Testing the effect of carbonate saturation on the Sr/Ca of biogenic aragonite: A case study from the River Ehen, Cumbria, UK

It has been suggested that the incorporation of strontium into biogenic aragonite may be influenced by the degree of carbonate saturation in aquatic environments. We measured the Sr/Ca ratios of river water and the aragonitic shells of freshwater bivalves (Margaritifera margaritifera) from two sites with different carbonate saturation states in the River Ehen, Cumbria, UK. Shell Sr/Ca and river water Sr/Ca are 0.1 mmol/mol and 0.42 mmol/mol lower, respectively, at the high carbonate saturation site. However, the distribution coefficients of strontium into aragonite (K-D) are the same (similar to 0.28) at both sites. These analyses show that Sr uptake into aragonite bivalve shells is not affected by the degree of carbonate saturation of the water, perhaps reflecting a strong biological control on trace element incorporation.