| The geochemical cycle of trace elements in rivers is one of the important material cycles in the Earth's ecosystem.The Mun River Basin is the largest river basin in northeastern Thailand,and plays an important role in local industrial & agricultural production and ecological balance.With the development of the economy,the ecological problems in the Mun river basin are increasing.Up to now,the research on the characteristics and migration changes of trace element in the water of the Mun River basin is still relatively rare.Based on these,this thesis is focus on the temporal and spatial distribution of dissolved trace elements in the Mun River during the wet and dry season,as well as the influencing factors and sources.In addition,this thesis conducts a water quality assessment and a health risk assessment on the water quality of the Mun River,and calculates the input flux of trace elements to the Mekong River,which will provide a scientific basis for water resources development and utilization,environmental protection and the production of industry and agriculture in the Mun basin.The main achievements of the thesis are as follows:1.The water temperature(Tw)of the Mun River varies little,with an average of 28.5?during the wet season and 28.6? during the dry season.The range of dissolved oxygen(DO)ranged from 2.97~7.94 mg/L with an average of 5.02 mg/L in the wet season,ranged from 3.26 to 11.82 mg/L with an average of 6.71 mg/L in the dry season.The average pH is 7.06 in the wet season,the river is neutral in general,the average pH value is 7.41 in the dry season,and the river is weakly alkaline;The average value of the conductivity(EC)is 198 ?S/cm in the wet season,and 435.17 ?S/cm in the dry season.The average value of total dissolved solids(TDS)is 97.35 mg/L in the wet season,much lower than the average of 283 mg/L in the world,the average is 266.74 mg/L in the dry season,close to the world average.2.The concentration of trace elements in the wet and dry season from high to low is that:Fe>Sr>Ba>Mn>Al>Zn>Cu.In time distribution,the maximum values of Mn,Zn,Fe,and Sr appear in the dry season.The maximum values of Cu,Al and Ba appear in the wet season.In spatial distribution,the average concentration of trace elements decreases from upstream to midstream and downstream,this has a certain relationship with the land use distribution in the Mun River Basin,with the largest industrial province in Thailand upstream.In addition,otherhuman activities such as industrial and agricultural production,as well as rock weathering in nature,are also the main factors affecting the spatial and temporal distribution of trace elements.3.The effect of water quality parameters on trace elements in the wet season is stronger than that in the dry season.Al-Fe,Mn-Zn and Fe-Ba showed strong correlations in the both seasons.Principal component analysis shows that Fe,Sr,Ba in the wet season might derive from the input of sediments and rock weathering;Al derives from the input of sediments;Mn,Cu,Zn derive from human activities;Fe and Mn are affected by colloidal instability at the same time.The source of Fe,Sr,Ba in the dry season might derive from the input of sediments and rock weathering;The source of Mn,Cu,and Zn are attributed to human activities,and Al derives from the input of sediments.The Mun River has excellent overall water quality and has little non-carcinogenic risk to the human body.Fe contributed the most to the Mekong River,and Cu contributed the least. |
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