海洋生态与环境科学重点实验室知识库

陆架边缘海是海洋有机质循环极为活跃的区域，在全球碳循环的研究中占有重要地位。本研究以南黄海、长江口及东海作为研究区域，对不同季节的183个水体颗粒物和84个表层沉积物中四种氨基糖，以及有机碳、氮、叶绿素a进行了分析，对水体异养细菌进行了计数，首次研究了氨基糖在黄东海的分布及组成特征，并利用氨基糖及相关生化和水文参数对研究区域有机质来源，活性和降解状态的分布特征和季节变化进行了研究，探讨了影响有机质来源，活性和降解状态的因素，并估算了细菌有机质对有机碳的贡献率，获得了一系列新的结果和认识：

（1）浮游生物和细菌是南黄海和长江口水体颗粒物中有机质的重要来源，其相对贡献在不同海域和季节时空差异明显。初级生产力水平是影响颗粒物中有机质来源和活性的关键因素，具有较高初级生产力或发生藻华的区域，颗粒物中具有较高的葡萄糖胺/半乳糖胺比值（GlcN/GalN）和碳、氮归一化含量（%AS-OC、%AS-N），指示颗粒有机质较强的浮游生物来源特征，而同时较高的胞壁酸（Mur）含量还表明了较高的新鲜细菌有机质含量，指示了颗粒有机质整体构成较为新鲜，活性较高，降解程度较低。而初级生产较低的区域，其颗粒物中较低的GlcN/GalN、%AS-OC、%AS-N和Mur共同指示了颗粒有机质中新鲜生物来源有机质的减少，有机质整体活性降低。此外，近岸沉积物的再悬浮可能显著降低颗粒有机质含量并影响其来源特征。根据胞壁酸估算，新鲜细菌有机质对研究海域颗粒有机碳的贡献率平均可达29%。

南黄海颗粒态氨基糖含量为2.1~128.4 nmol/(mg dw)，其中葡萄糖胺和半乳糖胺平均占95%以上，甘露糖胺和胞壁酸则不足5%。初级生产力相对较高的春季，典型断面颗粒物中GlcN/GalN平均为8.1±3.7，%AS-OC和%AS-N分别为11.0±6.2%和10.2±6.0%，指示了颗粒有机质具有较为明显的浮游生物来源。初级生产力相对较低的秋季，颗粒物中GlcN/GalN平均为5.1±2.0，%AS-OC和%AS-N分别为5.8±2.9%和7.4±3.5%，指示了颗粒有机质中浮游生物，尤其是浮游动物的贡献减弱。根据Mur估算，春季和秋季新鲜细菌有机质对南黄海典型断面颗粒有机碳的贡献率分别为33.8±18.4%和28.1±18.9%，说明细菌是南黄海颗粒有机碳的重要贡献者。秋季相比于春季，随着初级生产力的降低，颗粒有机质中浮游生物和新鲜细菌的贡献都出现降低，指示了其活性较高的组分比例减小，有机质的整体活性降低。颗粒有机质中碳氮比在秋季有所升高，也指示了秋季比春季颗粒有机质具有更高的降解程度。南黄海近岸站位尽管具有平均最高的叶绿素a含量，但其颗粒有机碳和GlcN/GalN却没有明显的高值，可能是受到沉积物再悬浮过程的影响，使其有机质来源和含量具有一定沉积物的特征。

长江口附近海域颗粒态氨基糖含量为1.2~107.0 nmol/(mg dw)，其中葡萄糖胺和半乳糖胺平均约占95%。长江口CJ断面近岸的初级生产力在春季较高而秋季较低，从春季到秋季，近岸颗粒物中GlcN/GalN从大于3降至小于3，%AS-OC也出现降低，指示了其颗粒有机质从浮游生物和细菌的混合来源向细菌来源为主进行转变，而秋季升高的%AS-N及水体较低的溶解氧则表明其颗粒有机质在秋季已经出现一定程度的降解，但降解程度不高。长江口CJ断面外海一侧的初级生产力在春季较低而秋季较高，从春季到秋季，其颗粒物中GlcN/GalN从小于3到大于8，%AS-OC和%AS-N也从小于3到大于5，表明其颗粒有机质来源从细菌向浮游生物转变。根据Mur估算，春季和秋季新鲜细菌有机质分别占长江口典型断面颗粒有机碳10.8±3.7%和40.5±19.1%，表明细菌对长江口颗粒有机碳具有较大贡献，且秋季的贡献更为明显。秋季外海浮游生物和细菌有机质贡献同时升高，表明其有机质的组成相比于春季更为新鲜，其生物可利用性更高。

