Consultant's Report - Minnesota State Legislature

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In contrast, fall sampling revealed significant changes in the invertebrate fauna. (Fig 2). Ephemeroptera were no longer collected in any samples from any sites, and the diversity ofTrichoptera was substantially reduced. Elmidae (Coleoptera) were still collected at all the sites. However, at the outlet site numbers oforganisms collected were extremely reduced compared to spring sampling. Downstream, diversity and abundance were higher at the Hwy 3 site compared to the outlet site in September; however, it was still very low compared to spring abundances. An exception to this was the Simuliidae, which were overwhelmingly dominant in abundance in the fall samples from Hwy 3. Non-insect inveliebrates also were substantially reduced. Only one snail was collected in all fall samples, from the Hwy 3 site. Additionally, no amphipods were found in any fall samples. No zebra mussels were found at the outlet sites on any rocks or other substrate where they had been collected from in spring. It would appear that the continual flush ofcopper at low levels from the lake into Pelican Brook had a significant negative impact on the aquatic invertebrate community at both the outlet and at least up to 2.5 miles downstream. This is not unexpected for the Mollusca (snails, bivalves) as copper sulfate is used to attempt to control swimmers itch outbreaks by killing snail populations (interrupting the cercaria life cycle by eliminating one host). However, literature suggested that adult zebra mussels were more resistant to copper, with LC50's reported in the 5 ppm range for several days. It would appear that constant presence ofmuch lower levels ofcopper killed attached zebra mussels in the stream. However, it also appeared to have eliminated the native unionid fauna in the outlet area. During spring sampling, many native mussels were observed in the stream. Observations in the fall found no live mussels, and many empty shells from what appeared to be recent mortality. At the Hwy 3 site, many empty shells were also seen, although a very small number oflive native mussels were also observed. It is possible that the distance had allowed some native unionids to survive the copper, although numbers may have been reduced below viable reproductive levels. While snails may repopulate the stream from export oflake populations, it is uncertain ifnative unionids will re-establish populations. Another group seriously impacted were the Amphipoda. While very common in spring samples and abundant at Hwy 3, no amphipods were collected in any samples in fall. It is unknown ifthis impact would be seen in the larger Crustacea (crayfish) as these were not sampled in any numbers in either sample period. The impacts seen in the invertebrate community are consistent with other studies that have examined impacts ofcopper on different aquatic invertebrates. Studies have suggested that Ephemeroptera are extremely sensitive to copper, as well as reports of sensitivities ofAmphipoda to levels lower than or equal to copper levels recorded in the brook. Some work has also suggested that some caddiflies, in particular the Hydropsychidae, are very resistant to copper. Indeed, this group was still present in samples collected in the fall. Also seen in fall samples were pupae ofLimnephilidae, suggesting that not only was this caddisfly not impacted in the larval stage, but grew to the pupal stage in their life cycle. 3
It might be argued that these impacts noticed cannot necessarily be attributed to the copper, as there was no real "control" stream in this survey. Only pre- and posttreatment samples in the brook receiving copper outflow were collected. However, the magnitude ofthe impacts and agreement with literature documenting similar impacts suggests that the copper flowing out ofMuskie Bay from veliger control treatments was responsible for the serious negative impacts seen. The significant negative impacts, however, need to be viewed in the context ofthe goal ofthe copper treatments. Managers and biologists realized at the beginning that copper might have major impacts. While it was hoped that the lower dosage rate (O.6ppm) would provide some safety, it was also recognized partway through the season that the copper would be present almost continually in the waters ofthe brook, although at very low levels. Data from veliger sampling in the bay and sampling in the brook for settled attached adult zebra mussels suggest that not only were veligers significantly eliminated from the bay, but that any which survived the initial copper treatment in the lake were unlikely to survive in the brook. Veligers that may have received less than a lethal dose ofcopper in the bay would be continually exposed as they drifted in the stream, suggesting that survival would be seriously compromised. Survival ofzebra mussels is highest once they develop a shell and settle. The apparent mortality or disappearance ofattached adults in the outflow area suggests a hostile and lethal environment to this more resistant stage. Thus, the objective ofpreventing export and establishment ofzebra mussels via Pelican Brook appears to have been successful, at cost to a substantial part ofthe invertebrate community. Copper treatments are viewed as a short-term, stopgap measure to buy time while alternatives for long-term physical interdiction ofthe veligers is investigated. It was assumed that this type oftreatment might be needed for one or two years, depending on the results ofa long-term control study. There is consensus that ifno viable long-term alternatives are found, copper treatments are not likely to be recommended as an annual operational treatment. Recommendations 1. Continue spring and fall invertebrate sampling at the established sites. Sampling should occur at minimum during any seasons with copper treatment, and should be extended for a number ofseasons after treatment is stopped to document recovery ofthe invertebrate community. 2. Investigate availability ofa second stream, comparable to Pelican Brook, to begin monitoring as a control stream. 3. Examine access further downstream on Pelican Brook or Pine River to assess distance oftravel for copper and potential impacts. 4. After treatments are stopped, examine possibility oftransplanting native unionids to upper reaches ofPelican Brook, to try and re-establish this fauna. 4
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List ofTables MINNESOTA DEPARTMENT
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I. Introduction Purpose MINNESOTA D
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Feasibility Study To Limit the Spre
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Hydrological Characteristics MINNES
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Outlet Structure MINNESOTA DEPARTME
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lBhsl Nllrtq Osso'winnomakee Pelica
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Age and Growth MINNESOTA DEPARTMENT
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Works Cited MINNESOTA DEPARTMENT OF
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Table V-1. Methods Available for Co
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Cavitation MINNESOTA DEPARTMENT OF
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Potassium Salts MINNESOTA DEPARTMEN
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Works Cited MINNESOTA DEPARTMENT OF
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Combined Treatments MINNESOTA DEPAR
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Feasibility Study To Limit the Spre
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METHOD OF INVESTIGATION MINNESOTA D
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VII-B. Treatment Alternatives Expan
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Message Page 3 of4 3/21/2005 best.
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enougl1 to eV8Juatc £1'
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I \ I iV!1';UJIOOiS for Estimaling
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FishPro Consulting Engineers and Sc
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Page 144 and 145: Zebra Mussel Feasibility Study-Main
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Page 186 and 187: VII-F. Meeting Summaries
Page 188 and 189: Rich Rezanka would like us to refer
Page 190 and 191: VII-G. List of Abbreviations Used
Page 192: VII-H. Glossary of Terms
Page 195 and 196: MINNESOTA DEPARTMENT OF NATURAL RES
Page 197: Secchi disc MINNESOTA DEPARTMENT OF
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Consultant's Report - Minnesota State Legislature

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