【作者】 张向上；

【导师】 张龙军；

【作者基本信息】 中国海洋大学 ， 环境科学， 2007， 博士

【摘要】 河口是陆地碳储库向海洋碳储库碳输运的通道,河口的物理、化学、生物过程在空间尺度和时间尺度上的变化程度相对于陆地和海洋都比较剧烈,这些剧烈的河口过程对陆地向海洋的碳循环能够产生明显的影响,从而导致碳的有效输送通量发生变化,河口有效的碳通量研究作为补充目前全球碳循环中的循环途径不闭合问题的重要方面,逐渐成为全球碳循环研究的热点。黄河是世界上著名的高浑浊度河流,其陆源碳的入海对渤海乃至整个西北太平洋边缘海的生物地球化学过程会产生重要影响,研究黄河口碳的输运过程及有效入海通量,对于更完整、更准确地探讨全球陆地碳储库向海洋碳储库碳的单向输运过程具有重要的代表性。本文在国家自然科学基金委员会、科技部项目的支持下,在黄河口淡咸水混合带进行了汛期（2004.9;2005.9）和非汛期（2004.4;2006.4）4个航次的考察,并结合黄河调水调沙过程对莱州湾内碳参数分布开展了2005.7;2005.9两个航次的调查,对汛期和非汛期黄河口碳的输运过程及有效入海通量进行了研究,并对黄河碳输运对莱州湾内碳体系的影响作了科学的评价。本文内容主要有四个部分:①黄河口混合带有机碳的输运特征及有效通量;②黄河口无机碳的输运过程及有效通量;③黄河口pCO₂的时空分布及维持机制;④黄河碳输运对莱州湾碳参数的影响。主要实验结果和结论如下:颗粒有机碳:黄河泥沙中POC%与泥沙中值粒径增加有良好的指数下降关系,黄河泥沙中POC%的极限值大约为0.60%。黄河悬浮物中颗粒有机碳的含量在进入河口前比较稳定,约为0.36%,接近于黄土高原土壤有机碳的背景值0.39%,在河口低盐度区（0<S<0.5）,随着大颗粒泥沙大量沉降,河口感潮河段悬浮物相对细化,从而导致悬浮物中POC%升高至0.51%左右,口门外近海悬浮物中海源悬浮物的比例逐渐增加,导致口外近海悬浮物中POC%超过黄河泥沙POC%的极限值（0.60%）,因此,在计算黄河颗粒有机碳的有效入海通量时,应该考虑到巨量大颗粒泥沙的沉降作用以及由此导致的POC%含量升高的影响,否则能够导致POC的入海通量被高估,黄河口泥沙的沉降作用对颗粒有机碳的截留效率约为72.8%;应用多元线性回归法对黄河不同粒级悬浮物中POC%的含量进行了优化处理,结合河口感潮河段悬浮物的粒径组成,可以发现小于32μm的细颗粒悬浮物承载了99.5%的黄河入海颗粒有机碳。溶解有机碳:可能受到人工堤坝调控的影响,汛期和非汛期黄河进入河口时溶解有机碳的含量较为稳定,分别为2.60mg/l和3.01mg/l;汛期和非汛期河口感潮河段沉积物向上覆水释放DOC能导致黄河DOC的有效入海通量分别增加10%和20%左右。当悬浮物含量超过455mg/l时,黄河入海的有机碳以颗粒态为主;反之,以溶解态为主。溶解无机碳:黄河口DIC含量普遍高于世界上其他河口,季节分布特征是汛期DIC小于非汛期。汛期和非汛期黄河口DIC分别在S>5和S>18的高盐度区保守性降低,低盐度区DIC亏损的原因是由于碳酸钙的沉降作用,这种沉降作用是以Ca2+ + HCO3-→CaCO3 + CO₂ （g） + H2O的形式进行的。受河口区域碳酸钙沉降作用的影响,黄河流域风化作用吸收的CO₂在河口将会有10%重新释放到大气中。黄河口淡咸水混合过程中pH会出现相对于淡水端异常升高的现象,这种现象的出现是由于混合过程中pCO₂相对于[HCO3-]更为迅速的降低引起的,可以通过黄河口混合区相对于淡水进入河口前pH的异常升高的区域来表征碳酸钙的沉降作用发生的盐度范围。颗粒无机碳:黄河口悬浮物中碳酸盐含量较高,这导致碱度受悬浮物影响较大,只有当悬浮物含量小于53mg/l时,悬浮物对碱度的影响可以忽略不计,因此测定黄河口的碱度时必须进行过滤;黄河口颗粒无机碳浓度主要受控于悬浮物含量,陆源悬浮物中PIC%稳定在1.75%左右,当悬浮物含量小于200mg/l时,由于浮游植物构成的海源悬浮物对陆源悬浮物的稀释作用,悬浮物中PIC%会迅速下降。黄河口泥沙沉降作用对颗粒无机碳的截留效率约为80%。二氧化碳分压（pCO₂）:黄河口悬浮物在低盐度区域大量沉降,颗粒有机碳也随之沉降下来,从而使耗氧细菌所利用的碳源迅速减少,表观耗氧量迅速降低,水体中的pCO₂也相应的在盐度0-5的区域迅速下降,由于高碳酸氢盐的黄河水中存在以下平衡: Ca2+ + HCO3-→CaCO3↓+ CO₂ （g） + H2O当pCO₂下降时,平衡会向右移动,导致黄河低盐度区发生碳酸钙的沉降现象使DIC发生亏损;因此,黄河口低盐度区悬浮泥沙的大量沉降作用能够导致pCO₂迅速下降,这是驱动黄河口发生碳酸钙沉降作用的主要机制。另外,非汛期（4月份）黄河口磷酸盐含量较高,随着盐度0-5的区域悬浮物的大量沉降,水体光的透射率增加,使得浮游植物消耗CO₂也能够加剧碳酸钙的沉降作用,因此非汛期黄河口碳酸钙的沉降范围会扩展到盐度为0-18的区域。从整体上看,黄河口在低盐度区域生物耗氧呼吸作用和碳酸钙的沉降作用是控制水体中pCO₂的主要因素,而高盐度区pCO₂可能主要来源于海水对高碱度、高pH的黄河水的酸化作用。受黄河调水调沙的影响,巨量的黄河淡水输入能够造成莱州湾盐度整体性下降,莱州湾溶解性碳（DOC、DIC）的分布都表现为由西南部向东北部外海逐渐降低的趋势,调水调沙期间莱州湾DOC、DIC具有同源性,应以黄河输入为主。但9月份小清河入海流量增大后明显能对莱州湾西南部DOC、DIC的分布产生影响。通过对悬浮物中POC%的分析可以发现造成莱州湾内靠近黄河口和南部沿岸区两个POC浓度高值区的因素分别是受黄河陆源输入和浮游植物的影响。黄河口水体中较高的碳酸盐对pCO₂可能具有缓冲作用,因此黄河口及莱州湾明显表现为大气CO₂的源区,不会成为汇区。通过PIC的分析,可以发现莱州湾内陆源和海源悬浮物的分界线约为30mg/l,悬浮物中的PIC可以示踪黄河泥沙在莱州湾的扩散范围,黄河调水调沙输入的巨量泥沙可能最终在莱州湾内堆积。更多还原

