Efeito do uso e ocupação do solo sobre as variáveis limnológicas e a composição da comunidade em um rio intermitente

Abstract

The consequences of human activities on water resources have had repercussions on theway and quality of life of populations and communities of aquatic organisms, affectingthe environmental balance of areas drained by hydrographic basins, thus contributing tochange their landscapes at local scales, regional and global. The Intermittent rivers arecharacteristic for their flow variability, due to alternations between the two extremes offlow, flooding and drying, which create complex mosaics of dry channels and lenticwaters. Intensive land use raises concerns about the threats posed by anthropogenichydrological changes to the ecological integrity of intermittent rivers. Given the context,our study aims to assess how land use and occupation influence limnological variablesand the composition of communities in an Intermittent River. In chapter 1, we evaluatedthe dynamics of the physical, chemical and biological variables of the waters of anintermittent river and of an artificial surface reservoir through multivariate analysis andin response to the use and occupation of the soils of its hydrographic basin. The studywas carried out in the Cruxati River watershed in four study areas (three river areas andone artificial reservoir) and the images were obtained from the Landsat-8 satellite OLIsensor. The limnological variables measured were: pH, electrical conductivity, dissolvedoxygen, turbidity, nutrients (total nitrogen and total phosphorus) and chlorophyll a.Limnological variables were analyzed using Principal Component Analysis - PCA,Tukey's test and Cluster Analysis. The eutrophication of the studied areas was calculatedusing the Trophic State Index. The PCA allowed the selection of three componentsindicating the quality of surface water, river and artificial reservoir, explaining 88.57%of the total variance. The limnological variables responsible for the grouping were:electrical conductivity; dissolved oxygen and turbidity. The use and occupation of thesoil influenced the water quality of the river stretches. Anthropization influenced thedissolved oxygen content and the presence of arable areas caused an increase in turbidity.However, the most conserved landscape (artificial reservoir) was the one with the highestdegree of eutrophication due to the difference in hydrological dynamics between lenticand lotic environments. In chapter 2, evaluated the historical effects of land use andoccupation on limnological variables and the composition of aquatic macroinvertebratesand fish in six Intermittent microbasins. For this purpose, land use and land cover mapswere made, as watersheds 4, 5 and 6 have been going through a process of intensedeforestation and an increase in non-vegetated and agricultural areas, adding an alert tothe compromise of environmental quality and to the management of water resources inthe semi-arid region.