Distribution, seasonality, and fluxes of dissolved organic matter in the Pearl River (Zhujiang) estuary, China

Distribution, seasonality, and fluxes of dissolved organic matter in the Pearl River (Zhujiang) estuary, China
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中国珠江口溶解有机物的分布、季节和通量

DOI：
10.5194/bg-16-2751-2019
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发表时间：
2019-07-12
期刊：
BIOGEOSCIENCES
影响因子：
4.9
通讯作者：
Xie, Huixiang
Xie, Huixiang
中科院分区：
地球科学2区
文献类型：
--
作者：
Li, Yang;Song, Guisheng;Xie, Huixiang

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抽象。珠江口水体溶解有机碳浓度 (PRE)2015年5月、8月和10月以及2015年1月， 2016.有色和荧光溶解有机物（CDOM和FDOM） 在后三个季节的特点是吸收， 荧光光谱学。CDOM和FDOM的季节性变化可以忽略不计 变化，而DOC显示出显着的季节性，平均 浓度在5月最高（156 µmol L−1）， 11月（87 µmol L−1），1月（118 µmol L−1）和8月（112 µmol L−1）之间相当。虽然DOC、CDOM和 表层水体中FDOM含量普遍高于底层水体， 两层之间的差异在统计学上不显著。DOC 在所有季节中，CDOM和FDOM的跨河口变化不大， 1月份，河口西侧高于东侧 的方面想所有这三个变量都显示出大脑皮层头部区域的快速下降。 河口（盐度<5），它们在主河口的动态是 主要由保守混合控制，导致线性下降 或相对恒定（仅5月和11月的DOC）的含量， 增加盐度。FDOM随盐度的增加下降速度加快5%-35 而CDOM比DOC快2-3倍。 盐度和CDOM吸收系数可以作为DOC的指示因子 在八月和一月。四季淡水端元主要为 新鲜的、富含蛋白质的微生物来源的DOM，其中很大一部分可能是污染源。蛋白质类物质优先被消耗， 但蛋白质特征的优势得以保持 整个河口。DOC和CDOM的出口（就吸收而言 在330 nm波长下，南海的平均辐射系数分别为195×109 g和266×109 m2， 362×109 g和493×109 m2 珠江三角洲PRE呈现最低浓度和出口 DOC和CDOM通量之间的世界主要河口。DOM交付自 然而，PRE富含蛋白质，因此可以增强 邻近沿海沃茨。总的来说，PRE表现出较低的丰度， DOM的时空变异性比预期的要小， 河口与河流径流明显的季节性，据推测， 珠江流域森林覆盖不良， 污染源DOM在上游的滞留时间短， 淡水
Abstract. Dissolved organic carbon (DOC) concentration in the Pearl River estuary (PRE) of China was measured in May, August, and October 2015 and January 2016. Chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) in the latter three seasons were characterized by absorption and fluorescence spectroscopy. CDOM and FDOM exhibited negligible seasonal variations, while DOC displayed a significant seasonality, with the average concentration being highest in May (156 µmol L−1), lowest in November (87 µmol L−1), and comparable between January (118 µmol L−1) and August (112 µmol L−1). Although DOC, CDOM, and FDOM in surface water were generally higher than in bottom water, the difference between the two layers was statistically insignificant. DOC showed little cross-estuary variations in all seasons, while CDOM and FDOM in January were higher on the west side of the estuary than on the east side. All three variables showed rapid drawdowns in the head region of the estuary (salinity <5); their dynamics in the main estuary were primarily controlled by conservative mixing, leading to linearly declining or relatively constant (for DOC in May and November only) contents with increasing salinity. The decrease in FDOM with salinity was 5 %–35 % faster than that of CDOM, which in turn was 2–3 times quicker than that of DOC. Salinity and CDOM absorption coefficients could serve as indicators of DOC in August and January. Freshwater endmembers in all seasons mainly contained fresh, protein-rich DOM of microbial origin, a large part of it likely being pollution-derived. Protein-like materials were preferentially consumed in the head region but the dominance of the protein signature was maintained throughout the estuary. Exports of DOC and CDOM (in terms of the absorption coefficient at 330 nm) into the South China Sea were estimated as 195×109 g and 266×109 m2 for the PRE and 362×109 g and 493×109 m2 for the entire Pearl River Delta. The PRE presents the lowest concentrations and export fluxes of DOC and CDOM among the world's major estuaries. DOM delivered from the PRE is, however, protein-rich and thus may enhance heterotrophs in the adjacent coastal waters. Overall, the PRE manifests lower abundance and smaller spatiotemporal variability of DOM than expected for a sizable estuary with a marked seasonality of river runoff due supposedly to the poorly forested watershed of the Pearl River, the rapid degradation of the pollution-derived DOM in the upper reach, and the short residence time of freshwater.