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primary production, Secchi depth, trophic classification, shallow lake


Changes in lake trophic state present concerns to water resource managers interested in maintaining water quality to support assigned beneficial uses. Contemporary methods of classifying lakes involve the use of surrogate indicators of production. However, some of these measurements are sensitive to wind induced resuspension of sediments, leading to inflated indications of basin production. This source of error is common to many shallow glacial lakes in eastern South Dakota and southwestern Minnesota. The objectives of this effort were to (1) estimate and define the trend in seasonal water column net and gross primary production and community respiration within a shallow pothole basin, (2) compare the mean net primary productivity values among three sub-basin sites and (3) evaluate trophic state classification using surrogate measures against actual production measurements. Water production as measured at three basin sites in Oak Lake, South Dakota, was evaluated using the light/dark bottle method once every two weeks throughout the 2010 growing season. Mean net primary productivity was 741 mg C•m-2•d-1and ranged from 35 to 1,462 mg C•m-2•d-1. Estimated to the light compensation depth, Oak Lake mean net primary production would lead to a eutrophic classification for this basin but would range between mesotrophic and hypereutrophic throughout the growing season. Trophic State Index values, derived from Secchi depth, ranged between 65 and 83, with a mean of 75, leading to an index classification of eutrophic or hypereutrophic. Secchi transparency explained 82% of the variation in net primary production while chlorophyll a explained only 17%. We concluded that Secchi transparency is an adequate surrogate for planktonic production despite consistently overestimating actual production levels within this basin.

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Proceedings of the South Dakota Academy of Science



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