Hydrochemistry characteristics of groundwater with the influence of spatial variability and water flow in Hetao Irrigation District, China

Groundwater is an important resource of water in arid and semi-arid agricultural regions. Thus, identification of hydrogeochemical characters and the influence of geospatial variability and flow pooling are of significance on groundwater resources management and making irrigation decisions in salinized areas. The study specifically focused on the Hetao Irrigation District located in the semi-arid region of northern China. A total of 85 groundwater samples (42 from the upstream Shenwu Irrigation Area (SWIA), 43 from the downstream Wulate Irrigation Area (WLTIA)) were collected, and 15 water quality indexes were analyzed. Methods including mathematical statistics, Piper diagram, Gibbs model, forward succession model, and ionic rations were used to analyze the hydrochemical characteristics and evolution mechanisms, RSBC, PS, SAR, WQI were selected to evaluate water quality and irrigation suitability from the perspective of salt and alkali damage. Results showed that the groundwater of the study area is weakly alkaline, SWIA is mainly fresh water (47.62%), WLTIA is mainly brackish water (65.12%), and the hydrochemistry of the groundwater consists of Cl-Na type and Cl center dot SO-Ca center dot Mg. The solute content of downstream (WLTIA) is higher than that of upstream (SWIA), Na+ and Cl- have obvious advantages in WLTIA, and they are the main contribution indicators of groundwater TDS in the study area. The groundwater is subjected to the ongoing influence of rock weathering, ions exchange, and evaporate crystallization Na+ mainly originates from the dissolution of evaporate salt rock and silicate rock, and Ca2+ from the dissolution of gypsum and carbonate. The order of contribution of different rocks is evaporation rock > silicate rock > carbonate rock. Based on the classifications of sodium absorption ratio (SAR), residual sodium bicarbonate (RSBC), and potential salinity (PS), most of the groundwater samples are unsuitable for irrigating, and the groundwater quality of the SWIA is better than that of the WLTIA.

Automated summary

Groundwater is an important water resource in arid and semi-arid agricultural regions, playing a significant role in groundwater resources management and irrigation decisions in salinized areas. By analyzing the hydrogeochemical characteristics and evolution mechanisms, as well as water quality indexes, it was found that the groundwater in the study area is weakly alkaline, with the upstream area mainly containing fresh water and the downstream area mainly containing brackish water. Based on classifications of salt and alkali damage, most of the groundwater samples were found unsuitable for irrigation, with the quality of the upstream groundwater being slightly better than that of the downstream.