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Attached algae as indicators of water quality in phosphorus enriched Kootenay Lake, British Columbia Ennis, Gordon Leonard


Kootenay Lake receives high phosphorus loads to its south end and low phosphorus loads to its north end. These loading differences, combined with the lake's 105 km long fjord morphology, should result in a regional trophic gradient in the lake. I studied attached algae to assess how well they supplemented nutrient data in providing a more accurate measure of regional water quality differences. Algal abundance, phosphorus storage, production, species composition and distribution were measured at up to 30 locations in the rocky littoral zone of Kootenay Lake. In addition, physical parameters were measured and water samples were analyzed for major nutrients, anions and cations. Loadings of total dissolved solids, calcium, and sodium are also highest to the south end of the lake, and concentration gradients of these biologically conservative elements conform to the expected pattern. On the other hand, dissolved and particulate inshore phosphate readings, although high, did not exhibit regional variations. Attached algae remove large amounts of phosphorus for growth, altering phosphorus concentrations in the lake. Also, attached algae store surplus phosphorus within their cells, more phosphorus being stored in the regions of highest phoshate loadings (over 1.0 μg P mg⁻¹ dry weight algae) than elsewhere. South arm algae had the highest chlorophyll "a" levels, organic weights and production rates. Their results were typical of eutrophic waters. In contrast, north arm algae were less abundant, had lower growth rates, and were typical of mesotrophic and oligotrophic waters. Eutrophic indicator species, such as the green alga Cladophora aegagropila and the diatom Fragilaria construens, were abundant in the south half of the lake and generally absent or less common at other locations. Diatom cluster analyses divided the lake into regions, stations in areas of low phosphate loadings forming groups distinct from stations located near high phosphorus inputs. One must conclude that aqueous phosphorus concentrations, altered by attached algae, are inadequate indicators of Kootenay Lake's trophic gradient. Attached algae do exhibit regional variations consistent with the lake's expected trophic gradient and are therefore good indicators of water quality in phosphorus enriched Kootenay Lake.

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