The Contribution of Macrophytes to the Metalimnetic Oxygen Maximum in a Montane, Oligotrophic Lake

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Abstract
Mountain Lake, Virginia [USA], is a montane, oligotrophic lake and is the only natural lake in the unglaciated portion of the southern Appalachians. The lake consistently exhibits a strong metalimnetic O2 maximum during summer thermal stratification. Dense beds of rooted macrophytes, primarily Nitella flexilis, grow around the circumference of the lake to a depth of 11 m. There was no correlation between the positive heterograde O2 curve and limnetic phytoplankton density or estimates of primary productivity. The strongest association existed between the metalimnetic O2 maximum and standing crop dry weights of the macrophyte community. All transects across the macrophyte beds indicated the greatest standing crop to be between depths of 6-10 m. Variation in total standing crop between transects is attributed to slope angle of the basin, substrate and direction of slope, in order of importance.