Sedimentary pigments as an index of the trophic status of Lake Mead

Abstract

Sedimentary pigment data were analysed from 6 cores from Lake Mead, the reservoir resulting from the impoundment of the Colorado River by Boulder (now Hoover) Dam in 1935. Surficial sedimentary pigments correlated well with contemporaneously measured primary productivity of the water column at the 6 coring stations. For the coring station nearest the sewerage inflow from the City of Las Vegas, the historical record of pigments closely paralleled the increase in human population, sewerage loading to the reservoir, and the associated phosphorus loadings. For three of the cores, pigments were closely correlated with total nitrogen from the same levels in the cores. Pigment concentrations in cores from different parts of the reservoir corroborate findings of other studies which indicate major differences in productivity of the upper and lower basins of Lake Mead (the lower basin having higher primary productivity). The pigment data from the cores provide some indications of the effect of the damming of the Colorado River above the Grand Canyon in 1963 to form Lake Powell, which significantly reduced phosphorus loading downstream to Lake Mead, and which may have adversely affected the largemouth bass fishery.

Formerly with the Lake Mead Limnological Research Center, University of Nevada, Las Vegas