Modeling freshwater quality scenarios with ecosystem-based adaptation in the headwaters of the Cantareira system, Brazil

Abstract

Abstract. Although hydrologic models provide hypothesis testing of complex dynamics occurring at catchments, freshwater quality modeling is still incipient at many subtropical headwaters. In Brazil, a few modeling studies assess freshwater nutrients, limiting policies on hydrologic ecosystem services. This paper aims to compare freshwater quality scenarios under different land-use and land-cover (LULC) change, one of them related to ecosystem-based adaptation (EbA), in Brazilian headwaters. Using the spatially semi-distributed Soil and Water Assessment Tool (SWAT) model, nitrate, total phosphorous (TP) and sediment were modeled in catchments ranging from 7.2 to 1037 km2. These headwaters were eligible areas of the Brazilian payment for ecosystem services (PES) projects in the Cantareira water supply system, which had supplied water to 9 million people in the São Paulo metropolitan region (SPMR). We considered SWAT modeling of three LULC scenarios: (i) recent past scenario (S1), with historical LULC in 1990; (ii) current land-use scenario (S2), with LULC for the period 2010–2015 with field validation; and (iii) future land-use scenario with PES (S2 + EbA). This latter scenario proposed forest cover restoration through EbA following the river basin plan by 2035. These three LULC scenarios were tested with a selected record of rainfall and evapotranspiration observed in 2006–2014, with the occurrence of extreme droughts. To assess hydrologic services, we proposed the hydrologic service index (HSI), as a new composite metric comparing water pollution levels (WPL) for reference catchments, related to the grey water footprint (greyWF) and water yield. On the one hand, water quality simulations allowed for the regionalization of greyWF at spatial scales under LULC scenarios. According to the critical threshold, HSI identified areas as less or more sustainable catchments. On the other hand, conservation practices simulated through the S2 + EbA scenario envisaged not only additional and viable best management practices (BMP), but also preventive decision-making at the headwaters of water supply systems.

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

“…The thermotolerant coliforms presented, in general, smaller variation in the rivers with greater drainage areas (means of 5 to 9 10 3 CFU/100 mL) ( Table 2). Taffarello et al (2016) found a variation of thermotolerant coliforms from 14 CFU/100 mL to 1,000 10 3 CFU/100 mL in catchments with drainage areas between 10 and 1,000 km 2 in their study. In our research, drainage areas varied between 27 and 26,500 km 2 (Table 1), and the coliforms varied from <1 10 3 -3,300 10 3 CFU/100 mL.…”

“…The different sizes of drainage areas and the contrasting land use types can significantly influence the quantitative and qualitative aspects of water resources. Taffarello et al (2016) observed significant correlations between nutrient loads and drainage areas in watersheds located in the Cantareira System (São Paulo and Minas Gerais States). The authors concluded that these results can serve as a basis for regionalization studies of pollutant loads and also to predict such loads and the pollution level in general affecting local aquatic systems.…”

“…Marques et al 3/13 (TAFFARELLO et al, 2017), some Brazilian projects on payment for ecosystem services consider total phosphorus loads in the calculation of the value to be paid, such as Oásis (SOVACOOL, 2011;NUNES et al, 2013;YOUNG;BAKKER, 2014). Other initiatives have quantified total phosphorus loads through environmental monitoring activities, such as in the Projeto Produtor de Águas/PCJ (Water Producer Project) (VIANI; BRACALE, 2015) in order to aid in the parameterization of hydrological models (TAFFARELLO et al, 2018).…”

“…Although thermotolerant coliforms are less effective indicators compared to Escherichia coli (PARUCH; MAEHLUM, 2012) and to some pathogenic viruses, they have been used to assess water quality and possible faecal contamination from anthropogenic sources. The lower effectiveness of thermotolerant coliforms as water quality indicators is associated to their lower resistance to several environmental conditions and significant variability in relation to different drainage areas (TAFFARELLO et al, 2016). However, thermotolerant coliforms are still used as indicators of faecal contamination in Brazilian water bodies.…”

“…A complementary approach to the qualitative-quantitative integration presented in our paper may be the Hydrological Services Index (HSI) developed by Taffarello et al (2018). HSI is a composite index, determined from qualitative-quantitative frequency curves Marques et al 9/13 that incorporate the gray water footprint (HOEKSTRA et al, 2011), i.e.…”