Influence of land use and occupation on the water quality of the Biritiba Mirim Reservoir (Upper Tietê Producer System/SP)

Abstract

The metropolitan region of São Paulo has around 21 million inhabitants, and eight water producer systems are used to supply water to this population, including the Upper Tietê Producer System, which is responsible for 15% of the supply and composed of five reservoirs. Agricultural activities are the economic base of the Biritiba Mirim reservoir and land use to this end is sometimes extended to its surroundings, which might compromise water quality due to the excessive use of fertilizers, and pesticides, among others. This study aimed to assess water quality from the Biritiba Mirim reservoir, in the city of Biritiba Mirim/SP, and its relationship with land use and occupation. We performed four quarterly collections (August and November 2019 and February and May 2020) in ten sampling stations spatially distributed in the reservoir (close to the area with the presence of riparian forest and agricultural areas). We measured the physical, chemical, and microbiological variables of water, in addition to the Water Quality Index and the Trophic State Index. The analyses revealed that all variables are within the limits established by the CONAMA 357/2005 legislation, except for phosphorus total, whose values, in two different areas, reached concentrations above the legal limit. We highlight the highest values were recorded in areas surrounding crops, as well as the higher concentration of total phosphorus in such areas, which might be linked to phosphate fertilization, carried out at each cultivation, whose residues end up loaded inside the water body.