陈慕雨, 陈霖, 韩露露, 等, 2023. 长江口及邻近海域有色溶解有机物的来源、组成和影响因素[J]. 海洋科学进展, 41(4): 637-656. doi: 10.12362/j.issn.1671-6647.20230227001.
引用本文: 陈慕雨, 陈霖, 韩露露, 等, 2023. 长江口及邻近海域有色溶解有机物的来源、组成和影响因素[J]. 海洋科学进展, 41(4): 637-656. doi: 10.12362/j.issn.1671-6647.20230227001.
CHEN M Y, CHEN L, HAN L L, et al, 2023. Sources, composition, and influencing factors of colored dissolved organic matter in the Changjiang estuary and adjacent waters[J]. Advances in Marine Science, 41(4): 637-656. doi: 10.12362/j.issn.1671-6647.20230227001
Citation: CHEN M Y, CHEN L, HAN L L, et al, 2023. Sources, composition, and influencing factors of colored dissolved organic matter in the Changjiang estuary and adjacent waters[J]. Advances in Marine Science, 41(4): 637-656. doi: 10.12362/j.issn.1671-6647.20230227001

长江口及邻近海域有色溶解有机物的来源、组成和影响因素

Sources, Composition, and Influencing Factors of Colored Dissolved Organic Matter in the Changjiang Estuary and Adjacent Waters

  • 摘要: 有色溶解有机物(CDOM)是河口与边缘海溶解有机物(DOM)的重要组成部分,可以示踪不同水团混合、输运过程中DOM的迁移转化等。通过测定2018年8月长江口及邻近海域分层水体中CDOM的紫外可见吸收光谱和三维荧光特征,结合温、盐和溶解氧等理化参数,研究其来源、组成和分布,并分析了外源输入和生物活动的影响。结果表明,溶解有机碳(DOC)浓度和CDOM的3个特征参数(芳香性指数SUVA254、吸收系数a350和腐殖化指数HIX)在长江口显著高于邻近海域的,从表层到中层再到底层逐渐降低,表明长江冲淡水中CDOM主要来源为陆源输入;而长江口外海域和浙闽沿岸附近特征参数相对较低,代表DOM分子量的光谱斜率S275-295和生物指数BIX相对较高,表明这些区域有较多的生物活动,应与长江、台湾暖流和黑潮次表层水所带来的丰富的营养物质有关。研究海域HIX数值较低,BIX数值较高,表明CDOM主要是自生源贡献。主成分分析的结果表明,pH、溶解氧、温度和叶绿素a等是影响DOC浓度、CDOM绝对含量和组成的主要因素,但在表层这种影响较其他层次弱。基于平行因子分析(PARAFAC)在CDOM中共识别出3种荧光组分,即类腐殖质组分C1(λex为240 nm和285 nm,λem为352 nm)、类蛋白组分C2(λex为270 nm,λem为306 nm)、类腐殖质C3(λex为265 nm和335 nm,λem为428 nm)。其中C1为海洋自生来源和陆源共同影响,C3主要来自陆源;C1和C3主要分布在长江口、杭州湾和浙闽沿岸附近,而C2主要分布在长江口门处和杭州湾外。在表层水体中,一些中高盐度的站位类蛋白组分C2的值较高,对应研究区域内较高质量浓度的叶绿素a和较低的表观耗氧量(AOU),说明C2主要来自浮游植物现场生产。一些中低盐度的站位C2组分的值较低,C1组分的值较高,且个别站位叶绿素a质量浓度也较高,说明高的初级生产促进了微生物活动,使得一些类蛋白组分被微生物分解消耗,产生类腐殖质组分C1。这些对长江口及邻近海域CDOM组成和分布及影响因素认识的丰富,有助于深入理解大河河口及邻近海域DOM的迁移转化过程。

     

    Abstract: Colored Dissolved Organic Matter (CDOM) is a crucial constituent of estuarine and coastal Dissolved Organic Matter (DOM), which can be utilized to track the transport and transformation of DOM during various water masses mixing and transportation. In this study, we investigated the sources, composition and distribution of CDOM in the Changjiang Estuary and adjacent waters in August 2018. We measured the UV-visible absorption spectra and three-dimensional fluorescence characteristics of CDOM in the different layers of water column, combined with physical and chemical parameters such as temperature, salinity and dissolved oxygen, etc. In particular, we discussed the influence of allochthonous inputs and biological activities. Our results showed that the dissolved organic carbon (DOC) content and CDOM characteristic parameters (such as the aromaticity index SUVA254, absorption coefficient a350, and humification index HIX) in the Changjiang Estuary were significantly higher than those in the adjacent sea areas. These parameters decreased gradually from the surface layer to the middle layer and then to the bottom layer, indicating that the primary source of CDOM in the Changjiang diluted water was from land-based inputs. The values of these parameters in the outer sea area of the Changjiang Estuary and the coastal area near Zhejiang-Fujian were relatively low, and the spectral slope S275-295 of DOM molecular weight and the biological index BIX were relatively high, indicating that there were more biological activities in these areas. This may be related to the abundant nutrients brought by the Changjiang and Taiwan warm currents, and the subsurface water of the Kuroshio. The low HIX values and high BIX values in the study area indicated that CDOM was mainly contributed by autochthonous sources. The results of principal component analysis showed that pH, dissolved oxygen, temperature and chlorophyll a were the main factors affecting the concentration and composition of DOC and CDOM. However, this influence was weaker in the surface layer compared to the other layers. Based on the parallel factor analysis (PARAFAC), we identified three fluorescent components in CDOM, namely humic-like components C1 Ex/Em, 240(285)/352 nm and C3 Ex/Em, 265(335)/428 nm, and protein-like components C2 (Ex/Em, 270/306 nm). C1 was jointly controlled by marine autochthonous and terrestrial sources, while C3 was mainly from terrestrial sources. C1 and C3 were mainly distributed in the Changjiang Estuary, Hangzhou Bay and the coastal area near Zhejiang-Fujian, while C2 was mainly distributed at the entrance and outside Hangzhou Bay. In surface water, the components of C2 had higher values at some middle-high salinity stations, corresponding to the higher concentrations of chlorophyll a and lower apparent oxygen utilization (AOU) in the study area, indicating that C2 mainly originated from phytoplankton production in situ. At certain stations with lower salinity levels, the C2 components exhibited lower values, whereas the C1 components displayed increased values. Additionally, some stations exhibited elevated concentrations of chlorophyll a, which suggested that the increased primary production promoted microbial activities, resulting in the decomposition and consumption of certain protein components and the production of C1 humic-like components. This study has enhanced our understanding of the composition, distribution, and influencing factors of CDOM in the Changjiang Estuary and adjacent waters, which is beneficial for gaining further insight in the transport and transformation of DOM in large river estuaries and adjacent sea areas.

     

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