| Trace metals can exist for a long time in the ecosystem due to their bioaccumulation and difficulty in degradation.Meanwhile,due to their carcinogenicity,trace metals can seriously harm animal,plant and human health.Trace metals in the atmosphere can enter the water and soil via dry and wet deposition and consequently threatening these ecosystems.As the largest water conservancy project in China,the three gorges reservoir area has attracted the attention of scholars within and outside of China for its species diversity,sensitivity and vulnerability of the ecosystem.The main urban area of Chongqing is located at the end of the three gorges reservoir area,which is the largest city in the reservoir area.To study the atmospheric deposition of trace metals in Chongqing is important for ecological protection and prevention of the three gorges reservoir area.This study collected 36 samples of dry and wet deposition in Chongqing and analyzed 11 kinds of trace metal concentrations and fluxes of time change,combined with organic indicator of dry wet subsidence and analyses the source of the trace metals,calculated the amount of subsidence of trace metals in all the year round.At the same time,the concentration levels and spatial and temporal distribution characteristics of 11 trace metals in 32 samples of water bodies of the Yangtze river and Jialing river in the main urban area of Chongqing from April to December 2019 were analyzed,and the contribution and ecological risks of the deposition of trace metals to water bodies were evaluated.The main conclusions are as follows:1.The concentrations of each trace metal in wet deposition(water soluble phase and particle phase)are below Ⅱ level of the national surface water standard limit.The correlation analysis between the concentrations of trace metals in the wet precipitation water-soluble phase and particle phase and the precipitation amount of particles shows that the concentrations of trace metals in the wet precipitation water-soluble phase are mainly affected by the rainfall amount,while the concentrations of trace metals in the wet precipitation particle phase are affected by the rainfall amount and the precipitation amount of particles.By analyzing the distribution of trace metals in wet precipitation water-soluble phase and granular phase,found that pH is the main factor affecting the distribution of water soluble and particle phase in wet deposition of trace metals.Influenced by rainfall and the pollution sources,wet trace metals of deposition flux in 5,6,7,8,11 and 12 is high,the deposition flux of 1,2,3,4,9 and 10 is relatively low,while the dry deposition flux has no obvious monthly trend.Through the dry and wet distribution of trace metals,found that most trace metals in the main urban areas of Chongqing mainly deposition by the form of dry deposition.2.Cluster analysis,principal component analysis combined with multiple linear regression analysis and redundancy analysis found that the trace metals in the wet settlement in the main urban areas of Chongqing were mainly from traffic sources(contribution rate 51.74%),industrial emissions(37.44%)and coal emissions(10.81%).The trace metals in dry deposition are mainly from coal burning and traffic sources,with a total contribution of more than 90%,followed by 9.45%from industrial sources.3.From April to December 2019,concentrations of trace metals in water body within the scope of Chongqing urban area has reached the national surface water Ⅱ level standard limit value.The average concentration of Mn was the highest(87.62 μg·L-1),and the average concentration of Cd was the lowest(0.122 μg·L-1).The concentration of trace metals in the non-impoundment period of the Yangtze river and the Jialing river is higher than that in the impoundment period,and the concentration of trace metals in the non-impoundment period of the Yangtze river is higher than that in the Jialing river.In terms of the proportion of trace metals in the water body,the fraction of Ba in Yangtze River is higher than that of Mn,while the fractions of these two elements in Jialing river is comparable.In the non-impoundment period,the proportion of Mn is the highest in both rivers,followed by Ba and Zn.4.The total deposit amount of Ni to water body in the main urban area of Chongqing was the highest(9.07 t·y-1),while that of Se(0.05 t·y-1)was the lowest.The total deposit amount of Ni to the main urban area of Chongqing was as high as 1591.53 t·y-1,while V and Se was the lowest(12.71 and 10.70 t·y-1,respectively).The contribution of atmospheric deposition to trace metals in water body estimated by Direct evaluation method is greater than that estimated by the box model method.The contributions of atmospheric deposition to trace metal in water body evaluated by box model were less than 0.1%in both impinged and non-impinged periods,while those calculated by the direct estimation method shows that the contribution of wet deposition to Se in water body in the main urban area of Chongqing in impinged period is up to 457.08%,and the contribution of V in non-impinged period(12.61%)was the lowest.Through comparison,results showed that the box model may be more suitable for evaluating the impact of atmospheric deposition on flowing water in a certain area,while the direct estimation method may be suitable for the contribution of atmospheric deposition to a static or less mobile water area.5.In this study,the potential ecological risk index(Eri)and the sum of potential ecological risks(RI)of each trace metal were lower than 40 and 150 respectively,indicating that the wet deposition trace metal had slight ecological risks to water.However,the toxicity of As,Cd and Pb should also be concerned. |
