Spatial distribution of major and trace elements in shallow reservoir sediments: an example from Lake Waco, Texas

Abstract

Sediment geochemistry of a shallow (6-m average) reservoir (Lake Waco) was evaluated for the spatial distribution of major and trace elements. Sixty bottom and core samples along a 21-km transect within the reservoir, 18 overbank sediment samples, and 8 rock types in the drainage area were collected and analyzed for major (Al, Ca, Fe) and trace elements (As, Ba, Cr, Cu, Hg, Mn, Ni, Pb, Sr, V, Zn). Elemental concentrations in the reservoir sediments closely correspond to concentrations in the regional rocks and represent a mixture of overbank sediment composition of the tributaries. Elemental concentrations were statistically regressed against Al concentrations in order to establish regional baseline levels and thereby distinguish natural from anthropogenic sources. Spatial geochemical trends, considered in terms of element-to-Al ratio versus V-to-Al ratio, relate to the natural and anthropogenic sources contributing to the elemental concentrations. The spatial elemental distribution in the reservoir, which receive sediments from two mineralogically contrasting basins, reflect textural and mineralogical transition within the reservoir and suggest a progressive mixing of sediment from the tributaries. The spatial elemental distribution and sediment texture suggest that the sediment-source, which determines the sediment-type, has a greater influence on the major- and trace-element distributions in shallow reservoir sediments than bathymetry.