| The Gahai wetland ecosystem is typical alpine wetland. The water conservationfunction, the characteristics of organic C, N accumulation and greenhouse gasesemission in alpine wetland ecosystem can provide information the source, history andpresent condition of C, N and water cycling, and is one of the important contents forresearching the global environment change.There are various wetland types existingin Gahai wetland ecosystem, including herbaceous peat, marsh wetland, mountainwetland and so on. These kinds of wetlands effect significantly on regulating peak,storing precipitation, conserving soil and water, improving microclimate as well asmaintaining regional carbon, nitrogen balance, and has extremely importantsignificance in maintaining regional economic development and ecological balance.The study on soil characteristics and emission of greenhouse gases in the Gahaiwetland ecosystem not only will provide technology strategies to develop effectiverecovery and reasonable protection Gahai wetland, but also help us to evaluate theresponsibility of greenhouse gas emissions for alpine wetland. That also provideresearch foundation for the study to control greenhouse gas emissions of alpinewetland.This paper studied four typical wetland types of Gahai wetland system, whichbased on the theories of ecology, hydrology, atmospheric physics and otherdisciplines theory, by using of fixed sample investigation, laboratory testmeasurement, mathematical and statistical analysis methods to reveal the spatialvariation about soil physical characteristics, water conservation function, soil organiccarbon density, organic carbon storage, nutrient content of Gahai wetland system. Thestudies also analyzed and discussed the influence of altitude on wetland soilcharacteristics, and monitoring and analysis of the CH4, CO2and N2O emissions lawsof space and time of the Gahai wetland ecosystem, while revealed the influence oftemperature factors on wetland greenhouse gas emissions. The main conclusions areas follows: (1) There were great differences in soil particle composition, soil bulk densityand soil porosity for the different wetland types in Gahai wetland system, and theyare fluctuating changes with the increase in soil depth. The average level of thick sandof soil were in order of herbaceous peat (63.00%)>marsh wetland (46.47%)>mountain wetland (37.60%), and the fine sand was opposite.The average soil bulkdensity was subalpine meadow>mountain wetland(0.90g·cm-3)> marsh wetland(0.49g·cm-3)> herbaceous peat(0.22g·cm-3).The total soil porosity was shown asherbaceous peat (86.52%)> marsh wetland(77.20%)>mountain wetland(63.21%)>subalpinemeadow(49.54%).The average level of maximum water holdingquantity of soil for herbaceous peats, marsh wetland, mountain wetland and subalpinemeadow was13143.94t·hm-2,11640.19t·hm-2,9060.79t·hm-2and7391.80t·hm-2,respectively. The non-capillary water holding quantity of soil for herbaceouspeat, subalpine meadow, mountain wetland and marsh wetlands was937.67,598.50,594.67and325.13t·hm-2, respectively. The average water draught capacity of soil forsubalpine meadow, permanent marsh wetland, mountain wetland and herbaceous peatwas51.49mm,49.66mm,43.42mm and22.45mm, respectively. The function ofwater conservation for herbaceous peats was the best and the function of waterdraught for subalpine meadows was the best in the Gahai wetland system.(2) There were sharp distinction among soil organic carbon content of differentwetland types in Gahai wetland system. The content of soil organic carbon ofherbaceous peats was higher than other types, with its average content of organiccarbon (286.80g·kg-1) was about2.91,4.99,7.31times as muchas that of marshwetland, mountain wetland and subalpine meadow, respectively. The averageorganic carbon densities were in order of herbaceous peat>subalpine meadow> marshwetland>mountain wetland, with the highest in the0～10cm layer. The change of theorganic carbon density along soil profile was basically in accordance with organiccarbon content in four typical marshes. they were volatility changes with soil depth.There were obviously two carbon storage layers in four typical marshes, butfluctuated with soil depth. There were obviously two carbon storage layers(0～10and 20～40cm, respectively) in four typical marshes.The total amount of organic carbonstored in the0-60cm of the four typical marshes was about9.50×106t. The soilorganic carbon storage of herbaceous peats was the highest, and the subalpinemeadows was the lowest the Gahai wetland system.(3) There were sharp distinction among soil nutrient content t of differentwetland types in Gahai wetland system. Soil pH in0~60cm layer were herbaceouspeat (6.03)<marsh wetland (6.26)<mountain wetland(7.72)<subalpine meadow(7.92); total N content were herbaceous peat (12.72g·kg-1)>marsh wetland (8.75g·kg-1)>mountain wetland (6.99g·kg-1)>sub alpine meadow (3.75g·kg-1), and therewere significant difference (P <0.05);soil hydrolytic N content were herbaceous peat(71.78mg·kg-1)> marsh wetland (45.96mg·kg-1)> mountain wetland (45.96mg·kg-1)> subalpine meadow (13.97mg·kg-1); total P content were herbaceouspeat(2.56g·kg-1)> mountain wetland (2.25g·kg-1)> subalpine meadow(2.24g·kg-1)> marsh wetland(2.17g·kg-1), available P content were mountainwetland(14.72mg·kg-1)> herbaceous peat(5.68mg·kg-1)> subalpine meadow(4.86mg·kg-1)> marsh wetland(2.92mg·kg-1); average order of total K content weresubalpine meadow(11.01g·kg-1)> mountain wetland (9.46g·kg-1)> herbaceouspeat(5.11g·kg-1)> marsh wetland(5.05g·kg-1), available K content were subalpinemeadow(80.93mg·kg-1)> mountain wetland(44.37mg·kg-1)> herbaceous peat(30.62mg·kg-1)> marsh wetland(20.93mg·kg-1). In four Gahai wetland types, herbaceouspeat soil N, P content of the highest, while subalpine meadow soil K content of thehighest.(4) soil physical properties changed as altitudes increased. Soil water contents,aeration porosity, total porosity showed an overall increasing trend as altitudeincreased. However, there was no clear change in soil bulk density and non-capillaryporosity which had no correlations with the altitude. The content of soil organicmatter，total N, total P, pH at the high altitude than low altitude, whereas, total Kwas higher than higher altitude at low altitude than high altitude.Except total k, thesoil chemical properties were increase with increasing elevation, but had not obviouscorrelation with elevation. (5) There were highly spatial variations CH4, CO2and N2O of emissions amongthe four wetlands, with the smallest CH4、CO2and N2O emission in the subalpinemeadow(－0.014±0.126mg·m-2·h-1), marsh wetland(137.17±284.51mg·m-2·h-1) andmountain wetland(－0.008±0.022mg·m-2·h-1), and the greatest in marshwetland(0.498±0.682mg·m-2·h-1),mountain wetland(497.81±473.09mg·m-2·h-1) andherbaceous peat(0.094±0.117mg·m-2·h-1).We found that the spatial variations of CH4、CO2and N2O emission are caused by difference in soil and vegetation. Results alsoshowed a special seasonal variation of CH4, CO2emissions in this wetland. Maximalemissions were between July–October2011and May–Jul2012, then decreased andmaintained relatively steady with some slight fluctuation in the winter and thawing orfreezing period. Air temperature, soil temperature (－5cm) and surface temperaturecontrolled the seasonal variation of CO2emissions in the Gahai wetland. No cleardrivers were found with CH4and N2O emissions. The annual emission values of CH4were－1.805,9.157,11.484, and30.144kg·ha-1·year-1from subalpine meadow,mountain wetland, herbaceous peat, marsh wetland respectively. Emission of CO2was29267.49,35044.53,32112.90and12369.45kg·ha-1·year-1, and N2O3.24,-1.34,9.55and1.67kg·ha-1·year-1, respectively. |
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