Análise dos efeitos naturais e antrópicos sobre os aspectos qualitativos da água na bacia hidrográfica do Rio Niquim

Abstract

Considering that knowledge of the variables that influence water quality and availability helps the management and better use of water resources, and that the use and occupation of soil in river basins is directly and indirectly related to the quality and availability of water in rivers, this study sought to analyze the natural and anthropogenic effects on the water quality of the Niquim River, located in the São Miguel Hydrographic Region. This research was divided into seven stages: I. Theoretical foundation; II. Diagnosis of the use and occupation of soil and water resources; III. Activity planning; IV. Survey of water use registration data; V. Basin mapping; SAW. Technical studies; VII. Assessment and presentation of the prognosis, divided into analysis of land use and occupation, quantitative and qualitative analysis of water, and the framework proposal. Quali-quantitative water monitoring was conducted at three collection points, the first point located in Lagoa Niquim (RNL); the second point located close to CASAL Station (RNEC) and the third point located close to the mouth (RNF), with monthly collections from July to December 2022. For each sample collected, physical, chemical and microbiological analyzes were carried out, totaling 19 parameters. The results found were subjected to descriptive statistics and statistical tests. In the analysis of land use and occupation, the basin was divided into contribution areas, to associate land use and occupation and the water quality results at the monitoring points. In the three areas of contribution there is a predominance of sugarcane areas, this explains the organic load possibly related to organic vegetable or animal matter, and in the last point there is a contribution from the expanding urban area, evidenced by the non-conformity of the BOD5 parameters, 20, total coliforms and E.coli. In the qualitative analysis, in relation to temporal variation, the COD of the RNEC point was the only parameter that showed significant variations between the rainy and dry periods. Spatially, turbidity, conductivity, total alkalinity and E. coli showed significant variations along the river, between collection points, in the dry period. In terms of time, the analysis carried out with primary and secondary data corresponding to the period 2005-2022, chloride and E.coli showed significant reductions over the years. In the qualitative-quantitative analysis of water, the correlation between water parameters and flow showed a strong correlation for the parameters of DO, total coliforms and E. coli, at the RNEC point and salinity, BOD5.20, total coliforms, at the next point the mouth (RNF). Regarding the behavior of water quality parameters with flow variation, it was identified that, throughout the monitoring period at the RNEC point, the DO showed an inverse variation to the flow behavior, decreasing with the increase in flow and increasing with the flow reduction. At the RNF point, BOD5.20 showed behavior similar to the flow variation. The results of the analyzes were compared with the limits established by CONAMA Resolution nº 357/05. It was found that, in some sections, their quality and framing do not meet their preponderant uses. In the classification proposal, the sections are classified in class 1 and class 2; To this end, in section 1, the aim is to increase DO, and reduce BOD5.20 and ammonia nitrogen, through the preservation of forest formations to reduce the organic load in this section. In section 2, the aim is to reduce the parameters through the preservation of vegetated areas, mainly the riparian forest, to reduce the organic load in this section. In section 3, the parameters BOD5.20, ammonia nitrogen, DO and E.coli are above those allowed by the Resolution; To achieve this, it is necessary to correctly dispose of effluents, preserve green areas, plan land use and occupation.