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Published 2011 | public
Journal Article

Potential for release of sediment phosphorus to Lake Powell (Utah and Arizona) due to sediment resuspension during low water level


The water level in Lake Powell, an important water-supply reservoir on the Colorado River, United States, decreased in most years from 1999 to 2010, exposing the sediment delta in the inflow region of this reservoir. This study assesses the potential for sediment-associated phosphorus (P) to enter the water column during sediment resuspension. We collected sediment samples from the reservoir inflow region and performed a sequential extraction and a sorption experiment that focused on P. We also collected water samples at locations upstream and downstream of the exposed sediment delta and measured soluble reactive P during base flow and during the yearly flood associated with spring runoff. Results indicate that extractable P is associated with various operationally defined fractions as follows: 50% with calcite and biogenic apatite, 29% with detrital apatite, 10% with Fe(III)-oxide minerals, 6% with organic matter and 4% with easily exchangeable solid-phase association sites. Sorption experiments indicate that the equilibrium P concentration is 0.19 ± 0.07 μM. Particle size is correlated with sediment P; coarse sediment contains and sorbs much less extractable P than fine sediment does. Measurements of water samples indicate that sediment resuspension probably releases P from sediment to overlying water during base flow, but the effect during floods is less clear. These results indicate that lowering reservoir levels introduces sediment-associated P to the reservoir when sediment resuspension occurs.

Additional Information

© 2011 North American Lake Management Society. Available online: 14 Dec 2011. The authors are very grateful to Jerry Miller (US Bureau of Reclamation) and Mike Easler (Caltech), without whom this study would not have been possible. Nick Williams, Robert Radtke (both USBR) and Bill Vernieu (USGS) provided essential sampling assistance and advice. The manuscript was improved by three anonymous reviewers. This work was funded by NSF SGER grant EAR-0621371, the Alice Tyler Foundation, and USBR grant 06PG400222. The US Bureau of Reclamation provided sampling assistance.

Additional details

August 19, 2023
October 24, 2023