Patterns of spatial and temporal variations in soil salinity: Example of a salt marsh in a semiarid climate

Spatial and temporal variations in soil salinity were measured in a salt marsh in semiarid southeastern Spain. A total of 108 samples were taken from the top 20 cm of soil during 2 years in a transect with nine sampling points, established according to plant zonation. Electrical conductivity (EC), pH, Cl-, SO42-, Ca2+, Mg2+, Na+, and K+ concentrations in saturation extracts were measured in order to determine any pattern of temporal and spatial variation. Correlations between the concentration of different ions, total dissolved salts (TDS), and EC were also examined. Although EC and ion concentrations usually appeared to be well correlated (rs > 0.7, significant at p < 0.01) and followed the same pattern of seasonal variation, a detailed study showed that at high TDS this was not always true. When mean values of TDS ranged between 2592 and 6070 mmol(c) L-1 the coefficient of correlation between EC and SO42- (rs = 0.471, significant atp < 0.01) was lower than that between EC and Na+, K+, Mg2+, and Cl-(rs greater than or equal to 0.886, significant at p < 0.01). In this range of TDS the coefficient of correlation between EC and Ca2+ was not significant (rs = -0.1972). Increased concentrations of certain ions, especially of Ca2+ and SO42-, were not always matched by increases in EC values, which were strongly influenced by ionic relationships, particularly the SO42-/Cl- and Ca2+/Mg2+ ratios. This indicated that EC was not always a good qualitative or quantitative indicator of the salt content and that, in these cases, the TDS should be used as an indicator of overall salinity.