Degradation of humic substances by UV irradiation

Allard, Bert; Borén, Hans; Pettersson, Catharina; Zhang, G.

doi:10.1016/0160-4120(94)90072-8

Cited by 132 publications

(70 citation statements)

References 3 publications

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“…A solution to this problem would be to increase the incubation time to several days or even weeks (De Haan 1993), in which case a measurable reduction in DOC can be expected; however, there is risk of bacterial growth causing respiratory production of DIC. In laboratory experiments with artificial light (UV) sources, substantial reductions in DOC have been measured over brief (1 d) periods (Kulovaara and Backlund 1993;Allard et al 1994). The UV-dose received in such experiments, however, is often exaggerated because of the long exposures to a constant light intensity usually with unnaturally high light intensities at short wavelengths.…”

Section: Discussionmentioning

confidence: 99%

Photo‐oxidative production of dissolved inorganic carbon in lakes of different humic content

Granéli

Lindell

Tranvik

1996

Limnology & Oceanography

317

245

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Photo-oxidation of dissolved organic carbon (DOC) to inorganic carbon (DIC) in five oligotrophic south Swedish lakes of different humic content (3.9-19 mg DOC liter-r, O-140 mg Pt liter-*, Secchi depth 7.6-1.5 m) was investigated. Sterile-filtered (0.2 pm) water was incubated in UV-transparent quartz tubes and in tubes covered with aluminum foil. Samples were incubated at different depths (0,0.20,0.65, and 2.00 m) from sunrise to sunset (0400 to 2200 hours) in July. Inorganic C was measured before and after incubation. Total plankton respiration in unfiltered lake-water (production of DIC) was also measured. At the surface, photo-oxidative DIC production was 86410 mg C m-3 d-l, while plankton community respiration was 10 l-274 mg C m-3 d-l. Photo-oxidation integrated over depth was 44-l 7 1 mg C m-2 d-r, while respiration was 201-547 mg C m-2 d-r to a depth of 2 m and 398-860 mg C m-2 d-* over the depth of the epilimnion. Depth-integrated photo-oxidation was independent of water color or DOC concentration in the lakes. Photooxidation was detected deeper than the penetration of UV-B radiation, indicating that longer wavelengths (UV-A and possibly PAR) are also active. DIC production was linearly related to loss of fluorescence (excitation 355 nm, emission 455 nm) in light-incubated samples. Our study shows that photo-oxidation of DOC may be an important process causing the regularly observed supersaturation of DIC in lakes.

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Section: Discussionmentioning

confidence: 99%

Photo‐oxidative production of dissolved inorganic carbon in lakes of different humic content

Granéli

Lindell

Tranvik

1996

Limnology & Oceanography

317

245

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“…Photolysis of individual proteinaceous and humic (plant polyphenols) compounds by UV radiation is well known (e.g. Manny et al 197 1;Zepp et al 198 1;Geller 1986;Allard et al 1994). Several of these studies have shown photolytic reductions or alterations of humic substances when exposed to variations in natural solar or enhanced UV irradiance, particularly over long periods of time (e.g.…”

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confidence: 99%

Natural photolysis by ultraviolet irradiance of recalcitrant dissolved organic matter to simple substrates for rapidbacterial metabolism

