Evidence of titanium mobility in soil profiles, Manaus, central Amazonia

Titanium minerals are classically considered to be very resistant to weathe ring in soils. Consequently, variations of titanium concentrations within t he soils were used to estimate rates of weathering of parent material. Mobi lity of Ti was studied in an Amazonian ferralsol using a large set of techn iques. Chemical and mineralogical studies of Ti distribution in the soil pr ofile showed that weathering of Ti minerals follows the mineral sequence: i lmenite, pseudorutile, rutile and anatase. This weathering leads to absolut e Ti losses on the profile scale. Mineral bags were located at different de pths within the top soil, and removed after 6, 12, 18 months in the soil. I n all bags the presence of newly generated anatase was recorded after the e xposure periods, showing the rapidity of the processes. The vegetation recy cles a significant quantity of Ti, increasing Ti mobility in soils. These r esults indicate that Ti can be mobile under certain conditions and thus sho uld not always be used to estimate weathering rates. (C) 1999 Elsevier Scie nce B.V. All rights reserved.