Salt-affected soils evolution and fluvial dynamics in the Pantanal wetland, Brazil

• Solonetz, Solodized Solonetz and Solod are formed around brackish lakes by solodization.
• Soils genesis occurs in a sequence of evolution strictly related to the lake geochemistry.
• Leaching of the previous Saline-Sodic soils occurs by atypical input of freshwaters.
• Freshwaters input occurs through the formation of new intermittent watercourses.
• The Nhecolândia subregion has likely passed through a general desalinization.

In the Nhecolândia, a subregion of the Pantanal wetland, saline lakes and their associated Saline-Sodic soils have been degraded due to the atypical input of freshwater from seasonal flooding. In the present work, the soils in and around three brackish lakes that have experienced degradation (Carandazal, Cerca and Banhado lakes) were studied through a detailed morphological survey and chemical analyses to understand their genesis and establish genetic relationship with the Saline-Sodic soils of the saline lakes. The studied soils have Bnc and Bc horizons with morphological and chemical similarities to the Bnx formed around the saline lakes, presenting greenish colors, hard consistencies and, generally, the highest values of pH, exchangeable sodium percentage (ESP), sodium adsorption ratio (SAR) and electrical conductivity in the saturated paste (ECs) of each profile. In contrast, the near-surface horizons tend to present the lowest values of pH and the highest amounts of Al3 + saturation and exchangeable H + Al. These data point to the replacement of salinization/solonization around the saline lakes to the solodization process in the studied soils, with leaching of exchangeable bases, their substitution by Al3 + and H+ and a consequent decrease in pH, first at shallow depths and later in the whole profile. Solodization occurs to a lower degree in the soils associated with the Carandazal lake, which has a predominance of Solonetzes and the closest water pH and electrical conductivity (EC) to the saline lakes, and to a higher degree in the soils related to the Banhado lake, which has a predominance of Solods and the most similar water pH and EC to the freshwaters of the Nhecolândia. The Cerca lake has an intermediate water geochemistry between the studied lakes and an equal prevalence of Solodized Solonetzes and Solods. Soil leaching occurs due to increasing inundation by freshwater through erosion around the saline lakes, primarily involving formation of new intermittent watercourses.