EXECUTIVE SUMMARY
As part of the Aquatic Effects Technology Evaluation (AETE) Program, a field survey was conducted of the Myra Falls Mine Site in British Columbia. This site has been suggested as a candidate for detailed testing of monitoring tools in 1997 studies sponsored by the AETE Program. The purpose of this survey was to provide information whether or not to include this site in 1997 studies and, if so, for what particular hypotheses.
As part of this field survey, available historical information was reviewed. Changes in water and sediment quality in Buttle Lake (e.g., copper, zinc concentrations) have occurred related to effluent discharges. In addition, plankton have been adversely affected in the lake and fish have accumulated metals in their tissues. Historic metallothionein measurements in Buttle Lake rainbow trout liver tissue have been correlated with metal concentrations in the water column. However, process changes at the mine have reduced historic impacts (e.g., differences between exposure and reference areas).
Effluent discharge is continuous. Sublethal toxicity testing indicated that the effluent affects survival and reproduction of Ceriodaphnia dubia, survival and growth of fathead minnows, and growth of both Selenastrum capricornutum and Lemna minor.
Field studies were conducted in both Buttle Lake (5 reference and 6 exposure stations) and in Myra Creek, which conveys mine effluent to Buttle Lake (1 reference and 1 exposure station). Significant elevations in some parameters (e.g., pH, conductivity, total dissolved solids, and several total and dissolved metals) occurred at the exposure area compared to the reference area. Some parameters exceeded Canadian freshwater guidelines for the protection of aquatic life at both exposure and reference areas.
Buttle Lake appears to be unique among the seven sites due to a relative lack of sediment or benthic studies in Buttle Lake (the focus has been on the water column and phytoplankton). It is also unique because water levels in Buttle Lake are controlled by B.C. Hydro for power generation and can vary substantially over short time periods. One of the results of this variation is periodic exposure of littoral sediments.
Despite efforts to sample similar sediment habitats, there were differences between the reference and exposure areas (e.g., fines, total organic carbon, loss on ignition). All metals were present at higher concentrations in the exposure than the reference area, but this difference may be partly related to substrate differences. Cadmium, copper, lead and particularly zinc exceeded Canadian sediment quality criteria in the exposure area.
There was no significant difference between reference and exposure areas for total abundance or species richness of the benthos in Buttle Lake. The Myra Creek exposure station had higher abundance and lower species richness than the reference area.
Only one potential sentinel fish species (rainbow trout) was collected in any numbers during this field survey. Historic data indicate additional sentinel species include cutthroat trout and Dolly Varden. Neither tissue nor metallothionein analyses were conducted because good historical data were available. Additional information regarding this site is provided in Table ES-1.
Overall, this is not an ideal site for 1997 studies by the AETE Program. Fine-grained sediment is limited and collection is difficult due to extensive wood debris. More importantly, benthic invertebrates may not be as important to the Buttle Lake food web as zooplankton.