（2）与颗粒物相比，黄东海内陆架表层沉积物中葡萄糖胺/胞壁酸和氨基糖的碳、氮归一化含量较低，指示了其降解程度整体高于颗粒物，但由于氨基糖相较于总有机质表现为相对富集的状态，因此沉积物有机质的降解处于初级阶段，仍具有较高活性。细菌有机质同样是黄东海内陆架表层沉积物有机质的重要来源，新鲜细菌有机质对研究海域沉积有机碳的贡献率平均为21.5%。上层水体有机质的沉降对表层沉积物有机质的来源和降解状态具有一定的影响，尤其在水深较浅的近岸区域。泥质区相比于非泥质区其有机碳、氮含量更高，但其与有机质的来源和降解程度没有绝对关系。东海泥质区比非泥质区有机质中几丁质成分更高，有机质更新鲜，而黄海泥质区则比非泥质区有机质中有更多的低活性细菌残体，其整体降解程度更高。

南黄海及长江口邻近海域表层沉积物氨基糖含量为0.18~8.25 nmol/(mg dw)，其中葡萄糖胺和半乳糖胺平均约占95%。在南黄海典型断面，GlcN/GalN在两个季节所有站位均小于2，指示了细菌是南黄海表层沉积物有机质的主要来源。外海泥质区相比于近岸非泥质区其沉积物中有机碳、氮含量更高，体现了粒度对有机质含量的影响。泥质区沉积物胞壁酸含量同样较高，但其在有机碳中的含量却较低，指示了泥质区较高的有机质含量并非来自新鲜细菌有机质的贡献。表层沉积物中较高的%AS-OC和%AS-N 表明有机质已产生一定程度的降解，但由于中等活性的氨基糖相比于总有机质仍然相对富集，因此沉积物总有机质的降解可能处于初期至中期水平。泥质区更高的GlcN/Mur则指示了其有机质的降解程度比近岸非泥质区更高。根据较低的GlcN/GlcN推测外海泥质区较高的有机质含量可能来源于降解程度较高的细菌有机质的贡献。根据胞壁酸估算，南黄海典型断面表层沉积物中较为新鲜的细菌有机质对有机碳的贡献率在春季和秋季分别为28.2±8.6%和21.7±8.7%，季节差异不大。

东海内陆架表层沉积物中氨基糖含量为0.48~7.23 nmol/(mg dw)，其中葡萄糖胺和半乳糖胺约占95%。GlcN/GalN在两个季节所有站位均小于2，说明细菌是东海内陆架表层沉积物有机质的主要来源。近岸泥质区相比于远岸非泥质区具有较高的有机质含量，同时其GlcN/GalN和胞壁酸含量也更高，表明了泥质区有机质中含有更多的几丁质及新鲜细菌有机质。尽管GlcN/GalN表明了有机质主要为细菌来源，但表层沉积物中%AS-OC和%AS-N却高于细菌中的特征值（分别为3.65±1.66%和4.49±1.98%），说明有机质已经产生一定程度的降解。同时，近岸泥质区比远岸非泥质区具有较低的GlcN/Mur，说明泥质区中有机质比非泥质区更新鲜。秋季相比于夏季，东海泥质区水体叶绿素a含量降低，沉积物中有机碳、氮含量下降，同时GlcN/GalN略有降低，Mur含量升高，说明夏季水体沉降至表层沉积物的有机质在秋季逐渐转变为细菌有机质，并且这种来源的变化在生产力较高的近岸更为明显，表明近岸水体颗粒物的沉降对表层沉积物有机质的组成具有重要影响。夏季水体叶绿素a含量较高，其与沉积物中的胞壁酸具有正相关关系，而秋季水体叶绿素a含量较低，其与沉积物中胞壁酸的相关性消失，同样说明水体颗粒物沉降对表层沉积物有机质来源的影响。根据胞壁酸估算，东海内陆架表层沉积物中较为新鲜的细菌有机质对有机碳的贡献率在春季和秋季分别为13.1±6.4%和28.5±17.9%，具有秋季高于春季，近岸泥质区高于远岸非泥质区的特征。

沉积物与颗粒物相比，其较低的GlcN/GalN表明其有机质主要为细菌来源，而颗粒物中较高的GlcN/GalN则表明其有机质具有更高的浮游生物来源。沉积物中指征有机质来源的氨基糖指标如GlcN/Mur和%AS-OC，%AS-N受到更多的降解过程影响而升高，从而在指征来源时与GlcN/GalN等不易受降解影响的指标相矛盾，说明了表层沉积物整体的降解程度高于水体颗粒物。

