Paleolimnological analysis of sediments from Killarney Lake, Manitoba

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Richmond, Kelly-Anne
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Sediment stratigraphic analyses of plant pigments, fossil diatoms, and selected chemical parameters were used to infer postglacial trends in primary production in Killarney Lake (southwestern Manitoba). Three 2.7 to 2.8 meter long cores and three surficial (top 30 cm) cores were collected from the lake during 1992 and 1993. The cores were predominantly organic, d rk olive grey silt, although the bottom of one long core contained coarse sand and gravel; a radiocarbon dated stratum immediately above this layer indicates the lake basin is at least 4,700 years old. The stratigraphic profiles of organic matter, phosphorus, chlorophyll, carotenoid, and diatom concentrations indicate that initially the lake was shallow with low primary production. Water levels and primary production began to rise in Killarney Lake likely in response to a cooler and wetter climate about 3,900 years BP. By about 2,100 years BP a deep lake with low primary production existed. A change in the climate about 1,200 years BP again caused low water levels and increased primary production. Water levels increased again about 500 years BP but did not reach the level of the previous deep water stand (2,100 years BP). Primary production was low at this time but showed a trend toward increasing production during the last 100 years. The most recent phase in the history of Killarney Lake, which began about 1940AD, was indicative of stable conditions relative to earlier periods, during which time only minor fluctuations were observed in sediment chemistry and pigments. In an effort to reduce chronic cyanobacterial blooms, the Town of Killarney's long history of copper sulphate use has resulted in very high surface sediment (top 2 cm) copper levels. Collectively, these analyses indicate that Killarney Lake has been naturally productive for at least the last five millennia.