THE ROLE OF GLOETRICHIA-ECHINULATA IN THE TRANSFER OF PHOSPHORUS FROMSEDIMENTS TO WATER IN LAKE ERKEN

The abundance of Gloeotrichia echinulata colonies in the sediments of Lake Erken and their phosphorus content were investigated to determine the contribution of Gloeotrichia colonies to total sediment phosphoru s. Moreover, the potential size of the algal inoculum and the migation to the water during summer were estimated. The surplus phosphorus con tent of the resting colonies in the sediment was about 45% of total ph osphorus, which maximized at 8.5 mug P (mg dw)-1 or 81 ng P colony-1. The C:P ratio (by weight) in the early colonies appearing in the lake water was 50:1, while the ratio stabilized at 150 during the major mig ration period. The internal supply of surplus phosphorus was used duri ng the pelagic growth of the colonies. The internal phosphorus loading to the epilimnion of Lake Erken due to Gloeotrichia migration could, from the measurements of the increase in particulate epilimnetic phosp horus, be estimated at 40 mg P m-2 or 2.5 mg p m-2 d-1 in late July an d early August. Determination of the number of colonies in the sedimen t before and during the migration verified this value to be a conserva tive estimate of the internal phosphorus loading due to Gloeotrichia m igration to the epilimnion in Lake Erken. The sediment P content calcu lated from the P concentration in early epilimnion colonies resulted i n a value of 35 mug P (g dw)-1 as a maximum. This corresponds to only 3% of the total phosphorus content in Lake Erken sediment.