[Hydrochemical characteristics and spatial-temporal variation of mineralization for the groundwater in Minqin oasis].

In order to curb the deterioration of ecological environment and promote the economic and social sustainable development of Shiyang River Basin, the Minqin government implemented water-saving measures of the shut-in and pressure fields and water discharge engineering in Shiyang River downstream in 2001 and in 2006, respectively. Sixty-five groundwater samples were collected in Minqin County in 2008 and the concentrations of major ions were analyzed in laboratory. The hydrochemistry characteristic of the groundwater was studied by traditional statistical analysis method. Results indicated the concentrations of the major ions, such as SO4(2-), Cl-, HCO3, CO3(2-), Na+, Mg2+, Ca2+ and K+ in the groundwater samples, were (921 +/- 1042), (241 +/- 211), (282 +/- 123), (4.7 +/- 11.7), (468 +/- 599), (156 +/- 166), (142 +/- 89) and (17.6 +/- 34.5) mg/L, respectively. There was increasing tendency for major ion concentrations along the groundwater flow direction. The groundwater mineralization was (2.2 +/- 1.9) g/L in 2008. The type of water samples in Minqin oasis mainly belonged to SO4(2-) - Cl- -Na+ -Mg2+. The average concentration of the NO3- was (8.1 +/- 9.9) mg/L in the groundwater of Minqin, and the nitrate-N content was over 10 mg/L in 1.54% of all of water samples, which was unsuitable for drinking. Based on the data of groundwater mineralization in 2002, 2005 and 2008, the spatial-temporal variations of groundwater mineralization were studied by geo-statistical analysis method. Kringing interpolation results showed that groundwater mineralization at the spatial distribution scale were took on a gradual increase pattern from south to north. As for the change trend of groundwater mineralization in south area of Minqin County, there was increasing trend from 2002 to 2005, but decreasing trend was occurred from 2005 to 2008. Change trend of groundwater mineralization in north area of Minqin oasis was opposite to that of in south area. There was decreasing trend for the groundwater mineralization in south area from 2005 to 2008, which was due to the impact on water discharge in Shiyang River Basin. There was no significant improvement for groundwater by single water-saving measure, but the quality of groundwater was improved after water discharge in Shiyang River Basin.