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Biodiversity in Canadian Lakes and Rivers

Trends in Pollutants in Lake and River Systems

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Contaminants entering the environment will partition into different environmental compartments (such as water and biota) in a fashion determined by their chemical and physical properties. Since the environment itself is in a state of constant physio-chemical flux, it is not always straightforward to predict by which pathway or in which compartment specific substances will accumulate. For this reason, spatial and temporal interpretation of contaminant monitoring data is often hampered by a lack of sufficient observations, and by other confounding factors such as analytical method inconsistencies (Braune et al., 1999). Moreover, observations within a single system may not easily be generalized to other systems: for example, where food web structure varies between lakes food-chain bioaccumulation of contaminants by top predators will vary according to food chain length and trophic position, even where contaminant levels at the base of the food web are similar (Baird et al., 2001). For this reason, and given the general lack of available time series data within Canada on contaminants, either in terms of water or tissue/biota concentrations (see below), it was not possible to carry out a scientifically credible analysis of contaminants trends across ecozones+.

Given public concerns regarding environmental pollution arising from the emission of contaminants from human activities, it is surprising that relevant data for assessing trends in substances of concern in river and lake ecosystems are almost completely lacking beyond the Great Lakes region (which is itself covered in a separate Technical Ecozone+ Report). This situation is clearly illustrated for a region where contaminants are considered to be an important ongoing threat to freshwater ecosystems: the Canadian Arctic. In an authoritative review of existing data on contaminants in this area, Braune et al. (1999) state unequivocally that:

"Reviews of contaminant data in freshwater fish from Arctic and sub-Arctic Canada available to 1991 (Muir et al., 1990; Lockhart et al., 1992) indicated that information on the levels and geographic variation of OCs, PAHs and heavy metals was limited while data on temporal trends were non-existent."

The limited number of studies carried out on contaminants in the Canadian Arctic have tended to focus on marine ecosystems (for example, Muir and Norstrom, 2000). Where trend data in freshwater ecosystems are reported, they tend to be locally focused, consist of relatively few sequential observations, and relate to the very recent past (for example, Michelutti et al., 2009). For example, in a research synopsis produced by the Northern Contaminants Program (2008), trends were observed in certain groups of persistent organic pollutants (POPs): HCH, PCBs, toxaphene, and DDT levels in fish tissue were generally seen to be declining across sites studied, whereas mercury trends in fish tissue showed a more complex pattern, with significant increases being observed for some species and locations (for example, lake trout (Salvelinus namaycush) in Great Slave Lake), and no change being reported for species in other areas (for example, charr in lakes in Qausuittuq and Quttinirpaaq). This pattern of spot measurements, patchily distributed and relying on opportunistic sampling as part of short-term local or regional initiatives, has resulted in the current situation, where for much of Canada, time series data on contaminants in freshwater ecosystems are absent. Despite a lack of temporal trend information, the appearance and persistence of bioaccumulative, persistent organic pollutants in remote areas such as the Arctic, which were originally emitted in the more developed southern parts of the North American continent, is a newly emerging trend. This phenomenon is a direct result of global fractionation, a process which was not fully recognised until recently (Wania and Mackay, 1993), and whose implications for transport of a host of substances from industrialised regions to more remote regions is still not completely understood.

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Results from the 2008 Canadian Environmental Sustainability Indicators report demonstrated that phosphorus water quality guideline limits were frequently exceeded at 125 of the 369 (34%) monitoring sites (Environment Canada, 2009b). Similarly, the percentages of sites exceeding guidelines in 2002–2004 and 2003–2005 were 38 and 37% respectively (Environment Canada, 2006a; Environment Canada, 2007). In part to evaluate these frequent exceedences, Environment Canada (2011) recently completed a national report exploring trends from 1990 to 2006 in phosphorus and nitrogen in lake and river systems across Canada. Trend analyses of data between 1990 and 2006 demonstrated that 39 of the 77 monitoring sites showed no change in phosphorus levels, 22 showed significant decreasing trends, while 16 showed increasing trends (Figure 29) (Environment Canada, 2011). 

