SEDIMENTATION OF PHOSPHORUS IN LIMNETIC AND ESTUARINE ENVIRONMENTS IN THE RIVER ORE SYSTEM, NORTHERN SWEDEN

Sedimentation of phosphorus was studied during the spring flood in April and May 1991 in Lake Ortrasket and the Ore Estuary, northern Sweden. Lake Ortrasket has an area of 7.3 km2 and a mean depth of 22 m and is located 100 km from the coast halfways along the course of the River Ore. The river ends in a semi-closed low salinity estuary with an area of ca. 50 kM2 and a mean depth of 16 m. Sedimentation of phosphorus, iron and organic carbon were measured with sediment traps in Lake Ortrasket and in the Ore Estuary. Characterization of particulate phosphorus in river water, sediment trap material and sediments were performed by the sequential extraction procedure proposed by Hieltjes & Lijklema (1980). Apart from being an efficient trap for suspended particles including particulate phosphorus, Lake Ortrasket was shown to serve as a source for particulate material during spring 1991. The Ore Estuary, on the other hand, constitutes an efficient trap for the total supply of river-borne phosphorus during the spring flood period. Phosphorus was shown to be closely related to iron in particulate material in both the lake and the estuary. Adsorption of phosphorus on settling inorganic particles seems to be an important process, which is particularly pronounced in the estuary.