Experimental Lakes Area

FIGURE 4.2 Concentrations of MeHg (mean 1 standard error) in zooplankton from Lake 240 of the Experimental Lakes Area (northwestern Ontario, Canada), showing seasonal variation during summer and pronounced rapid increases in mean concentration after the fall overturn. (Source Michael J. Paterson, Fisheries and Oceans Canada, Winnipeg, Manitoba, unpublished data.)... 

Malley, D. F. Chang, P. S. S. Schindler, D. W. Decline of Zooplankton Populations following Eutrophication of Lake 227, Experimental Lakes Area, Ontario 1969-1974 Dept. Fisheries Oceans, Freshwater Institute, Winnipeg, Manitoba, 1977. 

Rudd et al. (24) reported disruption of several processes in the nitrogen cycle during experimental acidification of Lakes 223 and 302S in Ontario s Experimental Lakes Area (ELA). In particular, they reported the inhibition of nitrification. 

Existing data lend mixed support to the hypothesis that sulfate reduction is limited by availability of electron donors. Laboratory studies have shown that sulfate reduction in sediments can be stimulated by addition of carbon substrates or hydrogen (e.g., 85, 86). Increases in storage of reduced sulfur in sediments caused by or associated with addition of organic matter (108, 109) also have been interpreted as an indication that sulfate reduction is carbon-limited. Addition of nutrients to Lake 227 in the Experimental Lakes Area resulted in increased primary production and increased storage of sulfur in sediments (110, 111). Natural eutrophication has been observed to cause the same effect (23, 24, 112). Small or negligible decreases in sulfate concentrations in pore waters of ultra-oligotrophic lakes have been interpreted... 

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. 

For lakes, relationships between DOC concentration and some measure of the relative size of the drainage area (e.g., drainage area/lake area ratio) and between DOC concentration and water residence time can be used to estimate the importance of autochthonous DOC by extrapolation. In the study of Experimental Lakes Area lakes by Curtis and Schindler (1997), the y intercept of the DOC concentration versus catchment/lake area ratio (the DOC value at minimal catchment area) is approximately l-2mgL 1. In the same study, the asymptote of the DOC concentration versus water residence time relationship at infinitely long residence times is roughly 2-3 mg L-1. This would suggest that for lakes in this region, autochthonous sources account for perhaps as much as 3 mg L 1 of the DOC present. 

Brunskill GJ, Wilkinson P. 1987. Annual supply of uranium-238, uranium- 234, thorium-230, radium-226, lead-210, polonium-210 and thorium-232 to lake 239 (Experimental Lakes Area, Ontario, (Canada) from terrestrial and atmospheric sources. Can J Fish Aquat Sci 44(Suppl l) 215-230. 

Figure 15.9. Phosphorus limitations in lakes, (a, b) In experimentally fertilized lakes of the experimental lakes area of the Freshwater Institute in Winnipeg (Environment Canada), ratios of mean annual concentrations C/P and N/P tend to become constant. (From Schindler, 1977.) In (a) we see that the C content increases as a consequence of P addition to the lakes, while (b) illustrates that the N content of a lake increases when the P input is increased, even when little or no nitrogen is added with fertilizer. Each point represents the results of a different lake.

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. 

P.R. Leavitt, D.L. Findlay (1994). Comparison of fossil pigments with 20 years of phytoplankton data from eutrophic Lake 227, Experimental Lakes Area, Ontario. Can. J. Fish. Aquat. Sci., 51, 2286-2299. 

D.W. Schindler (1971). Light, temperature and oxygen regimes of selected lakes in the Experimental Lakes Area, Northwestern Ontario. J. Fish. Res. Bd. Can., 28,157-169. 

In experimental fertilization studies at the Experimental Lakes Area in northwestern Ontario, Jeremiasson et al. (1999) compared rates of gas exchange, wet and dry deposition. 

Figure 5. Rates of PCB transfer proces.ses (mg year ) are shown for the experimentally fertilized Lake 227 from the Experimental Lakes Area, Ontario. Data are from Jeremiasson et al. (1999).

In addition to qnantification of organic constituents directly reflected in the MR absorbance spectra, constitnents not directly observed from the NIR spectra have been quantified. The success of these calibrations probably depends on correlation between the particnlar constituents (e.g., heavy metals), and organic components reflected in the NIR spectra. Malley Williams (1997) modelled the metal composition in the sediments of Lake 382 in the Experimental Lakes Area in north-western Ontario, Canada. The predictive power of the calibration models was generally very good. For instance, the between NIR-predicted metal concentrations and metal concentrations analysed by conventional chemical methods were 0.93 for Zn and Mn, 0.91 for Cu, 0.88 for Ni, 0.86 for Fe, and 0.81 for Pb,... 

---