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| Titel |
The effect of source material in determining the photoreactivity of DOM in peatland aquatic systems |
| VerfasserIn |
Amy Pickard, Kate Heal, Andy McLeod, Kerry Dinsmore |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250134351
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| Publikation (Nr.) |
 EGU/EGU2016-15063.pdf |
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| Zusammenfassung |
| Aquatic systems draining peatlands receive a high loading of dissolved organic matter
(DOM) from surrounding terrestrial environments. However the fate of aquatic DOM remains
poorly constrained, in part due to lack of knowledge regarding the photoreactivity
of DOM and how this changes as a function of variability in source material. In
this study water samples were collected monthly for a 13-month period from two
contrasting aquatic systems in Scotland: a stream draining a peatland with high
DOM concentrations (33.3 ± 14.2 mg DOC L−1) and a reservoir draining a peat
catchment with low DOM concentrations (4.16 ± 0.91 mg DOC L−1). Controlled UV
irradiation laboratory experiments were conducted on samples filtered to 0.2 μm in
order to assess the photoreactivity of the DOM, measured as the unit mass of DOC
lost upon irradiation. Experiments took place over 8h in temperature controlled
conditions, with unirradiated samples used as controls. After exposure, a range
of analytical techniques were used to characterise the DOM to yield information
about its source material and to determine how this was related to the observed
photoreactivity. Lignin phenol analyses indicate considerable contribution of Sphagnum
to DOM at the stream site, particularly during summer, as demonstrated by high
P-hydroxy/Vanillyl phenol ratios (P/V). Low P/V ratios were correlated with increased
photoreactivity, (Pearson’s: -0.410; p = 0.15, n = 13), suggesting that DOM from
woody lignin sources within the catchment was more photolabile. Photoreactivity
was also negatively correlated with Fluorescence Index (FI) values (Pearson’s:
-0.555; p = 0.055, n = 13), where low FI values are understood to indicate greater
contribution of terrestrially derived material to aquatic DOM. Excitation-emission
matrices (EEMs) indicate that DOM at the stream site was primarily comprised of a
humic-like peak (Ex/Em = 340, 380/460 nm). However, there was also contribution from
a protein-like peak (Ex/Em = 290, 320/350 nm), which was present in samples
with lower photoreactivity. DOM at the reservoir site was primarily composed of
the same identified protein-like peak, which may account for the lower observed
photoreactivity of these samples. Although total DOC concentration is the dominant
control on photo-induced DOC losses in peatland aquatic systems, these results show
that organic matter characterisation can be used to further comprehend changes
to DOM photoreactivity. Increased understanding of DOM processing in aquatic
freshwater systems will allow the fate of DOM to be more accurately determined. |
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