Temporal variability of stable carbon and nitrogen isotopic composition of size-fractionated particulate organic matter in the hypertrophic Sumida River Estuary of Tokyo Bay, Japan
Temporal variability of stable carbon and nitrogen isotopic composition of size-fractionated particulate organic matter in the hypertrophic Sumida River Estuary of Tokyo Bay, Japan
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DOI：
10.1016/j.ecss.2006.02.007
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发表时间：
2006-06
影响因子：
2.8
通讯作者：
Taeko Sato;T. Miyajima;H. Ogawa;Y. Umezawa;I. Koike
中科院分区：
文献类型：
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作者：
Taeko Sato;T. Miyajima;H. Ogawa;Y. Umezawa;I. Koike
为明确肥厚河口悬浮颗粒有机质稳定碳氮同位素组成（δ13C和δ15N）的主要控制因素，对东京都隅田河口悬浮颗粒有机质（POC、PN）、叶绿素a含量（Chl）和悬浮固体干重（SS）浓度和稳定同位素组成的季节变化进行了研究。将颗粒物料分为3 ~ 20、20 ~ 53、53 ~ 250、250 ~ 1000μm四个粒径段。2003年8 - 9月，在河口下游（LE）站点，较细粒径（<20μm）占主导地位（约占Chl的80%）。在春季华时（50 ~ 80% Chl； 2004年2 ~ 4月），浮游植物的中等大小组分（20 ~ 53 μm和53 ~ 250μm）有所增加，反映了浮游植物分类组成的差异。在河口上游和河流站点，<20μm分数在整个调查期间最为丰富。δ 13cpoc和δ 15npn分别在- 32 ~ - 16‰和- 8 ~ +12‰之间变化。δ 13cpocc与POC/Chl和POC/PN的关系可以通过假设两个端元来解释：δ13C接近- 26.5‰的外来（陆源）POC和δ13C变化较大的本地（浮游）POC，其δ13C与环境DIC（- 10 ~ 0‰）的δ13C和浮游植物丰度（Chl）明显相关。δ 15npn明显受水温和NH4+浓度的控制。δ13C和δ15N的变化在不同粒径组分之间存在差异，中等粒径组分（主要是硅藻）δ13C对Chl的依赖性和δ15N对水温的依赖性明显强于较细粒径组分（主要是微鞭毛虫），说明不同分类群之间存在不同的生理响应。本研究的第二个目的是利用LE位点分离叶绿素a的δ13C代替原生δ13C末端成员来评估陆源有机碳（TPOC）对POC大小组分的贡献。秋季开花期间，中等粒径组分（20 ~ 53和53 ~ 250μm）的TPOC平均值为23 ~ 36%，细粒组分（3 ~ 20μm）和粗粒组分（250 ~ 1000μm）的TPOC平均值≥59%。在春华期间，除了最细的部分（36%）外，TPOC的平均贡献普遍较低（≤21%）。盐度与计算TPOC呈负相关，表明陆相有机碳向河口的输运主要受河流流量控制。
To clarify the major factors that control stable carbon and nitrogen isotopic compositions (δ13C and δ15N) of suspended particulate organic matter in a hypertrophic estuary, seasonal variation in concentrations and stable isotopic compositions of particulate organic carbon and nitrogen (POC, PN), chlorophyll a content (Chl) and dry weight of suspended solid (SS) was studied in the Sumida River estuary of Tokyo Bay. Particulate material was fractioned into four size-fractions (3–20, 20–53, 53–250, 250–1000μm). At the lower-estuarine (LE) site, the finer size fraction (<20μm) was predominant (>80% Chl) during the autumnal bloom (Aug–Sep 2003). The middle size fractions (20–53 and 53–250μm) however increased during the spring bloom (50–80% Chl; Feb–Apr 2004), reflecting difference in taxonomic composition of phytoplankton. At the upper-estuarine and the riverine sites, the <20μm fraction was most abundant throughout the survey period. δ13CPOCand δ15NPNvaried between −32 and −16‰ and between −8 and +12‰, respectively. Relationships of δ13CPOCwith POC/Chl and POC/PN ratios could be explained by assuming two end members: allochthonous (terrestrial) POC with a δ13C close to −26.5‰, and autochthonous (planktonic) POC whose δ13C was variable and apparently correlated with δ13C of ambient DIC (−10 to 0‰) and phytoplankton abundance (Chl). δ15NPNwas apparently controlled by water temperature and NH4+concentration. The variability of δ13C and δ15N was different between size fractions: the apparent dependence of δ13C on Chl as well as that of δ15N on water temperature was significantly stronger for the middle size fractions (mainly diatoms) than the finer fraction (mainly microflagellates), suggesting different physiological response between taxa. The second objective of this study was to evaluate contribution of terrestrial organic carbon (TPOC) to the POC size fractions by using δ13C of isolated chlorophyll a at LE site as surrogate for the autochthonous δ13C end member. During the autumnal bloom, TPOC was 23–36% on average for the middle size fractions (20–53 and 53–250μm), and ≥59% for the finest (3–20μm) and coarsest (250–1000μm) fractions. During the spring bloom, the average contribution of TPOC was generally low (≤21%) except for the finest fraction (36%). Negative correlation between salinity and calculated TPOC suggested that transport of terrestrial organic carbon to this estuary was controlled principally by the river discharge.