Roberts, A.D., J. Besser, J. Hundley, D. Mosby, A. Rosenberger, K. L. Bouska, B. Simmons, L. Lueckenhoff, S. E. McMurray, S. Faiman, and L. Lueckenhoff. 2023. An assessment of the relation between metal contaminated sediment
and freshwater mussel populations in the Big River, Missouri. Science of the Total Environment. 876: https://doi.org/10.1016/j.scitotenv.2023.162743.
Abstract
The Big River in east-central Missouri drains the largest lead mining area in the United States. Releases of heavy metal contaminated sediments into this river is well documented and suspected to be suppressing freshwater mussel populations. During this study, we characterized the spatial extent of metal contaminated sediments and evaluated its relationship with mussel populations in the Big River. Mussels and sediments were collected at 34 sites in the Big River and 3 reference sites in the Big, Bourbeuse, and Meramec rivers in 2008 and 2013. Analysis of sediment samples with X-ray fluorescence showed that lead (Pb) and zinc (Zn) exceeded background concentrations by between 1.5 and 65 times for 168 km downstream of Pb mining releases. Mussel abundance decreased acutely downstream of releases of large volumes of heavy metal mine waste and showed consistent increases with distance downstream. We compared Big River species richness with historical surveys and with all data from 3 similar nearby rivers with similar physical habitat characteristics and threats to mussels, minus Pb mining impacts. Big River species richness predicted by these regressions was only about one-half that expected on average and 70-75% lower in reaches with high median Pb concentrations. Sediment Pb, Zn, and cadmium had significant negative correlations with species richness and abundance. The association of sediment metal concentrations with mussel community metrics in otherwise high quality habitat indicates that Pb and Zn toxicity are responsible for the observed mussel population declines within the Big River. We used concentration-response regressions of mussel density vs sediment Pb to determine that Big River mussel community was adversely affected when sediment Pb concentrations were above 160 ppm, the concentration associated with 20% decreases in mussel density. Thus, based on this sediment metal and mussel fauna assessment, our findings indicate that approximately 140 km of the Big River has a toxic effect to mussels from Pb and other heavy metals.