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Carbon dynamics in highly heterotrophic subarctic thaw ponds.
- Source :
- Biogeosciences Discussions; 2015, Vol. 12 Issue 14, p11707-11749, 43p, 6 Charts, 5 Graphs
- Publication Year :
- 2015
-
Abstract
- Global warming has accelerated the formation of permafrost thaw ponds in several subarctic and arctic regions. These ponds are net heterotrophic as evidenced by their greenhouse gas (GHG) supersaturation levels (CO<subscript>2</subscript> and CH<subscript>4</subscript>), and generally receive large terrestrial carbon inputs from the thawing and eroding permafrost. We measured seasonal and vertical variations in the concentration and type of dissolved organic matter (DOM) in five subarctic thaw (thermokarst) ponds in northern Quebec, and explored how environmental gradients influenced heterotrophic and phototrophic biomass and productivity. Late winter DOM had low aromaticity indicating reduced inputs of terres trial carbon, while the high concentration of dissolved organic carbon (DOC) suggests that some production of non-chromophoric dissolved compounds by the microbial food web took place under the ice cover. Summer DOM had a strong terrestrial signature, but was also characterized with significant inputs of algal-derived carbon, especially at the pond surface. During late winter, bacterial production was low (maximum of 0.8mgCm<superscript>-3</superscript> d<superscript>-1</superscript>) and was largely based on free-living bacterioplankton (58%). Bacterial production in summer was high (up to 58mgCm3 d1), dominated by particleattached bacteria (67%), and strongly correlated to the amount of terrestrial carbon. Primary production was restricted to summer surface waters due to strong light limitation deeper in the water column or in winter. The phototrophic biomass was equal to the heterotrophic biomass, but as the algae were mostly composed of mixotrophic species, most probably they used bacteria rather than solar energy in such shaded ponds. According to the δ<superscript>13</superscript>C analyses, non-algal carbon supported 51% of winter and 37% of summer biomass of the phantom midge larvae, Chaoborus sp., that are at the top of the trophic chain. Our results point to a strong heterotrophic energy pathway 25 in these thaw pond ecosystems, where bacterioplankton dominates the production of new carbon in both summer and winter. [ABSTRACT FROM AUTHOR]
- Subjects :
- GLOBAL warming
GREENHOUSE gases
BIOMASS
FOOD chains
CARBON dioxide
SUPERSATURATION
Subjects
Details
- Language :
- English
- ISSN :
- 18106277
- Volume :
- 12
- Issue :
- 14
- Database :
- Complementary Index
- Journal :
- Biogeosciences Discussions
- Publication Type :
- Academic Journal
- Accession number :
- 108758542
- Full Text :
- https://doi.org/10.5194/bgd-12-11707-2015