Spatial distribution and absorption characteristics with relation to fluorescence of chromophoric dissolved organic matter (CDOM) in Meiliang Bay of Lake Taihu
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    Abstract:

    Chromophoric dissolved organic matter (CDOM) is the light absorption fraction of dissolved organic carbon (DOC) that absorbs light in both the ultraviolet and visible ranges. The spatial and temporal distribution of CDOM in aquatic ecosystems can have important effects on ecosystem productivity, negatively impacting primary productivity due to CDOM absorbs light at both ultraviolet and visible wavelengths while positively impacting secondary productivity by fueling of microbial respiration by photo-degraded CDOM. In water color remote sensing, overlaps of pigment absorption spectra with CDOM absorption at blue wavelength generally complicate the use of chlorophyll a retrieval algorithms that are based on remotely sensed ocean color and lead to overestimated chlorophyll a concentration. In addition, high concentrations of CDOM can also act as a photoprotectant against UV damage for aquatic organisms. However, the protection against UV radiation provided by dissolved humic material for aquatic biota may be diminished if photodegradation of CDOM by UV radiation and acidification increase the UV transparency in lakes. CDOM absorption measurements and their relationship with DOC, and fluorescence are presented in Meiliang Bay of Lake Taihu based on a field investigation and lab analysis to show the spatial distribution of CDOM. Absorption spectral of CDOM was measured from 240 to 800 nm. Concentrations of DOC ranged from 10.48 to 19.72 mg/L with an average of 13.20 ±2.78 mg/L. CDOM absorption coefficients at 280 nm and 355 nm were in the range 18. 73-31. 91 m-1 ( average 23.19±4.36mm-1) and 4. 63-7. 14 mm-1 (average 5. 76±0. 90 mm-1),respectively. The values of the DOC-specific absorption coefficient at 355 nm ranged from 0. 34 to 0. 57 L/( mg · m). Fluorescence emission at 450 nm, excited at 355 nm, had a mean value of 1. 69 ±0. 77 nmm-1. A significant lake zone difference is found in DOC concentration, CDOM absorption coefficient and fluorescence. This regional distribution pattern was in agreement with the location of sources of yellow substance : highest concentrations close to river mouth under the influence of river inflow, lower values in outlet of Meiliang bay. CDOM fluorescence and absorption coefficient were significantly and positively correlated. The results show a good correlation between CDOM absorption and DOC coefficients during 280-500 nm short wavelength intervals. The coefficient of variation between CDOM absorption and DOC concentration decreased with the increase of wavelength from 280 to 500 nm. The linear regression equations between fluorescence, DOC concentration and absorption coefficients at 355 nm are: Fn ( 355 ) = 0.692( ±0. 135)a(355)-2.291 (±0.786),a(355) =0.233(±0.061)DOC +2.690(±0.816),respectively. The exponential slope coefficient ranged from 11.0 to 14.9 um-1 with a mean value 13. 86 ± 0. 91um-1, 15. 8-20. 7 um-1 with a mean value 18. 54 ± 1. 11 um-1 and 9.9-13. 9 um-1 with a mean value 12. 93 ± 0. 92um-1 over the 280-500 nm, 280-360 nm and 360-440 nm intervals. A significant negative linear correlation was found between spectral slope coefficient and DOC specific absorption coefficient, but a significant positive linear correlation for spectral slope coefficient and the ratio of a( 250)/a( 365 ). Larger specific absorption coefficient corresponds to smaller a (250)/a (365) and spectral slope coefficient, which shows higher ratio humic in CDOM.

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张运林,秦伯强,杨龙元.太湖梅梁湾有色可溶性有机物的空间分布及光学行为[J]. Journal of Lake Sciences,2006,18(4):319-326.

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History
  • Received:March 25,2005
  • Revised:August 29,2005
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  • Online: March 24,2015
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