Physical, Chemical, and Mineralogical Characteristics of a Reservoir Sediment Delta (Lake Powell, USA) and Implications for Water Quality during Low Water Level

Abstract

Lake Powell is a large reservoir in Utah and Arizona that has experienced large changes in water level during a recent drought. As a first step in assessing the connection between hydrologic and chemical changes at Lake Powell, we characterized the particle size and solid-phase bulk concentrations for 31 elements and 25 minerals in sediment from the inflow region and some shoreline locations by using laser diffractometry, X-ray fluorescence, elemental analysis, and X-ray diffraction. Our results are consistent with previous results that show a negative correlation between particle size and concentrations of most elements and most minerals other than quartz and some feldspars. In our samples, however, solid-phase iron, rather than particle size or organic carbon, is the best predictor variable for the solid-phase concentrations of elements and minerals. Sediment characteristics vary on a scale of tens of kilometers, with fine sediment that is enriched in trace elements nearer to the dam. These trends allow formulation of an algorithm for determining a water-level threshold below which sediment resuspension may alter water chemistry in a generic reservoir with a long and narrow sediment delta.

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