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| Titel |
Controls on dissolved organic matter (DOM) degradation in a headwater stream: the influence of photochemical and hydrological conditions in determining light-limitation or substrate-limitation of photo-degradation |
| VerfasserIn |
R. M. Cory, K. H. Harrold, B. T. Neilson, G. W. Kling |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 22 ; Nr. 12, no. 22 (2015-11-24), S.6669-6685 |
| Datensatznummer |
250118174
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| Publikation (Nr.) |
 copernicus.org/bg-12-6669-2015.pdf |
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| Zusammenfassung |
| We investigated how absorption of sunlight by chromophoric dissolved organic
matter (CDOM) controls the degradation and export of DOM from Imnavait Creek,
a beaded stream in the Alaskan Arctic. We measured concentrations of
dissolved organic carbon (DOC), as well as concentrations and characteristics
of CDOM and fluorescent dissolved organic matter (FDOM), during ice-free
periods of 2011–2012 in the pools of Imnavait Creek and in soil waters
draining to the creek. Spatial and temporal patterns in CDOM and FDOM in
Imnavait Creek were analyzed in conjunction with measures of DOM degradation
by sunlight and bacteria and assessments of hydrologic residence times and
in situ UV exposure. CDOM was the dominant light attenuating constituent in
the UV and visible portion of the solar spectrum, with high attenuation
coefficients ranging from 86 ± 12 m−1 at 305 nm to
3 ± 1 m−1 in the photosynthetically active region (PAR). High
rates of light absorption and thus light attenuation by CDOM contributed to
thermal stratification in the majority of pools in Imnavait Creek under
low-flow conditions. In turn, thermal stratification increased the residence
time of water and DOM, and resulted in a separation of water masses
distinguished by contrasting UV exposure (i.e., UV attenuation by CDOM with
depth resulted in bottom waters receiving less UV than surface waters). When
the pools in Imnavait Creek were stratified, DOM in the pool bottom water
closely resembled soil water DOM in character, while the concentration and
character of DOM in surface water was reproduced by experimental
photo-degradation of bottom water. These results, in combination with water
column rates of DOM degradation by sunlight and bacteria, suggest that
photo-degradation is the dominant process controlling DOM fate and export in
Imnavait Creek. A conceptual model is presented showing how CDOM amount and
lability interact with incident UV light and water residence time to
determine whether photo-degradation is "light-limited" or
"substrate-limited". We suggest that degradation of DOM in CDOM-rich
streams or ponds similar to Imnavait is typically light-limited under most
flow conditions. Thus, export of DOM from this stream will be less under
conditions that increase the light available for DOM photo-degradation (i.e.,
low flows, sunny days). |
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