Vertical Profile of Alkaline Phosphatase Activity in the Water Column of a Dam Reservoir

Water quality parameters in the water column of a dam reservoir were measured monthly in 2001. From July to November, the vertical profiles of alkaline phosphatase activity (APA) and related parameters were examined in detail. APA increased during the summer in epilimnion while it was almost stable in hypolimnion. A small increase in APA was observed at a depth immediately above the bottom of the lake. APA fluctuation was independent of soluble reactive phosphorus. It was assumed that APA is not indicative of the phosphorus status of aquatic microorganisms in the lake. A positive correlation was observed between chlorophyll a content and APA in the photic zone. In the aphotic zone, APA correlated positively with the colony count of heterotrophic bacteria, but not with microscopic total bacterial count.