Variation in Sr uptake in the shell of the freshwater gastropod Bithynia tentaculata from Lake Arreo (northern Spain) and culture experiments

The Sr uptake features in Bithynia tentaculata aragonite shells from monthly collections in Lake Arreo (northern Spain) over a two-year period are compared with those from the same species grown in culture experiments with similar waters under controlled temperature. The shell aragonite of B. tentaculata from Lake Arreo formed in isotopic equilibrium with the lake water. A comparison of the stable oxygen isotope values (δ18O) from the shells and waters allowed the selection of suitable shells for Sr uptake studies. The Sr/Ca molar ratio in B. tentaculata shells (Sr/Cashell) from the lake and from the culture experiments positively correlate with some chemical parameters like conductivity and solute composition. Some environmental factors such as pH and T have minor influence on Sr incorporation into shells, as reported from other aragonitic mollusks. The Sr/Cashell exhibits a good positive correlation with the Sr/Ca of the water (Sr/Caw) using linear regression. However, a polynomial function equation better fits the Sr/Cashell and the Sr/Caw (R2=0.890, p=2.923e−11). Above a value of 0.0025 for Sr/Caw, the ratios of Sr/Cashell present small changes. This pattern reveals a noticeable variation of the partitioning coefficient (KdSr) with Sr/Caw. The KdSr for B. tentaculata shell aragonite obtained in this study is 0.290±0.078 (n=25) and it is close to the mean values obtained for other non-marine aragonitic mollusks. KdSr values in B. tentaculata are influenced by the variations in Sr/Caw that mask the T effect. This feature, together with the influence of physiological processes on the trace element incorporation, may explain the observed KdSr pattern.