| 摘要: |
| 利用荧光光度计对2001—2003年期间九龙江口4个航次水样中有色溶解有机物(CDOM)的荧光光谱进行了测定,并对其荧光性质、荧光强度的分布与季节性变化特征及其河口行为进行了分析,同时与厦门岛周边海域进行了比较。结果表明,输入九龙江口的CDOM荧光强度季节变化明显,夏高(17.16QSU)冬低(5.73QSU)。所有站位表层荧光强度明显高于底层,与河口区垂直分层一致。南支CDOM荧光强度随盐度的变化率高于北支,说明九龙江河水主要沿河口南岸入海。4个航次CDOM荧光强度都呈保守混合趋势,但观测到CDOM表观荧光效率随盐度增加而降低,暗示在低盐度区可能有胡敏酸的絮凝沉降。厦门周边海域CDOM荧光强度以西海域北部最高,西海域南部和同安湾次之,厦门东侧水道最低。各水域表层CDOM荧光强度与盐度均呈反相关关系,但不同水域回归曲线的斜率有差异,九龙江口、厦门西海域南部及厦门东侧水道三个海域具有同一相关趋势线,表明西海域南部和东侧水道主要受九龙江水输入控制,而西海域北部有不同的趋势线,这主要受污水输入的影响,由此很好地证实了CDOM的水团示踪作用。 |
| 关键词: 有色可溶有机物 荧光强度 河口行为 九龙江口 厦门湾 |
| DOI： |
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| 基金项目:国家自然科学基金资助项目,40106007号 |
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| FLUORESCENT CHARACTERISTICS OF COLORED DISSOLVED ORGANIC MATTER (CDOM) IN THE JIULONG RIVER ESTUARY |
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GUO Wei-Dong1,2, XIA En-Qin1, HAN Yu-Chao1, WU Fang1, LI Meng1, WU Yi-Da1
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1.Department of Oceanography, Xiamen University, Xiamen, 361005;2.State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, 361005
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| Abstract: |
| We performed fluorescence analysis on chromophoric (colored) dissolved organic matter (CDOM) in the Jiulong River Estuary. There were four cruises in this estuary—December 30, 2001, June 1, 2002, September 1, 2002 and May 17, 2003, and one cruise in adjacent sea area around Xiamen Island on April 25, 2003 for comparison. Water samples were collected using 2.5L Niskin bottles and stored at 1L clean amber glass bottles in darkness. All samples were filtered immediately through precombusted 0.7μm Whatman GF/F glass fiber filters (Φ47mm) after they were taken back to laboratory. The filtrates were placed in 60ml amber glass bottles (precleaned and combusted at 450°C for 5 hours) and stored frozen and darkness before analyses. The aim of this study is to determine the fluorescent characteristics of CDOM in Jiulong River Estuary and adjacent Xiamen sea area, and to understand the distribution and estuarine behavior of fluorescence intensity of CDOM and their controlling factors.
RF-5301 fluorescence spectrometer was used to retrieve the fluorescence spectra of the samples, with the excitation wavelength at 355nm and emission wavelength at 450nm, and the width of slot is 10nm. The 1cm quartz cell was used and Milli-Q water was the blank. All the fluorescence intensity data were normalized to a quinine sulphate standard and are reported as quinine sulphate unit (QSU). The absorption coefficients of water samples were measured over the 280–800nm range with 1 nm increment by Cary-100 UV-Vis spectrometer. The 10cm quartz cell was used and Milli-Q water as the reference medium.
The range of CDOM fluorescence intensity in the Jiulong River Estuary were 5.73–1.22QSU (December 2001), 17.16–2.62QSU(June 2002), 11.38–4.73QSU (September 2002) and 10.17–1.83QSU(May 2003), respectively. The seasonal variation of CDOM fluorescence intensity was obvious for samples of river end-member, which was highest in wet summer season and lowest in dry winter season, reflecting the control of terrestrial runoff input on estuarine CDOM. Fluorescence intensity of CDOM in the estuary was consistently higher for surface samples than for bottom samples for spring (May) and autumn (September) cruise, which was controlled by the layer characteristics of the estuary during these seasons. In south channel of the estuary, variation of fluorescence intensity with salinity was higher than that of north channel, indicating that the river water flow into the sea mainly through south channel.
CDOM showed a conservative behavior during estuarine mixing for all four cruises, the correlation coefficients (R2) between CDOM and salinity were all above 0.88. However, the apparent fluorescence efficiency (AFE) changed with salinity. It increased with salinity and reached maximum at salinity 10, suggesting that there may exist flocculation and precipitation of humic acid in lower salinity area of the estuary. AFE then showed a decrease tendency with the increase of salinity and reduced to one-third of maximum value for water samples of salinity 30, reflecting the influence of marine CDOM at high salinity region.
In April 2003 cruise, the highest CDOM fluorescence intensity (6.59QSU) was observed in north of Xiamen West Harbour, next to the south of Xiamen West Harbour and Tong’an Bay, and the lowest value was found in eastern sea area of Xiamen(2.2QSU). The average AFE of CDOM from north of Xiamen West Harbour was 5.79, higher than that of the Jiulong River Estuary, indicating an anthropogenic sources from aquaculture and communal effluent. Vertical distribution of CDOM in Xiamen West Harbour also showed a similar pattern to the Jiulong River Estuary, which was controlled by both biological activity and Jiulong River plume. However, the CDOM fluorescence intensity of surface waters were lower than those of bottom samples in eastern sea area of Xiamen, reflecting the possible influence of photobleaching of CDOM in these high salinity regions. The obvious differences of CDOM fluorescence characteristics for different sources of CDOM in Xiamen Bay indicate that it was a useful indicator of water mixing. |
| Key words: Colored dissolved organic matter ( CDOM) , Fluorescence intensity, Estuarine behavior, Jiulong
River Estuary, Xiamen Bay |
