Mercury contamination of macroinvertebrates from ponds with and without fish at the LBJ National Grassland, Texas

The purpose of this study was to examine mercury in macroinvertebrate communities from grassland ponds with and without fish communities. We sampled macroinvertebrates from five ponds with fish and five ponds without fish, at the LBJ National Grassland in North Texas. In ponds without fish, the biomass of macroinvertebrates was significantly higher than in ponds with fish. The average mercury concentration of macroinvertebrates from ponds without fish was significantly higher than the average mercury concentration in ponds with fish. Because ponds without fish contained a higher biomass of macroinvertebrates and unique taxa with higher concentrations of mercury, the total amount of mercury in the macroinvertebrate community in ponds without fish was significantly higher than in the ponds with fish. In ponds with fish, the average mercury concentration of the fish community was 13 times greater than mercury concentration of the macroinvertebrates community. These data suggest that when fish are present, mercury accumulates in fish rather than in the macroinvertebrate community, which has implications for the movement of mercury into terrestrial ecosystems when macroinvertebrates emerge as aerial adults.