Treated domestic sewage irrigation effects on soil hydraulic properties in arid and semiarid zones: A review

In and and semiarid regions, the use of treated domestic sewage (effluent) for irrigation is becoming a common practice, because of the shortage of freshwater resources. However, the use of effluent for irrigation could have an impact on the chemical and hydraulic properties of soils. This paper reviews the effects of irrigation with effluents that have undergone various treatments on hydraulic properties of semiarid and and soils. Irrigation of semiarid clay and sandy soils with secondary effluent increased the salinity at depths down to similar to 1.5 m, and the sodicity down to similar to 1.5 and >4 m, respectively. The increase of the organic matter load in the effluents resulted in inconsistent effects on the organic matter content of the topsoil, but it could lead to its decrease in the subsoil because of a "priming effect" of the effluent. Percolation of effluent through the soil profile can reduce its saturated hydraulic conductivity (K(s)) to an extent that depends on the effluent quality, soil chemical properties, and the pore size distribution in the soil. Leaching a loamy and a clay soil with secondary effluent decreased the K(s) because of plugging of the pores with suspended solids, whereas the K(s) of a sandy soil was not affected because of its large average pore size. Irrigation of high sodicity, and soils with effluent that had undergone reverse osmosis treatment decreased K(s) because of the low electrolyte concentration of the effluent, which enhanced soil swelling and clay dispersion. An increase of soil sodicity, caused by effluent irrigation, decreased the K(s) of a clay soil leached with water of low electrolyte concentration, as a result of enhanced clay swelling and dispersion. In a non-calcareous, sandy soil, the higher sodicity in the effluent-irrigated soil led, under rainfall conditions, to enhanced seal formation, reduced infiltration, and increased runoff, as a result of enhanced clay dispersion. In contrast, for calcareous soil under similar conditions, no effect of effluent irrigation on runoff and soil loss was observed. This was, probably, because of the release of Ca during the dissolution of CaCO(3); this Ca replaced exchangeable Na, thereby reducing the soil sodicity to its natural levels. Because of the interaction between effluent irrigation and soil properties, it is necessary to identify sensitive regions and soils prior to irrigation with effluents, to prevent possible deleterious effects on soil structure and hydraulic properties. (C) 2009 Elsevier B.V. All rights reserved.