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Published December 2010 | public
Journal Article

Effect of changes in water level on sediment pore water redox geochemistry at a reservoir shoreline


Pore water samplers with high vertical resolution were used to evaluate the response of sediment redox geochemistry during transient hydrologic conditions at Lake Powell, a large reservoir in Utah and Arizona, USA. Samplers were deployed at two different yet proximal shoreline locations, White and Farley Canyons, before and after exposure of sediment to air and subsequent resubmersion, which resulted from fluctuations in the water level of the reservoir. Before exposure to air, an observed increase in dissolved Mn concentrations and, at Farley Canyon, an observed decrease in dissolved U concentrations across and immediately below the sediment–water interface indicated reducing conditions in the sub-surface. After exposure and resubmersion of the sediment, pore water profiles at each site differed distinctly from those observed before the fluctuation in water level. At White Canyon, an increase in U concentrations and a decrease in Mn concentrations in pore water after exposure and subsequent resubmersion are suggestive of oxidative processes occurring during the period of sediment exposure. Data from Farley Canyon suggest that the same processes may be occurring, but to a lesser extent. Depth profiles of As and Pb were also examined, but were relatively featureless compared to those of Mn and U. At both sites, sediment evaluated for pore water chemistry in the second sampling was only fully resubmerged for 2–5 days prior to the second sampling event, yet reducing conditions were clearly evident in the Mn pore water profiles. This suggests that the dynamics of the biogeochemical processes occurring in surface sediment at Lake Powell are responsive on the timescale defined by the fluctuating water levels in the reservoir.

Additional Information

© 2010 Elsevier Ltd. Received 31 May 2010; accepted 13 October 2010. Available online 21 October 2010. Editorial handling by D. Gooddy. The authors thank K.M. Campbell, M.A. Ferguson, A.A. Jones (each Caltech), and Z.E. Harris for laboratory assistance; C.E. Farnsworth, M. Vondrus, A.P. Kositsky, A.M. Cody (each Caltech), J.B. Miller (USBR), T. McDaniel, and Z.E. Harris for field assistance; and L.E. Bryant (Virginia Tech), C.E. Farnsworth (Caltech), L. Roberts, B. Wehrli, M. Schirmer (each Eawag), A. Voegelin (ETHZ), and M. Krom (Leeds University) for key thoughts during data interpretation. M. Huettel (Florida State University) assisted with the manuscript. Dr. Simon Bottrell and an anonymous reviewer provided helpful comments that improved the manuscript. This work was funded by NSF SGER Grants EAR-0408329 and EAR-0621371, the Alice Tyler Foundation, USBR Grant 06PG400222, and the Carolyn Ash Summer Undergraduate Research Fellowship awarded to Nathan Chan at Caltech. Some sampling resources were provided by Glen Canyon National Recreation Area. The use of trade names is for identification purposes only and does not imply endorsement by the United States National Park Service.

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