Abstract
Further objectives were to determine the different patterns of land use and occupation within the microbasin formed by these rivers, and to assess the influence of the quantity of riparian vegetation on the presser/vation of the aquatic ecosystems. The studied basin extends over a total area of 77.75 km2, of which 92.98% comprised agriculture (44.11%) and native forest (48.87%). The drainage area of the sampling site P1 was 87.57% covered by crops, and so was 22.30% of the area of the sampling site P4. However, the application of the Tukey test (p < 0.05) to the data for thermotolerant coliforms (also known as faecal coliforms - FC) led to the inference of similarity (p<0.05) between the sampling sites P1 and P4. This indicates that the agriculture impact is probably mitigated by the area of native forest around the source of the spring that feeds P1. From the sampling site P2 to P3, the drainage area showed an improvement in the preservation of natural areas, with the area covered by crops decreasing to 44.41% and an increase of 47.93% in the land covered by native forest. Sampling sites P2 and P3 also showed significant similarity between their annual averages for FC, displaying a reduction in the concentration of these microorganisms from 2.15 to 1.61 (× 10³ MPN/100 mL), which again provided evidence of the positive influence of the recovery of plant cover within the drainage area. Recognising that the other sampling sites with very similar land use characteristics did not display significant alterations in the water quality, the influence of the vegetation and its role as a buffer were made evident, since for these sampling sites most water sources are not bereft of surrounding vegetation. In this way, the lack of correlation (Pearson and Spearman) between the seasonal variations for the assessed water quality parameters allowed us to provide evidence for the positive effect of riparian vegetation in the maintenance of the integrity of aquatic ecosystems and the preservation of the water quality. The water quality comprises physical, chemical, and microbiological parameters related to the different land uses within the river basin. Key words: Monitoring, total and thermotolerant coliforms, biological indicators, human impact, water quality, multifactorial analysis.
Highlights
Hydrographic basins where farming takes place have higher concentrations of sediments and nutrients in their flowing waters in comparison to hydrographic basins protected by native vegetation (Allan, 2004)
The area of the São João River Basin whose quality was monitored through P1 was influenced primarily by Agriculture Native forest Pasture and reservoirs Area of afforestation by exotic species Residential area Total area
The São João River Microbasin is composed of five different classes of land use: Native forest, pasture and reservoirs, agriculture, residential areas, and areas of afforestation by exotic species
Summary
Hydrographic basins where farming takes place have higher concentrations of sediments and nutrients in their flowing waters in comparison to hydrographic basins protected by native vegetation (Allan, 2004). The integrity of riparian forests lessens the removal of adjacent soil, the loss of aquatic habitats, and the decline of biological diversity by mitigating the effects of surface runoff (Berkman and Rabeni, 1987). When these functions are jeopardised by alterations in the composition of the riparian zone, this zone becomes unstable and may no longer be able to ameliorate changes in physical, chemical (Monaghan and Smith, 2012), and biological (coliforms) parameters of the water resources, which result from surface runoff caused by rainfall (Hong et al, 2010). In the case of small water basins, the extent and condition of the riparian vegetation can be used as hydrological indicators of the sustainability of human activities that are associated with different land uses (Lima and Zákia, 1998)
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