Phosphorus budgets and forms of phosphorus in the Sau reservoir sediment: An interpretation of the limnological record

The phosphorus compounds in the sediment of Sau reservoir have been analysed and related to the annual phosphorus budgets from 1965 to 1969. With the increase of eutrophy, the phosphorus inputs leave the water in two ways: to the sediment and to the water outflow. The second way becomes more important throughout the eutrophication process.Of the three phosphorus forms studied, apatite-P is related to annual water flow, which is also directly related to sedimentation rate. By contrast, the other two phosphorus forms (organic-P and inorganic non apatite-P) are linked to phosphorus outputs. These relationships enable us to propose an historical sequence for the sediment. Finally, the dating of sediment allows us to develop an equation relating the total phosphorus in the sediment to the annual phosphorus inputs and water flow into the reservoir (r = 0.94).