Effects of metal mine and municipal wastewater on growth and energy stores in juvenile fishes

Abstract

The Sudbury, ON, Canada region has been the site of metal mining and processing operations for more than 100 years. The study site for my thesis, Junction Creek, flows southwest through the City of Greater Sudbury and receives cumulative inputs including from the Garson Mine wastewater treatment plant (WWTP), Nolin Creek WWTP (stormwater) and CVRD Inco Limited WWTP (process water) as well as effluent from municipal WWTPs and untreated urban runoff, aerial deposition and historical contamination from multiple sources. Elevated levels of ammonia, Ni, Cu, Co, Pb and As, as well as reduced benthic invertebrate community diversity and density have been observed in the Junction Creek system below certain mine inputs. In addition, the Sudbury region has cold winters, with average daily air temperatures below 0°C from November to March.

The winter stress syndrome hypothesis proposes that the combination of winter conditions and contaminants (acting as physiological stressors) in the aquatic environment could reduce fish condition and deplete energy (lipid) reserves to the point of decreased survival, thus negatively impacting wild fish populations. However the winter stress syndrome hypothesis has rarely been tested in the field. I hypothesized that juvenile fish challenged with a physiological stressor (treated wastewater) in combination with winter conditions would have decreased growth and energy stores as a result of increased metabolism.

The approach I used to examine the potential effects of treated metal mine and municipal wastewaters on bioenergetics and growth, as they related to overwinter survival potential and the winter stress syndrome, of juvenile fish was a combination of a field study and a laboratory experiment. The first objective was to test the winter stress syndrome hypothesis under field conditions. Juvenile fathead minnows (Pimephales promelas), creek chub (Semotilus atromaculatus) and white sucker (Catostomus commersoni) were collected in fall and the following spring from sites along Junction Creek, Sudbury, ON downstream of two metal mining wastewater treatment plants as well as a municipal wastewater treatment plant. The second objective was to test the winter stress syndrome hypothesis in the laboratory by determining the effect of diluted (45 percent) treated CVRD Inco Limited wastewater effluent (CCWWTP) on juvenile fathead minnow growth and energy storage under simulated summer and winter conditions of reduced temperature, photoperiod and food ration. The effect on growth and energy storage of exposure to environmentally relevant ammonia concentrations was also assessed. In both the field and laboratory portions of this study, overwinter survival potential was assessed indirectly through measurements of growth (length, weight, muscle RNA/DNA ratio, muscle proteins) and energy stores (whole body triglycerides). There were inconsistent effects between the field study and the laboratory experiment. In contrast to my hypothesis, fathead minnows in the field study were larger with greater triglyceride stores at exposure sites compared to the reference site. White suckers were smaller at exposure sites but did not differ in triglycerides among sites and creek chub had no clear trend. For the laboratory portion of this study, only fathead minnows were used. After a 90 day exposure to reference or diluted CCWWTP water under simulated winter or summer conditions, juvenile fathead minnows raised in winter CCWWTP water (4°C) had lower whole body triglyceride concentration than those raised in winter reference water. There was no difference in triglycerides in fathead minnows raised in diluted CCWWTP or reference water under summer conditions. This lends support to the winter stress syndrome hypothesis, but the traditional measures of growth showed no significant differences in any of the treatments. In a separate experiment, fathead minnows were exposed from 10-100 days post hatch to graded concentrations of ammonia (0.02 to 0.40 mg unionized NH3/L) under summer conditions only. There was no effect of ammonia exposure on growth parameters, but a significant increase in total body triglycerides at the highest exposure concentration (0.40 mg/L) was observed.

The results of this study emphasize that laboratory-based hypotheses must be tested in the field to determine their environmental significance. The winter stress syndrome may not apply to northern fish adapted to living and feeding in colder climates and was not strongly supported by my study.