中国主要河流的颗粒有机碳来源及通量

SOURCES AND FLUXES OF THE RIVERINE PARTICULATE ORGANIC CARBON OF CHINESE RIVERS

河流系统是连接陆地和海洋的纽带,在全球碳循环中起着重要的作用。河流中的颗粒有机碳(POC)主要由来源于土壤和植被的生物有机碳和来源于岩石的化石有机碳组成,POC的侵蚀、搬运、氧化和埋藏对不同时间尺度的碳循环有着重要的意义。本研究统计了我国31条主要河流(包括台湾12条)的POC含量、碳同位素和悬浮物通量等数据,获得生物POC和化石POC的年通量,探讨了我国河流POC来源和通量的控制因素。结果表明,这些河流的POC的来源和通量表现出明显的差异:黄河和长江侵蚀大量的年老生物POC,而台湾河流主要为化石POC;我国河流POC来源与通量主要受控于物理侵蚀、气候、地质地貌和人类活动等因素的影响。这些河流的流域面积占我国国土面积的47%,近10年其生物POC和化石POC的总年通量分别为4.25±0.78 Mt C/a和2.04±0.22 Mt C/a,各占世界河流通量的2.7+1.3/-0.9%和4.7+6.6/-2.8%,表现出对全球海洋有机碳的一定贡献。过去几十年,我国河流输沙量显著减少,改变了河流有机碳氧化和水库埋藏过程及通量,其过程和通量的进一步监测和研究对理解有机碳侵蚀、输运、氧化和埋藏及其在全球碳循环中的作用至关重要。

Rivers play an important role in the global carbon cycle,exporting terrestrial carbon to the ocean and acting as biogeochemical reactors which can exchange carbon dioxide(CO_(2))with the atmosphere.Physical erosion in river catchments can mobilize particulate organic carbon(POC)from the terrestrial biosphere(biospheric POC)and organic carbon derived from sedimentary rocks(petrogenic POC).Erosion and transport of biospheric and petrogenic POC have different impacts on the atmospheric CO_(2)budget across a range of timescales.Although Chinese rivers export large amount of sediment and organic carbon into the marine system,there remain few comprehensive attempts to synthesize the national pattern of the sources and fluxes of riverine POC.Here,we synthesize the content,carbon isotopic ratios and flux of POC in main Chinese rivers,along with the fluxes of sediment.Our analysis reveals that the POC content and carbon isotopic ratios vary across the different rivers with wide difference in the hydro-climate background.The POC of the main Chinese rivers could be explained as a mixture of petrogenic carbon and C3 vegetation with minor input of C4 plants.The POC sources and fluxes of these rivers are controlled by the physical erosion,climate,geology,geomorphology,and human activities.We recalculate the particulate organic caron flux and find that the biospheric and petrogenic POC in 31 rivers(including 12 rivers of Taiwan and draining 47%of Chinese territory)are 4.29±0.81 Mt C/a and 2.04±0.22 Mt C/a,accounting for 2.7+1.3/-0.9%and 4.7+6.6/-2.8%of global POC fluxes into the ocean,respectively.In the last decades,the Chinese rivers had been suffering suspended sediment flux reduce,which changes the POC oxidation and burial in the reservoir.Further assessing these processes and fluxes are important for understanding the role of Chinese rivers on the global carbon erosion,export,oxidation,and burial.