Boreal lakes

FIGURE 4.3 Recent changes in concentrations of total mercury in axial muscle of walleyes from 13 boreal lakes in northwestern Ontario and Manitoba, Canada. Standardized concentrations for 50-cm walleye sampled during 1996-2000 are plotted against standardized concentrations for fish sampled during 1977-1983 (data are for reference lakes reported in Johnston et al. 2003). Each point below the diagonal line, which has a slope of 1.0, represents a lake where the standardized concentration declined between the 2 sampling intervals. 

Johnston TA, Leggett WC, Bodaly RA, Swanson HK. 2003. Temporal changes in mercury bioaccumulation by predatory fishes of boreal lakes following the invasion of an exotic forage fish. Environ Toxicol Chem 22 2057-2062. 

Even within the subset of boreal lakes there is probably a direct relationship between external inputs of organic matter and their importance to zooplankton (Meili, M. Fry, B. Kling, G. W. unpublished data). In the case of Lake N2 and other upland arctic lakes, thermokarst processes and active erosion of shoreline peat banks are much less important than they are in coastal plain lakes (62, 75, 103). In addition, DOC made up less of the total organic carbon in Lake N2 than it did in the humic lake studied by Hessen (72) the ratio of DIC DOC.POC in Lake N2 was 25 8 1 (Table II), whereas in the humic lake the ratio was 1.6 21 1. The lower loading rates of particulate carbon and the smaller relative amounts of DOM in Lake N2 may explain the observation that pelagic productivity depended mainly on new algal production. 

Suominen KP, Liukkonen M, Salkinoja-Salonen M (2001) Origin of Organic Halogen in Boreal Lakes. J Soils Sediments 1 2... 

France, R., H. Culbert, and R. Peters. 1996. Decreased carbon and nutrient input to boreal lakes from particulate organic matter following riparian clear-cutting. Environmental Management 20 579-583. 

Schindler, D. W., P. J. Curtis, B. R. Parker, and M. P. Stainton. 1996. Consequences of climate warming and lake acidification for UV-B penetration in North American boreal lakes. 

Climate changes may also have significant effects on lake DOC concentrations. In a 20-year study of boreal lakes in the Experimental Lakes Area of northwestern Ontario, Schindler et al. (1997) reported that lake DOC concentrations declined by 15-25% as mean annual temperatures increased by 1.6°C, precipitation declined by 40%, and runoff declined by 70% due to increased evaporation and decreased precipitation. The primary reason for the decline in lake DOC was reduced inputs of DOC from terrestrial catchments, although in-lake removal of DOC also increased slightly via either increased acidification, UV light penetration, or microbial degradation. 

France, R., R. Steedman, R. Lehmann, and R. Peters. 2000. Landscape modification of DOC concentration in boreal lakes implications for UV-B sensitivity. Water, Air, and Soil Pollution 122 153-162. 

Hurme TS, Puhakka JA. 1997. Polychlorinated biphenyl biotransformations by aerobic and anaerobic boreal lake sediment microorganisms. In Alleman BC, Leeson A, eds. In situ and on-site bioremediation Volume 2. Columbus, OH Battelle Press, 427-432. 

D.W. Schindler, S.E. Bayley, B.R. Parker, K.G. Beaty, D.R. Cruikshank, E.J. Fee, E.U. Schindler, M.P. Stainton (1996). The effects of climatic warming on the properties of boreal lakes and streams at the Experimental Lakes Area, northwestern Ontario. Limnol. Oceanogr., 41,1004-1017. 

M.A. Xenopoulos, D.W. Schindler (2001). The environmental control of near-surface thermoclines in boreal lakes. Ecosystems, 4,699-707. 

E.M. Watkins, D.W. Schindler, M.A. Turner, D. Finlay (2001). Effects of solar ultraviolet radiation on epilithic metabolism, and nutrient and community composition in a dear-water boreal lake. Can. J. Fish. Aquat. Sci., 58,2059-2070. 

As a result of a major reduction in the emission of acidifying S and N compounds since the 1970s in Europe (see Section 7.4.5), acid deposition on boreal lakes and their catchments has also strongly declined. Recently, Stendera and Johnson (2008), assessing the recovery of boreal lake ecosystems from acidification, used different indicators (water chemistry, biota), different trophic levels (primary producers and consumers) and different habitats within the lakes (pelagic, benthic) to compare the response of both acidified and reference lakes to the reduction in acid deposition. 

Enhanced production of MeHg in boreal lake ecosystems. 

Stendera, S. and Johnson, R.K. (2008) Tracking recovery trends of boreal lakes use of multiple indicators and habitats. Journal of North American Benthological Society, 27 529-540 Stoddard, J.L. et al. (1999) Nature, 401, p. 575. 

Long-Term Changes in Boreal Lake and Stream Chemistry Recovery From Acid Deposition and the Role of Climate... 

---