【Abstract】 The transport of carbon by rivers is an important component of the global carbon cycle. Of the well-documented 0.9 Gt carbon carried by world rivers each year, about 40% is organic and the remaining 60% is inorganic. Despite the large quantities of carbon delivered from rivers, only a small fraction of it is transported to the adjacent shelf and open ocean. Estuaries are the primary fresh-salt water interface. They are extremely dynamic systems, characterized by strong physico -chemical gradients, enhanced biological activity （both heterotrophic and autotrophic） and intense sedimentation and resuspension. Estuaries play an important role in transportation of dissolved and particulate material from the continent to the marine system, however very little is known about the estuarine processes that control the fate of riverine inorganic and organic carbon. The Yellow River, as one of the high turbid river, has important effect on carbon cycle of North -west Pacific Ocean, to better understand the effect of estuarine processes on riverine inorganic and organic carbon, during this study, the distributions of DOC, DIC, POC and PIC in Yellow river estuary were investigated during both dry （April, 2004; April, 2006） and wet （September, 2004; September,2005） seasons. Estuarine processes controlling carbon transport in the estuaries were discussed, and net carbon flux was calculated. Moreover, the effects of Yellow River carbon transport on Laizhou Bay were estimated by July and September 2005 cruises.DOC and DIC concentrations of Yellow river during dry seasons were higher than during wet seasons. The effective concentrations of DOC （CDOC*） were higher than the observed DOC at zero salinity. This input of DOC in the Yellow River estuary was due to sediment de-sorption processes in low salinity region. In contrast to DOC, the effective concentrations of DIC were 10% lower than the DIC measured at freshwater end, the loss of DIC was caused by CaCO3 precipitation in low salinity region.POC and PIC content of the particles stabilized to a constant value （ 0.51% and 1.75% respectively ） within the turbidity maximum zone （TMZ） and showed no noticeable seasonal variations . A rapid drop of PIC and rose of POC occurred simultaneously dropped of PIC% and rose of POC% outside the TMZ. POC% increase