TRANSPORT OF GROUNDWATER-BORNE PHOSPHORUS TO LAKE BYSJON, SOUTH SWEDEN

Lake Bysjon is a hypertrophic seepage lake, with groundwater as a main external source of phosphorus. Twelve groundwater samples from the vi cinity of the lake were high in phosphate (0.4 to 11 mg l-1, mean valu e 2.57 mg l-1 PO4-P), both within the riparian zone and in two shallow wells located upstreams the lake in the nearby village. Phosphorus so rption capacity of four sand samples measured with the Langmuir isothe rm method was low (7.3 to 121.1 mg kg-1 PO4-P), with the lowest values found within the riparian zone. It is suggested that the phosphorus o riginates from garden fertilizers and other human sources, and that th e low absorption capacity of the soils is caused by the leaching of ca lcium from the watershed, a process which started some 3000 years ago. Riparian zone itself has almost no retention capacity, and processes within it (e.g., redox-related) have only secondary importance for the transport of phosphorus to the lake.