The influence of particles recycling on the geochemistry of sediments in a large tropical dam lake in the Amazonian region, Brazil

The influence of particles recycling on the geochemistry of sediments in a large tropical dam lake in the Amazonian region, Brazil. Article in Journal of South American Earth Sciences 72 · December 2016 DOI: 10.1016/j.jsames.2016.09.012 1st Rita Fonseca 16.85 · Universidade de Évora 2nd Catarina Pinho 3rd Manuela Oliveira 22.6 · Universidade de Évora Abstract As a result of over-erosion of soils, the fine particles, which contain the majority of nutrients, are easily washed away from soils, which become deficient in a host of components, accumulating in lakes. On one hand, the accumulation of nutrients-rich sediments are a problem, as they affect the quality of the overlying water and decrease the water storage capacity of the system; on the other hand, sediments may constitute an important resource, as they are often extremely rich in organic and inorganic nutrients in readily available forms. In the framework of an extensive work on the use of rock related materials to enhance the fertility of impoverish soils, this study aimed to evaluate the role on the nutrients cycle, of particles recycling processes from the watershed to the bottom of a large dam reservoir, at a wet tropical region under high weathering conditions. The study focus on the mineralogical transformations that clay particles undergo from the soils of the drainage basin to their final deposition within the reservoir and their influence in terms of the geochemical characteristics of sediments. We studied the bottom sediments that accumulate in two distinct seasonal periods in Tucuruí reservoir, located in the Amazonian Basin, Brazil, and soils from its drainage basin. The surface layers of sediments in twenty sampling points with variable depths, are representative of the different morphological sections of the reservoir. Nineteen soil samples, representing the main soil classes, were collected near the margins of the reservoir. Sediments and soils were subjected to the same array of physical, mineralogical and geochemical analyses: (1) texture, (2) characterization and semi-quantification of the clay fraction mineralogy and (3) geochemical analysis of the total concentration of major elements, organic compounds (organic C and nitrogen), soluble fractions of nutrients (P and K), exchangeable fractions (cation exchange capacity, exchangeable bases and acidity) and pH(H2O).

Impactes do Preço da Água na Agricultura no Perímetro Irrigado do Vale de Caxito

O aumento da pressão sobre os recursos hídricos tem levado muitos países a reconsiderarem os mecanismos utilizados na indução do uso eficiente da água, especialmente na agricultura irrigada. Estabelecer o preço correto da água é um dos mecanismos de tornar mais eficiente a alocação da água. O presente trabalho tem como objetivo a análise dos impactes económicos, sociais e ambientais de políticas de preço da água. A metodologia utilizada foi a Programação Linear, aplicada ao Perímetro Irrigado do Vale de Caxito, Província do Bengo, a 45 km de Luanda, que tem como fonte o rio Dande. Foram testados três cenários relativos a políticas de tarifação de água: tarifa volumétrica simples, tarifa volumétrica variável, e tarifa fixa por superfície. As principais conclusões mostram que, do ponto de vista do uso eficiente da água na agricultura, os melhores resultados obtêm-se com a tarifa volumétrica variável; do ponto de vista social, a tarifação volumétrica simples apresenta os melhores resultados; o método de tarifa volumétrica variável foi o mais penalizador, reduzindo rapidamente a área das culturas mais consumidoras de água, sendo o melhor do ponto de vista ambiental. Qualquer um dos métodos traz aspetos negativos relativamente à redução da margem bruta total. Palavras-chaves: Recursos hídricos; Preço da água; Programação linear. Abstract: Increased pressure on water resources has led many countries to reconsider the mechanisms used in the induction of efficient water use, especially for irrigated agriculture, a major consumer of water. Establishing the correct price of water is one of the mechanisms for more efficient allocation of water. This paper aims to analyze the economic, social and essenenvironmental impacts of water price policies. The methodology used is the linear programming, applied to the Irrigated Valley Caxito, in Bengo Province, 45 kilometers from Luanda, which has the river Dande as its source. Three scenarios concerning water price policies were tested: simple volumetric rate, variable volumetric rate and flat rate per surface. The main findings show that from the point of view of the efficient use of water in agriculture, the best results are obtained with variable volumetric rate; from the social point of view, the simple volumetric rate has the best results; the volume variable rate method proved to be the most penalizing, quickly reducing the area of most water consuming cultures, being the method in which the environmental objectives would be more readily achieved. Either methods bring negative aspects in relation to the reduction of total gross margin. Key-words: Water resources; Water price; Linear programming.