The impact of improving irrigation efficiency on wetland distribution in an agricultural landscape in the upper reaches of the Yellow River in China.

摘要

Wetlands in irrigated agricultural areas have great environmental benefits as agricultural pollution sinks; but agricultural development and water resources redistribution have caused these wetlands to diminish rapidly worldwide. This is the case in the YinNan Irrigation District (YNID) in the upper reaches of the Yellow River in China, where wetlands once flourished as the result of large amount of irrigation diversion and low irrigation efficiency. In this paper, we presented an analytical study on the impact of irrigation water saving practices on wetland distribution in YNID; we also discussed the effect of considering wetland water consumption as beneficial or efficient use on the overall water use efficiency. The study area has a maximal wetland to farmland areal ratio of 10.5% during the irrigation season due to recharges from canal seepage and field percolation; and 45% of the wetland area remains as the permanent pool area during the non-irrigation season. The observed maximum water table rise in the irrigation season is 1.5 m. The current irrigation system efficiency in YNID is 0.30, which is a product of the field level efficiency of 0.68 and the conveyance efficiency of 0.44. Our analysis presented in this paper shows that improving the application efficiency to 0.90 at the field level will reduce the maximum water table rise by 0.53 m, causing the wetland area to shrink by 17% and the subsequent wetland water consumption to decrease by 11%; further improving conveyance efficiency to 0.60 will reduce the maximum water table rise by 0.95 m, causing the wetland area to shrink by 30% and the subsequent wetland water consumption to decrease by 19%. These results indicate that water saving at the conveyance level will have greater impact on wetland water use than that at the field level. If wetland water consumption is considered as efficient use, this fraction of the irrigation water loss becomes efficient use, which will increase the system efficiency proportionally by the percentage of wetland water consumption. The amount of wetlands, and thus additional beneficial wetland water use, is directly dependent on the amount of traditional water losses, such as wetland consumption here. The key question then becomes: where lies the optimum level or the acceptable balance between increasing efficiencies at irrigation scheme level while providing optimal beneficial use for wetlands.