J Environ Eng Sci 13:117–126

The behaviour of phosphorus forms and loads under conditions of drought and rainfall and based on real measurements was studied in the Timbú River Basin, an important water source in the metropolitan region of Curitiba, Paraná State, Brazil. Quantitative and qualitative chronosequential analyses were performed in different points of the river during a period of drought and every 5–10 min before, during and after rainfall in the basin. The main results showed that the phosphorus load at the river mouth during drought periods was 2·8 kg/d, five times lower than the normal flow of 8·8 kg/d. At its peak during medium rainfall, the load reached 175·3 kg/d, highlighting the significant influence of diffuse loads in the catchment area. The parameters total phosphorus and reactive phosphorus differed based on river compartments and land uses, mainly urban, agricultural and preserved areas. Therefore, basin action plans must consider varying weather conditions, including both drought and rainy periods, and implement long-term monitoring programmes.