Abstract. Analysis was made of the redox conditions and Fe species present in 8 soil profiles from the Ría de Ortigueira (N Galicia). The soils were from different types of salt marsh (high and low), different physiographical positions and had different types of plant cover. The Fe species considered were: amorphous or poorly crystalline oxyhydroxides of Fe (soluble in ascorbate-citrate), crystalline Fe (soluble en dithionite), pyrite-Fe (soluble in nitric acid), metastable Fe sulfides (Fe-AVS) and residual Fe (soluble in HF). The results indicated large spatial variations and variations with depth in the redox conditions of these soils and therefore in the Fe species present. Oxic conditions prevailed throughout the high salt marsh soil profiles (Eh> 300 mV; profiles 3 and 4) and iron oxyhydroxides dominated. Pyrite-Fe was pre-sent at very low concentrations in these soils. In soils with oxic or suboxic surface layers and anoxic dee-per layers, concentrations of reactive-Fe (amorphous and crystalline oxyhydroxides of Fe) were high in the first 15 cm; below the rhizosphere the levels of amorphous oxyhydroxides of Fe decreased, whereas the amount of pyrite-Fe and therefore the degree of pyritization (DOP), increased significantly. The levels of crystalline oxyhydroxides of Fe also decreased with depth in these soils but more gradually, with high concentrations being maintained under strongly reduced conditions. The distribution of Fe species in the soil from the salt pan was anomalous; levels of pyrite-Fe were higher than those of oxyhydroxides of Fe in the surface layers and the DOP was therefore also high. Paradoxically, the amount of pyrite-Fe decreased significantly at depth and there was an increase in levels of iron oxyhydroxides.
The low salt marsh and channel bottom soil profiles were anoxic throughout. Pyrite-Fe was the most abundant species in these soils; the degree of pyritization for the amorphous or poorly crystalline Fe was close to 100% and for Fe soluble in dithionite it was greater than 60%.
Key words: Potential redox (Eh), Soil classification, FAO, Soil Taxonomy, Fluvisols, Aquents, salt marsh.