| Human activities are important drivers of the evolution and development of irrigated agricultural systems.Human activities have negatively affected sensitive groundwater systems,resulting in a series of groundwater challenges that have restricted development of irrigation areas.Irrigated agriculture in the Yinchuan Plain has a long history and the plain is affected by complex human activities.Consequently,the Yinchuan Plain experiences a range of groundwater challenges,including groundwater salinization,nitrogen pollution,and soil salinization.These challenges pose serious threats to food security,human health,and to ecological health in irrigated agricultural areas.The aim of this study was to analyze the temporal and spatial evolution of groundwater in an irrigated agricultural area affected by human activities based on the“phenomenon-mechanism-quantification-prediction” paradigm,with the Yinchuan Plain adopted as the study area.The study was based on 529 and 984 observations of well data and groundwater quality data,respectively.The objectives of the present study were to:characterize the mechanisms under which groundwater challenges emerge;quantify the intensity of human activities;simulate the responses of the groundwater environment to different control measures;propose measures for protecting the groundwater environment.The results of this study can act as a scientific basis for water resources protection and environmental management,and for promoting sustainable development in irrigation areas.(1)An analysis of water level monitoring data from 1991 to 2020 and groundwater quality data for 2003,2016,and 2020 revealed the temporal and spatial evolution of groundwater under the influence of human activities.Groundwater of the Yinchuan Plain was apportioned between natural groups,such as phreatic runoff,phreatic climate groundwater,and confined water runoff,and groups representative of human influences,including phreatic irrigation and exploitation of phreatic/confined water.The temporal evolution of the groundwater level in the piedmont area was affected by climate,with the groundwater level showing a trend of fluctuating decline followed by a rapid rise.The levels of phreatic water and confined water showed similar variations,mainly manifested as a continuous decline in groundwater level during the stage of increasing groundwater exploitation(1991–2010)and as a fluctuating increase during the period of groundwater exploitation management(2012–2020).An analysis of groundwater chemistry showed that the piedmont area of the Yinchuan Plain has simple hydrochemical types and is of long-term good quality,indicating that this area is less affected by human activities.Groundwater quality in the plain area was spatially heterogeneous and was influenced by evaporation and agricultural activities.Poor quality phreatic water extended northward in “bead” formations,whereas the quality of confined water decreased from west to east.There was an increasing trend in groundwater salinization during the study period,whereas the salinity of phreatic water first increased and then decreased.An analysis of the water and salt balances showed that groundwater resources of the Yinchuan Plain were in a positive balance in 2003,2016,and 2020,with the accumulation of groundwater salt gradually transitioning to discharge.(2)This study analyzed of the influences of human activities on groundwater salinization using information entropy,Kohonen’s self-organizing map(SOM),and hydrogeochemical analysis.The Yinchuan Plain is affected by intense human activities and has a layered structure,which can be divided into four representative groups of groundwater:(1)natural;(2)groundwater affected by siltation and evaporation;(3)groundwater affected by leakage and evaporation;(4)groundwater affected by irrigation and evaporation.Groundwater affected by siltation and evaporation tended to be the most salinized.Sources of salt of this type of groundwater were possibly related to polyhalite(2Ca SO4·Mg SO4·K2SO4·2H2O),mirabilite(Na2SO4),and rock salt(Na Cl).Groundwater affected by irrigation and evaporation was also salinized,with sources of salt possibly related to mineral dissolution and chemical fertilizer.The other types of groundwater were affected to varying degrees by evaporation,ion exchange,and mineral dissolution.Isotope analysis and the Mix SIAR model were used to identify sources of groundwater nitrogen pollution and their relative contributions.Groundwater nitrogen pollution was mainly distributed in areas of intensive agricultural activities along the Yellow River.Sources of nitrogen in groundwater were mainly soil nitrogen,ammonium nitrogen fertilizer,and fecal sewage,contributing to 28.8%,22.2%,and 23.8% of total groundwater nitrogen,respectively.Groundwater nitrogen was affected by ammonia nitrogen accumulating in drainage ditches due to the combined influences of nitrogen fertilizer and domestic sewage.The results showed that 82% of the soil in Yinchuan Plain could be classified as salinized,with soil salinization increasing from south to north and concentrated locally.K++Na+,SO42-,and Cl-were identified as the main salts contributing to soil salinization.The rank of ions in groundwater according to their sensitivity to salinization was: HCO3-> Ca2+ > Mg2+ >SO42-> Cl-> K++Na+.Geographically weighted regression(GWR)was used to simulate the influence of the natural environment on salinization.Environmental factors were found to regulate the distribution of salinization,whereas human activities affected changes in salinization.(3)This study established an integrated system to evaluate the intensity of human activity in the Yinchuan Plain.A quantitative model of the effect of the intensity of human activities on the groundwater environment was established based on socioeconomic indicators.The intensities of human activities in Yinchuan Plain in 2003,2016,and 2020 were 0.3070,0.3807,and 0.3869,respectively,indication a year-on-year increasing trend;intensities of agricultural activities were 0.2463,0.2985,and 0.2870,respectively,increasing first and then falling.A quantitative model of the intensity of human activity was established based on the groundwater quality index.The intensities of human activity in the Yinchuan Plain in 2003,2016,and 2020 were 0.1544,0.1931,and 0.1721,respectively,with a trend similar to that of agricultural activity.The present study revised and refined the intensities of human activities according to the differences in quantified human activities.The rank of different regions in the Yinchuan Plain according to the sensitivity of groundwater was: Qingtongxia < Litong District < Yinchuan City < Yongning County < Huinong District < Dawukou District < Helan County < Lingwu City < Pingluo County.Moreover,there was a positive correlation between the corrected human activity intensity and the water quality index.(4)This study adopted Cl-in groundwater as an index of human activities.The influence of different management scenarios on the groundwater environment were then simulated.The results indicated that regulating manual groundwater exploitation can act to mitigate pollutants in phreatic groundwater.The simulations indicated that adjusting the structure of water consumption in the study area(Water of the Yellow River completely replacing groundwater as a source of drinking water)can allow the water level in the groundwater exploitation area to recover and for a decrease in groundwater overflow recharge.This scenario not only ensures the safety of domestic water and the sustainable development of industry and agriculture,but also reduces the pollution pressure on confined water and extends the window of phreatic restoration.Under this scenario in combination with continuous improvement in the treatment of phreatic water,the pollutant concentration of confined water can also be improved.Based on the results,this study proposes three strategies for supporting the sustainable development of irrigation areas. |
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