METALIMNETIC GRADIENTS AND THE VERTICAL-DISTRIBUTION OF PHOSPHORUS INA EUTROPHIC LAKE

Analyses of the vertical distribution of phosphorus in a eutrophic lak e showed constant accumulation of soluble reactive phosphorus and tota l P in the hypolimnion following spring diatom blooming. The downward flux of phosphorus was realised mostly in spring due to high rates of sedimentation and aerobic decomposition of algal biomass. Nearly two t hirds of hypolimnetic phosphate-P accumulation had occurred before the hypolimnion became deoxygenated. An increase in soluble reactive P in the hypolimnion by a further 100 mg P m(-3) took place during summer, most probably due to internal P loading from bottom sediments. Distin ct gradients of phosphorus, chlorophyll, alkaline phosphatase activity and seston across the thermocline coupled with a low sedimentation ra te in the summer presented evidence for the barrier role of the metali mnetic zone in vertical fluxes of matter in a lake. Possible consequen ces of this phenomenon for phosphorus cycling in a lake are discussed.