Analysis of Sedimnetar Deposition and Geochronological the Past Five Decades in Urban Lake
A primary outcome of water basin urbanization is the set of changes of the natural environment into an anthropic environment, favoring the formation of residential and industrial conglomerates. Such changes lead to increases in water demand, causing higher production and release of effluents from anthropic actions, in addition to originating diffuse sources of pollution. These changes can drastically deteriorate the physicochemical characteristics of the local water resources.The purpose of this paper is to analyse the results of particle size profiles carried out in the dam Mãe d’água, located in the metropolitan region of Porto Alegre, Rio Grande do Sul, becoming a tool of support for geochemistry evaluation works of sediments in this basin.The "Piston core" sediment sampler was used to extract the samples for analyzes of geochronology and granulometry at different depths. The granulometric laboratory analysis of the samples was performed according to the protocol referring to Brazilian standards of analysis NBR 7.181 and mathematically modeled data using ArcMap software version 10.5. The geochronological analyzes used the tracer Lead 2010 to identify the period of sedimentary deposition.The results show that, for the different depths, the sedimentary profiles present similarity in their layers of sedimentary deposition. It can be seen in this work that the sediment flow energy reaches it differently, creating these three sectors (first, sand with gravel, second, sand with mud and third, mud) with different characteristics - morphodynamic and sedimentological. These characteristics are important for produce plans mitigating environmental liabilities the thus to reduce the risk of contamination of watercourses. Thus, identification of the layer’s deposition period, by combining techniques such as 210Pb geochronology and granulometry, enables to find possible causes of sediment contribution to the reservoir , such as urban expansion, industrialization, erosion, agricultural practices. Therefore, the present study describes the impacts caused by urbanization on the Mãe d’Água water basin.
Keywords - Sediment, 210Pb radium isotope, Geochronology, Remote sensing, Mãe d’Água dam.