Soil hydraulic conductivity changes caused by irrigation with reclaimed waste water

Use of reclaimed waste water (RWW) in arid and semiarid regions may allevia te problems of fresh water shortage; however, it also involves some potenti al risks among which are degradation of soil hydraulic properties. The obje ctives 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 cond uctivity of a clayey grumusol (Typic Chromoxerert), a typic loamy loess (Ca lcic Haploxeralf), and a sandy loam hamra (Typic Rhodexeralf) was determine d in the laboratory using soil columns, by leaching with RWW containing zer o, low, or high OM load, followed by leaching with distilled water (DW). Th e effects of suspended solids' size fraction on the HC Has determined by fi ltering RWW. Leaching with high OM load RWW caused the relative NC of the g rumusol, 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 H C of the grumusol and loess. Leaching with low OM load RWW did not signific antly decrease the HC beyond the decrease attributed to the effects of the concentration and composition of the electrolytes present in the zero OM lo ad RWW. Subsequent leaching with DW caused an additional decrease in HC, wh ose magnitude for a given soil did not depend on the quality of the RWW pre viously used. The presence of OM in the irrigation water did not seem to ha ve 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 p ose the hazard to soil hydraulic properties, especially during subsequent l eaching with DW.