Impact of irrigation on regional groundwater quality in arid area - an multiple water quality assessment

Observed data at 32 monitoring wells in Yichang Irrigation Sub-district of Hetao Irrigation District and Groundwater Quality Standards (GB/T 14848—2017) were used to evaluate regional groundwater quality before and after irrigation with multiple water quality assessment methods including Nemerow Index, improved-Nemerow Index, fuzzy comprehensive evaluation method and Single-factor assessment. Effectiveness of different comprehensive assessment methods was evaluated. Fuzzy comprehensive evaluation was found to be more effective and more objective, consistency between this evaluation method and Single-factor method was 85.9%, fuzzy comprehensive evaluation can therefore be used to evaluate regional groundwater quality, particularly in arid areas. Fuzzy comprehensive evaluation classified the groundwater quality in five grades. The percent before irrigation was V 81.25%, IV 6.25%, III 9.38%, II 3.12%; after irrigation V 84.38%, IV 6.25%, III 9.38%. Analysis of groundwater quality indicators before and after irrigation identified predominant impacting factors: chloride, ammonia nitrogen, sulfate and total dissolved solids (TDS). These findings will be useful for the protection and sustainable utilization of regional groundwater in Hetao Irrigation District.