Cause of the Metalimnetic Oxygen Maximum in Mountain Lake, Virginia

ABSTRACT

Mountain Lake, Virginia, is an alpine oligotrophic lake in the unglaciated southern Appalachians. This lake often exhibits a metalimnetic oxygen maximum at 6–10 m during late summer thermal stratification which has been attributed previously to the dense attached beds of Nitella at those depths. By contrast, we show that phytoplankton chlorophyll a and photosynthesis, but riot Nitella photosynthesis, correlate closely with the metalimnion oxygen maximum over four summers. Physical factors are unlikely causes. Specifically at the depths of the metalimnion in Mountain Lake, the biomass of Nitella is about I 1x that of the phytoplankton, but the photosynthetic productivity of the phytoplankton is about 25x that of the Nitella.