Osoyoos Lake Sediment Core Project

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University of British Columbia - Okanagan

Project Description:

In 2007 at the Osoyoos Lake Water Science Forum, scientists, researchers, First Nations and political leaders met to discuss the current condition of Osoyoos Lake and its future. Participants identified the need for better historical data as a priority. To address this need, a proposal for collaborative research was submitted to the Okanagan Basin Water Board, backed by the British Columbia Ministry of Environment, Osoyoos Lake Water Quality Society, Okanagan Nation Alliance, and the University of British Columbia Okanagan. The partners sought to reconstruct historical nutrient concentrations in Osoyoos Lake from palaeoenvironmental data – specifically through pigment and diatom analyses on dated sediment cores collected from the north and south basins. Some palaeoecological research had been conducted at Osoyoos Lake many years earlier, as a part of the Okanagan Basin Study (Anderson, 1973; Pinsent & Stockner, 1974), and as an Okanagan University College student project (Ryder 1994), but recent advances in palaeoecological methods now facilitate a much more detailed assessment of lake nutrient levels and human impacts.

To obtain better historical information on nutrient loading to Osoyoos Lake, sediment cores were collected from the north and south basins of Osoyoos Lake in June 2008. A special method, known as 210Pb dating was used to develop a chronology for the cores, and to estimate rates of sediment accumulation. Changes in algal pigment concentrations and diatom communities, as preserved in the cores, were used to infer changes in algal production and Total Phosphorus (TP) concentrations since European settlement. The pigment data and diatom-inferred TP levels for Osoyoos Lake generally indicate mesotrophic conditions over the past ~200 years, with highest levels in the north basin between ~ 1950 to 1990, and in the south basin from ~ 1960 to 1990. Post-1990 the diatom-inferred TP values decrease, corresponding to a similar finding in measured phosphorus levels. Other factors include climatic variability, which can influence the ice-free period and consequently other limnological variables. Climate and its influence on nutrients, water column stability and the ice free period is likely one of the forcing factors influencing the abrupt increase of C. comensis in both basins. This study scientifically confirms the changes in water quality over the past 200 years, and shows the effects of recent human activity around the lake. The method of the study could be used to understand trends in other water bodies in the Okanagan.

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