Bacterial production in subarctic peatland lakes enriched by thawing permafrost

Peatlands extend over vast areas of the northern landscape. Within some of these areas, lakes and ponds are changing in size as a result of permafrost thawing and erosion, resulting in mobilization of the carbon-rich peatland soils. Our aims in the present study were to characterize the particle, ca...

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Published in:Biogeosciences
Main Authors: Deshpande, Bethany N., Crevecoeur, Sophie, Matveev, Alex, Vincent, Warwick F.
Format: Text
Language:English
Published: 2018
Subjects:
Ice
Online Access:https://doi.org/10.5194/bg-13-4411-2016
https://www.biogeosciences.net/13/4411/2016/
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spelling ftcopernicus:oai:publications.copernicus.org:bg49669 2023-05-15T16:37:32+02:00 Bacterial production in subarctic peatland lakes enriched by thawing permafrost Deshpande, Bethany N. Crevecoeur, Sophie Matveev, Alex Vincent, Warwick F. 2018-09-27 application/pdf https://doi.org/10.5194/bg-13-4411-2016 https://www.biogeosciences.net/13/4411/2016/ eng eng doi:10.5194/bg-13-4411-2016 https://www.biogeosciences.net/13/4411/2016/ eISSN: 1726-4189 Text 2018 ftcopernicus https://doi.org/10.5194/bg-13-4411-2016 2019-12-24T09:52:04Z Peatlands extend over vast areas of the northern landscape. Within some of these areas, lakes and ponds are changing in size as a result of permafrost thawing and erosion, resulting in mobilization of the carbon-rich peatland soils. Our aims in the present study were to characterize the particle, carbon and nutrient regime of a set of thermokarst (thaw) lakes and their adjacent peatland permafrost soils in a rapidly degrading landscape in subarctic Québec, Canada, and by way of fluorescence microscopy, flow cytometry, production measurements and an in situ enrichment experiment, determine the bacterial characteristics of these waters relative to other thaw lakes and rock-basin lakes in the region. The soil active layer in a degrading palsa (peatland permafrost mound) adjacent to one of the lakes contained an elevated carbon content (51 % of dry weight), high C : N ratios (17 : 1 by mass), and large stocks of other elements including N (3 % of dry weight), Fe (0.6 %), S (0.5 %), Ca (0.5 %) and P (0.05 %). Two permafrost cores were obtained to a depth of 2.77 m in the palsa, and computerized tomography scans of the cores confirmed that they contained high concentrations (> 80 %) of ice. Upon thawing, the cores released nitrate and dissolved organic carbon (from all core depths sampled), and soluble reactive phosphorus (from bottom depths), at concentrations well above those in the adjacent lake waters. The active layer soil showed a range of particle sizes with a peak at 229 µm, and this was similar to the distribution of particles in the upper permafrost cores. The particle spectrum for the lake water overlapped with those for the soil, but extended to larger (surface water) or finer (bottom water) particles. On average, more than 50 % of the bacterial cells and bacterial production was associated with particles > 3 µm. This relatively low contribution of free-living cells (operationally defined as the < 1 µm fraction) to bacterial production was a general feature of all of the northern lakes sampled, including other thaw lakes and shallow rock-basin lakes (average ± SE of 25 ± 6 %). However, a distinguishing feature of the peatland thaw lakes was significantly higher bacterial specific growth rates, which averaged 4 to 7 times higher values than in the other lake types. The in situ enrichment experiment showed no difference between organic carbon or phosphorus enrichment treatments at day 5 relative to the control, however there was an apparent increase in bacterial growth rates between days 1 and 5 in the soil and the carbon plus phosphorus enrichments. Collectively these results indicate that particles, nutrients and carbon are released by degrading permafrost peatland soils into their associated thermokarst lakes, creating favorable conditions for production by particle-based as well as free-living aquatic bacterial communities. The reduced bacterial concentrations despite high cellular growth rates imply that there is control of their population size by loss-related factors such as grazing and viral lysis. Text Ice palsa permafrost Subarctic Thermokarst Copernicus Publications: E-Journals Canada Biogeosciences 13 15 4411 4427
institution Open Polar
collection Copernicus Publications: E-Journals
op_collection_id ftcopernicus
language English
