Effects of Long-term Irrigation with Water from Wastewater Receiving River on Soil Chemical and Microbiological Properties in Hebei, China

In arid and semi-arid regions in China, a large amount of treated wastewater is discharged into rivers that supply water for agriculture. Treated wastewater contains not only valuable nutrients, but also toxic contaminants that might affect soil quality. This study investigated how long-term irrigation with water from a wastewater receiving river affected soil chemical and microbiological properties in Hebei Province, China. Soil samples were collected from three river water irrigated fields adjacent to Wangyang River, and three groundwater irrigated fields far from the river. The results showed that irrigation with river water for more than 20 years had significantly increased dissolved organic C, microbial biomass C and permanganate oxidizable C contents, and beta-glucosidase, urease, alkaline phosphatase, arylsulphatase and dehydrogenase activities in the surface soil, reflecting a stimulated microbial activity in river water irrigated soils. Long-term irrigation with river water has also resulted in accumulation of Hg, Cd, As, Pb, Cu, Cr and Zn in the soil, and may pose potential risk to soil quality and food safety. We conclude that although the river water irrigation has beneficial effects on soil microbiological characteristics, a controlled irrigation management based on periodic monitoring of soil quality parameters is needed to ensure its safe and long-term use in agriculture.