Figure 30. Number of water quality monitoring sites in each major ocean drainage basin with increasing, decreasing, and unchanged phosphorus levels between 1990 and 2006. Only sites with statistically significant results are shown (p<0.05).
graph shows water quality monitoring sites in each major ocean drainage basin
Source: Environment Canada (2011)
Long Description for Figure 30

This bar graph shows the following information:

Figure 30. Detailed data
Major Ocean
Drainage Basin
Number of
sites -
Number of
sites -
No change
Number of
sites -
Pacific Ocean (n=17)692
Arctic Ocean    (n=12)273
Hudson Bay     (n=18)3114
Atlantic Ocean (n=30)11127

Glozier et al. (2004) quantified long-term trends in water quality in Banff and Jasper National Parks to assess the effectiveness of sewage treatment plants. Their report applied non‑parametric seasonal Mann-Kendall analysis to assess trends in phosphorus concentrations at five monitoring locations on the Bow, North Saskatchewan, and Athabasca rivers. Results from the first report (Glozier et al., 2004) showed improvements in concentrations of nutrient and bacteriological parameters were observed at downstream sites, particularly in the lower Bow River for the period since 1989. These improvements are largely related to the upgrade of the sewage treatment facility in Banff. Glozier (Glozier, 2009, pers. comm.) reported the results of a follow-up analysis to assess the effectiveness of an upgrade in all three municipalities to tertiary treatment with phosphorus removal. Trend analyses showed that the new facility dramatically reduced phosphorus concentrations in the Bow and Athabasca rivers with median concentrations restored to levels similar to upstream, naturally occurring concentrations  (Figure 31). Thus, management practices have dramatically improved water chemistry in these rivers. With continued monitoring, the effects of improved water quality on aquatic communities can be observed.

Figure 31. A) Median total phosphorus and B) dissolved phosphorus concentrations in the Bow River, 1975–2010. Three distinct municipal treatment regimes through the period of record are indicated as: T1–secondary treatment and settling aeration, T2–high rate activated sludge plant with UV disinfection, and T3–tertiary treatment including phosphorus removal.
two line graphs showing the median total phosphorus and dissolved phosphorus concentrations in the Bow River
Source: Glozier et al. (2004) and updated by Glozier with unpublished data
Long Description for Figure 31.

This figure is comprised of two line graphs showing the median total phosphorus and dissolved phosphorus concentrations in the Bow River for the years 1975–2010. The graph shows that after 2003, phosphorus concentrations in the Bow River were dramatically reduced with median concentrations restored to levels similar to upstream, naturally occurring concentrations. This change coincides with the construction of a new sewage treatment facility.

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Concerns about acidification of surface waters arising from atmospheric release of sulphur dioxide (SO2) and nitrogen oxides (NOx) have been prevalent since the 1970s, when scientists first observed declining pH levels, particularly in southeastern Canada (Jeffries et al., 2003a). From 1980 to 2006, SO2 emissions in Canada and the U.S. declined by about 45% and NOx emissions declined by about 19% (Canada-United States, 2008)(Figure 32), due in part to declines in calcium which are also related to acid deposition (Canada-United States, 2008). Declines in calcium also threaten keystone zooplankton species (Jeziorski et al., 2008).Encouraging biological improvements have been seen in some locations (Snucins, 2003; Snucins and Gunn, 2003; Weeber et al., 2005; Environment Canada, 2005; Aurora Trout Recovery Team, 2006; Yan et al., 2008b). Even with chemical recovery, however, biological communities remain altered from their pre-acidification state because many factors beyond acidity influence biological recovery (Yan et al., 2008a; Yan et al., 2008b). The widespread devastation arising from deposition of pollutants carried by atmospheric transport (see also the example of contaminants) presents significant challenges beyond simple emission reduction targets, which challenge our knowledge of ecosystem recolonization and the re-establishment of ecosystem services.

Figure 32. Trends in sulphate levels and acidity (pH) in lakes at five intensive monitoring sites in southeastern Canada, 1972 to 2008.
Note that the strong response for Clearwater Lake (relative to the others) is related to its location very near the strong SO2 emission source (nickel smelter) at Sudbury.
two line graphs and a small map showing the locations and trends in sulphate levels and acidity
Source: updated from Jeffries et al. (2003b) by author
Long Description for Figure 32.

This figure is comprised of two line graphs and a small map showing the locations and trends in sulphate levels and acidity (pH) in lakes at five intensive monitoring sites in southeastern Canada for the years 1972 to 2008. These graphs show that although significant declines in lake sulfates followed closely behind the emission reductions, the recovery of natural levels of lake acidity, measured by pH, has been slow.

