闽江下游不同碳组分及其通量特征

河流连接着地表主要碳库，在全球碳循环中发挥着重要作用.河流水体中不同碳组分的水平输送、水-气界面通量及其比例对认识河流在区域碳循环的作用具有重要意义.2013年11月-2014年10月在闽江下游竹岐水文站连续进行采样，分析水样中c（DIC）（dissolved inorganic carbon，溶解性无机碳）、c（DOC）（dissolved organic carbon，溶解性有机碳）和c（POC）（particulate organic carbon，颗粒性有机碳），并结合相关参数估算闽江不同碳组分的水平及垂直通量.结果表明:① c（DIC）、c（DOC）、c（POC）分别为230~892、112~209、14~183 μmol/L.②调查期间闽江总碳水平通量达46×1010 g/a，其中，DIC水平通量为29×1010 g/a，占总碳水平通量的63%；POC水平通量为6×1010 g/a，相当于DOC水平通量（11×1010 g/a）的55%.③不同组分的季节变化特征不同，c（DIC）在丰水期较低、枯水期升高，表明DIC输出受流域生态系统的供应限制；各月c（DOC）变化不大，表明流域DOC输出潜力较大；c（POC）在丰水期明显升高，枯水季较低；溶解态碳是河水碳组分的主要部分；年内各月DIC水平通量分配较均匀，有机碳水平通量集中在丰水期.④闽江竹岐水体pCO₂（二氧化碳分压）为1 500~6 400 μatm（1 atm=101 325 Pa），是大气CO₂的"源"，闽江下游水-气界面CO₂垂直通量约为DIC水平通量的2%，闽江下游河流DIC输出以水平输出为主.建议今后进一步开展闽江中典型流域和水域的碳组分调查，加强闽江碳组分输出的控制机制研究. 

Carbon Fractions and Fluxes in the Lower Reach of Minjiang River

Linking the largest carbon pools, rivers play an essential role in global carbon cycle. Evaluating the horizontal flux of various carbon fractions, carbon dioxide emission and their proportion in the Minjiang River is important for understanding the regional carbon cycle. The monthly water sampling was conducted at Zhuqi hydrographic station in the lower reach of the Minjiang River from November 2013 to October 2014. The contents of the DIC (dissolved inorganic carbon), DOC (dissolved organic carbon) and POC (particulate organic carbon) were determined and the horizontal/vertical fluxes of carbon fractions were estimated with relevant parameters. The results indicated that the ranges of c(DIC), c(DOC) and c(POC) were 230-892, 112-209 and 14-183 μmol/L, respectively. The annual carbon horizontal flux of the Minjiang River was 46×1010 g/a, 63% of which was DIC, serving as the main component. Meanwhile, DOC horizontal flux was 11×1010 g/a and POC horizontal flux was 6×1010 g/a, equivalent to 55% that of DOC. The dissolved carbon represented the majority of all fractions. Moreover, seasonal variabilities of carbon fractions were different. The DIC concentration decreased in wet season while increased during dry season, which indicated that DIC output was restricted by the supply of watershed ecosystem. The DOC concentration was largely invariable in contrast to the runoff variation and the POC concentration correlated positively with the discharge amounts. The DIC horizontal flux was evenly distributed throughout the year while organic carbon flux peaked in the wet season. The partial pressure of CO₂ on river surface ranged from 1, 500 to 6, 400 μatm (1 atm=101, 325 Pa). Thus, lower reach of the Minjiang River was CO₂ source of the atmosphere. The estimated CO₂ vertical flux amounted to only 2% of DIC horizontal flux, which was the major components of the DIC efflux for the Minjiang River.