Weathering rates at Alto Sorocaba basin, Brazil, using U-isotopes and major cations

• Published in: Environmental earth sciences Vol. 61; no. 5; pp. 1025 - 1036
• Main Authors: Sardinha, D. S., Bonotto, Daniel Marcos, da Conceição, F. T.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.09.2010; Springer; Springer Nature B.V
• Subjects: Biogeosciences; Cations; Climatic conditions; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Science and Engineering; Exact sciences and technology; Freshwater; Geochemistry; Geology; Geomorphology; Hydrology/Water Resources; Isotope geochemistry; Isotope geochemistry. Geochronology; Mineralogy; Original Article; Pollution, environment geology; Radioisotopes; Rivers; Rocks; Silicates; Terrestrial Pollution; Uranium; Water geochemistry; Weathering; South America; Brazil; Sao Paulo Brazil; Brazil, Sao Paulo, Sorocaba R; Brazil, Sao Paulo; Hydrographic basin; Weathering rate; Uranium isotopes; rivers; chemical weathering; cations; calcium; potassium; river discharge; tracers; dissolution; bicarbonate ion; reservoirs; magnesium; concentration; continents; U-238/U-234; sodium; balance; hydrochemistry; isotopes; uranium; soils; correlation coefficient
• ISSN: 1866-6280; 1866-6299
• DOI: 10.1007/s12665-009-0424-7

The aim of this paper was to evaluate the chemical weathering rate at Alto Sorocaba basin, São Paulo State, Brazil, as it is an important parameter on geomorphological characterization of continents. Several tools may be used for such evaluation, and this work compares the results obtained from analytical data involving the uranium concentration, the 234 U/ 238 U activity ratio and the major cation concentration for samples of waters, soils, and rocks from that basin. The use of the natural uranium as a tracer in weathering rate rocks studies is advantageous since this element is virtually absent in rainwater and also allows obtaining the dissolution rocks coefficient by the 234 U/ 238 U activity ratio. The Alto Sorocaba basin has serious environmental problems in terms of the quality of the rainwater and river waters, and, consequently, the geochemical balance using the main cations presented some difficulties. However, measuring of the weathering rate utilizing the U-isotopes method corresponded to 14 μm/year that allows estimating a time of 72,000 years to weather 1 m of rock at Sorocaba River upstream from Itupararanga Reservoir, under the present climatic conditions.