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 Area of Concern 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 as well as the zooplankton and macroinvertebrate community. The effects of the remediation of the Fox River dredging were assessed by collecting zooplankton, macroinvertebrates, total suspended solids (TSS), algal biomass, and secchi depth. Zooplankton samples were counted, measured, and identified to species; macroinvertebrates were counted, measured, and identified to family; and TSS, algal biomass, and secchi depth were analyzed using standard methodology. Monthly sampling was conducted in two dredged sites as well as two sites upstream and two sites downstream of the dredging from May-September each year; 2013-2016. Data were analyzed using a repeated measures ANOVA in SPSS.
Results/Conclusions
Total zooplankton density was significantly lower at the dredged site (p<0.001) with all sites statistically different from each other (p≤0.008). Diacyclops navus was also significantly lower at the dredged site (p≤0.033) compared to the upstream and downstream sites. Bosmina longirostris and nauplii density was significantly lower at the upstream and dredged site compared to the downstream site (p<0.001; p=0.002, respectively).This pattern was repeated in B. longirostris, D. navus, and nauplii biomass where the biomass was significantly lower at the dredged site and upstream site compared to the downstream site (p≤0.017). TSS, secchi depth, algal biomass, macroinvertebrate abundance, Hilsenhoff-Biotic index, and zooplankton species length were not significantly different between sites. These results show that sediment dredging can have negative consequences on the zooplankton community as a whole, but not necessarily on every individual species. A potential mechanism that is causing decreased zooplankton density may be a reduction in filter feeding efficiency, interference in predator-prey interactions, and destruction of Cladoceran diapausing eggs as a result of the resuspension and removal of sediment caused by dredging.