Estimating Sediment-water P exchange in Lake Rio Verde (Paraná State, Brazil)

Monthly and annual water and phosphorus mass budgets were set up over the year 2010 for the Lake Rio Verde, Brazil. Limited data for the water budget was compensated using an interpolation method with data water budget data of a nearby reservoir. Thus, errors of ca. 1.5% were estimated for the water budgets. Dominant P mass input terms were inflows from the rivers and direct run off into the reservoir. Main output terms were P outflow via rivers and industrial water abstraction. Equalizing the P inputs and outputs leads to a sediment phosphorus uptake term were estimated at 35% of the annual P inflow, but with a possible weak correlation between monthly P sediment/water exchange and monthly precipitation figures. Sediment characteristics likely play an important role in the P sediment-water exchange. High concentrations of P in sediment pore water, and seasonal reductions in the oxidized surface layer of sediment suggests reduction of the potential of the sediment to retain P under current and likely, increased, P loads to the reservoir. Future management of the reservoir, therefore, requires continued monitoring and catchment management to mitigate nutrient both point source and diffuse loads. This necessitates an integrated approach to reduce pressures on the reservoir. Failure to address potential problems can lead to reduced water quality, with associated increased treatment costs for water supply