Paleolimnological analyses of cultural eutrophication patterns in British Columbia lakes

Diatom-based paleolimnological approaches were used to determine the effects of cultural impacts on eutrophication histories in four lakes from central British Columbia. Stratigraphic analysis of fossil diatoms in 210Pb-dated cores and inferences of past total phosphorus concentrations using diatom-based models were used to reconstruct the nutrient histories of Takysie, Tchesinkut, Francois, and Tyhee lakes. Diatom microfossils indicate that these lakes are probably naturally productive, but some nutrient enrichment has likely occurred in response to human development (since A.D. 1850), particularly in Tyhee Lake. However, in Tchesinkut and Francois lakes, some reduction in total phosphorus may have occurred in recent decades. Takysie, Tchesinkut, and Francois lakes have been dominated by planktonic diatoms indicative of high productivity (e.g., Stephanodiscus, Asterionella, Fragilaria crotonensis, Aulacoseira). Tyhee Lake has been dominated by benthic Fragilaria species, but Stephanodiscus minutulus has increased in recent decades. These data were pooled with previously published paleolimnological data from British Columbia to summarize cultural eutrophication patterns in this region. Out of 11 British Columbia lakes considered, 10 were productive before human intervention, but 7 eutrophied further as a result of human activities. One lake exhibited no obvious post-1850 change in diatom assemblage, suggesting little human impact on water quality. In three of the lakes, recent improvements in water quality may have occurred in response to recent mitigation efforts.Key words: eutrophication, paleolimnology, British Columbia, diatoms, lakes, mining.