Redox conditions and Indicator of Reduction in Soils (IRIS) films in soils of a hypersaline wetland

Abstract

Information about the reducing conditions in hypersaline wetland soils is scarce though redox traits are of ecological and agronomical interest. We studied the soils and water in Salineta playa-lake (NE Spain) plus the soil redox conditions using IRIS (Indicators of Reduction in Soils) films during 17 months. Soils had a pH varying from 6.8 to 7.8, a mean gypsum content of 38 %, a mean organic carbon content of 0.6 %, and soil salinity ranged from 219 to 66 dS m⁻¹ in the saturated paste extract. Soil horizons showed distinct morphological features consistent with a redox potential (Eh) ranging from +434 to −108 mV. Minimum Eh occurred in the upper soil horizon indicating intensified reducing conditions with a transition to aerobic conditions with depth. Sulfidic and Anoxic conditions prevailed during the annual cycle despite temporary drying. The IRIS films revealed an irregular removal of manganese and iron oxide coatings through time and through the film depth as triggered by pulses of the water level. The monthly removal rate was 10.6 % for manganese and 5 % for iron films. Iron removal showed a delayed and irregular response due to the alkaline conditions. The persistent accumulation of sulfides in the soil resulted in a distinctive black soil layer which can be a key feature for future monitoring of the impacts of the agricultural flows from surrounding irrigated lands. Further research on pedogenesis of arid wetlands will help the soil resource inventories and the understanding of the various life adaptations to these conditions.