Degradation of agricultural drainage water quantity and quality due to farmland expansion and water-saving operations in arid basins

Understanding the impacts of agricultural activities on drainage is increasingly important element of water resources management in arid regions. This study analyzed the effects of recent changes in agricultural activities on drainage water quantity and quality from farmlands in Aksu River Basin in Northwest China. Based on drainage water analysis for 2003-2010, implementation water-saving measures resulted in the reduction of irrigation quota by up to 48%. This in turn resulted in a decline in drainage water by up to 44% in 2010, compared with that in 2004. Na-Cl was the main drainage water type, driven by the dissolution of soluble salts and cation exchange. Analysis further showed that while TDS (total dissolved solids) in drainage water increased to 4.7-10.8 g/L (an average of 7.6 g/L) in period 2005-2010, that in 2003-2004 was 28% lower. In contrast to irrigation water, TDS in drainage was 6-18 times higher than that in irrigation water. Yet further analysis showed that while the increase in TDS in drainage water was mainly driven by farmland expansion, drainage water was as well affected by groundwater exploitation. It was therefore recommended to restrict farmland expansion and to intensify water-saving operations in order to prevent destructive declines in water flow to downstream ecosystems.