Evaluation of the water quality monitoring network in São Francisco River - Brazil

Water quality information is essential for water managers and the design, assessment and optimization of monitoring networks are essential to ensure good quality information and better allocate resources. However, water managers often ignore the assessment and optimization steps of the existing monitoring networks. This work aims to evaluate the water quality monitoring network in 10 sub-basins of the São Francisco River Basin (SFRB), Brazil. The São Francisco River Basin is located in Northeast Brazil, a water stressed region, and is essential for the region's development. This river basin presents many asymmetries in terms of environmental and socio-economic conditions. In SFRB, the water quality is coupled with water quantity and there are multiple uses of water along the river course, being a potential region for water conflicts. This work combines literature review and data analysis, for the basic parameters, from 2001 to 2013. The main issues related to the degradation water quality in SFRB are derived from domestic sewage and solid residues, livestock, industrial and mining effluents, agricultural runoff, erosion, and natural salinization. It is important to highlight that those water quality threats are uneven distributed over the SFRB, characterizing some local issues. The issues that are common to the whole basin are the contamination by domestic sewage, pointed out by both literature review and data analysis. More than 25% of the valid observations showed levels that were not in conformity with the environmental standards. This problem was more evident in sub-basins SF1, SF2 and SF5 which, besides high levels of faecal coliforms, also appear to have punctual problems with organic loads; they are the only parts where it is possible to find BOD contents > 100 mg O2 L-1. In terms of temporal behaviour it was possible to identify a seasonal cycle for river flow, temperature and turbidity. Decreasing trends were found for total solids (in sub-basins 6 and 9), total phosphorus (sub-basins 6 and 10), turbidity, and trophic status index (both in sub-basins 9 and 10). According to the literature review and data analysis, relevant water quality parameters in SFRB are: suspendend solids, turbidity, dissolved oxygen, biochemical oxygen demand, nitrate, phosphate, faecal coliforms, ammonium, pH, chlorides, Al, Cu, Fe, Mn, Ni, Pb, Cd, Zn, fertilizers and pesticides. However, the importance of nutrient species can be higher since the available data presented many missing values, especially nitrogenates, hampering a proper analysis of these parameters. Water quality monitoring in SFRB and Brazil is still a challenge for water managers, lacking standardization of sampling frequencies, parameters and procedures. On the other hand, an effort on the national level is on course in Brazil, for the standardization of these basic features and expansion of the current network. The need to expand and standardize the monitozing activities has already been pointed out, but in SFRB there is still a gap on the monitoring of metals and agricultural chemicals, which are likely to causing chronic effects on the biota. This work helps in understanding the temporal and spatial behavior of significant aspects of the water quality in SFRB