description Peatlands extend over vast areas of the northern landscape. Within some of these areas, lakes and ponds are changing in size as a result of permafrost thawing and erosion, resulting in mobilization of the carbon-rich peatland soils. Our aims in the present study were to characterize the particle, carbon and nutrient regime of a set of thermokarst (thaw) lakes and their adjacent peatland permafrost soils in a rapidly degrading landscape in subarctic Québec, Canada, and by way of fluorescence microscopy, flow cytometry, production measurements and an in situ enrichment experiment, determine the bacterial characteristics of these waters relative to other thaw lakes and rock-basin lakes in the region. The soil active layer in a degrading palsa (peatland permafrost mound) adjacent to one of the lakes contained an elevated carbon content (51 % of dry weight), high C : N ratios (17 : 1 by mass), and large stocks of other elements including N (3 % of dry weight), Fe (0.6 %), S (0.5 %), Ca (0.5 %) and P (0.05 %). Two permafrost cores were obtained to a depth of 2.77 m in the palsa, and computerized tomography scans of the cores confirmed that they contained high concentrations (> 80 %) of ice. Upon thawing, the cores released nitrate and dissolved organic carbon (from all core depths sampled), and soluble reactive phosphorus (from bottom depths), at concentrations well above those in the adjacent lake waters. The active layer soil showed a range of particle sizes with a peak at 229 µm, and this was similar to the distribution of particles in the upper permafrost cores. The particle spectrum for the lake water overlapped with those for the soil, but extended to larger (surface water) or finer (bottom water) particles. On average, more than 50 % of the bacterial cells and bacterial production was associated with particles > 3 µm. This relatively low contribution of free-living cells (operationally defined as the < 1 µm fraction) to bacterial production was a general feature of all of the northern lakes sampled, including other thaw lakes and shallow rock-basin lakes (average ± SE of 25 ± 6 %). However, a distinguishing feature of the peatland thaw lakes was significantly higher bacterial specific growth rates, which averaged 4 to 7 times higher values than in the other lake types. The in situ enrichment experiment showed no difference between organic carbon or phosphorus enrichment treatments at day 5 relative to the control, however there was an apparent increase in bacterial growth rates between days 1 and 5 in the soil and the carbon plus phosphorus enrichments. Collectively these results indicate that particles, nutrients and carbon are released by degrading permafrost peatland soils into their associated thermokarst lakes, creating favorable conditions for production by particle-based as well as free-living aquatic bacterial communities. The reduced bacterial concentrations despite high cellular growth rates imply that there is control of their population size by loss-related factors such as grazing and viral lysis.
format Text
author Deshpande, Bethany N.
Crevecoeur, Sophie
Matveev, Alex
Vincent, Warwick F.
spellingShingle Deshpande, Bethany N.
Crevecoeur, Sophie
Matveev, Alex
Vincent, Warwick F.
Bacterial production in subarctic peatland lakes enriched by thawing permafrost
author_facet Deshpande, Bethany N.
Crevecoeur, Sophie
Matveev, Alex
Vincent, Warwick F.
author_sort Deshpande, Bethany N.
title Bacterial production in subarctic peatland lakes enriched by thawing permafrost
title_short Bacterial production in subarctic peatland lakes enriched by thawing permafrost
title_full Bacterial production in subarctic peatland lakes enriched by thawing permafrost
title_fullStr Bacterial production in subarctic peatland lakes enriched by thawing permafrost
title_full_unstemmed Bacterial production in subarctic peatland lakes enriched by thawing permafrost
title_sort bacterial production in subarctic peatland lakes enriched by thawing permafrost
publishDate 2018
url https://doi.org/10.5194/bg-13-4411-2016
https://www.biogeosciences.net/13/4411/2016/
geographic Canada
geographic_facet Canada
genre Ice
palsa
permafrost
Subarctic
Thermokarst
genre_facet Ice
palsa
permafrost
Subarctic
Thermokarst
op_source eISSN: 1726-4189
op_relation doi:10.5194/bg-13-4411-2016
https://www.biogeosciences.net/13/4411/2016/
op_doi https://doi.org/10.5194/bg-13-4411-2016
container_title Biogeosciences
container_volume 13
container_issue 15
container_start_page 4411
op_container_end_page 4427
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