Changes in near-saturated infiltration and soil hydraulic characteristics due to wastewater irrigation in green space

Using wastewater for irrigation introduces various ions and compounds into the soil which may have variable impacts on soil infiltrability and hydraulic characteristics. This study investigates the effects of irrigating with wastewater on soil hydraulic characteristics, crucial for plant growth. Specifically, the research focuses on the impact of effluent from the Mobarakeh Steel Complex located in Isfahan, Iran, over three different periods: 3, 7 and 19 years. Field experiments were conducted at 35 locations using a randomized block design. Sampling sites were selected based on three irrigation durations (3, 7, and 19 years) and two water sources (well water and treated wastewater), with non-irrigated areas serving as the control. The unsaturated 3D infiltration of water into the soil was measured using a tension infiltrometer. The collected data were analyzed using Wooding's analytical and DISC software’s numerical solutions. The saturated hydraulic conductivity of undisturbed soil samples was also evaluated using the constant-head method. The findings indicate that the use of wastewater for irrigation significantly reduces both the saturated and unsaturated hydraulic conductivity due to the presence of suspended particles and hydrophobic substances, which can block soil pores. Wastewater irrigation also decreases the steady-state flux rate and soil water sorptivity. Generally, both wastewater and well water had a similar effect on infiltration and soil hydraulic properties in the region. Consequently, the use of wastewater for irrigating green spaces may be considered as an option, provided that soil quality indicators are regularly monitored. • Treated wastewater impacts soil: Lowers infiltration, hydraulic conductivity, and water flux. • Wastewater and well water impact similarly: Potential preference for wastewater in irrigation. • Filtration processes recommended: To separate particles and enhance irrigation efficiency. • Regular soil monitoring is crucial: Assess long-term impact and ensure soil health.