2014年夏季长江口有色溶解有机物(CDOM)的分布、光学特性及其来源探究

OPTICAL CHARACTERIZATION, DISTRIBUTION AND SOURCES OF CHROMOPHORIC DISSOLVED ORGANIC MATERIAL(CDOM) IN THE CHANGJIANG RIVER ESTUARY IN JULY 2014

通过测定有色溶解有机物(CDOM)的吸收光谱、荧光光谱、溶解有机碳(DOC)浓度,探究了2014年夏季长江口CDOM的来源及河口混合行为。结合吸收系数a(355)、光谱斜率S275-295、比紫外吸光度SUVA254与盐度的关系,结果表明南港水道受黄浦江输入影响显著,北港水道由长江径流控制呈保守性混合行为,二者CDOM的物质结构性质较为相似。DOC的浓度可通过a(275)与a(295)模拟估算:ln[DOC]=4.94–0.87ln[a(275)]+0.90ln[a(295)],a(275)<8.0 m–1;ln[DOC]=4.77–6.79ln[a(275)]+8.05ln[a(295)],a(275)≥8.0 m–1。模拟结果表明,在长江口及邻近海域,CDOM对DOC具有示踪意义。利用三维荧光光谱-平行因子分析(EEMs-PARAFAC)技术,可得到夏季长江口FDOM含有3个类腐殖质组分(C2,C4和C5)和3个类蛋白质组分(C1,C3和C6)。类腐殖质组分具有相似的来源及地球化学行为,且与a(355)及盐度存在显著相关性;类蛋白质组分则与a(355)及盐度之间无显著相关性,揭示其与区域内微生物的活动有关。

Absorption and fluorescence spectroscopy, along with dissolved organic carbon(DOC) quantification, were employed to examine the sources and estuarine mixing behavior of chromophoric dissolved organic matter(CDOM) in the Changjiang River estuary in July 2014. CDOM abundance(as quantified by the absorption coefficient at 355 nm, a(355)), the absorption spectral slope over 275-295 nm(S275-295), and the specific UV absorbance at 254 nm(SUVA254) were all generally conservative across the freshwater-saltwater transitional zone. A localized elevation of CDOM occurred downstream in the mouth of the Huangpu River, revealing a subtle difference in the mixing pattern of CDOM between the North Port and the South Port, where as the constitutive property between the two ports was similar. DOC concentration([DOC]) can be predicted from the CDOM absorption coefficients at 275 nm(a(275)) and 295 nm(a(295)): ln[DOC] = 4.94–0.87ln[a(275)] + 0.90ln[a(295)], a(275)<8.0 m–1; ln[DOC] = 4.77–6.79ln[a(275)] + 8.05ln[a(295)], a(275)≥8.0 m–1. The regression results demonstrate that CDOM absorbance could be used as the DOC tracer along the Changjiang River estuary. EEMs-PARAFAC(excitation-emission matrix fluorescence spectroscopy-parallel factor) analysis identified three humic-like components(C2, C4, and C5) and three protein-like components(C1, C3 and C6). The humic-like components possessed similar origins and correlated with a(355) and salinity. The protein-like components C1 and C6 were not significantly correlated to salinity and a(355), suggesting the protein-like components were closely related to the in situ microbial activities.