Causal processes of soil salinization in Tunisia, Spain and Hungary

Abstract

Soil salinization arises due to the build up of soluble salts at or near the soil surface. Salts accumulate by primary and secondary processes that alter the soils physicochemical properties and lead to direct and indirect soil degradation. Results are presented here from the study of three contrasting salt-affected landscapes. The Chott el Fedjadj, Tunisia, is a naturally salt-affected basin containing saline sediments deposited during a marine incursion. The endoreic conditions lead to salt recirculation, concentration and reprecipitation. In the Guadalentin Valley, Spain, increased irrigated agriculture has led to aquifer overexploitation releasing gas and salts. Irrigating with the resultant contaminated groundwater has induced soil salinization. The salt accumulation and translocation is dictated predominantly by irrigation method, water quality and quantity. Hungary has the largest expanse of naturally salt-affected soil in Europe, with the dominant soil type being solonetz. In Hungary the type of salt-affected soil development is related to the salts present, hydraulic properties of the soil and depth and quality of the watertable. In Tunisia a catenary relationship of increased water and soil salinity towards the centre of the chott is found, whereas in Spain the highest salinities were found under¯ood irrigation with the valley displaying a complex spatial distribution of soil salinity. The sediment distribution in Hungary dictates that solonchak soils are found mostly in the Danube± Tisza inter¯uve and solonetz soils in the Tisza¯oodplain, with localized variations in soil type related to watertable characteristics.

The effects of tree establishment on water and salt dynamics in naturally salt-affected grasslands

“…The vertical distribution of salts in grassland soils, with a bulge at~50-150 cm, suggests that they date from pre-drainage times when the water table was shallower. Likely, these salts remained unflushed because the high sodium content and fine soil texture interacted severely hindering the downward movement of water and salts (Schofield et al 2001;Szabolcs 1989;Figs. 2, 4, 6).…”

“…Although this large operation led to a significant decline of groundwater levels, the results were not completely satisfactory because, in most places, salts still remain in the soil profile as a result of poor soil physical conditions preventing their leaching (Schofield et al 2001;Szabolcs 1989). Soil properties here constrain land use options to the raising of livestock on native pastures (Á brahám and Bocskai 1971).…”

“…Before the hydrological regulation of the region, considerable parts of the Plain were permanently or temporarily inundated (Á brahám and Bocskai 1971). These conditions, together with the poor soil hydrophysical properties, favoured the development of salt-affected soils, mainly solonetz and solonchak types (Schofield et al 2001). The native vegetation of the area is dominated by grasses and the mean annual temperature and precipitation approach 10.2°C and 540 mm, respectively (Béla 1972;Toth et al 1991).…”

“…This surplus water often causes shallow groundwater levels, favouring local discharge through plant transpiration, soil evaporation, or pond evaporation in the lowest landscape positions, with all these water evacuation pathways leading to salt accumulation. Reclamation measures aimed at interrupting the discharge regime by lowering the water table and channelling excess water to large rivers, as happened in Hungary~150 years ago, have proved to be insufficient to solve the problem, because the poor soil physical properties hinder the salt leaching process (Schofield et al 2001;Szabolcs 1989). Tree establishment in these situations could lead to contrasting outcomes, modifying water flows and processes operating in opposite ways.…”

A global perspective on wetland salinization: ecological consequences of a growing threat to freshwater wetlands

“…In both cases, capillary action can draw saline water to the surface even when the water table remains as deep as two meters from the surface (Eamus et al 2006). Human-induced movement of saline groundwater has resulted in the salinization of soils across the world (Ghassemi et al 1995, Schofield et al 2001, Mazi et al 2014. Even in regions without shallow saline groundwater, the surface or groundwater used to irrigate crops is invariably more saline than rainwater.…”