Paleolimnological analyses of cultural eutrophication patterns in British Columbia lakes

Diatom-based paleolimnological approaches were used to determine the effect s of cultural impacts on eutrophication histories in four lakes from centra l British Columbia. Stratigraphic analysis of fossil diatoms in Pb-210-date d cores and inferences of past total phosphorus concentrations using diatom -based models were used to reconstruct the nutrient histories of Takysie, T chesinkut, Francois, and Tyhee lakes. Diatom microfossils indicate that the se lakes are probably naturally productive, but some nutrient enrichment ha s likely occurred in response to human development (since A.D. 1850), parti cularly in Tyhee Lake. However, in Tchesinkut and Francois lakes, some redu ction in total phosphorus may have occurred in recent decades. Takysie, Tch esinkut, and Francois lakes have been dominated by planktonic diatoms indic ative of high productivity (e.g., Stephanodiscus, Asterionella, Fragilaria crotonensis, Aulacoseira). Tyhee Lake has been dominated by benthic Fragila ria species, but Stephanodiscus minutulus has increased in recent decades. These data were pooled with previously published paleolimnological data fro m British Columbia to summarize cultural eutrophication patterns in this re gion. Out of 11 British Columbia lakes considered, 10 were productive befor e human intervention, but 7 eutrophied further as a result of human activit ies. One lake exhibited no obvious post-1850 change in diatom assemblage, s uggesting little human impact on water quality. In three of the lakes, rece nt improvements in water quality may have occurred in response to recent mi tigation efforts.