Metabolic patch dynamics in small headwater streams: exploring spatial and temporal variability in benthic processes
Clapcott, JE and Barmuta, LA, Metabolic patch dynamics in small headwater streams: exploring spatial and temporal variability in benthic processes, Freshwater Biology, 55, (4) pp. 806-824. ISSN 0046-5070 (2010) [Refereed Article]
1. To gain a better understanding of the heterotrophic nature of small headwater streams
in forested landscapes we explored the spatial and temporal variability of in-stream
organic matter processes. Three methods were used to measure the benthic metabolism of
different in-stream habitats in seven streams throughout a calendar year. This allowed
us to analyse the contribution of various metabolic habitats (i.e. sediment, leaf litter,
cobbles) to in-stream metabolism during a natural flow regime. Furthermore, it allowed us
to define in-stream patchiness based on functional rather than structural elements.
2. Bacterial growth, measured using a leucine assay, displayed a quadratic relationship
over time with a peak in warmer months and consistently higher bacterial growth in fine
depositional (3.00�710.64 mg C m)2 day)1) than coarse gravel (38.84�582.85 mg C m)2
3. Community metabolism, measured using dissolved oxygen chambers, showed distinct
diel patterns and consistently greater net daily metabolism in leaf packs ()261.76 to
)24.50 mg C m)2 day)1) than ﬁne depositional sediments ()155.00 to
)15.56 mg C m)2 day)1). Coarse gravel sediments ()49.55 to )16.88 mg C m)2 day)1) and
cobble habitats ()151.98 to 55.38 mg C m)2 day)1) exhibited the lowest metabolic rates.
Modelled whole-stream metabolism was highly variable among streams and temporal
patterns appeared driven by temperature and the relative contribution of patch
conﬁguration as a function of ﬂow.
4. Cellulose decomposition potential showed higher rates of microbial activity in fine
depositional compared to coarse gravel sediments (30.5 and 29.1 kg average cotton tensile
strength loss respectively), though there were higher rates of thread loss indicative of
macroinvertebrate activity in gravel compared to depositional sediment (21% and 13%
average thread loss respectively), with a slight quadratic trend. The high variability among
habitats, streams and over time in this integrative measure may be explained by variability
in local microbial activity as well as the potential for macroinvertebrates to contribute
5. There were strong relationships among benthic processes and habitat structure, nutrient
status, stream temperature and flow. Different habitats had distinct metabolic character-
istics and these characteristics appear to influence stream food webs and biogeochemical
cycling depending on the relative abundance of habitats. Generally, within habitat
variability was less than among habitat variability and among stream variability was less
than temporal variability. Hence, in terms of the spatial and temporal heterogeneity of benthic processes, these small headwater streams showed predictable metabolic patterns.
However, there were few correlations between differing measures of benthic metabolism
at the same patch and this suggests that caution should be taken when attempting to infer
the rates of one level of metabolic activity (e.g. whole community metabolism) based on
another (e.g. bacterial productivity).