Study On Water-sediment-soil Chemical Characteristics In The Middle And Lower Reaches Of The Yellow River

The hydrochemical characteristics of rivers reflect the source and migration and transformation of chemical components in water bodies,and to a certain extent,the chemical weathering in river basins and its relationship with chemical components in sediments and coastal soils.Analyzing the hydrochemical characteristics and influencing factors of the basin and discussing the main sources of ions can provide the basis for the sustainable development and utilization of water and soil resources and the protection and construction of ecological environment in the basin.Taking the main stream of the middle and lower reaches of the Yellow River?Fenglingdu section to Dongying section?as the research area,water samples were collected in the flood season?June 2017 and September 2018?and the dry season?December 2017 and April 2018?,and sediments and bank soil samples at corresponding locations were collected in September 2018.The chemical characteristics of water,sediments and soil in the middle and lower reaches of the Yellow River were analyzed.Pearson correlation analysis method was used to study the correlation of main chemical components in river water,sediment and soil in the middle and lower reaches of the Yellow River.The main chemical weathering processes in the basin were discussed by Gibbs map,triangle map and ion ratio map.The main conclusions of this study are as follows:?1?The mean water temperature and dissolved oxygen?DO?of the middle and lower reaches of the Yellow River were 19.58?and 7.85 mg·L^-1 respectively.The average value of pH was 8.25,and the water body was weak alkaline.The average value of TDS was 743.19 mg·L^-1,which was higher than the average value of 100mg·L^-1 in the world rivers.The average concentration of TDS in dry season?November 2017 and April 2018?was higher than that in flood season?June 2017 and September 2018?.The hydrochemical type was Na⁺-Cl^--HCO₃^-type in June 2017,and Na⁺-HCO₃^--Cl^-type in November 2017,April 2018 and September 2018.In the four periods,Na⁺accounted for 60.78%,61.13%,59.81%and 60.60%of the total cations;in June 2017,Cl^-,which accounted for 37.96%of the total anions,and in November2017,April 2018 and September 2018,HCO₃^-,which accounted for 38.41%,39.09%and 37.89%of the total anions,respectively.The concentration of Na⁺,Ca²⁺,Cl^-and SO₄^2-in dry season was higher than that in high season,while Mg²⁺and K⁺were opposite.The spatial distribution of main chemical components in Xiaolangdi reservoir area shows that the concentration of Na⁺,K⁺,Cl^-and SO₄^2-gradually decreases from the end of reservoir to the front of dam,while Ca²⁺,Mg²⁺,HCO₃^-and NO₃^-increase from the end of reservoir to the front of dam.On the vertical distribution,the concentrations of Na⁺,K⁺,Cl^-and SO₄^2-decreased from surface layer to surface layer,but the concentrations of Ca²⁺,Mg²⁺and NO₃^-increased from surface layer to surface layer,while HCO₃^-decreased from surface layer to surface layer in April 2018,and increased from surface layer to surface layer in the other three periods.?2?The sediment pH in the middle and lower reaches of the Yellow River was alkaline as a whole,with an average value of 8.59,Ca²⁺78.00 mg·kg^-1,Cl^-41.00mg·kg^-1,SO₄^2-74.00 mg·kg^-1,HCO₃^-20.58 mg·kg^-1,K⁺114.00 mg·kg^-1,available silicon 76.53 mg·kg^-1 and NO₃^-10.22 mg·kg^-1.HCO₃^-concentration showed a decreasing trend from Fenglingdu to Huayuankou,and an increasing trend from Huayuankou to Dongying;Available silicon concentration showed an increasing trend from Fenglingdu to Xiaolangdi Dam,decreased from Xiaolangdi Dam to Donga Dam,and increased from Donga to Dongying Dam;NO₃^-concentration showed a decreasing trend from Fenglingdu to Kaifeng,and an increasing trend from Kaifeng to Dongying Dam.?3?Soil pH in the middle and lower reaches of the Yellow River was alkaline as a whole,with an average value of 8.87,Ca²⁺86.00 mg·kg^-1,Cl^-68.00 mg·kg^-1,SO₄^2-176.00 mg·kg^-1,HCO₃^-18.06 mg·kg^-1,K⁺41.00 mg·kg^-1,available silicon 46.22mg·kg^-1 and NO₃^-3.31 mg·kg^-1.HCO₃^-and available silicon concentration showed a decreasing trend downstream;NO₃^-concentration also showed a decreasing trend from Fenglingdu to Xiaolangdi Dam,while that from Xiaolangdi Dam to Dongying Dam showed an increasing trend.The concentrations of HCO₃^-,available silicon and NO3-in sediments at the same sites were higher than those in soils,while the concentrations of Ca²⁺,Cl^-,SO4^2-and K⁺in sediments were lower than those in soils.?4?The correlation analysis of the main chemical components of water,sediment and soil in the middle and lower reaches of the Yellow River shows that there was a certain correlation between the main chemical components in the same research object,which proves that they have similar sources.The correlation of the same chemical components between water and sediment,water and soil,sediment and soil was not significant,indicating that the chemical components of soil and sediment were not the main source of river water chemical components.However,SO₄^2-,Cl^-and NO₃^-were correlated with each other,which indicates that the main chemical components of water,sediment and soil were greatly affected by human activities.?5?Gibbs diagram method was used to determine that the main ions in the middle and lower reaches of the Yellow River were controlled by evaporation-concentration process and rock weathering,but the evaporation-concentration process was dominant,and the influence of atmospheric precipitation on the hydrochemical characteristics was small.The main weathering types of rocks in the middle and lower reaches of the Yellow River were evaporite and carbonate rocks,and the weathering effect of silicate rocks was relatively weak.In addition,the ratio of 2SO₄^2-+HCO₃^-?HCO₃^-to 2(Ca²⁺+Mg ²⁺)in the study area shows that sulfuric acid produced by human activities was widely involved in the weathering process of carbonate rocks.The results of principal component analysis show that the highest contribution rate of hydrochemical characteristics in the basin comes from the anthropogenic input factors such as evaporative salt rock dissolution and irrigation backwater,domestic sewage or industrial wastewater discharge,which were 46.55%?June 2017?,43.28%?November 2017?,56.62%?April 2018?and 41.05%?September2018?,respectively.The dry season was higher than the flood season,followed by the weathering of carbonate rock.The contribution of chemical composition was 35.90%?June 2017?,38.90%?November 2017?,20.64%?April 2018?and 41.05%?September2018?,respectively.The high water period was higher than the low water period.In conclusion,the chemical characteristics of water-sediment-soil and its chemical weathering process in the middle and lower reaches of the Yellow River were revealed,which provides a theoretical basis for the protection of water and soil resources in the study area.