Continental marginal seas are important regions for the production, transformation and burial of organic matters (OM), and they play an important role in the global carbon cycle. In this study, 183 particulate matter samples and 84 surface sediment samples were collected from the Southern Yellow Sea (SYS), Yangtze River Estuary (YRE) and East China Sea (ECS), the amino sugars (AS) together with organic carbon, nitrogen, chlorophyll a, heterotrophic bacterial cell count and hydrological parameters were studied. The distribution and composition of amino sugars were firstly reported in the studying area, and the source, bioavailability and diagenetic states of the OM as well as their seasonal changes and influence factors were studied, and the bacterial OM contributions to organic carbon were estimated. The major results of this study are as followed:

1. Planktons and bacteria are important sources of particulate organic matters (POM) in the SYS and YRE, and their relative contributions varied in different sea areas and seasons. The level of primary production was a key influence factor of the source and bioavailability of POM. In the places that had high primary production, the higher ratios of glucosamine to galactosamine (GlcN/GalN) and C- and N- normalized yields of amino sugars (%AS-OC, %AS-N) indicated a feature of plankton source of POM, and the higher concentration of muramic acid (Mur) showed a higher concentration of fresh bacterial OM. The higher proportion of fresh plankton and bacterial OM indicated the POM had higher bioavailability. On the contrary, in the places where the primary production was low, the lower GlcN/GalN, %AS-OC and %AS-N implied a lower contribution of plankton (especially zooplankton) to POM, and the lower Mur concentration also indicated a lower contribution of fresh bacterial OM. The lower contribution of fresh OM indicated the POM was more degraded. Besides, the resuspension of surface sediments could significantly decrease the contents of particulate carbon and nitrogen (POC and PN) and had an effect on the source of POM. The contributions of relative fresh bacterial OM to particulate organic carbon (POC) were on average 29% in the studing area.

The concentrations of particulate amino sugars (PAS) were 2.1~128.4 nmol/(mg dw) in the SYS. The PAS consisted of more than 95% of GlcN and GalN and less than 5% of mannosamine (ManN) and Mur. In 35°N section, the primary production was relatively high in spring, the GlcN/GalN was 8.1±3.7 on average and the %AS-OC and %AS-N were 11.0±6.2% and 10.2±6.0% on average, respectively, which clearly indicated a plankton source of POM. Then in autumn, when the primary production became lower, the GlcN/GalN decreased to 5.1±2.0, and the %AS-OC and %AS-N were 5.8±2.9% and 7.4±3.5% on average, respectively, indicating the contribution of plankton to POM decreased. The estimation based on Mur showed the contribution rate of fresh bacterial OM to POC were 33.8±18.4% and 28.1±18.9% in spring and autumn, respectively, demonstrating bacteria was an important source of POM in the SYS. As the primary production decreased from spring to autumn, the contribution of plankton and fresh bacterial OM to POM were both decreased, indicating the decrease of the labile part of POM and leading to a more degraded nature. The increase of C/N in autumn could also indicated the POM were more degraded than spring. The nearshore site had the highest primary production, however, the POC and GlcN/GalN were not very high. This might because the resuspension of surface sediments influenced the contents and sources of POM.

In the YRE and adjacent sea area, the PAS concentrations were 1.2~107.0 nmol/(mg dw). The PAS consisted of more than 95% of GlcN and GalN and less than 5% of mannosamine (ManN) and Mur. In typical section of the YRE, the primary production was higher in spring and lower in autumn in nearshore area, meanwhile, the GlcN/GalN decreased from ＞3 to ＜3, and %AS-OC also decreased from spring to autumn, implying the source of POM transformed from plankton to bacteria. The higher %AS-N and lower DO concentrations in autumn than spring indicated the POM was more degraded in autumn. In offshore site (CJ-4), the primary production was higher in autumn than spirng, the GlcN/GalN increased from ＜3 in spring to ＞8 in autumn, the %AS-OC and %AS-N also increased from ＜3 in spring to ＞5 in autumn, indicating the source of POM transformed from bacteria to plankton. The estimation based on Mur showed the fresh bacterial OM contributed 10.8±3.7% and 40.5±19.1% of the POC in spring and autumn, respectively. In autumn, the contributions of plankton and fresh bacterial OM to POM both increased in offshore site, indicating a more labile nature than spirng.

