The role of Sarcocornia perennis in the interstitial water salinization process

Abstract

In salt marshes, there seems to be a trade-off between the presence of plants and some abiotic factors. Inparticular, it was observed that while groundwater salinity conditions the plant distribution pattern in certainsalt marshes, it does not do so in others. In the salt marsh of Fracasso beach (Península Valdes, Argentina) thegroundwater has a higher salinity than the seawater. Previous studies have proposed that salinization is aconsequence of the concentration and/or precipitation of salts as a result of partial evaporation/evapotranspirationof the tidal water that floods the salt marsh. However, the role of vegetation in the salinization process hasnot been thoroughly studied so far; therefore, this research work aims to explore this relationship. To this end, 10soils samples with plants and 10 soil samples without plants were taken from the unsaturated zone in Fracassomarsh. At the laboratory, the soil samples were centrifuged to obtain the interstitial water to determine theelectrical conductivity, the concentration of chloride, and the isotopic composition. Also, texture and moisture content were determined. The results indicate that fine fraction and moisture contents were higher in the patches with plants than in those without plants. Conversely, electrical conductivity, chloride concentration and δ18O and δ2H values were higher in the interstitial water of the non-vegetated samples. These results indicate that in patches without plants, the evaporation process is higher than in patches with plants. The presence of low permeability soils reduces infiltration favouring the evaporation of tidal water. Under these conditions, the distribution of vegetation within the salt marsh plays an essential role in attenuating evaporation. S. perennis has a shadow effect that locally attenuates water evaporation causing the soil beneath the vegetation canopy to have less salinity than the adjacent soil without vegetation.