The effects of dredging to remediate the lower Fox River, WI, EPA Superfund Site on water quality, clarity and invertebrate species diversity

Background/Question/Methods

Water bodies adjacent to paper mills and other industries are often contaminated by polychlorinated biphenyl (PCBs). Remediation via dredging to remove contaminated sediments may have unintended consequences for the local water clarity, quality and species diversity. In Brown County Wisconsin, the lower Fox River, an EPA Superfund site, is currently being dredged to remove naturally capped contaminated sediments. Water quality, clarity and species diversity of zooplankton and macroinvertebrates in dredged sites, and upstream and downstream of the dredged sites, were measured to assess the effects of the remediation efforts on the aquatic ecosystem. We hypothesized that the dredged sites would have lower diversity, water clarity and water quality compared to the upstream and downstream sites. Total suspended solids, zooplankton and macroinvertebrate abundance were assessed approximately every two weeks during July and August 2012. Species diversity of zooplankton and macroinvertebrates were calculated using the Shannon-Weiner Index.  

Results/Conclusions

Preliminary results indicate significantly lower zooplankton species diversity at the dredged site (F_2,18 = 11.43, p = 0.009), while macroinvertebrate species diversity did not differ across sites (F_2,18 = 1.55, p = 0.29). Low zooplankton species diversity at the dredged site suggests that zooplankton are more sensitive to dredging activity compared to macroinvertebrates. TSS changed significantly over time (F_3,18 = 6.76, p = 0.0007) demonstrating an increasing trend over the course of the experiment. TSS was significantly greater at the downstream site compared to the upstream site on all sample dates. TSS was also highest at the downstream site during three of the four sample dates. Higher TSS at the downstream site suggests that dredging activity may have contributed to higher downstream turbidity. Dredging activity affected zooplankton species diversity and turbidity, and thus may potentially affect additional components of the aquatic ecosystem.