Transferring Process Of Heavy Metals In Subalpine Coniferous Forest-stream-river Meta-Ecosystem

Stream displays a linkage role in biogeochemistry contact of the forests and water.Study elements migration process of the forest-stream-river continuum is very significant to understand the biogeochemical contact of forest and docking of aquatic ecosystems.Western Sichuan subalpine coniferous forest,located in the eastern margin of Qinghai-Tibet plateau and the region of upper Yangtze River,which is the third largest forest area and the core protection area of upper Yangtze river forest freshwater resources.It not only has vital strategic position in biodiversity conservation,carbon sequestration,water conservation,soil conservation,but also has irreplaceable ecological function in maintaining aquatic ecosystem structure and function of upper Yangtze River.Therefore,a deep understanding of biogeochemical contact of western Sichuan subalpine coniferous forest and its docking aquatic ecosystem could prove key scientific basis for protection and ecological security barrier construction of Yangtze River water conservation region.However,the migration characteristics of heavy metal elements in subalpine coniferous forest-stream-river continuum have not been reported so far.Therefore,in order to understand the heavy metal element of biological geochemistry western for Sichuan subalpine coniferous forest ecosystem and the upper Yangtze River water,a study which based on the meta-ecosystem theory was conducted in Bipenggou ecological station of Sichuan Agriculture school,Li country,Sichuan province,china during July 2015 to September 2016,and the research platform focused on subalpine coniferous forest,stream and river was constructed.We investigated the heavy metals storage(Hg,As,Zn,Ni,Cu,Cd)of litter fall,water and sediment in forest,stream and river as well as their dynamics and distributions patterns which in order to provide a scientific basis for the protection and management for upper Yangtze River.The results showed that,storage of heavy metals is directly related to hyd rological characteristics.The heavy metal elements storage of stream-river syste m were Zn>Ni>Cu>Cd>As>Hg.Hg,As and Zn had similar dynamics:their sto rage decreased during September to November 2015,then increased during No vember 2015 to April 2016,and finally decreased during April to August 2016.Dynamics of Ni,Cd are litter different:their storage decreased during Septem ber to November 2015,then increased during November 2015 to May 2016,a nd finally decreased during May to August 2016.Cu had an inconsistent dyna mic:it’s storage increased till October 2015 and then decreased.That mainly b ecause litter decomposition,sediments migration,atmospheric precipitation,sno w melting,which will result in changes of heavy metals content and different components storage(litter,water,sediment).More specifically,in the subalpine coniferous forest-stream-river ecosystem,Hg storage were 72.04 mg/m2,As storage were 725.94 mg/m2,Zn storage we re 147350.00 mg/m2,Ni storage were 20702.03 mg/m2,Cu storage were 9543.53 mg/m2,Cd storage were 2108.89 mg/m2.In the river,Hg storage were 59.41 mg/m2,As storage were 357.69 mg/m2,Zn storage were 107850.00 mg/m2,Ni storage were 16284.35 mg/m2,Cu storage were 4190.48 mg/m2,Cd storage were 1759.71 mg/m2.In the stream,Hg storage were 0.86 mg/m2,As storage were 21.86 mg/m2,Zn storage were 2640.10 mg/m2,Ni storage were 295.03 mg/m2,Cu storage were 357.68 mg/m2,Cd storage were 23.29 mg/m2.Distribu tion of heavy metals storage in the subalpine coniferous forest-stream-river ecos ystem was influenced by different components(litter,water,sediment).Sedimen t had the largest heavy metal storage,accounting for 99.42%-99.98%of the w hole ecosystem,litter accounts for 0.02%-0.58%,water was the smallest,accou nting for 0.01%-0.04%.Besides,distributions of different heavy metals showed a consistent pattern:storage of heavy metals in upstream and downstream was larger,while middle reached the minimum.There were no significant differenc es of heavy metals storage between 15 headwater streams,but the other way a round between river and stream.Storage of the same heavy metal element in r iver was dozens times as much as stream.It illustrated that the distribution of heavy metal in river-stream ecosystem were not evenly,which closely related to element concentration and storage of different components in stream.Howev er,the differences among different heavy metal elements were dozens or even thousands of times.It showed that there were significant differences between h eavy metals which mainly because of its nature.During the study period,variation range of stream-river meta-ecosystem w as 33.59-1625.04 kg/hm2.More specific,input of subalpine coniferous forest-str eam-river through litter of Hg,As,Zn,Ni,Cu,Cd element were 10.26 ug/m2,64.93 ug/m2,26.01 mg/m2,1.07 mg/m2,2.24 mg/m2,0.32 mg/m2 separately.Output through litter of Hg,As,Zn,Ni,Cu,Cd element were 0.24 ug/m2,4.60 ug/m2,0.60 mg/m2,0.05 mg/m2,0.10 mg/m2,0.01 mg/m2 separately.Litter output/input result showed that the vast majority of litter was kept in subalpine coniferous forest-stream-river ecosystem.Hg,Cd content of litter decreased in the process of from upper stream to the estuaries,it means that they were rel eased from litter into the stream.On the contrary is that As,Ni and Cu conte nt of litter increased in the same process,it means that these element were ad sorbed from stream.While Zn content didn’t change much which showed that litter Zn is stable.We only detected Hg,As element in water under this experi ment condition.Hg element content of water reached the peak during Septemb er to November 2015,then decreased,however it had an increased tendency af ter August 2016.As element content of water had different trends,it increased during June to July 2016 and then decreased after August.In conclusion,heavy metals in subalpine coniferous forest were migrated with sediment,litter and water in stream and river,the heavy metals storage showed that it had a decreased tendency.The distribution patterns showed that most of the heavy metals deposits in sediment.While litter had lower heavy metals storage,it had certain adsorption capacity to some heavy metals(As,Ni,Cu)in water system,which could reduce the concentration of heavy metals and have certain water quality purification effect.At the same time,some heavy metals(Zn,Cd)could import water system with litters,they might influence the environment safety of downstream water system during the degradation of litter.There were low content and stock of heavy metals in stream and water system,which proved a high water quality in study area.These results could not only provide basic date in understanding source and sink process of heavy metals of subalpine forest and drainage basin,but also offer new thought and scientific evidences in managing the environment of alpine forest in upper of Yangtze River.