The Characteristics Of Dissolved Organic Carbon In Rainfall,Snow And Ice In The Mt.Yulong Region

Dissolved organic carbon?DOC?is an important part in atmospheric aerosols and plays an important role in global carbon cycle.The DOC in the atmosphere can not only influence the albedo of the cloud,increase the concentration of cloud condensation nuclei,but also have an impact on the composition of PH values,visibility and photochemical process of precipitation.Additionally,precipitation is an important method for the removal of DOC in atmosphere.Thus,studying the contents and sources of DOC in atmospheric precipitation is an important way to understand the DOC in atmosphere.In addition,DOC has strong light-absorbing ability,and it can easily reduce the surface snow albedo and accelerate melting amount of glaciers.Studying the distribution of DOC in glacier is another way to research the glacier changes.Yulong Snow Mountain is located in the southeast of Tibetan Plateau,south of Hengduan Mountain,occupying a special geographical location.Due to the intersection of summer southwest and southeast monsoon,the climate condition in this area are complex and changeable.The glaciers and atmospheric precipitation in Mt.Yulong region are very sensitive response to climate change,and therefore the study of DOC deposition in this area has high scientific value and practical significance.In this study,129 precipitation samples and 77 snow samples were collected from Yulong Snow Mountain region between June and September 2014.The rainwater samples were collected at five sites,including Lijiang City?LJ?,Ganhaizi Basin?GHZ?,?upper or lower??Cable Station?CS?,Longpan Town?LP?,Daju Town?DJ?.Meanwhile,the various snow and ice samples,including fresh snow,surface ice,ice meltwater,surface snow,snow meltwater,snowpit and ice lake,were also collected at and around the Glacier Baishui No 1 on Mt.Yulong.The DOC and inorganic ions of all samples were detected by DX-600,ICS-2500 and Shimadzu TOC 5000.The results show that:On the spatial scale,the mean contents of the DOC in precipitation are according the order of LP>CS>DJ>GHZ>LJ.The highest value of DOC in LP was attributed with special valley topography,high loaded transportation and frequent agricultural activities.The high speed of valley wind was the main factor of high concentration of DOC in CS.The relatively dry-warm climate condition and frequent agricultural activities led to the highest content of precipitation DOC in DJ.In addition,the content of precipitation DOC in GHZ and LJ were basically at the same with the lowest value.It was related to that the collecting sites were close to the scenic spot and the environmental protection was better.On the temporal scale,the content of precipitation DOC at LP varied between 0.53-1.29 mg L^-1,showing a trend of gradual decline,resulted from the DOC photochemical characteristics and the leaching of rainwater.The analytical results of the principal component?PCA?between DOC and inorganic ions showed that DOC and SO₄^2-,NO₃^-had higher loaded and significant relativity,suggesting that they were from similar sources,such as human activities.The backward trajectory analysis has quantitatively described that the air mass from southwest direction?accounted for46%?was the main source of long-distance transmission in Mt.Yulong region.The mean DOC content in this type of air mass was 1.25±0.56 mg L^-1.Additionally,the annual wet deposition flux of DOC in Mt.Yulong region was estimated to be 1.99 g C m^-2 year^-1.The mean contents of the DOC in snow and ice samples were in the order of fresh snow>ice lake>surface snow>snow meltwater>surface ice>older snow>ice meltwater.The highest value of DOC content in fresh snow indicated a higher efficiency of scavenging and gathering pollutants in snow than that of raindrop.The variations of DOC contents in different types of snow and ice samples were caused by the photolysis of DOC,post-depositional processes and glacier quick-melt effects.For the vertical distribution in snow,the variation of DOC in snowpit is basically consistent with the distribution of ions,and the relatively high content was obtained in the pollution layer in the snowpit.Based on the PCA in snowpit,the main source of DOC in snow and ice was from the pollution generated by human activities.For the altitude distribution,the highest DOC content in surface ice was found in 4650-4675 m,which can be related to slope direction,glacial ablation and human activities.The interaction of DOC,precipitation and glacier showed that a local microclimate may be caused by the cold island effect formed by glacier,which can promote the formation of precipitation in glacier areas,and glaciers melting process will promote the enrichment of DOC,thus increasing its concentration in ice,snow and melt water;In addition,the rainwater during ablation period can increase the glacier heat?accounted for 1.45 W/m²?,resulting in accelerated glacier ablation,and precipitation may have the effect of dilution of atmospheric aerosols,making gradually reduction of the DOC content in precipitation;Meanwhile,glacier melt can be accelerated by the strong light-absorbing ability of DOC.Additionally,this study can fill the vacancy of studies about DOC in precipitation in the Mt.Yulong region,further perfect the research system in this area and better reveal the influence of the local and remote transmission of pollutants.It also provides the basis for further study of human activities and climate change.