Impact of bleached kraft pulp mill effluent on the nearshore benthic community of Jackfish Bay, Lake Superior

We assessed the impact of bleached kraft pulp mill effluent on benthic inve rtebrate community structure in the shallow (1 m) nearshore waters of Jackf ish Bay, Lake Superior. Duplicate benthic samples were collected from 0.5 m (2) quadrats at twenty-three stations along two shorelines of Jackfish Bay up to 1800 m from the point of effluent discharge, and from a reference sta tion located within the Jackfish Bay study area. Detrended correspondence a nalysis (DCA) revealed a gradient of stations on both shorelines which was strongly correlated with distance from effluent outfall and hence exposure to the effluent plume. Within this gradient were two distinct clusters of s tations. The first cluster contained all but one station on both shores < 3 00 m from the outfall, these stations receive constant exposure to the effl uent and were dominated (> 90%) by tubificids (Limnodrilus hoffmeisteri, Tu bifex tubifex, T. ignotus and Spirosperma ferox) and the naidid Chaetogaste r diaphanus. The second cluster contained all stations on both shores > 300 m from the outfall; community structure at these stations was generally co mparable to that at the reference site and was characterized by several spe cies of Chironomidae, C. diaphanus and Nais barbata, and low numbers of sev eral insect taxa. The results of this study show that benthic community str ucture in nearshore environments can be significantly impacted by pulp mill effluent and should be considered in monitoring assessments. At Jackfish B ay, such impacts appear to be restricted primarily to within the first 500 m of effluent discharge.