| Wulate irrigation area is located in the lower reaches of Hetao irrigation area in Inner Mongolia.It is responsible for drainage of the entire irrigation area and is an important food production base in China.Because of effects of primary geology and human activity,the water quality deteriorates,groundwater utilization efficiency is low.Therefore,it has great practical significance to explore the chemical characteristics and sources of groundwater in this area.In this paper,the Piper diagram,Shukalev classification,Gibbs model,and Schoeller diagram are used to analyze the groundwater chemical characteristics and main controlling factors in the Wulate irrigation area.The single-factor evaluation is conjuncted with groundwater environmental background value to evaluate groundwater quality,it uses factor analysis and absolute principal component multivariate linear regression model to quantitatively analyze the sources and causes of groundwater pollution in the study area,providing a scientific basis for the rational management of groundwater environment and efficient use of groundwater.The main conclusions are as follows:(1)Significance tests were conducted on the nutrient concentration of groundwater in different periods in the study area.Each nutrient concentration was significantly different,and was mainly composed of nitrogen.NO3--N(nitrate nitrogen)was the main form of existence,and the coefficient of variation during the irrigation period Significantly higher than other periods,irrigation only affects TN(total nitrogen)and NO3--N.Comparing its concentration with the standard value and statistically found that NH4+-N exceeded the standard seriously,and the rate of exceeding standard in different periods was above 87%.The spatial distribution of nutrients showed that the spatial distribution of nitrogen was southwest>northwest>east,and there was no obvious regularity in the spatial distribution of TP content.Comprehensive analysis found that TN(total nitrogen)is mainly affected by factors such as irrigation,rainfall,and human activities,while TP is affected by various factors such as soil adsorption and agriculture,animal husbandry,and urbanization.(2)The significant results of the main salt segregants in the study area show that K++Na+(sodium ions)and Cl-(chloride ions)are the main ions in the irrigation area and are strongly variable.Combining the Kriging spatial interpolation results,the spatial distribution is found to be more consistent According to its spatial distribution,the study is divided into 4 areas,and the salt content of each area is expressed as Ⅰ>Ⅱ>Ⅲ>Ⅳ.Among them,the Cl-content is 5099.97 mg/L(area Ⅰ)and 1215.99 mg/L(areaⅡ),647.71 mg/L(area Ⅲ),521.67 mg/L(area Ⅳ),K++Na+ content is 4823.87 mg/L(Zone Ⅰ),890.43 mg/L(Zone Ⅱ),634.34 mg/L(Zone Ⅲ),485.85 mg/L(Zone Ⅳ).The Piper three-line diagram and Gibbs diagram were used to analyze the water chemistry types and main control factors of the groundwater in the irrigation area.The study showed that the primary salinity of most groundwater sampling points in the area was more than 50%,and Na+-Cl--SO42-and Na+-Cl-were the main type of groundwater chemistry in the Wulate irrigation area,evaporative concentration is the main controlling factor of the groundwater ion composition in this area,and it is also greatly affected by human activities.The results of the Schoeller diagram study show that the source of drainage is basically same as groundwater recharge.Ⅰrrigation water is not the entire source of ions in groundwater.The infiltration of soil salt carried by irrigation water is one of the reasons for the higher salt content in groundwater.Ⅰn addition,it is found that in addition to the original conditions,irrigation from the Yellow River and geological factors are the main factors that lead to higher salt content in groundwater.(3)According to the geological conditions of the Wulate Ⅰrrigation Area,it is divided into detention-gathering area,structural intrusion-gathering area,and piedmont alluvial-recharge area.The calculation results of groundwater environmental background value are mostly shown as area Ⅱ>area Ⅰ>area Ⅲ,area Ⅱ alone The factor indexes are all above 5 and the maximum can reach more than 30.The exceeding standard is the most serious.The single factor index of groundwater in area Ⅲ is within 5 and it can be seen that the water quality in this area is relatively best.The analysis found that Cl-(chloride ion),SO42-(sulfate ion),Ca2+(calcium ion),Mg2+(magnesium ion),Na++K+(sodium ion),HCO3-(bicarbonate ion)and TH(Total hardness)is related to factors such as groundwater flow,evaporation and structural infestation.According to the results of groundwater evaluation in different periods,salt segregants in the groundwater in spring irrigation and autumn irrigation exceeded the standard,and the nitrogen content in the groundwater exceeded the standard after the spring sowing and before the autumn harvest(during the crop growth period).The water-soluble salt component in groundwater,and nitrogen is mainly affected by fertilization during the growth period.(4)The common factors of groundwater quality in the Wulate Irrigation Basin based on factor analysis are leaching-migration-enrichment factor(F1,whose contribution rate is 42.15%).The high-value areas are mainly distributed in the southwest;agricultural production-human activity dissolution factor(F2,with a contribution rate of 15.79%),with severe pollution:in the west and the highest in the middle;native geological factors(F3,with a contribution rate of 13.56%),with high-value areas distributed in the northwest;environmental background factor(F4,with a contribution rate 19.29%),the high-value area is distributed patch-like throughout the irrigation area,and the distribution law is relatively random.The results based on the factor score function show that the spatial distribution of the comprehensive factor score(F)is basically consistent with the F1 distribution rule.It can be seen that the leaching-migration-enrichment factor(F1)is the main pollution factor of groundwater in the Wulate irrigation district.The predicted values of groundwater quality indicators obtained using APCS-MLR are highly consistent with the measured values.Combining factor analysis and multiple linear regression receptor models can effectively identify and analyze the source of groundwater chemical pollution. |
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