Soil hydraulic conductivity changes caused by irrigation with reclaimed waste water

Use of reclaimed waste water (RWW) in arid and semiarid regions may alleviate problems of fresh water shortage; however, it also involves some potential risks among which are degradation of soil hydraulic properties. The objectives of the current study were to study the effects of organic matter (OM) loads found in RWW obtained from a secondary treatment plant in Tel Aviv, Israel, and different size fractions of the suspended solids in the RWW on the hydraulic conductivity (HC) of three Israeli soils. The hydraulic conductivity of a clayey grumusol (Typic Chromoxerert), a typic loamy loess (Calcic Haploxeralf), and a sandy loam hamra (Typic Rhodexeralf) was determined in the laboratory using soil columns, by leaching with RWW containing zero, low, or high OM load, followed by leaching with distilled water (DW). The effects of suspended solids' size fraction on the HC Has determined by filtering RWW. Leaching with high OM load RWW caused the relative NC of the grumusol, loess and hamra to drop to final values of 13.9, 24.2, and 58.8%, respectively. Filtering out suspended solids >1.2 mu in this water improved the HC of the hamra, but did not significantly affect the final relative HC of the grumusol and loess. Leaching with low OM load RWW did not significantly decrease the HC beyond the decrease attributed to the effects of the concentration and composition of the electrolytes present in the zero OM load RWW. Subsequent leaching with DW caused an additional decrease in HC, whose magnitude for a given soil did not depend on the quality of the RWW previously used. The presence of OM in the irrigation water did not seem to have significant residual effects on soil HC. Evidently, in high OM load RWW the OM fraction determines the soils' HC, whereas in low OM load RWW, it is the electrolyte concentration and composition in the water, that seem to pose the hazard to soil hydraulic properties, especially during subsequent leaching with DW.