Figure 9

Element concentrations and mass ratios are from the 1988-89 river data and from the 1998 Salton Sea sediment data.Nonvolatile elements, such as molybdenum (Mo) and uranium (U), also exist as soluble oxyanions in the oxygenated river water and as insoluble species in reducing bottom sediment beneath the Salton Sea. Nitrogen (N) and selenium (Se) have geochemical properties similar to those of U and Mo, except that Se and N can potentially be lost as gases. The fact that relative proportions (mass ratios) for all four of the above elements are about the same in river water and in lake sediment indicates that nearly all the N and Se discharged by the rivers is retained within the sediment accumulating beneath the Salton Sea. Extending similar calculation methods reveals that at least 78% of organic carbon is derived from autochthonous (within lake) production and that no more than 22% is derived from outside the Sea.