River Water Influenced by Shale Gas Wastewater Discharge Used for Rice Irrigation Has Limited Effects

The process of hydraulic fracturing to extract shale gas generates a large amount of shale gas wastewater, and the potential impacts of wastewater discharge after treatment are concerning. In this study, we investigated the effects of the irrigation of paddy fields by river water that has been influenced by wastewater discharge for 2 consecutive years on soil physicochemical properties, microbial community structure and function, and rice fruit quality. The results showed that irrigation using river water significantly increased conductivity and Cl- in paddy soils downstream of the outfall, that the effects were limited, and that the concentrations were significantly reduced in other paddy soils downstream (>500 m). Irrigation did not cause the accumulation of trace metals (Ba, Cd, Cr, Cu, Pb, Sr, Zn, Ni, and U) in soil and rice fruits. After two years of irrigation, the Shannon diversity increased in the paddy soil, but these changes occurred on a small scale and did not occur after one year of irrigation. Overall, despite the changes in microbial biodiversity and composition, surface water influenced by shale gas wastewater discharge used for agricultural irrigation exerted limited effects on agroecosystems over a short period.