2. Comaring with those in POM, the source indicators based on AS such as GlcN/Mur, %AS-OC and %AS-N were more easily affected by degradation process, indicating the bioavailability of SOM was lower than that of POM. But as the AS was a kind of semi-labile biomolecules and temporarily enriched during the degradation in SOM, it is speculated that the degradation state of SOM in the inner shelf of SYS and ECS was at early or medium stage. Bacterial OM was an important source of sediment organic matters (SOM) in the inner shelf of the SYS and ECS，and the contributions of relative fresh bacterial OM to sediment organic carbon were on average 21.5% in the studing area. The sedimentation of particulate matters from upper water column had a certain of influence on the source and diagenetic states of the SOM, especially in nearshore area where the water was shallow. Comparing with sand area, the mud area contained more organic matters in sediments, but the particle size could not decide the source and diagenetic states of SOM. In the ECS, the sediments of nearshore mud area contained more chitin material than offshore area and had higher bioavailability. While in the mud area of the SYS, the sediments contained higher proportions of degraded bacterial OM and the SOM was more degraded than those in non-mud area.

In SYS and YRE, the concentrations of AS in the surface sediments were 0.18~8.25 nmol/ (mg dw), and the AS consisted of on average 95% of GlcN and GalN and less than 5% of ManN and Mur. In the 35°N section of the SYS, GlcN/GalN ratios were ＜2 in all sites and both seasons and indicated a major bacterial source. In the offshore mud area, the contents of organic carbon and nitrogen were higher than those in nearshore area. The Mur (nmol/ mg dw) was also higher in mud area, but the Mur (nmol/ (mg C)) was lower, indicating the higher contents of OM in mud area was not mainly contributed by fresh bacterial OM. The relatively high %AS-OC and %AS-N implied that the OM in SYS surface sediments had undergone degradation, but as the AS were semi-labile biomolecules and temporarily enriched during the degradation process, it is speculated that the degradation state of SOM in SYS was at early or medium stage. At the meantime, the higher ratios of GlcN/Mur in mud area demonstrated that the SOM was more degraded in mud area than that in sand area. The low GlcN/GalN in sediments implied that the high contents in organic carbon and nitrogen in mud area could be contributed by degraded bacterial OM. The estimation based on Mur showed the fresh bacterial OM contributed 28.2±8.6% and 21.7±8.7% of the sediment organic carbon in spring and autumn, respectively.

In the inner shelf of the ECS, the concentrations of AS in surface sediments were

0.48~7.23 nmol/ (mg dw). The AS consisted of on average 95% of GlcN and GalN and less than 5% of ManN and Mur. GlcN/GalN ratios were ＜2 in all sites and both seasons and indicated a major bacterial OM source. Comparing with offshore sand area, the contents of OM, GlcN/GalN ratios and Mur concentrations were all higher in nearshore mud area, indicating the surface sediments in nearshore mud area contained more OM and the SOM contained more chitin material and fresh bacterial OM than those in offshore area. Although the low GlcN/GalN indicated a major bacterial OM source, the %AS-OC and %AS-N were higher than those in bacteria OM, which implied that the SOM had undergone degradation, and the degradation was at early or medium stage. In the meantime, the GlcN/Mur ratios were lower in nearshore mud area than those in offshore area, indicating the SOM in mud area was fresher. The Chl-a in surface water, the SOM contents and GlcN/GalN ratios in surface sediments were lower, and the Mur concentrations were higher in autumn than summer, indicating the settling particles in surface sediments in summer were degraded and converted to bacterial OM in autumn. these seasonal changes were more obvious in nearshore area, where the primary production was relatively high and water depth was shallow, indicating the settling of POM had important influence on the source of SOM in nearshore. In summer, the Chl-a in seawater had positive correlations with Mur in surface sediments, however in autumn, the correlations disappeared as the Chl-a contents decreased, which further indicated that the settling of POM had important influence on the source of POM. The estimation based on Mur showed the fresh bacterial OM contributed 13.1±6.4% and 28.5±17.9% of the sediment organic matters in the inner shelf of the ECS in spring and autumn, respectively. The contribution was higher in autumn than summer and also higher in nearshore mud area than offshore sand area.

The AS parameters showed obvious differences of source and diagenetic states between POM and SOM. The lower GlcN/GalN ratios in SOM showed the higher contribution of bacterial OM, while the higher GlcN/GalN ratios in POM indicated the higher contribution of plankton OM. Comparing with those in POM, the source indicators such as GlcN/Mur, %AS-OC and %AS-N in SOM could be obviously elevated by degradation process, leading to a conflict result with GlcN/GalN, which indicated that the SOM was more degraded than POM.