Wetzel

Hatcher

Bianchi

1995

Limnology & Oceanography

490

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Whole leachate and humic and fulvic acid fractions of dissolved organic matter (DOM) released from senescent littoral aquatic plants were exposed to varying spectra of ultraviolet radiation as well as natural UV of sunlight over different periods of time. Examination of the DOM by solid-state 13C nuclear magnetic resonance and pyrolytic gas chromatography-mass spectrometry before and after photolysis revealed only subtle changes to the bulk DOM. However, the DOM exposed to natural UV radiation showed immediate stimulation of and sustained bacterial growth. Chemical analyses by high performance liquid chromatography (HPLC) of the small organic fractions generated by photolysis of humic substances showed marked, pro-' gressively increasing release of numerous small fatty acids, particularly acetic, formic, citric, pyruvic, and levulinic, among others. Use of radiolabeled humic substances demonstrated that these small compounds photolyzed from the humic substances were readily metabolized by the bacteria.Dissolved organic matter (DOM) of the open ocean apparently originates largely from planktonic photosynthesis, and concentrations are usually quite low (0.5-2 mg C liter-l) (Wangersky 1984;Wetzel 1984;Meybeck 1993;Hedges et al. 1993). In inland waters, however, phenolic and other aromatic-based humic compounds, largely of terrestrial and higher aquatic plant origin, form a major component of dissolved organic acids of freshwaters and can constitute some 80% of the total DOM, 30-40% of which is composed of aromatic carbons (Malcolm 1990). Concentrations of 4-8 mg organic acids liter-l are common in surface waters and often exceed 25 mg liter-l in organic-rich waters, such as those of wetlands, floodplains of river ecosystems, and interstitial waters of hydrosoils (Wetzel 1984;Mann and Wetzel 1995).The higher concentrations of DOM in inland surface waters clearly result from high photosynthetic productivity within lake ecosystems, particularly associated with littoral and wetland regions, as well as large loadings of DOM from decomposition of plant materials within the drainage basin (Wetzel 1990(Wetzel , 1992. Similarly, the high photosynthesis and decomposition within the extensive Acknowledgments

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“…Photochemical oxidation of colored dissolved organic matter (CDOM), may explain the hitherto unknown fate of a large portion of the terrestrially derived dissolved organic carbon that enters the ocean [Kieber et al, 1989;Mopper et al, 1991]. Its photochemical products include dissolved inorganic carbon, DIC (CO 2 , HCO 3 À , and CO 3 À2 ); [Chen et al, 1978;Miles and Brezonik, 1981;Allard et al, 1994;Vähätalo et al, 2000;Miller and Zepp, 1995;Granéli et al, 1996;Moore, 1999], CO [Kettle, 1994;Valentine and Zepp, 1993], H 2 O 2 Zika, 1993a, 1993b;Miller and Kester, 1994;Moore et al, 1993], OH . Mopper and Zhou, 1990], oxygen radicals [Cooper et al, 1989;Blough and Zepp, 1995], and many small, biologically labile organic molecules [Bushaw et al, 1996;Moran and Zepp, 1997].…”

Section: Introductionmentioning

confidence: 99%

Calculation of UV attenuation and colored dissolved organic matter absorption spectra from measurements of ocean color

2003

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[1] The absorption of ultraviolet and visible radiation by colored or chromophoric dissolved organic matter (CDOM) drives much of marine photochemistry. It also affects the penetration of ultraviolet radiation (UV) into the water column and can confound remote estimates of chlorophyll concentration. Measurements of ocean color from satellites can be used to predict UV attenuation and CDOM absorption spectra from relationships between visible reflectance, UV attenuation, and absorption by CDOM. Samples were taken from the Bering Sea and from the Mid-Atlantic Bight, and water types ranged from turbid, inshore waters to the Gulf Stream. We determined the following relationships between in situ visible radiance reflectance, L u /E d (l) (sr À1 ), and diffuse attenuation of UV,. Consistent with published observations, these empirical relationships predict that the spectral slope coefficient of CDOM absorption increases as diffuse attenuation of UV decreases. Excluding samples from turbid bays, the ratio of the CDOM absorption coefficient to K d is 0.90 at 323 nm, 0.86 at 338 nm, and 0.97 at 380 nm. We applied these relationships to SeaWiFS images of normalized water-leaving radiance to calculate the CDOM absorption and UV attenuation in the Mid-Atlantic Bight in May, July, and August 1998. The images showed a decrease in UV attenuation from May to August of approximately 50%. We also produced images of the areal distribution of the spectral slope coefficient of CDOM absorption in the Georgia Bight. The spectral slope coefficient increased offshore and changed with season.

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Degradation of humic substances by UV irradiation

Cited by 132 publications

References 3 publications

Photo‐oxidative production of dissolved inorganic carbon in lakes of different humic content

Photo‐oxidative production of dissolved inorganic carbon in lakes of different humic content

Natural photolysis by ultraviolet irradiance of recalcitrant dissolved organic matter to simple substrates for rapidbacterial metabolism

Calculation of UV attenuation and colored dissolved organic matter absorption spectra from measurements of ocean color

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