【作者】 刘志媛；

【导师】 张龙军；

【作者基本信息】 中国海洋大学 ， 环境科学， 2014， 博士

【摘要】 河口是陆海相互作用最活跃的场所，在全球碳循环中发挥着重要作用。由于强烈的生物活动以及复杂的沉积动力学过程等，河口区往往对陆源入海物质起到“过滤”或“缓冲”的作用，使得入海物质的形态和量在河口区发生改变。了解河口过程对各形态碳分布的影响，对于研究河流向海洋的碳输运过程十分重要。黄河作为中纬度干旱半干旱地区高浑浊度河流的典型代表，对其河口区碳输运行为及影响因素的探讨，对于讨论同类河口碳输运行为具有重要的借鉴意义。本文根据2010.7-2011.7对利津站的逐月连续观测资料；2005-2013年间积累的各形态碳的观测数据；2005-2010年6个航次对黄河口的采样调查；以及2009-2010年4个航次对河口区pCO2的走航调查，对黄河口淡水端各形态碳的季节变化，上世纪50年代以来淡水端碳输运通量的改变，淡咸水混合过程对各形态碳输运的影响，以及河口区pCO2分布的影响因素和水-气界面CO2通量进行探讨。主要结果与结论如下：1.与世界多数河流不同的是，黄河入海（利津站）各形态碳的输运通量无机碳大于有机碳，颗粒态碳大于溶解态碳。2010-2011水文年利津站DIC、DOC及POC的年输运通量分别为56.2×104tC、3.97×104tC、35.0×104tC。各形态碳输运通量在夏季（夏季黄河经历调水调沙）时最高，DIC、DOC通量分别占全年的55.6%，58.4%，POC则高达全年的88.6%。黄河淡水端多年累积数据的统计显示：DIC、DOC浓度随径流量的增加，悬浮物中PIC%、POC%随中值粒径的增大呈负对数型降低趋势。以此为依据，反演的1950-2012年黄河利津站各形态碳的输运通量总体呈现下降趋势，其中由于径流量和输沙量的减少，2000年以后较上世纪50年代DIC、PIC、POC年输运通量则分别下降了60%，90%，91%。2.黄河口低盐区存在DIC的亏损现象，河流输入的DIC未被有效输入海洋。研究证明，生物活动和碳酸钙沉降是导致黄河口低盐区DIC的亏损的主要原因，并且Chl a含量及淡水输入DIC浓度越高，碳酸钙过饱和程度越大，河口淡咸水混合时间越长，DIC亏损程度及亏损区间越大。在世界河口区已报道的DIC非保守现象研究中，黄河口是目前唯一一个碳酸钙沉降起了重要作用的实例。黄河DOC含量（2.39mg L-1）低于世界河流平均值（5.0mgL-1），然而黄河口低盐区存在DOC的盈余现象，以淡水端浓度评估的DOC入海通量偏低。3.与世界多数河口一致，pCO2在淡咸水混合过程中总体呈降低趋势。然而不同的是，黄河口在盐度小于0.5的区域内随TSS、PIC的沉降，pCO2呈现急剧下降。浮游生物活动是水体pCO2主要清除机制，黄河输入极高DIC浓度的碳酸盐体系是河口CO2的主要来源。只有当黄河下游普遍降雨，大量有机物冲刷进入河流时，耗氧呼吸提供CO2所占的比例才会增大。黄河口虽然整体上表现为大气CO2的源，但其CO2释放通量低于世界中纬度地区河口CO2释放通量的平均值，在世界大河中处于较低的水平。更多还原

【Abstract】 Estuaries are regions of active land-ocean interaction and very important toglobal carbon cycles. Due to strong internal biogeochemical activities and a numberof complex sedimentary dynamic processes, mass transported into estuaries usuallyexhibits nonconservative behavior during estuarine mixing. As a result, riverinecarbon fluxes can be over-or underestimated if these physical and biogeochemicalprocesses are not considered. The Yellow River represents typically rivers which arelocated in arid and semiarid regions and hold high turbidity. Studies on carbon cyclesand influence factors in the Yellow River estuary can provide some meaningfuladvice to other rivers with the same characteristics.Using data from monthly investigation at the Lijin station during July2010toJuly2011, six cruises in the Yellow River estuary during2005-2010, within four ofwhich pCO2data were investigated between2009and2010, we discussed seasonalvariations of carbon in the freshwater end member, long time-scale carbon flux from1950s, behaviors of carbon in the estuarine mixing processes, pCO2distribution andair-sea flux in the Yellow River Estuary. Conclusions are as follows:1. Carbon transported in the Yellow River is mainly in inorganic and particulateforms. DIC, DOC and POC flux amonted to56.2×104t C yr-1,3.97×104t C yr-1and35.0×104t C yr-1respectively, from Auguest2010to July2011. Fluxes ofDIC, DOC and POC in summer were much higher than those in other seasons,accounting for55.6%,58.4%,88.6%of the whole year, respectively. In the longtime-scale (1950-2012), fluxes of discharge, sediment and all kinds of carbon areall showing decreasing trend. Compared with1950s, fluxes of discharge,sediment dropped67%,90%respectively in the first decade in21stcentury. As aresult,fluxes of DIC, POC, PIC are decreasing60%,90%and91%, respectively.2. DIC acts non-conservatively and some of it is removed in the estuarine mixingzone. CaCO3precipitation and biological activities are the main reasons for thisphenomenon. Longer freshwater-seawater mixing distances and times, andhigher DIC concentrations in the freshwater end member promote net biologicalproduction and CaCO3precipitation, thus encouraging DIC removal. To our bestknowledge, the Yellow River Estuary is the only example where CaCO3precipitation has been demonstrated to play a very important role in estuarine DIC removal. DOC concentration in the Yellow River (2.39mg L-1) are muchlower than the world average (5.0mg L-1), but it increases in the estuary mixingprocess. Therefore, DOC flux is under-estimated using DOC concentration in thefreshwater.3. Agreed with other estuaries, pCO2in the Yellow River estuary decreased sharplyin the very low salinity area (S<0.5), due to the severe deposition of TSS.Photosynthesis is the main removal mechanism for pCO2while carbonate system(high DIC) in the freshwater end member acts as the dominant factor sustainingthe high pCO2in the Yellow River Estuary. During the heavy rains, lots oforganic materials flushed into the estuary, which may cause biological respirationenhanced and pCO2increased. The Yellow River acts as a CO2source comparedwith atmosphere, but its flux is much lower than other large river estuaries.更多还原