Relationship between the shell geochemistry of the modern aquatic gastropod Radix and water chemistry of lakes of the Tibetan Plateau

Fossil shells of the aquatic mollusk Radix are common in the exposed sediments of lake terraces on the Tibetan Plateau. However, the living environment of Radix, and the geochemical characteristics of its shells, is unclear. Here, we report the results of an investigation of the occurrence of modern Radix in lakes of the southeastern and central Tibetan Plateau, as well as measurements of various geochemical characteristics of the shells. The results indicate that the nutritional status of the lake waters is the main limiting factor for the survival of Radix in these lakes. The Sr/Ca ratio of the Radix shells is significantly positively correlated with both the Sr/Ca ratio and the conductivity of the lake water. Initially, Kd(Sr) decreases rapidly with low values of Sr/Ca-water; however, in the case of Sr/Ca-water values above 0.0076, Kd(Sr) exhibits only a small range of variation. The delta C-13(shell) values are controlled by the delta C-13 of lake water dissolved inorganic carbon (DIC). In addition, the contribution of DIC of organic origin to the Radix shells increases when the lake water is deficient in DIC of inorganic origin. The delta O-18 values of the Radix shells provide useful information about the isotopic composition of the ambient waters.