with decreasing particles size, more than 80% POC concentrate onΦ<16μm size particles and POC inΦ<32μm size particles account to 95% flux from Yellow river estuary to Bohai sea. When TSS=455mg/l, the ratio of DOC/POC is 1, which indicate that organic carbon transport in Yellow river is in the form of POC. They are due to an intense dilution of riverine inorganic-rich particles into a pool of aquatic organic-poor particles outside TMZ. Annually, the Yellow River transported 4.13×105 t of DIC, 3.84×104 t of DOC, 1.21×106 t of PIC and 3.54×104 t of POC to the ocean.With the dramatically sediment of POC in upper estuary, the partial pressure of CO₂ （pCO₂）, which is derived from biogenic respiration, swiftly decrease and lead to CaCO3 precipitation in low salinity regions, the pH value will simultaneously increase in this area. Instant increasing pH value can be used as index of CaCO3 precipitation in Yellow river estuary, during dry season, photosynthesis will enlarge CaCO3 precipitation to salinity of 18. According to dissolved matter mixing model in estuary, the observation of 1-to-1 removal of TA and DIC provide just evidence that DIC removal we observed in the field is a result of HCO3- removal. The process can clean 10%（4.59×104 tons）DIC which is transported by freshwater both in dry and wet weathers, and ten percent of CO₂ （8.40×104t） which is absorbed by chemical weathering process in drainage basin will release to atmosphere in Yellow river estuary.The distribution of DOC and DIC in Laizhou Bay were controlled by Yellow river during the test of water-sediment regulation of the Yellow river （July,2005）, however, with runoff of Yellow river decreasing and Xiaoqing river increasing in September 2005, DOC and DIC from Xiaoqing river will influence Southwest Laizhou Bay. According to the analysis of chlorophyll-a and mineral in TSS, when TSS is less than 30mg/l, phytoplankton increase but sediment from Yellow river decrease in TSS. Simultaneously,∑C20-/∑C20+ and CPI of n-alkane respectively increase and decrease. TSS=30mg/l can be regarded as effective boundary between allochthonous TSS and autochthonous TSS. Sediment from the Yellow river diffuse to southern river-mouth in surface layer; However in bottom layer, sediments diffusion range concentrate at northern and southern river-mouth of Yellow river, the central section of Laizhou Bay is possible habitation of sediment from the Yellow river.更多还原