Colloidal size spectra, composition and estuarine mixing behavior of DOM in river and estuarine waters of the northern Gulf of Mexico
Colloidal size spectra, composition and estuarine mixing behavior of DOM in river and estuarine waters of the northern Gulf of Mexico
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DOI：
10.1016/j.gca.2016.02.032
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发表时间：
2016-05
影响因子：
5
通讯作者：
Zhengzhen Zhou;Björn Stolpe;Laodong Guo;A. Shiller
中科院分区：
文献类型：
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作者：
Zhengzhen Zhou;Björn Stolpe;Laodong Guo;A. Shiller
采用流场-流分级（FlFFF）技术，结合紫外吸收和荧光检测器，对密西西比河下游、东珠江、圣路易斯湾河口和墨西哥湾北方沿岸沃茨中光学活性溶解有机物（DOM）的胶体组成和粒径分布进行了研究。除了现场研究，实验室混合实验，使用河流和海水端员进行了研究控制河口混合行为和不同尺寸和组成的胶体的尺寸分配的过程。发色DOM和类腐殖DOM的胶体粒径谱在0.5-4 nm范围内显示出一个主峰，占总FLFFF可回收胶体的75%以上。与此相反，蛋白质样DOM表现出双峰分布，峰在0.5-4 nm和4-8 nm，以及大部分（从EPR中的约41%到密西西比湾中的约72%）分配到>20 nm的尺寸级分。与EPR相比，MR中的本体DOM在丰度和分子量上较低，而与EPR相比，MR中的>20 nm尺寸范围内的胶体蛋白样DOM的比例略大。这些特征与两个流域的土地利用、水文条件和水停留时间的差异相一致，MR沃茨中有更多的原生DOM。在SLB河口，不同的DOM组分表现出不同的混合行为。胶态发色DOM的丰度随盐度的增加而降低，在河口混合过程中表现出明显的去除，尽管大部分DOM表现出保守性。与此相反，胶体腐殖类DOM表现保守内SLB和在实验室混合实验。胶体类蛋白质DOM与类腐殖酸DOM的比例一般随盐度的增加而增加，这与河口和沿海沃茨中原生类蛋白质DOM的增加和陆源类腐殖酸DOM的去除是一致的。在短期实验室混合实验中，观察到了类似的混合行为的散装DOM和胶体，这表明物理化学过程是在河口胶体去除的主要控制因素。这项研究第一次显示了直接的证据，对比不同粒径的光学活性胶体DOM的河口混合行为。
Flow field-flow fractionation (FlFFF) coupled on-line with UV absorbance and fluorescence detectors was used to examine the colloidal composition and size distribution of optically active dissolved organic matter (DOM) in the lower Mississippi River (MR), the East Pearl River (EPR), the St. Louis Bay (SLB) estuary, and coastal waters of the northern Gulf of Mexico. In addition to field studies, laboratory mixing experiments using river and seawater end-members were carried out to study the processes controlling the estuarine mixing behavior and size partitioning of colloids with different sizes and composition. The colloidal size spectra of chromophoric DOM and humic-like DOM showed one dominant peak in the 0.5–4 nm size range, representing >75% of the total FlFFF-recoverable colloids. In contrast, protein-like DOM showed a bi-modal distribution with peaks at 0.5–4 nm and 4–8 nm, as well as a major portion (from ∼41% in the EPR to ∼72% in the Mississippi Bight) partitioned to the >20 nm size fraction. Bulk DOM was lower in abundance and molecular-weight in the MR compared with the EPR, while the proportion of colloidal protein-like DOM in the >20 nm size range was slightly larger in the MR compared with the EPR. These features are consistent with differences in land use, hydrological conditions, and water residence time between the two river basins, with more autochthonous DOM in MR waters. In the SLB estuary, different DOM components demonstrated different mixing behaviors. The abundance of colloidal chromophoric DOM decreased with increasing salinity and showed evident removal during estuarine mixing even though the bulk DOM appeared to be conservative. In contrast, colloidal humic-like DOM behaved conservatively inside SLB and during laboratory mixing experiments. The ratio of colloidal protein-like to humic-like DOM generally increased with increasing salinity, consistent with increasing autochthonous protein-like DOM and removal of terrestrially-derived humic-like DOM in estuarine and coastal waters. Similar mixing behavior for the bulk DOM and colloids was observed in short-term laboratory mixing experiments, suggesting that physicochemical processes are the major controlling factor for colloidal removal in the estuary. For the first time, this study showed direct evidence of contrasting estuarine mixing behavior for different size fractions of optically active colloidal DOM.