Edaphic and geomorphic evidences of water level fluctuations in Gallocanta Lake, NE Spain

Abstract

The pedological implications of lake water level fluctuations are complex, especially in lake margin, where topographical, hydrological, and sedimentary conditions are most variable. Lake water level fluctuations generate landscape elements, which provide insights into the processes involved in soil development and the extent of the zones affected by flooding/desiccation. Coupling information from detailed geomorphological inspections in the field, the mapping of the lakeshore, and the pedogenesis of each landscape element can provide a better understanding of these relationships, which was used to study the saline Gallocanta Lake, NE Spain, a semiarid intramontane lacustrine system that undergoes significant and rapid water level fluctuations. Geomorphic classification of the lake margin forms and environments served as a guide for soil sampling. The geomorphological survey revealed high diversity and contrast in the lake margin environment, from shores affected by coastal erosion to zones characterized by progradation/aggradation. Two soil toposequences and 11 pedons that were on different geomorphic units were studied on two margins of the lake. Following gradients in elevation, moisture, and salinity, soils showed a succession of Inceptisols to Aridisols, with Mollisols developed at intermediate positions and Aquic soils at the lake floor and southern shore. Soils had a sandy, loamy texture and a predominantly carbonatic composition, high variation in CCE (mean=37%), texture, and coarse fragments throughout the soil profiles. Soil salinity was the highest at the lowest topographic position and in the upper soil horizons, where mean ECe=188.6dSm−1 at 25°C. In addition, the highest organic matter (6%) and gypsum (34%) content occurred at the lake floor. Soil color characteristics and concentrations, and depletions of Fe and Mn indicated redox changes associated with soil water saturation under carbonate and or saline conditions. Macro and micromorphological features of oxidized and reduced horizons indicated the alternation between palustrine (reduced) and non-palustrine (detrital, emerged, oxidized) events at different geomorphic and topographic positions, from the lake floor up to 7m above it. Pedogenesis inferred and the littoral/submerged forms located at permanently emerged areas confirmed the past and present trend towards the desiccation of the lake. This study has improved our understanding of how soils form and develop within the context of geomorphic units, and can be used in making land-use decisions in the protected reserve and agricultural surroundings of the lake.