| As a part of the global surface water cycle, the river has the important function ofsubstance transportation and environment transformation and its carbon sink arousedconsiderable attention from scholars. Based on the status of the international research,in this paper, we take the Meijiang River Basin under typical subtropical climateconditions as the research object. Using the research method of field investigation,soil sampling and laboratory analysis, it has been discussed for the storage,distribution of soil organic carbon and the main factors affecting soil organic carbonaccumulation of the fiver main forest types in the humid mountainous area. At thesame time, using the main chemical composition of river water, we investigated thesource of major ions in river water and its formation mechanism, discussd the mainchemical weathering processes of the river basin and determined the distribution ofthe three different rock, Atmospheric Precipitation and human activities. We analysefinally the correlation of chemical weathering process and its carbon sink effect. Theresults are showed as follow:(1) The average soil organic carbon content for the five forest types was4.14g·kg-1～22.14g·kg-1, the soil organic carbon content in evergreen broad-leaved forestwas highest but lowest in eucalypt forest. Soil organic carbon contents generallydecreased with depth, but decrease range was different for the five forest types. Thesoil organic carbon assembled obviously in surface layer soils. Soil carbon density inthe five forest types change greatly, with a range of1.57kg·m-2～5.74kg·m-2for fivesoil depth intervals. Soil carbon density under natural vegetation was significantlyhigher than that under secondary vegetation. (2) The total mean value of carbon storage was148.76t·hm-2in the five foresttypes. By comparisons, soil carbon storage of the main forest types in mountain areaof Northeast Guangdong was lower than that of other regions. These results showedthat human impact was one of factors that exert a tremendous influence on soil carbonstorage. The correlation analysis showed5kinds of forest SOC and the content ofclay, water, nutrient or the number of water stable aggregates were positivelycorrelated, but negatively correlated with soil bulk density, pH. The relationshipbetween the influencing factors forest soil organic carbon accumulation is close.(3) The main chemical composition of river water in Meijiang river basin is Ca2+,Na+and HCO3-，Secondly by SO42-and Cl-. Water chemistry type is heavy carbonatecalcium type Ⅰ. The value of pH is6.03~8.54, but EC is relatively low. Accordingto the analysis of Gibbs graph and Temary diagram, Meijiang river basin belongs torock weathering controlling type, and chemical compositions of water are mainlyfrom weathering of carbonate rocks, secondly from silicate rocks, it is show thatprecipitation influenced them obviously. The contribution rate of precipitation is22.85%for dissolved solids in river water, and it is higher than the mean value of theworld. But molar concentration rate of Cl-/Na+of river water is less than1.17, thisshowed that the rivers are affected faintly by artificial actions overall.(4) On the basis of factor analysis and principal composition analysis, thecontributions of silicate rock to the total dissolved solids of river water is19.7%, it ishigh relatively. The primary weathering processes is the carbonate rock dissolutionand the second is the weathering of silicate rocks in Meijiang river basin. Annual ratesof chemical weathering in river basin is32.21t/km2.a, it is lower than Yangtze Riverand mean value of the world. Based on contribution rate of atmospheric CO2to theHCO3-in the river water, the quantity of CO2consumption by rock weathering isestimated to be2.32×108mol/yr，and the rates of CO2consumption by rockweathering is194.29×103mol/km2.yr, close to the world average level.(5) DIC contents of river water in Meijiang river basin are between4.14~87.59mg/L, the annual mean value is28.38mg/L, higher than that of the YellowRiver and the Indus River. The annual denudation flux of DIC is calculated to be 23.67×106g/km2.y. The Annual mean value of DOC content of river water is2.72mg/L, annual denudation flux of DOC is calculated to be2.27×106g/km2.y, whichis medium level of output compare with the main large rivers in the world.(6) According to the correlation analysis of influence factors, DIC carbon sinkeffect is significantly affected by lithology, soil, climate and other natural factors inMeijiang river basin, whereas SOC content of the5kinds of forest and DOC contentof rivers did not show significant correlation, this maybe connected with the naturalfactors and artificial disturbance. The correlation analysis show that contribution rateof the5types of forest SOC for the river DOC was the highest in Masson pine forest,secondly is coniferous and broad-leaved mixed forest and Eucalypt forest, bambooforest is the minimum. The relational sequence represents the influence level of the5kinds of forest for the ecological effect of the whole study area. |
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