新疆尾闾盐湖滨岸盐碱土中碳酸盐的固碳效应及影响因素

Carbon sequestration effect and influential factors in pedogenic carbonates of saline-alkaline soils from shore of rump salt lake in Xinjiang

土壤碳酸盐对现代大气CO_2的截存与土壤中的硅酸盐矿物组成、盐基元素供给、有机碳含量等因子密切相关。该文结合土壤理化性质和碳同位素分馏特性,以新疆艾比湖为例,探讨了干旱区尾闾盐湖滨岸盐碱土中碳酸盐的固碳效应和影响因素,研究结果表明:1)土壤碳酸盐是干旱区最重要的碳库,艾比湖滨岸土壤碳酸盐的平均碳密度是有机碳的4.05倍;2)艾比湖滨岸盐碱土中的δ13CSCC介于-7.9‰～0.3‰之间,δ13CSCC与HCO3-存在良好的线性负相关关系,决定系数高达0.669 9,大气碳以重碳酸盐形式存在是次生碳酸盐淀积的关键环节之一;3)土壤δ13CSCC值与硅酸盐矿物阳起石、绿泥石、伊利石存在着良好的线性负相关关系,δ13CSCC值随着富Ca、Mg、Fe矿物的含量增加明显向负向漂移;4)土壤中有机碳含量越高,生物风化过程越强烈时,δ13CSCC负向漂移越大,土壤碳酸盐截存较多大气中的轻碳;当土壤含盐量超过一定程度时,有机过程受到抑制,土壤碳酸盐则截存较多大气中的重碳。因此,干旱区存在着有机-无机耦合固碳效应,提高干旱区植被覆盖,可以增加有机碳库储量,同时,经有机过程分馏转移到土壤中的CO_2可进一步促进土壤硅酸盐矿物风化,使这部分CO_2不再返回大气,而是以碳酸盐形式被长久固存。

China has a large area of arid and semi-arid zone.The soil carbonate is the main form of soil carbon pool in arid and semi-arid regions,which has an important scientific research value.Soil carbonate contains weathering information during soil formation,and the capacity of carbon sequestration of pedogenic carbonates is closely related to the base cations supplying,silicate minerals comprising and organic matters in the soils.In this study,to keep away the agricultural areas and the entering water system,we set 3 different typical sample plots(N、W、E)in the north,west,and east shore of the rump salt Lake Abi.Respecting to the physical and chemical properties of soil and the characteristics of carbon isotopic fractionation of pedogenic carbonates,the carbon sequestration effect and influential factors in pedogenic carbonates of saline-alkaline soils from the shore of the Abi Lake had been investigated.The research results showed that there was a long-term and stable supply of Ca^2+、Mg^2+、Fe^2+and other cations derived from the weathering of silicate minerals during the process of saline-alkaline soils'formation in this study region.These cations of non-lithogenic carbonate sources came from the highlands around the lake basin carried into the low-lying catchment area in continuously by the water,wind and other forces etc.,providing sufficient materials for soil carbonate to sequestrate modern atmospheric CO2.The average carbon density of soil carbonate carbon(SCC)was 4.05 times as many as that in soil organic carbon(SOC)in the saline-alkaline soils from shore of the Abi Lake.The results ofδ^13CSCC had indicated that the value ranged from-7.9‰to 0.3‰,and there was a very significant negative correlation betweenδ13CSCC and HCO3^-,and the correlation value(R2)is 0.669 9.One of the critical segment of secondary carbonate precipitation was that atmospheric carbon dioxide was dissolved into soil water in the form of bicarbonate ion.However,theδ^13CSCC was also very significantly negatively correlated with the soil silicate minerals(actinolite,clinochlore and lllite).And with the increase of those Ca,Mg and Fe rich minerals in the soil,δ^13CSCC decreased.Similarly,with more SOC content and higher biological weathering intensity in the soil,theδ^13CSCC increased to bigger negative values.And in these cases,the pedogenic carbonate would sequestrate more light carbon from atmosphere.Ca^2+and Mg^2+contents of water-soluble salts and total salt with soil carbonate contents correlation value were not too high,but they were significantly correlated with theδ^13CSCC in a concordant logarithmic relationship.The value was 0.758 7 and 0.694 7 respectively.If the biological weathering process was restrained by extremely higher soil salinity,the results implied that the pedogenic carbonate would sequestrate more heavy carbon.In this research,the transfer of carbon dioxide to bicarbonate-carbonate was mainly an inorganic process,when the salt content was more than 20 g/kg,and theδ^13CSCC basically value was greater than-2.However,there was a coupling effect between organic process and inorganic process in carbon sequestrating.If the vegetation coverage was considered,the SOC pool could be increased.And in this way,the silicate weathering in soil could be strengthened by high concentration CO2 that was fractionated from biological process,and instead of returning to atmosphere.Hence,the pedogenic carbonate in arid areas has great potential capacity for atmospheric CO2 sequestration.