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| Titel |
Natural and anthropogenic impacts on biogeochemical cycle in Yangtze River basin: Source, transformation and fate of dissolved organic matter (DOM) characterized by 3-D fluorescence spectroscopy |
| VerfasserIn |
Shuchai Gan, Ying Wu, Hongyan Bao, Jing Zhang |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250072157
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| Zusammenfassung |
| Inland waters play an important role in the global carbon cycle as reactors for DOM
cycling, transformation and transportation. With large amounts of terrestrial DOM, the
Yangtze River is vital for coastal environment and ecosystem. In the context of climate
change, it’s critical to evaluate both hydrodynamic conditions and increasing human
activities’ impacts on biogeochemical cycle of DOM in Yangtze River across different
climatic and hydrologic regions which are poorly understood. What’s more, the
hydrologic condition changes caused by the Three Gorges Dam (TGD, world’s
largest power station in terms of installed capacity) have recently proven to be a
partition factor for fluvial particle. However, it’s still an enigma for dissolved matter
cycle.
To address those issues, this study applies EEMs combined with bulk characteristics,
chlorophyll and absorption spectrum in an attempt to assess characteristics and dynamics of
DOM in Yangtze River. It’s a novel optical approach that could ‘see’ molecular structure of
DOM without the limits of time-consuming and laborious molecular measurements.
Combined with parallel factor analysis, 5 individual fluorescent components have been
identified: 3 humic-like (H1, H2, H3) and 2 protein-like components (P1, P2). With typical
bioavailability and photo-reactivity, these components suggest different sources and
dynamics. On the whole, both DOC and the sum of all 5 components (-
Fluo) increased
remarkably from the upper reach especially to the Three Gorge Dam and thereafter
remained constant (R2between DOC and -
Fluo: 0.92). The protein-like components
(-
P) accounted for 1/4 of -
Fluo with apparently weak correlations with DOC
and chlorophyll, which implied that the DOM is not dominated by autochthonous
production, especially for the upper reach with high concentration of total suspended
matter. As for Humic-like component, increasing H1 and DOC in the TGD reservoir
area implied impacts from human activities there with intercept of sewage rather
than an enabling environment for degradation. While in the lower reach where
H3(Ex/Em:250/450~485nm) was accumulated, the other components (H1, H2) and a350
(absorption coefficient at 350nm) seemed to be degraded faster than H3 indicating that
DOM might be subjected to selective biological and photochemical degradation
processes, combined with remarkably higher Sr (absorption coefficient slope ratio,
indicator of the degradation degree and aromatic property) in the lower reach after
TGD, these facts suggests that the contrasting hydrology before and after TGD
has led to a more significant composition differences and selective degradation of
DOM. In case of any biased views, we conducted both dark and light incubations
which showed consistency with the conclusion above. Besides, a comparison of
Yangtze River and the other large rivers shows that the EEMs and a350 vary with
land use, latitude and human activities, which verified their potential to trace the
source and fate of fluvial DOM, even for different regions and water masses. Such
knowledge on compositional differences of DOM resulting from variations in DOM
sources and local environmental conditions (different photo-/bio-reactivity associated
re-mineralization potential) during fluvial transport, would undoubtedly assist in predicting
the consequences of global change and its relationship to global carbon cycling. |
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