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Ecosystems have different sensitivities to acid depending upon their geology and soils. Thus the maximum level of acid deposition that terrain can withstand without harming ecological integrity, called the “critical load”, differs across ecosystems (Figure 33) (Jeffries and Ouimet, 2005). Acid-sensitive terrain is generally underlain by slightly soluble bedrock and overlain by thin, glacially derived soils (National Atlas of Canada, 1991) and has less buffering capacity.

Critical loads can be exceeded either when extremely sensitive terrain receives low levels of acid deposition or when less-sensitive terrain receives high levels of acid deposition. Figure 34 shows where critical loads have been exceeded in the Boreal Shield Ecozone+.

Figure 33. Combined aquatic and terrestrial atmospheric deposition critical load index for Canada, 2008.
Map of Canada displaying combined aquatic and terrestrial atmospheric deposition critical load index for Canada in 2008
Source: Jeffries et al. (2010a)
Long Description for Figure 33.

This map of Canada shows the combined aquatic and terrestrial atmospheric deposition critical load index for Canada for the year 2008. The critical load index ranges from greater than or equal to 1000 units per hectare per year to less than or equal to 100 units per hectare per year. This map shows the diversity of sensitivity to acidification across ecosystems in Canada. Larges areas sensitive to acid deposition are concentrated in the Atlantic Maritime Ecozone+ and the western end of the Boreal Shield Ecozone+.

Figure 34. Areas where the critical load has been exceeded in the Boreal Shield Ecozone+, 2009.
map of the Boreal Shield Ecozone+
Source: Jeffries et al. (2010b)
Long Description for Figure 34.

This map of the Boreal Shield Ecozone+ shows the areas where the critical load has been exceeded in the year 2009. The map shows a large area in the southeastern portion of the ecozone+ that has exceeded the critical load, much of which is in the highest category of exceedance of greater than 300 units over the critical load. This area is within the provinces of Ontario and Quebec surrounding the Great Lakes and St. Lawrence River. Other smaller areas of exceedance exist along the western boundary of ecozone+.

Despite having the lowest rates of acid deposition in eastern North America, the Atlantic Maritime Ecozone+ has some of the most acidic waters due to the poor buffering ability of the terrain (Clair et al., 2004; Clair et al., 2007). Since the 1980s, there has been no measurable recovery in pH despite declines in sulphur dioxide emissions. This has resulted in the most heavily impacted fish habitat in North America (Figure 35) (Clair et al., 2007). Atlantic salmon are highly sensitive to acidity, and by 1996, 14 runs in coastal Nova Scotia were extinct because of water acidity, 20 were severely impacted, and a further 15 were lightly impacted (Watt et al., 2000). Recovery of water chemistry and ecology is expected to take several more decades in Nova Scotia than in other parts of Canada (Watt et al., 2000; Clair et al., 2004; Clair et al., 2007).

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Figure 35. Impact of acidification on Atlantic salmon, 1996
map of Nova Scotia shows the status of salmon rivers in Nova Scotia in 1996
Source: adapted from Watt et al. (2000)
Long Description for Figure 35.

This map of Nova Scotia shows the status of salmon rivers in Nova Scotia in 1996. The three statuses are: depletion in some tributaries, remnant population, and extinct run. The map shows that in 1996, 14 rivers along the south coast of Nova Scotia had extinct runs, mostly along the south west coast, 20 rivers, spread along the south shore and the Bay of Fundy, had remnant populations, and a further 15, mainly along the southeastern shore, had depletion in some tributaries.

While the acidification of lakes has largely been seen as an issue for the Boreal Shield and Atlantic Maritime ecozones+, concerns are being voiced about the potential vulnerability of areas in western Canada. In particular, the potential for critical loads to be exceeded in northwest Saskatchewan is a concern due to the high degree of acid sensitivity of many of the lakes in this area (68% of 259 lakes assessed in 2007/2008) and its location downwind of acidifying emissions from oil and gas developments (Scott et al., 2010) . Similarly, transportation-related sulphur emissions in southwest British Columbia are an emerging issue, with terrestrial critical loads exceeded in 32% of the Georgia Basin in 2005/2006 (Nasr et al., 2010).

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