Análise da fragilidade ambiental sazonal integrando a equação revisada de perda de solos e a qualidade das águas superficiais

Abstract

Interventions in the different components of the environment, such as relief, soil and land cover, can result in the appearance of erosion and in the impairment of water quality and system functionality, with this intervention being greater or lesser depending on the intrinsic characteristics of the environment, in order words, of environmental fragility. These modifications may come from anthropic interventions or even from natural causes, in association with climatic seasonality. Thus, the central hypothesis to be investigated starts from the premise that the state of seasonal environmental conservation, evaluated from the environmental fragility, using the estimate of soil loss and surface water quality as a participatory element of the environmental analysis, can reflect the state for the conservation of the hydrographic basin of the Urutu stream – MS. Thus, this work aimed to evaluate the environmental fragility in a seasonal way based on the implementation of variables such as rainfall erosivity, soil erodibility, slope, Vegetation Index by Normalized Difference – IVDN and surface water quality. Based on this set of these variables, it was also carried out, on the seasonal influence, the estimate of soil loss from the revised soil loss equation and the classification of water quality through resolution 357/2005 of the National Council for the Environment - CONAMA. In this way, the environmental analysis models made from the seasonal influence, resulted in the distribution of their classes spatially from the sensitivity of the environment to soil loss. The results showed that there was an influence of seasonality on environmental fragility, soil loss and also on water quality, with rainfall erosivity and NDVI being one of the main factors responsible for this difference. In detail, among the seasons, spring was the season that resulted in the largest area classified as high (27%) and medium (46%) environmental fragility (27%), with an estimated soil loss averaging 0.3733 t. ha-1month-3 and with water quality class II. Summer was the second season with the highest areas of high (20%) and medium (42%) environmental fragility, but it had the highest estimated rate of soil loss, with an average value of 0.4393 t.ha-1month-3. Soil losses in autumn (0.07683 t.ha-1month-3) and winter (0.0569 t.ha-1month-3) showed the lowest rates, with the largest areas classified as low class of fragility environmental and resulting in class II water quality. The validation of the seasonal models of the environmental analysis resulted in the detection of areas that need intervention, regarding the control of soil loss. From the seasonal validation of environmental fragility, by points of erosion, the seasonal classification of water quality was used as a participatory variable in the environmental analysis. For this, the compartmentalization of the hydrographic basin was the main condition for the environmental analysis, as this allowed there to be no generalization of the classification of both environmental fragility and water quality. Furthermore, water quality as a participatory variable of environmental fragility showed a direct relationship with areas of natural/planted forests, with the exception of spring. In general, the assessment of environmental fragility using this set of variables and in association with climate influence (seasonality) reflected the state of conservation of the BHCU.