Four analytical methods for determination of cation exchange capacity (CEC) in tropical soils were tested, aiming to define what the most appropriate based on the requirements: analysis time, degree of reliability and cost of operation. A total of 444 soil samples from the Amazon rainforest and Atlantic rainforest were analyzed in eleven soils types. Organic matter, pH and ions Na + , K + , Ca 2+ , Mg 2+ and H + +Al 3+ were also analyzed. The influence of the action of fire on the release of ions to the soil was also tested. The results indicated that there was a momentary increase in CEC in the soil after a fire. Tropical soils have a high humidity and acidity, contributing to an overall increase of CEC. Adverse climatic conditions in the tropics affect soil properties, so that practical methods and low cost have the advantage that they can be applied periodically to analyze the quality of the soil.
A compreensão do processo de expansão das atividades antrópicas, em bacias hidrográficas, se mostra fundamental nos dias atuais. No que tange ao problema da contaminação das águas subterrâneas, a análise do uso e cobertura do solo existente e das variáveis do meio físico podem auxiliar na compreensão e gestão desta problemática. O presente trabalho teve por objetivo elaborar a carta de potencial de contaminação de aquíferos por atividades humanas na bacia hidrográfica do Ribeirão do Meio (Leme, SP), abrangendo uma área de 246,81 km 2 na escala 1:50.000. A produção da carta englobou a análise do mapa de substrato geológico, a elaboração da carta de unidades aquíferas, da carta de declividades e de uso e cobertura do solo. Com o uso do software ArcGIS® e de uma metodologia de análise multicritério, chegou-se a uma classificação do potencial de contaminação envolvendo cinco classes (muito baixo, baixo, médio, alto e muito alto). No caso específico desta área, verificou-se que as classes de potencial médio (47,71%) e muito baixo (33,68%), foram mais representativas.
Degradation of hydrological conditions can adversely impact water resource quality and quantity. This degradation can generate social and economic losses, including losses for users outside the basin area. Therefore, studies focusing on surface runoff and accelerated erosion processes are needed to enable interventions that address degradation-induced challenges.In the present study, the surface runoff and accelerated erosion potential of the Feijão River basin were presented in charts at a 1:50,000 scale. The Feijão River basin has an area of 243.16 km 2 and is used as the main water source for the city of São Carlos, Brazil. Geoenvironmental attributes, such as substrate, climate, relief, soil, water bodies and land cover and use, were integrated and assessed in a GIS environment, using a multicriteria analysis and weighted sum tool. The results show that a large part of the area (86.12% of the basin) exhibits a low surface runoff potential and a moderate accelerated erosion potential. Accelerated erosive processes are triggered by changes in soil cover and have a direct relationship with the removal of existing vegetation and implementation of anthropogenic activities. In this case, as well as for most of the areas in southeastern Brazil, extensive grazing followed by sugar cane cultivation was the main driving force of erosion, acting as trigger for accelerated erosive processes at the water source area.
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