Phosphorus and thermotolerant coliforms’ loads in Brazilian watersheds with limited data: considerations on the integrated analysis of water quality and quantity

Abstract

Integrated analyses of the qualitative and quantitative aspects of aquatic ecosystems play an important role in decision making, which is linked to water resources management and promotion of ecosystem services. However, the possible advantages of such integration are still hampered by basic aspects, such as high uncertainties due to the partial and non-synchronized monitoring of discharges and observed concentrations of water quality variables. The lack of data has been limiting the adequate representation of a more accurate hydrological regime, which is in turn possibly affected by the potential effects of land use and size of drainage areas. The aim of this research was to discuss the advantages of the integrated analysis of qualitative and quantitative data from water bodies. Under different specific discharge regimes (L.s -1.km-2), we assessed the total phosphorus (TP, t.day-1 .km-2) and thermotolerant coliforms’ (TC, CFU.day-1.km -2) specific loads in rivers with different drainage areas (27-26,500 km 2) and land uses. We compared such loads with the admissible specific loads for these variables, which were estimated based on long-term average discharges and water quality guidelines (i.e., Brazilian environmental standards). Based on data from 2001-2013, we sought to contribute to the qualitative and quantitative analysis of surface waters, focusing on the discussion of the results on critical thresholds of duration and critical loads and discharges. The results showed the existence of significant time intervals with conflicts between the specific admissible and observed loads. This non-compliance varied between 10 and 100% of the duration of the regime for TP, and between 25 and 100% for TC, with a more critical situation observed in rivers with smaller drainage areas. The critical loads ranged from 1 10-4 to 8 10-3 t.day-1.km-2 (TP) and 1 10-2 to 1 10-1 CFU.day-1.km-2 (TC). Although a relatively limited dataset was considered (total N=1,402), the significant variations in discharges and critical loads highlighted the need for considering how these dynamics would affect the traditional methodology for estimating ecological flows, whose current approach is almost exclusively quantitative.

Phosphorus mass balance and input load estimation from the wet and dry periods in tropical semiarid reservoirs

“…The TP load presents some well-known characteristics and strong correlations with parameters related to the catchment or the reservoir. Firstly, larger catchments have the potential to produce more TP load (Marques et al 2019). Additionally, there is a relation between phosphorus pollution from nonpoint sources with flow conditions, as runoff events widely contribute on P load to rivers (Greene et al 2011).…”

Aspects that should be considered in a possible revision of the Brazilian Guideline Conama Resolution 357/05

“…The structure of the CR is composed of unique values for concentrations and reference discharges, a situation that confers challenges in relation to ecological flows proposition in a determined hydrographic basin. 8 The first element that deserves attention is the fact that CR does not consider the different ecoregions in the country as well as the information related to biotic communities, 6,9 and intrinsic characteristics, such as the high concentrations of Fe and Mg in water bodies inserted in Brazilian savannas areas.…”

A New Approach to Use Load Duration Curves to Evaluate Water Quality: A Study in the Doce River Basin, Brazil

“…For instance, the LDCs can easily portray the streamflow classes in disagreement with the regulations, and therefore, shed light on best management practices to improve water quality [14,15]. In that context, pollution events related to shorter permanence (i.e., high flows) are usually associated with diffuse pollution sources, whereas events related to higher permanence (i.e., low flows) are commonly linked to point source pollution [11,13,16].In Brazil, there have been some attempts to use LDCs, but the frequent non-synchronous streamflow and water quality sampling represented a limitation [17][18][19][20]. For instance, FDCs were developed for rivers in the state of São Paulo, Minas Gerais and Paraná (SP) but considered the monthly average of streamflow in the estimation of the load [18,20].…”

“…In that context, pollution events related to shorter permanence (i.e., high flows) are usually associated with diffuse pollution sources, whereas events related to higher permanence (i.e., low flows) are commonly linked to point source pollution [11,13,16].In Brazil, there have been some attempts to use LDCs, but the frequent non-synchronous streamflow and water quality sampling represented a limitation [17][18][19][20]. For instance, FDCs were developed for rivers in the state of São Paulo, Minas Gerais and Paraná (SP) but considered the monthly average of streamflow in the estimation of the load [18,20]. The monthly average makes the day-to-day flow variation smoother, thereby, hampering the comparison between the loading capacity and the observed pollutant load into the river.A relevant application of LDCs refers to the quantification of a potential load reduction per hydrological regime.…”

“…In Brazil, there have been some attempts to use LDCs, but the frequent non-synchronous streamflow and water quality sampling represented a limitation [17][18][19][20]. For instance, FDCs were developed for rivers in the state of São Paulo, Minas Gerais and Paraná (SP) but considered the monthly average of streamflow in the estimation of the load [18,20]. The monthly average makes the day-to-day flow variation smoother, thereby, hampering the comparison between the loading capacity and the observed pollutant load into the river.…”