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Other Titles: Fluvial Hidrogeochemistry from paquequer watershed, Teresópolis-RJ
Keywords: Geoquímica;  Intemperismo;  Mineralogia;  Poluição;  Efluente doméstico;  Geochemistry;  Weathering;  Mineralogy;  Pollution;  Domestic waste
Issue Date: 1-Apr-2011
Abstract: Surface water chemistry varies according to geology, atmospheric inputs and anthropogenic factors, such as discharges of domestic and industrial effluents, agricultural activities and others. The main purpose of this study is to identify the anthropogenic and geological contributions in determining the hydrogeochemistry of the Paquequer river basin, Teresópolis, RJ. This basin covers a 269 km² area, its springs lie within a conservation area (Parque Nacional da Serra dos Órgãos) with preserved Atlantic Forest. The Paquequer River mid-stream crosses the city of Teresopolis and receives domestic waste. Contributions of agricultural effluent also occur in its lower stream. The Paquequer river has singular importance for Teresópolis because it is a water supply source. The present geological units are classified as Batólito Serra dos Órgãos (gneissic granites), Granito Teresópolis (monzogranite), the Rio Negro Unit and basic dykes. Soils are predominantly Red-Yellow Cambissoils and Gleissoils in river valleys. In this study, river samples consider different lithologies and land uses. Samples were collected during the dry season in August 2010 when weathering comprises the main source of natural elements to the river system. Measurements of pH, conductivity, temperature, redox potential and river flow were made in site. Besides these measures, chemical analysis of dissolved elements have been carried out (Na, K, Ba, Ca, Mg, Pb, Cu, Co, Ni, Cr, Zn, Sr, Rb, Al, Si, Fe, Mn, Li, La, Cd, PO43- , Cl- and SO42-). Mineralogy (XRD) of the suspended particles was also identified. XRD results showed that the mineralogy of the suspended particles is predominantly composed of kaolinite, gibbsite and quartz. Secondarily it was also observed halloysite, mica, illite and rarely microcline. Theoretical stability diagrams were prepared to identify the transfer of elements from the dissolved phase to solid phase. Chemical results of the dissolved elements indicated concentrations of Si approximately constant along the main Paquequer river channel, only natural sources (weathering) were found for this element. Na, K, Ca, Cl, SO4 and PO4 shows natural (weathering) and anthropogenic (urban and agricultural effluents) sources and concentrations peak while crossing the urban center and, in the tributary that drains the sanitary landfill. The ratio Na / Si indicated domestic sewage influences. Copper, Ni, Co, Zn and Mn indicates anthropogenic pollution from urban sources and agriculture. Rocks with higher contents of K and Al are more resistant to weathering processes, explaining why the river water that drains those lithotype do not present higher concentrations of these metals. Multivariate analysis identified four subgroups of sampling sites according to their degree of anthropogenic influence. Points located in the upper stream of the river are unaffected. Almost all tributaries shows characteristic of low impact. Along the main channel, after the city influence, all place have noticeable pollution features. Lastly points, which receive direct influence of the urban center and sanitary landfill sites, are highly impacted.
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