EDAFOLOGIA, Vol. 9 (3), pp. 257-272, 2002
X. L. OTERO, F. MACÍAS
Departamento de Edafoloxía e Química Agrícola. Universidade de Santiago de Compostela. 15782 Santiago de Compostela. e-mail: email@example.com.
Abstract. A total of 8 profiles from different physiographical positions in Ría of Ortigueira (Galicia-NW Spain) salt marshes were studied. The Fe species considered (amorphous, crystalline, pyritic, AVS and residual Fe) varied significantly with position and depth. In soils with oxic (Eh>300mV) or suboxic conditions (Eh = 100-300mV) the dominant forms of free Fe (Fe oxyhydroxides, Fe-pyrite and Fe-AVS) were amorphous and crystalline oxyhydroxides of Fe. In soils with anoxic conditions throughout the profile (Eh <-100 mV) Fe-pyrite was the most abundant form. Where conditions were oxic or slightly reduced (Eh = 100-300mV) at the surface and anoxic at depth, high concentrations of reactive-Fe (amorphous and crystalline oxyhydroxides of Fe) were found in the top 10 cm. The amorphous oxyhydroxides of Fe quickly disappeared with depth, whereas Fe-pyrite levels increased significantly. The amount of crystalline oxyhydroxides of Fe also decreased with depth, but more gradually.
Key words: redox conditions, oxyhydroxides of Fe, pyrite, AVS, Fluvisols, salt marsh.