| The river basin,as a relatively independent combined system,is the recueillir and comprehensive reflection of the environmental impact by all sorts of human activities and natural processes.With the sustainable development of economy,the human activities on the river basin being more and more frequent,which make the river pollution becoming more and more serious.Heavy metals,with the the characteristics of refractory,easy accumulation and toxicity,once entering into the river basin will pose long-term potential damage to the ecosystem and human health.For these years,heavy metal pollution in river basin becomes a research hotspot at home and abroad.At present,the research of distribution and risk assessment of heavy metal pollution is mainly on water and sediment,while has nothing to do with suspended solids and the pore water.Up to now,there is no exact research to focus on the distribution of heavy metals in river water,suspended solids,sediments and pore water and their relationship with the surrounding conditions at the same time.In addition,the environmental scientists had realized that the river basin suffered combined pollution long time ago,and had studied a number of cases about the composite effect among heavy metals or heavy metals and organic matters.However,the definition of composite pollution water quality and evaluation methods havn't been put forward yet,also lacked a comprehensive ecological risk assessment method of heavy metal pollution in watershed.This study takes the Beijiang River and its tributaries affected by typical point sources?Guangdong Province,China?as the research objects,discuss and study the multi phases,seasonal,vertical and fraction distribution of the heavy metals in the river basin;analysis the distribution relationship,interaction mechanism and influence factors of heavy metals in each phase from multiple aspects of water dynamics,water chemical characteristics and human activity types;reveal the pollution source and the migration and transformation rule of heavy metals from the perspective of complex environmental system combining the natural environment of the Beijiang River;explore the influence on the formation of heavy metal pollution characteristics of the Beijiang River by human driving factors and nature driving factors;evaluate the pollution status of heavy metals in river basin;predict the development trend of pollution and harm to ecological environment;first attempt put forward the classification and definition method of compound pollution water quality from the perspective of material composition;and establish the comprehensive ecological risk evaluation method of heavy metals in river basin with comprehensive considering water quality,toxicity coefficients and evaluation factors.The main results are listed as follows:?1?The basic water quality indexes in the Beijiang River did not obviously exceed the standard values,TDS had significant correlation with SS,EC,SAL,pH,DO and T and could be used as alternative water quality indicator.The water quality types were Ca-HCO3 and NaK-HCO3 due to affected by the regional geology.The C/N ratio was in the range of 0.16-3.21,indicating that the water quality characteristics being low phosphorus and high carbon and nitrogen.The concentration of TDN in several sections of the Beijiang River exceeded the standard values affected by man-made factors,and the TOC had significant linear relationship with UVA254.The spectrum analysis showed that the water body exist risk caused by trace toxic and harmful organic compounds.In a word,due to influencing by point sources,the water quality at the confluence sites presented to be compound pollution.?2?The heavy metals in the Beijiang River were mainly distributed in sediments and suspended solids,mainly influenced by chemical industry,followed by tourism,agriculture and dam construction.The allocation proportion had relationship with metallic characteristics,suspended solids composition,water p H and sediment mineral properties.The main pollution sections were at S11,S23,S32 and S33.Heavy metals in surface sediment was given priority to residual state,while the percentage of bio-available state of Cd and Zn was relatively high.Heavy metals were mainly distributed in the range of 0-1 m deep columns of sediments,and the sedimentary depth of 90% sections were not more than 3 m.?3?The results by traditional evaluation methods showed that As and Tl in water and pore water exist carcinogenic risk and non-carcinogenic risk,Cd and Hg in suspended solids and sediments had higher risk.The new constructed CERI methods had considered the water quality,metal toxicity coefficients and the traditional evaluation factors,thus the evaluation results should be more reliability.The comprehensive evaluation results showed that the Beijiang River except S11,S33,S1 and S14 sections?medium to high degree?manifests as low potential ecological risk degree.?4?The source resolution results by PCM,HCA,PCA and FA-MLR methods showed that 82.23% of Tl comes from smelting,87.17% of Hg comes from smelting and city life,86.51%,90.67%,84.11%,90.67% of Pb,Cd,As,Mn are mainly from smelting and mining,96.21% and 92.18% of C u and Zn are mainly from smelting,mining and e-waste dismantling.The total flux of heavy metals come from 10 main tributaries of the Beijiang River were in the order of Mn>Zn>As>C u>N i>Pb> Cr >Tl>Cd> Hg,and the fluxes into the Beijiang River were greater than out of the river,indicating that there was obvious accumulation of heavy metals in the sediments of the Beijiang River every year,thus becoming the long-term hidden trouble on the water quality of the Beijiang River.?5?The mixed region of the Maba River,affected by man-made and natural sources of smelting,mining,urban lives,agricultural non-point source,geological weathering and atmospheric precipitation,where Pb,As,Zn,C u,Tl and Hg were severely polluted,and the distribution characteristics were significantly affected by C lay ratio and hydraulic retention time.The Igeo evaluation results showed that Pb,As,Zn,Mn,C u,Tl and Hg were in moderate pollution to severe pollution degree,while the mERM-Q evaluation results showed that the probability of biological harm caused by heavy metals in the mixed region was more than 76%.Source analysis showed that 84% of C u comes from mine tailing,77%,66% and 72% of Tl,Hg and Cd originates from smelting waste water,both 80% of Cr and N i comes from geological weathering and atmospheric precipitation.?6?The high initial concentration of heavy metals in ech phase of the Hengshi River affected by acid mine drainage had a fast migration speed and were affected by p H,and the mineral composition also transformed rapidly.The heavy metals in sediments were given priority to residual state,the content of bio-available state?F1 and F2?was following the order of Cd>Mn>Zn>Pb>C u>As.The order of heavy metals in each phase was sediments> suspended solids>water>pore water,the proportion of water and pore water was small.In the system of heavy metals-soil-crops,Cd could easily transform from soil to crops due to having a high content of exchangeable state,while As and Pb mainly came from atmospheric precipitation.The total non-carcinogenic risk and carcinogenic risk values of heavy metal pollution by three kinds of crops were as high as 48.00 and 0.056,respectively,indicating that ingestion of these kind of food crops for a long time can cause serious health risks.Moreover,sugarcane can be used in the repairing of heavy metal contaminated soil due to its strong root system and the ability to adapt to the bad environment.In a word,studying the formation,distribution and transformation of heavy metals in complex environmental system,analyzing the source of target heavy metals and estimating the fluxes from all tributaries,and evaluating the effect of comprehensive ecological risk by surrounding environmental factors can provide basic data and theoretical foundation for management and repair of heavy metal pollution in river basin. |
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