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Metabolism in a groundwater-fed river system in the Australian wet/dry tropics: tight coupling of photosynthesis and respiration.

Townsend, Simon A., Webster, Ian T. and Schult, Julia H. (2011). Metabolism in a groundwater-fed river system in the Australian wet/dry tropics: tight coupling of photosynthesis and respiration.. Journal of the North American Benthological Society,30(3):603-620.

Document type: Journal Article

IRMA ID 82057923xPUB146
Title Metabolism in a groundwater-fed river system in the Australian wet/dry tropics: tight coupling of photosynthesis and respiration.
Author Townsend, Simon A.
Webster, Ian T.
Schult, Julia H.
Journal Name Journal of the North American Benthological Society
Publication Date 2011
Volume Number 30
Issue Number 3
ISSN 0887-3593   (check CDU catalogue  open catalogue search in new window)
Scopus ID 2-s2.0-79960220164
Start Page 603
End Page 620
Total Pages 18
Place of Publication Canada
Publisher North American Benthological Society
HERDC Category C1 - Journal Article (DIISR)
Abstract The temporal pattern of river metabolism was estimated for high-order rivers (5-7 th) in the Daly watershed, tropical Australia, during the dry season (May-October) when discharge was supplied predominantly by groundwater. Rates of photosynthesis (P) and respiration (R) were calculated at 4 sites using the open-channel method based on a model of the river's O 2 budget and measured diurnal cycles of dissolved O 2 concentrations and temperatures. The rivers were shallow (average depth = 0.8 m), clear (1-2 NTU), and had low concentrations of nutrients (≤15 μg/L soluble N and P at most sites) and generally open canopy. At the reach scale, P was limited by light with no evidence of light saturation. An increase in primary producer biomass over the dry season probably underpinned an approximate doubling of P at the 4 sites over the dry season, but increased water temperatures would have contributed, too. P (0.1-4.6 g O 2 m -2 d -1) in the Daly watershed was similar to rates in a shaded tropical Puerto Rican stream and some temperate rivers but was lower than in nutrient-enriched temperate rivers. We surmise that most P resulted in production of dissolved organic C (DOC), rather than growth of primary producer biomass, which was nutrient limited. R exceeded P (P/R ≈ 0.5), and increased approximately linearly with P (r 2 = 0.79-0.99) over the dry season with no statistically significant difference among sites. The similar environmental setting of the 4 sites underpinned their similar temporal pattern of metabolism. Bacterial metabolism of photosynthetically produced DOC (PDOC) could partially explain the tight coupling of R and P but could not account for the river's overall net heterotrophy. The priming effect of bacterial degradation of labile PDOC to increase the mineralization of recalcitrant DOC (e.g., humic acids) provides an explanation for the river's heterotrophy and tight coupling between P and R.
Keywords river metabolism
photosynthesis
primary production
respiration
priming effect
heterotrophy
DOI http://dx.doi.org/10.1899/10-066.1   (check subscription with CDU E-Gateway service for CDU Staff and Students  check subscription with CDU E-Gateway in new window)
 
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