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U.S. GEOLOGICAL SURVEY
Open File Report 2007–1276

Quantifying the Benthic Source of Nutrients to the Water Column of Upper Klamath Lake, Oregon

Prepared in cooperation with the U.S. Bureau of Reclamation

By James S. Kuwabara, Dennis D. Lynch, Brent R. Topping, Fred Murphy, James L. Carter, Nancy S. Simon, Francis Parchaso, Tamara M. Wood, Mary K. Lindenberg, Katryn Wiese, Ronald J. Avanzino

Executive Summary

Five sampling trips were coordinated in April, May and August 2006, and May and July 2007 to sample the water column and be nthos of Upper Klamath Lake, OR ( Fig. 1 ; Table 1 ), before, during and after the annual cyanophyte bloom of Aphanizomenon flos-aquae (AFA). A pore-water profiler was designed and fab ricated to obtain the first high-resolution (centimeter-scale) estimates of the vertical concentration gradients for diffusive-flux deter minations. Estimates based on molecular diffusion m ay underestimate benthic flux because solute transport across the sediment-water interface c an be enhanced by proces ses including bioturbation, b ioirrigation and ground-water advection. Water-column and benthic samples were also collec ted to help interpret spatial and temporal trends in diffusive-flux estimates. Data from these samples complement geochemical analyses of bottom-sediments taken from Upper Klamath Lake (UKL) in 2 005.

This ongoing study provides information necessary for developing process-interdependent solute-transport models for the watershed (that is, models integrating physical, geochemical and biological processes), and supports efforts to evaluate remediation or load-allocation strategies. To augment studies funded by the U.S. Bureau of Reclamation (USBR), the Department of Inter ior supported an additional full deployment of pore-water profilers in July 2007, during the summer AFA bloom. Results from this recent field trip are not fully completed. Data not presented herein will be included in a subsequent publication, scheduled for March 2009.

Contents

Executive Summary
Background
Objectives
Results and Discussion
Study Design and Methods
Referenced Cited
Acknowledgments

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