Phosphate concentration and association as revealed by sequential extraction and microprobe analysis: The case of sediments from two Argentinean reservoirs

L. BORGNINO; C. ORONA; M. AVENA; A. MAINE; A. RODRÍGUEZ; C. P DE PAULI

WATER RESOURCES RESEARCH

AGU. American Geophysical Union

Año: 2006 vol. 42 p. 1 - 12

0043-1397

This article reports the general characteristics of the sediments of two Argentinean reservoirs, which are used for water supply. The chemical composition, granulometry,  and specific surface area are presented together with a study of total phosphate  concentration and phosphate association by combining sequential extraction and  microprobe analysis. In general, the sediments of both reservoirs have similar  characteristics. Sequential extraction reveals that the main P fractions in the studied  sediments are Ca-bound phosphate in river mouths and Fe-bound phosphate in the rest of  the reservoir stations. Microprobe analysis appears to be an important complementary  technique to sequential extraction. Combined with chemical fractionation and specific  surface area measurements, these analyses indicate that Ca-bound phosphate is mainly distributed within grains or particles highly concentrated in Ca and P, whereas Fe-bound  phosphate is rather homogeneously distributed in the sediments at the surface of fine  particles. Microprobe analyses also revealed an important coating of phyllosilicate  surfaces with Fe (hydr)oxides, which explains the good correlation found between  Fe-bound phosphate, clay fraction, and specific surface area. The role of sediments as  a potential source of phosphate is discussed in terms of P association in the solid phase and  dissolved oxygen concentration profiles in the water column.reservoirs, which are used for water supply. The chemical composition, granulometry,  and specific surface area are presented together with a study of total phosphate  concentration and phosphate association by combining sequential extraction and  microprobe analysis. In general, the sediments of both reservoirs have similar  characteristics. Sequential extraction reveals that the main P fractions in the studied  sediments are Ca-bound phosphate in river mouths and Fe-bound phosphate in the rest of  the reservoir stations. Microprobe analysis appears to be an important complementary  technique to sequential extraction. Combined with chemical fractionation and specific  surface area measurements, these analyses indicate that Ca-bound phosphate is mainly distributed within grains or particles highly concentrated in Ca and P, whereas Fe-bound  phosphate is rather homogeneously distributed in the sediments at the surface of fine  particles. Microprobe analyses also revealed an important coating of phyllosilicate  surfaces with Fe (hydr)oxides, which explains the good correlation found between  Fe-bound phosphate, clay fraction, and specific surface area. The role of sediments as  a potential source of phosphate is discussed in terms of P association in the solid phase and  dissolved oxygen concentration profiles in the water column.