column were collected and processed for dissolved-total mercury, dissolved-methylmercury, phytoplankton mercury speciation, phytoplankton taxonomy and biomass, zooplankton mercury speciation, and zooplankton taxonomy and biomass. The timing of this sampling event was coordinated with sampling and analysis of fish from these five water bodies, during a period of the year when vertical stratification in the reservoirs generates a primary source of methylmercury to the watershed. Ancillary data, including dissolved organic carbon and trace-metal concentrations as well as vertical profiles of temperature, dissolved oxygen, specific conductance and pH, were gathered to provide a water-quality framework from which to compare the results for mercury. This work, in support of the Guadalupe River Mercury Total Maximum Daily Load (TMDL) Study, provides the first measurements of mercury trophic transfer through planktonic communities in this watershed. It is worth reemphasizing that this data set represents a single “snap shot” of conditions in water bodies within the Guadalupe River watershed to: (1) fill gaps in trophic transfer information, and (2) provide a scientific basis for future process-based studies with enhanced temporal and spatial coverage. This electronic document was unconventionally formatted to enhance the accessibility of information to a wide range of interest groups.


Executive Summary

Physical and Biological Characterizations

Chemical Characterizations

Potential Management Implications


Results and Discussion

Physical Data

Biological Data

Chemical Data

Study Design and Methods

Water-column Sampling

Phytoplankton Sampling

Zooplankton Sampling

Small-fish Sampling

Chemical Parameters

References Cited


Appendix 1: Comments on the Report Structure

Appendix 2: Quality Control on Mercury-speciation Analyses

Appendix 3: List of Figures

Appendix 4: List of Tables


For additional information, contact:


James S. Kuwabara or Brent R. Topping

U.S. Geological Survey

345 Middlefield Road, MS 439

Menlo Park, CA 94025


Copies of this report may be obtained from the authors.

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