COMPARISON OF THREATENED NEOSHO MADTOM DENSITIES BETWEEN RIVERSCAPES DIFFERING IN ANTHROPOGENIC STRESSORS, WITH A PARTICULAR FOCUS ON RECOVERY FROM MINING-DERIVED METAL POLLUTION

Abstract

Water pollution imperils the Neosho Madtom (Noturus placidus), which is threatened in Kansas and federally. Within Kansas madtom densities were historically lower in the Spring River compared to the Cottonwood and Neosho Rivers, especially within the Spring River below tributary inputs that delivered cadmium, lead, and zinc pollution from the Tri-State Mining District. Studies suggest that madtoms are less numerous in waters containing elevated metal concentrations because of direct toxicity and lower benthic macroinvertebrate availability, which is also depressed by elevated metal concentrations. However, long-term reductions in metal concentrations in the Spring River have occurred, but to date no study has examined whether madtom and macroinvertebrate densities have responded to this improving water quality. We addressed this question by comparing madtom densities and macroinvertebrate biomass between the Neosho-Cottonwood and Spring Rivers, and within the Spring River above and below metal pollution inputs. However, madtoms are imperiled by environmental factors and anthropogenic stressors beyond mining-derived metal pollution, so we also examined if food availability (i.e., macroinvertebrate biomass), watershed characteristics (i.e., the upstream proximity of small and large dams, upstream watershed area, and percent open water in the upstream watershed), and local habitat variables (i.e., turbidity, depth, velocity, and percent gravel/pebble substrate) were related to madtom densities. We found that madtom and macroinvertebrate population densities in the Spring River were similar to those of the Neosho-Cottonwood River system, and densities in the Spring River downstream of mining-impacted tributaries were similar to those upstream of pollution. Furthermore, macroinvertebrate availability and watershed characteristics were not associated with madtom abundance. However, turbidity and depth were associated with madtom densities, such that an increase in turbidity or decrease in depth resulted in higher madtom densities. Our results highlight the benefits that water quality improvements can have on stream organisms, especially those that are imperiled