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

Mead lake was impounded in 1935 by damming the Colorado river in Black canyon on the Nevada-Arizona border. Sediment samples were collected by coring and subject to spectrophotometric pigment analysis. Surficial sediment indices of derived plant pigments (phaeophytin and carotenoids) and phytoplankton productivity are presented for the 6 sampling stations. A second table correlated sedimentary pigments with nitrogen in the sediment cores, and figures showed pigment concentration in relation to sediment depth. There was a good correlation between pigments and contemporaneously measured primary productivity of the water column. One station nearest the sewerage inflow from Las Vegas reflected in its historical record of pigments the increase in human population and associated sewage and phosphorus loadings. Pigments from 3 cores were closely correlated with total nitrogen at the same depth. Other studies had indicated that the lower basin of Mead lake had a higher primary productivity than the upper basin. This was corroborated by the pigment study.