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 (b~10 dS m −1 ) ECe. In contrast, the ECe profile at Paúl de Anzano (AN) ranged from 40 dS m −1 to 50 dS m −1 in the upper meter of the soil, which decreased steadily to 20 dS m −1 at a 2-m depth. At Saladar de Agustín (AG), ECe was much higher and the profile had the opposite shape, ECe~55 dS m −1 at the surface and N80 dS m −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 Ca 2+ plus Mg 2+ . 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.

Analysis and Mapping of the Spectral Characteristics of Fractional Green Cover in Saline Wetlands (NE Spain) Using Field and Remote Sensing Data

“…The general low density cover of the vegetation of the Monegros wetlands and the high variability of its spectral response ( Figure 6) required tailored thresholds for classifying remotely sensed data. For this purpose, we used expert judgement based on more than twenty years of field research [46,51]. By applying the thresholds summarized in Table 3, we obtained a map with six classes of fCover, three of soil moisture, plus one of water.…”

“…The development stage of vegetation in saline wetlands is subjected to water and salt stresses resulting in a complex and highly variable environment [46] with sudden unpredictable changes. There is no a standard methodology to examine the temporal changes of such environments.…”

Monitoring the seasonal dynamics of soil salinization in the Yellow River delta of China using Landsat data

“…Therefore, traditional vegetation indices (VIs), such as the normalized difference vegetation index (NDVI), ratio vegetation index (RVI) and difference vegetation index (DVI), can be used as indicators to determine the degree of soil salinization (Elmetwalli et al, 2012;Li et al, 2013;Goto et al, 2015). However, the accuracy of the models based on traditional VIs must be improved (Iqbal, 2011). Traditional VIs involve data from only the bands in the visible and near-infrared regions and do not consider other bands (such as the shortwave infrared band, which has a large amount of information), and thus performing comprehensive analyses with these indices is difficult.…”

An attempt to monitor seasonal dynamics of soil salinization in the Yellow River Delta region of China using Landsat data

“…Saline soils are widespread throughout the world, especially in arid, semi-arid and some sub-humid regions. Saline soils cause severe environmental degradation that can impede crop growth, as well as overall regional production (Metternicht and Zinck 2003;Huang et al 2015). Obtaining soil characteristics, such as degree of salinity and geographical 5 distribution of saline soil in real time, and improving our ability to forecast soil salinization dynamics is a necessary prerequisite for scientific management, reasonable improvement and utilization of regional saline soil (Melendez-Pastor et al 2012).…”