Assessment of long term wastewater irrigation impacts

In this study, the effects of long term use of urban wastewater (over 40 years) on soil salt content and related parameters were evaluated in the lands south of Tehran. For this analysis, Kriging methods were tested. According to the suitable model indices, Ordinary Kriging (OK) was suitable for pH, Clay, Na, Mg2 and sodium adsorption ratio (SAR) interpolation; Log-normal Kriging (log-normal K) was suitable for soil EC and Cl-; DK was suitable for soil Ca2. In this study, Na, Cl- and sodium adsorption ratio (SAR) variables with the highest nugget-to-sill ratio showed most affected by extrinsic variations (long term irrigation with wastewater). In spite of wastewater irrigation, results showed low amounts for EC of soils (less than half the critical limit) attributed to good leaching through high and permanent water bodies. However, Na and sodium adsorption ratio (SAR) with amounts higher than critical limit showed need to management measures like gypsum application. Heavy soil of area is a reinforcing factor in sodicity trend related to clay percent higher than 25, so sodicity risk treats total area of study region.