Guo Yuedong, Song Changchun, Wan Zhongmei, Tan Wenwen, Lu Yongzheng, Qiao Tianhua
Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130012, China.
Environ Sci Process Impacts. 2014 Nov;16(11):2496-506. doi: 10.1039/c4em00283k.
Permafrost soils act as large sinks of organic carbon but are highly sensitive to interference such as changes in land use, which can greatly influence dissolved carbon loads in streams. This study examines the effects of long-term land reclamation on seasonal concentrations of dissolved carbons in the upper reaches of the Nenjiang River, northeast China. A comparison of streams in natural and agricultural systems shows that the dissolved organic carbon (DOC) concentration is much lower in the agricultural stream (AG) than in the two natural streams (WAF, wetland dominated; FR, forest dominated), suggesting that land use change is associated with reduced DOC exporting capacity. Moreover, the fluorescence indexes and the ratio of dissolved carbon to nitrogen also differ greatly between the natural and agricultural streams, indicating that the chemical characteristics and the origin of the DOC released from the whole reaches are also altered to some extent. Importantly, the exporting concentration of dissolved inorganic carbon (DIC) and its proportion of total dissolved carbon (TDC) substantially increase following land reclamation, which would largely alter the carbon cycling processes in the downstream fluvial system. Although the strong association between the stream discharge and the DOC concentration was unchanged, the reduction in total soil organic carbon following land reclamation led to remarkable decline of the total flux and exporting coefficient of the dissolved carbons. The results suggest that dissolved carbons in permafrost streams have been greatly affected by changes in land use since the 1970s, and the changes in the concentration and chemical characteristics of dissolved carbons will last until the alteration in both the traditional agriculture pattern and the persistent reclamation activities.
多年冻土土壤是有机碳的巨大储存库，但对土地利用变化等干扰高度敏感，这可能极大地影响河流中的溶解碳负荷。本研究考察了中国东北嫩江上游长期土地复垦对溶解碳季节浓度的影响。对自然系统和农业系统中的溪流进行比较表明，农业溪流（AG）中的溶解有机碳（DOC）浓度远低于两条自然溪流（WAF，以湿地为主；FR，以森林为主），这表明土地利用变化与DOC输出能力下降有关。此外，自然溪流和农业溪流之间的荧光指数以及溶解碳与氮的比率也有很大差异，这表明整个河段释放的DOC的化学特征和来源也在一定程度上发生了改变。重要的是，土地复垦后溶解无机碳（DIC）的输出浓度及其在总溶解碳（TDC）中的比例大幅增加，这将在很大程度上改变下游河流系统中的碳循环过程。尽管溪流流量与DOC浓度之间的强关联未变，但土地复垦后土壤总有机碳的减少导致溶解碳的总通量和输出系数显著下降。结果表明，自20世纪70年代以来，多年冻土溪流中的溶解碳受到土地利用变化的极大影响，溶解碳浓度和化学特征的变化将持续到传统农业模式和持续复垦活动的改变。
