Temporal changes in soil salinity at four saline wetlands in NE Spain

Abstract

The knowledge of soil salinity and the temporal changes of its distribution in the soil profiles can give warnings for the protection of saline habitats. This study described and compared the salinity profiles of the soils from four hypersaline wetlands at inland, ill-drained depressions in NE Spain, which were sampled throughout the year in 1979–1980 and 1999–2000, and differed in land use. The halophytic communities dictated the location of sampling sites. After the saturated pastes of 404 soil samples were prepared, the electrical conductivity of the extracts (ECe) and the concentrations of major ions were measured, and additional supplementary analyses were performed. A subset of the samples was titrated for calcium carbonate equivalent and gypsum content. ECe and ion concentrations calculated for synthetic soil layers facilitated the comparisons of the vertical distribution of soil salinity among dates, depths, and sites. The shape of the mean ECe profiles over all sampling dates indicated moderate differences between the two wetlands closest to each other, Plan de Callén (PC) and Paúl de Almuniente (AL), which had similar (<~10dSm−1) ECe. In contrast, the ECe profile at Paúl de Anzano (AN) ranged from 40dSm−1 to 50dSm−1 in the upper meter of the soil, which decreased steadily to 20dSm−1 at a 2-m depth. At Saladar de Agustín (AG), ECe was much higher and the profile had the opposite shape, ECe~55dSm−1 at the surface and >80dSm−1 at an 80-cm depth. The shape of ECe profiles at AL, PC, and AG was rather stable over time, contrasting with the measured desalination of the soil at AL after its conversion into a rice paddy. The changes in the sodium adsorption ratio (SAR) in the soil profiles at AN, PC, and AL are indicators of the potential extremes in the hydric behavior of the soils. At AG, the mineralogical clays are a minor component of these gypseous soils; therefore, the SAR, only, was used as a measure of the relative concentrations of Na+ versus Ca2+ plus Mg2+. The median SAR of all AG soil samples did not differ significantly among sampling sites or dates. The shorter sampling depth intervals used in 1979–80 were responsible for the greater spread in the distribution and the increase in extreme SAR values compared to the data collected in 1999–2000.