Abundance, stable isotopic composition, and export fluxes of DOC, POC, and DIC from the Lower Mississippi River during 2006-2008
Abundance, stable isotopic composition, and export fluxes of DOC, POC, and DIC from the Lower Mississippi River during 2006-2008
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2006 年至 2008 年密西西比河下游 DOC、POC 和 DIC 的丰度、稳定同位素组成以及输出通量
DOI：
10.1002/2015jg003139
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发表时间：
2015-11-01
影响因子：
3.7
通讯作者：
Aiken, George
中科院分区：
文献类型：
--
作者：
Cai, Yihua;Guo, Laodong;Aiken, George
通过 2006-2008 年密西西比河下游的每月采样，研究了溶解无机碳 (DIC)、溶解和胶体有机碳 (DOC 和 COC) 以及颗粒有机碳 (POC) 的来源、丰度、同位素组成和输出通量，以及它们对水文状况的响应。 DIC 是最丰富的碳物种，其次是 POC 和 DOC。 DIC的浓度和δ13C随着河流流量的增加而降低，而DOC的浓度和δ13C则保持相当稳定。 COC 占主体 DOC 的 61±3%，具有相似的 δ13C 丰度，但疏水性有机酸的百分比高于 DOC，表明其芳香族和成岩作用较年轻。 POC 在中等洪水事件期间和大洪水事件的上升边缘显示出峰值浓度。随着排放量的增加，颗粒氮的 δ13C-POC 增加，而 δ15N 减少。总体而言，DOC 或 DIC 与 POC 之间 δ13C 的差异与河流流量呈负相关。湿季期间土壤有机质和呼吸二氧化碳的较高输入可能是 DIC 和 DOC 或 POC 之间 δ13C 趋同的主要驱动力，而旱季期间原位初级生产和呼吸的增强可能是其同位素发散的原因。 2006-2008年间，密西西比河的碳输出通量估计为DIC为13.6 Tg C yr−1，DOC为1.88 Tg C yr−1，POC为2.30 Tg C yr−1。雨季期间，排放归一化的 DIC 产量下降，而 POC 和 DOC 产量则分别增加并保持不变，这意味着碳输出对排放量增加的不同反应。
Sources, abundance, isotopic compositions, and export fluxes of dissolved inorganic carbon (DIC), dissolved and colloidal organic carbon (DOC and COC), and particulate organic carbon (POC), and their response to hydrologic regimes were examined through monthly sampling from the Lower Mississippi River during 2006–2008. DIC was the most abundant carbon species, followed by POC and DOC. Concentration and δ13C of DIC decreased with increasing river discharge, while those of DOC remained fairly stable. COC comprised 61 ± 3% of the bulk DOC with similar δ13C abundances but higher percentages of hydrophobic organic acids than DOC, suggesting its aromatic and diagenetically younger status. POC showed peak concentrations during medium flooding events and at the rising limb of large flooding events. While δ13C‐POC increased, δ15N of particulate nitrogen decreased with increasing discharge. Overall, the differences in δ13C between DOC or DIC and POC show an inverse correlation with river discharge. The higher input of soil organic matter and respired CO2 during wet seasons was likely the main driver for the convergence of δ13C between DIC and DOC or POC, whereas enhanced in situ primary production and respiration during dry seasons might be responsible for their isotopic divergence. Carbon export fluxes from the Mississippi River were estimated to be 13.6 Tg C yr−1 for DIC, 1.88 Tg C yr−1 for DOC, and 2.30 Tg C yr−1 for POC during 2006–2008. The discharge‐normalized DIC yield decreased during wet seasons, while those of POC and DOC increased and remained constant, respectively, implying variable responses in carbon export to the increasing discharge.