Changes in nutrient loads (N, P and Si) in the S？o Francisco estuary after the construction of dams

the aim of this study was to investigate the post-dam conditions of the loads and yields of dissolved inorganic nitrogen (din), orthophosphate (dip, silicate (dsi) and total phosphorous (tp) in the lower s？o francisco river estuary (ne-brazil) after the river was regulated to a constant flow by the dams. loads and yields of monthly measurements performed from november 2000 to march 2002 at a gauging station downstream of the dams (80 km from the coast) showed 4.1 x 103 t/yr and 0.006 t/km2 /yr of din, 0.2 x 103 t/yr and 0.002 t/km2 /yr of dip, and 448 x 103 t/yr and 0.71 t/km2 /yr of dsi, respectively. over the last 15 years, din loads reduced by 94 % and dsi by 31%. the river turned into an oligotrophic system with primary production limited by nitrogen and nutrient yields being among the lowest of brazilian coastal rivers.