Paleolimnological study of Elk Lake: 150-500 years of inferred water quality developments
Date
2002
Authors
Groeneveld, Roel
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Publisher
University of Victoria
Abstract
Elk Lake is a relatively small (246 ha) and shallow (>18m) lake situated on Vancouver Island (BC, Canada). It turned into a eutrophic system over the last 50 years, most likely due to anthropogenic disturbances of its watershed. Because the state of the ecosystem before settlement of the area is not known, the present situation cannot be compared to the original condition of the lake. This hampers present day water quality management because there is no reference value against which current ecological information and scenarios for the lake’s future can be compared.
Paleolimnological methods and techniques can enable researchers to retrieve historic data from sediment cores. This approach can be very useful for identifying the important developments in the state of the water quality of the Elk Lake ecosystem over the past 150 years, and for linking these to historic records on natural and anthropogenic disturbances that occurred in the watershed.
In this project, the sediment cores were retrieved form the lake using a modified gravity corer. 210Pb-dating of sediment subsamples was done using alpha spectrometry. Concentrations of nutrients, heavy metals and other elements were determined, and for each subsample the relative abundance of the present diatom species (or genera) was assessed as well. Furthermore, water quality data on Elk Lake for the past decades was retrieved from government databases.
Readily visible are the doubling and tripling of heavy metal concentrations in the lakes sediment between the first and second half of the 19th century. Sediment accumulation rates show a sharp increase from 1950 onward. The stable C:N ratio indicates that sources of organic matter present in the water column hardly changed over the past 400 years.
Of the present diatoms, Aulacoseira was the most dominant genus over the past centuries. During the last decades, eutrophic genera like Stephanodiscus became increasingly abundant. This is in line with public observations that the water quality of Elk Lake has been deteriorating since the mid 1980s.
The integration of the results of all analyses made it possible to identify three important events or developments affecting the lake’s condition: the 16th century megadrought; the settlement of the Greater Victoria area, and the intensified land use after World War II. Against expectations, the construction of both the Victoria Waterworks and the Patricia Bay Highway were not extractable from the results.
Advanced statistical analyses may be necessary to retrieve more information from the collected data set. In that aspect, the diatom data should be verified before this set of data is reused in other (follow-up) projects. After verification, this subset can be used for detailed inferences of water quality developments in Elk Lake.
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Citation
Groeneveld, R. Paleolimnological study of Elk Lake: 150-500 years of inferred water quality developments. (2002). Wageningen University Environmental Sciences and University of Victoria.