Water bodies adjacent to paper mills and other industries are often contaminated by polychlorinated biphenyls (PCBs). The Lower Fox River in Green Bay, WI, USA, is an EPA Superfund site due to PCB contamination, and is currently being dredged to remove the sediment contaminants. We hypothesized that remediation via sediment dredging has detrimental consequences on the water clarity and zooplankton community. The effects of the remediation of the Fox River dredging were assessed by collecting zooplankton, total suspended solids (TSS) and secchi depth. Zooplankton samples were counted, measured, and identified to species, and TSS and secchi depth were analyzed using standard methodology. Monthly sampling was conducted in dredged sites as well as sites upstream and downstream of the dredging from May-September each year; 2013-2016. Data were analyzed using a repeated measures ANOVA in SPSS.
Total zooplankton density and biomass decreased significantly (F2,24=55.11, p<0.001; F2,24=22.70, p<0.001, respectively) at the dredged site (p<0.022). These patterns were likely driven by a significant decrease in Bosmina longirostris density and biomass (F2,24=78.33, p<0.001; F2,24=4.67, p=0.019, respectively) at the dredged site (p<0.001). Diacyclops navus density decreased significantly (F2,24=7.91, p=0.002) at the dredged and downstream site (p<0.007). Zooplankton species diversity also decreased significantly (F2,24=6.266, p=0.006) at the dredged and downstream site (p<0.020). TSS and secchi depth were not significantly different at the dredged site or downstream of dredging. These results show sediment dredging can have negative consequences on the zooplankton community through possible reduction in filter feeding efficiency or interference in predator-prey interactions.