Reducing conditions in soil of Gallocanta Lake, northeast Spain

Saline wetlands have received limited attention from researchers and this neglect has often resulted in their degradation and limited conservation, and insufficient information to design conservation and management plans. Gallocanta Lake is a nature reserve of international importance for winter birds. The importance of the soil here, which supports niches and protected habitats for certain species of birds, has been recognized more recently. The soil of Gallocanta Lake undergoes strong oscillations of saturation and drainage followed by drying because of irregular rain and variable flooding conditions associated with fluctuations in the level of the lake. This study examined reducing conditions and morphological indicators of reduction in the soil around the lake with indicators of reduction in soils (IRIS) tubes, which are coated with iron oxides. We surveyed five sites for between 22 and 34 weeks. The average amount of iron removed from the IRIS tubes during the period studied ranged between 4 and 96%. The intensity of reduction in the soil differs according to subtle topographic differences between sites; it increases with the decrease in elevation. The large soil salinity (electrical conductivity saturated soil extract, ECe, from 18.1 to 182 dS m–¹), carbonate‐rich composition (from 18.4 to 69.7% calcium carbonate equivalent, CCE) and overall small organic matter content (from 0.4 to 6.2% organic matter) do not seem to constrain iron mobilization because of the reducing conditions. Differences in iron depletion and patterns on the IRIS tubes show the heterogeneity of soil conditions and the complexity of factors involved in redox processes. Further research is needed to gain knowledge of the redox processes in the context of pedogenesis in semiarid lacustrine environments. HIGHLIGHTS: How soil intermittently exposed to waterlogging expresses redox conditions. Current reducing conditions are evident in a fluctuating saline lake by IRIS tubes. Soil reduction occurs in alkaline soil with intermittent waterlogging. IRIS tubes are suitable field indicators of the heterogeneity of soil reducing conditions in saline lakes.