River Hydrochemistry In Middle And High Latitude Regions

In the research of global carbon(C)cycle,much attention has been paid to the imbalances of the C-sink.The consumption of atmospheric carbondioxide(CO2)by rock weathering is about to 6.08×108 t/a,nearly one third of the consumed carbon.Therefore many researhers have focused on rock weathering.The Polar Regions are covered by large amounts of glaciers,and hold approximately 78%of the world’s freshwater resources.Under the background of global climate change,polar glaciers are easily subj ected to rapid melting when temperatures rising.In this situation,water-rock interaction in Polar Regions can be an important factor to affect carbon cycling.Rock weathering and chemical denudation rates are relatively high in Polar regions.It’s worth to discuss the effects of weathering and CO2 drawdown during the accelerating melt glaciers in Polar Regions.The strength of rock weathering and denudation can be reflected by the hydrochemical characteristics.Hydrochemistry can not only reflect the environmental changes,but also help us to understand the distribution,migration and transformation of various substances,water-rock interaction,and the relationship between materials and biological utilization.In this thesis,we mainly discussed on the distribution,sources,controlling factors in hydrochemistry.At the same time,we estimated the weathering denudation in Polar Regions and compared with the Changjiang drainage basin.The main results and conclusions are as follows:1.The Ny-Alesund,ArcticWith the background of the global warming,glaciers in Ny-Alesund have retreated over years.The Bayelva River which is mainly derived from the Austre Lovenbreen,reflects the calcite weathering signatures,while Pedersonbreen glacier mainly reflects dolomite weathering.Besides the dominance of carbonate weathering,the silicate weathering process also exists.It is estimated that the rate of silicate weathering was 3.3 5±2.75 t/(km2·"a),the rate of carbonate weathering was 13.85±4.02 t/(km2·a).Total chemical weathering rate is 17.20±6.12 t/(km2·a).The rate of atmospheric CO2 consumption is 142×103±41 ×103 mol/(km2·a).The total atmospheric CO2 consumption is 5.39×107±1.57×107 mol/aWe compared the migration factor(MF,migration factor)to study the trace metals behavior in meltwater in Ny-Alesund.The differences in the MF of the different types of glacial meltwater were studied.High values of MF were found in the supraglacial meltwater of glacier,such as Pb and Zn,indicating the possible effects from human activities and anthropogenic aerosols.We also found that Mn and Cd in this region tend to migrate into dissolved phase in meltwater2.Fildes Peninsula,AntarcticaBy applying the two end-member mixing model to calculate the contribution of ice melting and the snow melting,we compared the results with atmospheric temperature and precipitation.We found that temperature variation and the amount of snow cover affected the hydrochemical composition of the stream water on Fildes PeninsulaThe Ca2+*/Si ratios(*refers to elemental concentration after seasalt correction)in stream water on Fildes Peninsula were discussed,rock weathering and secondary minerals correspondence to the ratio changes.The weathering rate and atmospheric CO2 consumption in this region were estimated.The result shows that the silicate weathering rate in this region is about 1.19±0.38 t/(km2·a),and the carbonate weathering rate is about 2.78±2.81 t/(km2·a).Total weathering rate is 3.97±2.82 t/(km2·a),the rate of atmospheric CO2 consumption is 32.9×103±28.3×103 mol/(km2·a)and the total atmospheric CO2 consumption is 9.71 ×105±8.21 ×105 mol/a on Fildes PeninsulaAccording to the calculation,the results of silicon flux indicated the concentration of dissolved silicon was low in stream waters on Fildes Peninsula.This indicates the streamwater is not an important silicon source to the adj acent seawaters.As glaciers are degrading,the effects of atmospheric deposition on the hydrochemistry in streamwater on Fildes Peninsula are likely to increase3.The ChangjiangThe midstream and downstream of Changjiang River is heavily influenced by human activites.This thesis discussed the characteristics of the hydrochemical in Changjiang and its branches.The results show that the concentration of the major ions is lower when the runoff is larger,which shows a certain dilution effect.When the runoff is small,some tributaries will increase the contribution ratio of the ion concentration to the main streamOur results suggest the weathering process of the Changjiang watershed is mainly dominated by carbonate weathering.The rock weathering denudation rate of the Changjiang River was estimated to be 76.95±11.93 t/(km2·a)in midstream and 60.15±2.46 t/(km2·a)in downstream;the rate of toatal CO2 consumption is 843×103±193×103 mol/a in midstream and 410×103±14×103 mol/a in downstream Silicate weathering accounts for 34%of total chemical weathering4.The differences of hydrochemistry and chemical weathering of polar regionWe combined our observed data and other data from literatures,and then we compared the representative river from different latitude and discussed the hydrochemical and weathering processes.For the rock weathering,this thesis collected the data form big rivers and compared the variation in weathering rate with latitude variation.These results showed that high rates of weathering were located in the middle latitude,and some polar regions have higher CO2 consumption rate.The differences in rock weathering rates are determined by the geological charicters in their drainagebasin According to the weathering diagram,some of the polar rivers are close to the Na+*K+*end member.But in the anion diagram,they are close to HCO3-*end member.Combine the information of bed rock,weathering and environment,this thesis figures out that carbonate weathering may stronger than silicate weathering because of the polar climate,constantly exposed fresh rocks and silicate rock do not dissolve.This thesis compared the intensity of the weathering among the Ny-Alesund,Fildes Peninsula and Changjiang.The results show that the CO2 consumption rate in Ny-Alesund and Fildes Peninsula is lower than that in Changjiang.