Postsettlement eutrophication histories of six British Columbia (Canada) lakes

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Abstract
Eutrophication is a serious problem in many British Columbia lakes. However, long-term nutrient data are rare or unavailable for most lake systems, so the natural, predisturbance characteristics of lakes are unknown, as are the trajectories of past environmental change. We used paleolimnological analyses of diatoms to quantitatively assess eutrophication trends for approximately the last 150 years in six British Columbia lakes. A transfer function was used to infer past lake-water total phosphorus concentrations from the sedimentary diatom assemblages in210Pb-dated sediment cores: all of the lakes had relatively high total phosphorus levels (> 13 μg/L) prior to European settlement. Three of the lakes showed significant eutrophication since that time, whereas the others were only mildly affected. Total phosphorus inferences using the transfer function satisfactorily estimated the modern total phosphorus concentrations of our six study lakes. Minor quantitative problems arose when some fossil assemblages provided poor analogues to the calibration function, but eutrophication trends were still clearly apparent. Our results confirm that some British Columbia lakes have suffered considerable eutrophication as a result of anthropogenically related nutrient inputs, while others, although situated within human-influenced regions, have been relatively unaffected. These results can now be used to help set realistic goals for restoration projects.

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