Cumulative effects are defined by the Canadian Council of Ministers of the Environment (CCME, 2014, p.1) as “a change in the The first objective of this report describes the available literature on cumulative impacts to water quality in the Upper Coppermine River Basin, NWT. Results show the chemistry of the soft, oligotrophic, shield lakes, characteristic of the area, can be vulnerable to even slight natural and anthropogenic disturbances (Moiseenko and Gashkina, 2009). Already, localized natural resource development has been shown to cause chemical changes in the water in and around Lac de Gras (Stantec, 2015). Road expansion has the potential to alter the major ions, conductivity and pH of nearby lakes. Regionally, climate change is showing its ability to influence natural processes on a larger scale. Air temperature warming has been observed to be triggering increased active layer thickness, further driving permafrost thaw and slumping in Baker Creek, NWT which serves as a potential future example of changes in the Coppermine under increasing climate change. Freshlyexposed soils and glacial sediments, rich in major ions and trace elements, are being eroded and transported to the unspoiled Shield lakes via overland runoff during peak summer flow (Houben et al., 2016). The behaviour of such compounds in these lakes is not well understood. Increased DOC and N may increase primary production or, perhaps, sedimentation will intervene. Alternatively, the vastness of the watershed will simply dilute the chemical disturbances over time. The lack of specific research on water quality in the Upper Coppermine serves as a call for action to invest in better understanding the short and long term results of cumulative effects.
Results from the second objective provide a detailed analysis of water quality parameters at Daring Lake, Desteffany Lake, Lac de Gras and Rocknest Lake. The mean and median values of all parameters in the Upper Coppermine are below the CCME Freshwater Aquatic Life Water Quality Guidelines. Median total phosphorus levels indicate the lakes are ultra-oligotrophic to oligotrophic. All of the lakes show a median pH between 6.5 and 7.5 indicating that they are circumneutral. All the lakes are low in ions and show spatial homogeneity. An average mean hardness of 9 mg/L classifies the Upper Coppermine lakes as soft water. Much of the data is slightly skewed to the right, as is typical of water quality data. Rocknest Lake likely owes its higher median hardness, alkalinity, barium, pH, TDS, DOC, total nitrogen, calcium and magnesium to its location below the treeline and in the Bear Geological Province, a different geological setting with more vegetation and higher erosion rates, as compared to other studied lakes in the Upper Coppermine. Lac de Gras and Desteffany Lake have similar water quality characteristics and concentrations. Many of the water quality parameters show significant temporal trends at Lac de Gras and Desteffany Lake, which is in contrast to Daring Lake and Rocknest Lake where there are fewer significant changes in water quality parameters. Increasing major ion concentrations in Na (by 419% at Lac de Gras and 174% at Desteffany) and DOC (by 9% at Lac de Gras and 26% at Desteffany) are warning signs of potential active layer thickening and thermokarst slumping (Burd et al. 2018 and Kokelj, 2009). Increasing conductivity (by 94% at Lac de Gras and 45% at Desteffany) is a possible sign of impacts from road dust (Zhu et al. 2019), or more likely, the treated mine effluent. As well, increasing strontium concentrations (by 223% at Lac de Gras and 103% at Desteffany) and pH (by 5% at Lac de Gras and 6% at Desteffany) are potentially a sign of impacts from upstream effluent from diamond mine operations (Deton’ Cho Stantec, 2015). Therefore, at these two lakes, there is evidence of cumulative effects to water quality. Daring Lake appears to be a good choice for a reference lake in the tundra environment above the treeline in the Upper Coppermine. Its small interquartile ranges (Appendix B2) and lack of significant temporal trends suggest that it has undergone little transformation and impacts from disturbance over the period of record.
Finally, the third objective provides a preliminary evaluation of the Ecofish cumulative effect indexing tool. The results from the tool are similar to the results from the analysis of nearly 20 years of water quality data at Daring Lake, Desteffany Lake and Lac de Gras. Lac de Gras and Desteffany show higher cumulative effects, mainly contributed by anthropogenic disturbance in their sub-basin. The actual data supports the tool’s interpretation of Desteffany and Lac de Gras with a high number of significant temporal trends and significant increases in anthropogenic related parameters, such as strontium and conductance. Daring Lake is predicted to have low cumulative effect risk and its baseline data supports this with few temporal trends and a lack of changing anthropogenic related parameters. Future work with the tool should include layers that address permafrost thaw, slumping, and forest fires in the natural disturbance section and land cover and surficial geology in the landscape vulnerability section.