Effect of desalinized water derived treated wastewater on soil structure stability and hydraulic properties

Irrigation with treated wastewater (TWW) has become a common practice in Israel and is accepted as an environmentally responsible way of managing water resources. Although negative effects of high sodium (Na+) and dissolved organic carbon (DOC) concentrations have been reported, many fields have been irrigated with TWW for more than three decades. It is therefore assumed that chemical equilibrium has been reached. In recent years, however, desalination has become the main water source for urban and industrial use. Thus, the salinity of TWW is expected to decrease and the relative concentration of Na+ to calcium (Ca+2) and magnesium (Mg+2), quantified by the Sodium Adsorption Ratio (SAR), may increase. The effects of this new TWW quality need to be understood in order to mitigate potential damage to irrigated soils structure and hydraulic characteristics. The main objective of this study was to quantify the effects of desalinized water derived TWW with different levels of salinity, SAR and DOC on soil structural and hydraulic properties. The results demonstrated that irrigation with TWW derived from desalination is more detrimental for the soil hydraulic and structural properties when compared to TWW derived from freshwater sources. Particularly, the combination of lower salinity and higher SAR in desalination derived TWW results in a depth dependent increase of exchangeable sodium. Consequently, clay dispersion and pore clogging occurred, thus reducing the saturated hydraulic conductivity of the examined soils. Further results will be presented and the implications for long-term sustainable irrigation will be discussed.