Net pelagic heterotrophy in mesotrophic and oligotrophic basins of a large, temperate lake |
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Authors: | Adrian M Bass Susan Waldron Tom Preston and Colin E Adams |
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Institution: | (1) Department of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, UK;(2) Department of Earth and Environmental Sciences, James Cook University, Queensland, QLD, 4870, Australia;(3) Isotope Biogeochemistry Group, Scottish Universities Environmental Research Centre, East Kilbride, G75 0QF, UK;(4) Scottish Centre for Ecology and the Natural Environment, Institute of Biomedical & Life Sciences, Rowardennan, Glasgow, G63 0AW, UK |
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Abstract: | Understanding the effects of trophic status and dissolved organic carbon concentration (DOC) on lake carbon cycling is essential
for accurate ecosystem carbon models. Using isotopically labelled substrates we assessed spatial and temporal variability
in bacterial respiration (BR) and algal primary production (PP) in two trophically, morphometrically and hydrologically different
basins in Loch Lomond, a large temperate lake in Scotland. GIS modelling was used to construct a whole lake balance for bacterial
production/respiration and PP, and from this the proportion of heterotrophy fuelled by allochthonous carbon was estimated.
We tested the hypotheses that trophic status and DOC concentration affect the balance between PP and BR and examined which
is the more significant driving factor. Additionally we estimated the percentage of BR that is fuelled by terrestrial carbon.
PP varied seasonally and showed inter-basin homogeneity. BR was greatest in the mesotrophic south basin in autumn, which corresponded
to measured peak DOC input, though over an annual cycle no relationship was observed between BR and DOC concentration. The
PP:BR ratio was 0.37 ± 0.30 and 0.3 ± 0.45 in the north and south basins, respectively, assuming a bacterial growth efficiency
of 0.1. We have found that allochthonous carbon potentially supports a substantial quantity of pelagic production, even during
periods of high photosynthesis. Less productive systems are thought to be dominated by heterotrophic processes. However, we
have found that the mesotrophic basin of a large lake to be as heterotrophic as its neighbouring oligotrophic basin, an observation
that has implications for our understanding of modelling of the role of lakes in linking the terrestrial-atmospheric carbon
cycle. |
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