The impact of iron coagulant on the behavior and biochemistry of freshwater mussels Anodonta cygnea and Unio tumidus during lake restoration

Abstract

Iron (Fe) treatment is one of the most commonly used methods to restore eutrophic lakes and reservoirs. The Fe-based coagulants dosage results in an almost immediate improvement in water quality at a relatively low cost. However, the effects of the application of coagulants are not always predictable, and the scale of the risks is not fully understood. The dosage of coagulants changes the chemical and physical properties of water, thereby affecting aquatic biocenoses. In this study, several laboratory experiments were conducted to evaluate the effects of Fe-based coagulant dosage on two bivalves species: Anodonta anatina and Unio tumidus. Their ability to efficiently filter water and reduce seston makes them a key component of aquatic ecosystems in terms of maintaining proper ecological health and stable functioning. Behavioral response, biochemical parameters, and body chemistry changes in mussels exposed to different doses of coagulant were surveyed. A dose-dependent reduction in filtration activity of both species was observed. As early as 10g Fe m2 (which is a moderate dose used in lakes restoration), mussels of both species almost completely reduced their filtration activity and remained with closed valves for several subsequent days. Significant Fe accumulation in muscles of bivalves exposed to coagulant was also observed. This was particularly the case when very high doses of coagulant were applied. Then, the iron content in leg muscles of both species increased over fourfold. At the same time, a decrease in muscles calcium and phosphorus content was observed. No symptoms of oxidative stress (TBARS, H2O2) after mussels exposure to coagulants were found. The results suggest that the application of Fe-based coagulant for water ecosystem restoration may be a threat to the mussels population. These findings are significant for decisions on the selection of restoration methods for a specific lake.