Hydrochemical effects of degrading freshwater mussel shells

Living freshwater mussels of the order Unionoida are considered important ecosystem engineers for aquatic habitats, but the role of their dead shells in ecosystem dynamics is not yet fully understood. Therefore, we investigated the influence of decomposing dead mussel shells on freshwater chemistry, particularly with regard to their effects on pH and their potential buffering capacity in acidified water bodies through remineralization. To address this objective, we conducted standardized laboratory (28 d) and field (6 mo) experiments, considering different geology (siliceous and carbonate), pH, and conductivity. In the laboratory experiment, fresh, dead shells were exposed to 9 different hydrochemical settings, consisting of 3 different ambient media with varying ionic strengths and 3 different starting pH levels, to monitor the effects of the shells on the media. In parallel, shells were exposed in 3 streams with extant mussel populations in Bavaria, Germany, to monitor the degradation of the shells in a natural setting. In the laboratory experiment, mussel shells increased total hardness, pH, Ca2+ concentrations, and conductivity, which was attributed to the dissolution of CaCO3 from the shells. These effects were stronger in soft than hard water, and in hard water these effects were higher at lower pH values. In the field experiment, the mass loss of the shells was highest in siliceous streams. These findings indicate that dead shells can play a role in buffering pH fluctuations, especially if they occur in high numbers and in acidified siliceous regions with low ionic strength. The stabilizing effect of dead shells on water chemistry should be considered in restoration projects and in decision-making concerning their removal, for example, after mass die-off events.     «

Living freshwater mussels of the order Unionoida are considered important ecosystem engineers for aquatic habitats, but the role of their dead shells in ecosystem dynamics is not yet fully understood. Therefore, we investigated the influence of decomposing dead mussel shells on freshwater chemistry, particularly with regard to their effects on pH and their potential buffering capacity in acidified water bodies through remineralization. To address this objective, we conducted standardized laborat...     »