Research On Surfur Biogeochemistry In Hypolentic Zone Of Lake In Kubuqi Desert Plateau Area

Hyporheic zone，which is the interface of groundwater and surface water interaction,has great significance on protecting and preserving water resources, biodiversity andeven ecosystem of desert plateau area, and is important component of lake ecosystem.As an important biogenic element, sulfur is important content in hypolentic zonebiogeochemistry research, which is closely correlated with nutrient cycling, carboncycling, water acidification, origination of ferromanganese minerals, trace metalelements redox, transport and transformation of some toxic heavy metal and inorganicmatter (such as As) etc in hypolentic zone.The thesis relies on National Natural Science Foundation of “Surfur Biogeochemistryin Hypolentic Zone of Lake in Desert Plateau Area”. In the thesis, based on field insitu monitoring and sample analysis in laboratory, coupled of water chemical analysis,multivariate statistical analysis and numerical simulation method are used to exploresulfur geochemistry in hypolentic zone of Da Haizi lake from aspects of structure,hydrodynamic, hydrogeochemistry, isotope, environment parameters,hydrogeochemistry evolve, sulfur migration and transformation etc, from which, thefollowing opinions are obtained:1.There is a spacial zonation of topography, lithology etc along water flow direction inhypolentic zone, which result in gradients of hydrodynamic and ratios of lake watervariatin in pore water along the hypolentic profile. Hydrodynamic is determined byhydrological texture. Components and ratios of each pore water sample of hypolenticprofile, which reflects that: spatial variation of lake-groundwater hydraulic connectioncan be calculated through the mass conservation principle of isotope.2. In the range of0to-90centimeters in sediment profile of DaHaizi Lake,environmental parameters of temperature, pH, each major zwitterion of pore waterand related solid components in sediment all exhibit their respective gradients that aredifferent from surface water and shallow groundwater, ranges of hypolentic zonedetermined by these gradients above are deferment from that determined directly bysurface water-groundwater mixing ratios besides, that is because there are correlativehydrology、geochemistry and biology characteristics in hypolentic zone, and there arephysical, chemical and biological processes in the range of sampling area except for migmatization and diffusion; All of which are similar with hyporheic zone. So,indexes of geophysics, geochemistry and biology should be comprehensivelyconsidered when determining hypolentic zone range.3. In the aspects of geochemistry and sulfur biogeochemistry, the followingconcluctions are drawn:①hydrogeochemistry evolve and sulfur transport and transformation are controlled bymigmatization, cation exchange, dissolution and precipitation of mineral and salt,redox catalyzed by microorganisms, in which inorganic processes of sulfur are mainlydissolving of sulphate mineral and precipitating of sulfide, each process exhibits itsown gradients in vertical profile.②sulfur biogeochemistry in hypolentic zone are mainly a variety of redox processescatalyzed by microorganisms. in surface with high Eh, pyrite in the sediment can beoxidized to sulphate by dissolved O2and active Fe3+; and in deeper layer with lowerEh and a plenty of organic carbon, sulphate is reduced to sulphide that currentlyprecipitated with active Fe2+by the activity of sulfur reducing bacteria decompositingorganic matter anaerobically and further transformed to pyrite.③Transport and transformation of sulfur are mainly correlated with redox matters oforganic carbon, DO etc and the respecting vertical Eh gradient of environmentdetermined by them. In early of surface water infiltration, sulfate reducing rateincreasing with depth, and reaches the maximum at depth of about-30centimeter,below-30centimeter, reduces with TOC reduces. In late infiltration and in the surface0to about-30centimeter, pyrite formed previously is oxidized again because of TOCconsumption and Eh increasing, and the oxidizing rate is highest in the nearest lakebed; below-30centimeter, sulfate reducing gets more weaker as Eh increasing andTOC consumption. The result is that: concentration of pyrite in vertical hypolenticprofile first increase and then decrease with depth.