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| Titel |
Changing scales of hydrological control on dissolved organic matter composition in pools of intermittent streams |
| VerfasserIn |
Andre Siebers, Neil Pettit, Grzegorz Skrzypek, Jason Fellman, Shawan Dogramaci, Pauline Grierson |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093679
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| Publikation (Nr.) |
 EGU/EGU2014-8635.pdf |
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| Zusammenfassung |
| Changes in both the frequency and intensity of flood-drought cycles of intermittent streams,
either through changing climate or anthropogenic management, may have significant impacts
on stream functioning. However, little is known about how and to what extent droughts
already modify the concentration and composition of dissolved organic matter (DOM) and
how this relates to local variation in stream hydrology. We hypothesize that with increasing
time since flooding, controls on biogeochemical processes in surface water during
droughts (isolated pools along main drainage channels) switch from predominantly
hydrological at the catchment level to more localized environmental factors. We
used δ18O and δ2H values of surface water and groundwater together with DOM
fluorescence excitation-emission spectroscopy to identify: (i) the origin and extent of
evaporation of pool water and (ii) the concentration and chemical composition of
DOM across four intermittent streams of semi-arid northwest Australia between
May 2011 and November 2012. Pool water δ18O and δ2H values showed wide
variation both within and among streams, with greater enrichment reflecting pool
evaporation as groundwater or shallow alluvial water inputs decreased with time since
flooding. Parallel factor analysis (PARAFAC) revealed that DOM fluorescence in
pools was generally dominated by humic-like components, most likely derived from
terrestrial organic matter. Humic-like fluorescence was linearly related to δ18O and δ2H
values, but this relationship weakened as pools dried. However, where pools were
isolated from groundwater inputs, protein-like components were often the major
contributor to total DOM fluorescence, suggesting greater authochthonous contributions.
Complementary principal component analysis of DOM fluorescence identified that with
increasing time since flooding, local factors such as channel position, UV exposure, and
aquatic vegetation persistence were more important in explaining the amount and
composition of pool DOM. Our findings show that progressive drought after flooding
strongly influences the biogeochemistry of intermittent streams, and amplifies the
spatial heterogeneity of organic matter and nutrients among pools. This should be
characterised by a shift in controls from catchment scale factors during and after floods to
progressively more localized environmental factors as pools dry down, reflecting the
changing spatial scale of the hydrological forces themselves. Recognition of the
hydrologic complexity of intermittent streams is clearly necessary for more effective
management strategies that seek to preserve the long-term integrity of riverine ecosystems. |
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