Consultant's Report - Minnesota State Legislature

Chironomidae, which were left at the family level. Other invertebrate taxa (snails,
amphipods, flatworms, etc) were identified to varying levels, depending on available
taxonomic keys.
Results and Discussion
Copper levels: Monitoring showed consistent declines in copper levels from day
oftreatment to at or near baseline levels within 5 - 7 days (Fig. 1). Each treatment
spiked copper levels back up, with peak concentrations between 0.6 - 0.8ppm. Highest
levels ofcopper were recorded at the outlet site. The downstream site levels were often
approximately halfthe peak levels recorded at the lake outlet site. However, three times
during the summer the downstream site recorded peak levels near or at that recorded at
the outlet site. Field notes indicate that two ofthese coincided with precipitation events
during or prior to application. This suggests that perhaps increased discharge could have
transported more dissolved copper further downstream at an increased rate, accelerating
the dissipation normally seen during the summer. Copper levels never exceeded label
restrictions for the product. However, monitoring suggests that low levels (0.6ppm or
less) were present in the waters ofPelican Brook at least 2.5 miles downstream
throughout the majority ofthe summer during the treatment period.
Veliger densities: Sampling in the lake and bay pre-treatment showed veliger
production at a low level in the beginning ofthe season. However, while densities rose in
lake samples, veliger densities collected one-day post-treatment in various weeks in the
bay remained at low or undetectable levels (often less than 0.1 per liter). This suggested
that successful reproduction was occurring in the main body ofthe lake, but densities
were not rising in the bay. Additional contracted research with the Army Corps of
Engineers suggested that LC 100 levels for veligers were lOx less than the dosage rates
used for treatments during the season. It appears that the copper treatments were
successful in dramatically reducing or eliminating veligers in Muskie Bay, thus cutting
offthe downstream flow ofthe zebra mussel larval stages.
Aquatic macroinvertebrates: Aquatic invertebrate communities sampled in spring
showed a diverse assemblage oftaxa. Ephemeroptera and Trichoptera were predominant
in numbers oftaxa as well as numbers oforganisms collected. Coleoptera were also
commonly collected, all belonging to the family Elmidae. Plecoptera were uncommon,
represented by only a few specimens in one family. Also uncommon were Odonata,
although the habitat sampled may have missed species more associated with bank
vegetation. The rock/cobble in the sites sampled was not a common substrate for the
brook, which was dominated by sand, and sand/silt bottom. However, it presented a
consistent habitat and showed good diversity in the aquatic invertebrate fauna.
Non-insect invertebrates were present in the samples, often in substantial
numbers. Snails were more abundant at the outlet site than at other sites. This may be a
consequence ofexport from the lake ofthese taxa, or a result ofmore algal production
due to nutrients exported from the lake. Also present were single zebra mussels, attached
to rock or more commonly to woody debris in the brook. At the Hwy 3 site, Amphipoda
were very abundant, while no zebra mussels were collected.
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