| dc.description.abstract | Two adjacent pit-lakes, Caland and Hogarth, formed after the flooding of open pit iron
mines near Atikokan, Ontario, Canada, were examined for their water quality relationships
and potential to support aquaculture. Detailed sampling for physical and chemical
parameters took place during 1998.1999. and early 2000.
Since mining terminated in 1979. both pits have continued to fill with water from rainfall,
snowmelt. and groundwater seepage, and. by 2000. had water depths in excess o f 160 m.
Water quality in both pit-lakes was largely dependent on proximal waste rock composition
and surficial geology of the area. Limestone and dolostone deposits at the site countered
production of acid from waste rock and resulted in neutral water pH’s in Caland and
Hogarth pit-lakes. Drainage was a major factor in distinguishing the water quality between
the two pit-lakes. Inflow of freshwater was much greater into Caland and resulted in
meromictic conditions with a well defined mixolimnion, chemocline and anoxic
monimolimnion. Hogarth pit-lake had less inflow and the entire water column was sulfate-saline
and aerobic. Statistically significant variations occurred between the two pit lakes
for metal, anion, cation, conductivity, hardness, and dissolved oxygen concentrations.
Variations in precipitation and evaporation between the two sampling years resulted in
increased or decreased ion concentrations for the same seasons or depths within the two
pit-lakes.
Caland pit-lake has supported an aquaculture operation for the production o f rainbow trout
(Oncorhynchus mykiss) since 1989. Production increased from 20,000 kg in 1998 to
163,325 kg in 1999. Nutrient loading from excess fish food and waste increased
phosphorus and ammonia levels during 1999 and 2000. The expanding fish form also
decreased the volume of usable (>6.0 mg 1) dissolved oxygen. Hogarth pit-lake was
devoid of aquatic life. Using water from Hogarth, standard LC50 tests showed 100%
mortality of Daphnia magna at full strength concentrations. None of the tested metal
parameters had levels that would be considered toxic and elevated salinity was suspected
as the cause of mortality. Any future aquaculture in Hogarth pit-lake w ill require the use
of species tolerant to such saline conditions. | |
