| Dagze Co, a typical deepwater salt lake situated in North-Tibet, was chosen for the study. The different experiments were conducted and previous unpublished results were summarized to analyze the carbon fixation and sinking capacity of the lake. The carbon balance in the lake ecosystem (primary productivity, carbon exchange with the outside world, carbon deposition flux in the water column, and carbon content in surface sediments) was assessed. Based on the research, the carbon fixation potential and sedimentation rate were evaluated, the conclusions were made as follows:(1) Carbon in the water column exists in two forms:organic carbon (OC) and inorganic carbon (IC). CO32-dominated in IC (accounting for79.60%), and particulate organic carbon (POC) dominated in OC (58.53%). The composition of carbon form varied in the lake; it was different in regions with different water depth as well as in different water layers in the same site.(2) Carbon balance in the lake was calculated:Total primary production-899.64t CO2/d, net primary production-378.76t CO2/d, biological respiration and water chemical oxidation-520.88t CO2/d, exchange through the water-air interface-138.06t CO2/d, import by rivers-171.79t CO2/d, a release from sediments-68.91t CO2/d. That is to say, in fact, there would be378.76t CO2/d input permanent carbon pool of sediments.(3) The sediment trap experiment showed that POC depositional fluxes increased with increasing water depth. The POC depositional fluxes was0.0413g C/(m2·d) in8m water column,0.067g C/(m2·d) in10m, and0.089g C/(m2·d) in12m. Carbonate contribution was quite large-22.83%-in deposited matters, and D. tibetana exoskelets and fecal pellets dominated in the organic matters.(4) In Lake Dagze Co, water content in surface layer of sediments varied from22.59%to67.32%with average46.16%. Comparison of this parameter in different sites shows that in open waters it was higher (average53.83%). Dry bulk density was between0.43and1.37g/cm3, with an average value of0.48g/cm3; and this parameter decreased with increasing distance from estuary. Mostly grain size were centered in0.01～0.031mm, followed by0.30mm～0.074mm and0.45mm～0.30mm.(5)The total carbon in surface layer sediments ranged from4.16%to5.76%with an average value of5.01%. The OC was between4.46g/kg and23.64g/kg with an average value of12.66g/kg. The IC was between3.21%and4.99%. The IC in surface sediments was14.59～51.35mg/cm3and OC was4.88～13.26 mg/cm3. From the estuary to open region, OC grew as the water depth increased, then it kept a stable value, but the IC was in the opposite. Changes of OC and IC from estuary to the open region reveal that inorganic carbonates mainly dominated carbon deposition in the lake, and with the increasing of water depth, the role that the OC played became more and more important. The results from source study show that organic matter mainly consisted of D. tibetana exoskelets and fecal pellets.(6) Comprehensive analysis showed that the sedimentation rate in Dagze Co ranged from0.06to2.34mm/yr with an average value of1.1989mm/yr. From the estuary to open region, the sedimentation rate grew as the water depth increased. The average sedimentation rate in estuary region was0.286mm/yr and2.049mm/yr in open region (＞10m).(7) In Lake Dagze Co sedimentation ranged from70.359to1635.504g/(m2·yr); it grew with the increasing of water depth from the estuary to open region. Average sedimentation in estuary region was272.681g/(m2·yr) and1357.952g/(m2·yr) in open region.(8) The sedimentation rate of IC ranged from0.329to5.887mg/(cm2·yr)(average3.561mg/(cm·yr)). In comparison with the estuary region and shallow waters, the value was higher in open region(average4.591mg/(cm2·yr)). The sedimentation rate of OC varied from0.031to2.898mg/(cm2·yr), with an average value of2.264mg/(cm2·yr).(9) The deposited carbon in the whole lake was about11862.78t C/yr, among which,2994.38t C/yr were OC, and the others were IC.23.82%of primary production (12567.9t C/yr), sank in bottom sediments of the lake.As a part of Geological Survey Project, the study reports on the carbon fixation and deposition capability of the saline lake in Northern-Tibetan. New data about sedimentation rate may improve our understanding of salt lake ecosystems in Tibet. |
PDF Full Text Request