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 theLake Rio Verde, Brazil. Limited data for the water budget was compensated using an interpolation methodwith data water budget data of a nearby reservoir. Thus, errors of ca. 1.5% were estimated for the waterbudgets. Dominant P mass input terms were inflows from the rivers and direct run off into the reservoir. Mainoutput terms were P outflow via rivers and industrial water abstraction. Equalizing the P inputs and outputsleads to a sediment phosphorus uptake term were estimated at 35% of the annual P inflow, but with a possibleweak correlation between monthly P sediment/water exchange and monthly precipitation figures. Sedimentcharacteristics likely play an important role in the P sediment-water exchange. High concentrations of P insediment pore water, and seasonal reductions in the oxidized surface layer of sediment suggests reduction ofthe potential of the sediment to retain P under current and likely, increased, P loads to the reservoir. Futuremanagement of the reservoir, therefore, requires continued monitoring and catchment management to mitigatenutrient both point source and diffuse loads. This necessitates an integrated approach to reduce pressures onthe reservoir. Failure to address potential problems can lead to reduced water quality, with associated increasedtreatment costs for water supply.