SPATIOTEMPORAL CHANGES IN THE IMPERILED AND DIVERSE MUSSEL ASSEMBLAGE OF THE SPRING RIVER IN KANSAS IN RESPONSE TO KNOWN AND EMERGING POLLUTANTS

Kansas was historically home to 50 species of freshwater mussels, of which 42 remain extant. The Spring River of southeastern Kansas is home to 34 of the remaining 42 mussels, many of which are imperiled. Elevated metal concentrations that resulted from past lead and zinc mining in the Tri-State Mining District historically imperiled Spring River mussels, but this threat has abated over the last 20 years. Ammonia pollution may have replaced the threat of metals, however, with potentially severe consequences for Spring River mussels. Our objectives were to evaluate contemporary mussel assemblage structure, in addition to spatiotemporal trends in the density and richness of Spring River mussels, in relation to changing concentrations of metals and ammonia. We accomplished these objectives by performing quantitative mussel surveys across twelve Spring River sites during the summers of 2023 and 2024, and we then compared our data to surveys performed over the past four decades. We also performed widespread and frequent monitoring of ammonia concentrations in the Spring River during 2023-2024. We found that metal concentrations no longer appeared to be a major factor structuring freshwater mussel assemblages in the Spring River of Kansas, as species richness and densities were relatively comparable both above and below historical sources of heavy metal contamination. However, temporal trends suggested that mussel assemblages above and below historical metal inputs have been trending divergently over the past 40 years. Species richness remained relatively stable in the upper Spring River, but densities have drastically declined in this reach. In contrast, both richness and densities substantially increased in the lower Spring River below historical metal inputs. These patterns were consistent with ammonia as the causative agent behind mussel declines in the upper reach, as concentrations were highest near the Missouri border and decreased downstream. Furthermore, likely due to reduced metal concentrations, the Bleufer (Potamilus purpuratus), Fawnsfoot (Truncilla donaciformis), Fragile Papershell (Leptodea fragilis), and Threehorn Wartyback (Obliquaria reflexa) have expanded their ranges to occupy all reaches in the Spring River of Kansas. In the 1990s, all four focal species were absent or scarce in the Spring River of Kansas. This research has critical conservation implications considering the numerous imperiled species of freshwater mussels in the Spring River.