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| Titel |
Feedbacks between element availability, (diel) cycling and assimilatory
uptake in a biologically productive spring-fed river |
| VerfasserIn |
Marie J. Kurz, Matthew J. Cohen, Jonathan B. Martin, Rachel L. Nifong |
| 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 |
250133656
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| Publikation (Nr.) |
 EGU/EGU2016-14291.pdf |
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| Zusammenfassung |
| The metabolism of submerged aquatic vegetation directly and indirectly controls the cycling
of solutes in streams at diel (24-hour) frequencies. Photosynthesis and respiration induce diel
variation in dissolved oxygen (DO) concentrations and pH which, in turn, mediate elemental
concentrations via a host of geochemical reactions. Plant metabolism also directly exerts
control on water composition via assimilatory uptake, creating diel variation in major
nutrients. Trace elements can be essential micronutrients, suggesting their assimilatory uptake
could also contribute to diel variation in element concentrations in streams. If diel
element variation is indicative of metabolic processing, assessing the magnitude and
timing of this diel variation relative to other inorganic controls could be used to
estimate the ecosystem demand for those elements, infer ecosystem function, and
predict how stream ecosystems may respond to changes in environmental element
availability.
We evaluated the relationship between the elemental requirements of submerged
vegetation and the availability and cycling of elements in streams by comparing spatial and
diel variation in stream chemistry with measurements of tissue stoichiometry from
submerged vascular plants and algae in the Ichetucknee River (Q = 8 m3/s) , a highly
productive spring-fed system in north-central Florida. Diel variations were observed in the
concentrations of soluble reactive phosphorus (SRP), Ca, Mg, K, Mn, Fe, V, Cr,
Co, Cu, Sr, Ba, and U. Autotrophic assimilation, estimated using the measured
stoichiometry and calculations of primary production from diel DO variation, accounted for
a significant portion of the in-stream diel variation of some elements, including
approximately 100% for K and >30% for Fe and Mn. However, the exact timing of
assimilation of these elements remains uncertain relative to the other inorganic controls.
Correcting the observed SRP diel signal for the effect of calcite co-precipitation
revealed both the magnitude of the two major P retention pathways (66% geochemical,
34% assimilatory) and the timing of assimilatory P uptake (asynchronous with N
uptake). Variations in measured tissue stoichiometry between major vegetation types,
and between sampling sites, suggests that elemental availability may affect the
productivity and relative abundance of invasive algae and submerged macrophytes.
Conversely, changes in species abundance could lead to corresponding changes in
in-stream element cycling, illustrating the reciprocal interactions between solute
dynamics in streams and the elemental requirements of submerged aquatic vegetation. |
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