CGRG Bibliography of Canadian Geomorphology
Search Results
Author : Breton, J.; and Laurion, I.
Date : 2005.
Title : Carbon cycling in thermokarst ponds: comparison between arctic and subarctic ponds.
Publication : Arctic Net 2005 Programme. Annual Scientific Meeting, December 13-16, 2005. Banff, Alberta
Issue :
Page(s) : 72.
Abstract
According with climatic models, vast extents of permafrost are susceptible of disappearance from polar and subpolar regions. Recent climate changes have initiated the melting of permafrost in boreal and subarctic regions. This melting creates depressions where water accumulates to form thermokarst ponds. Further north, the continuous permafrost landscape presents thermokarsts with different morphologies (ice wedges and depressed center polygons). Melting mobilizes the organic carbon stocked in peat and permafrost and makes it available to transformation. Water in these ponds present very different optical conditions and shelters an active microbial food web. This changing environment represents a perfect system to study the photochemical and microbial transformation of organic matter of different nature. Melting of permafrost in polar regions raises concerns since a massive liberation of CO2 and CH4 to the atmosphere would act as a positive feedback on climate and accelerate global warming. The extent and duration of this liberation is not known but it has generated a lot of interest from the scientific community. On the other hand, the rising export of organic matter to aquatic environments can have an impact on annual temperature and light budgets, which largely influence the microbial productivity. The main objective of this project is thus to determine the role of thermokarst ponds on carbon transfer from the tundra to the atmosphere and to the aquatic systems. We want to examine the exporting mechanisms and the balance between autotrophic and heterotrophic processes in polar aquatic systems. This project is part of ArcticNet theme 2.6. We have sampled several sites in Nunavik and Nunavut during two sampling seasons in 2004 and 2005. These sites cover three ecosystems: the south limit of discontinuous permafrost (two sites at Kuujjuarapik ~55.2°N), the forest tundra (Umiujaq 56.6°N and Boniface 57.7°N) and the tundra (Bylot Island 73.1°N). To understand the functioning of these ecosystems, we have collected samples describing the biological components of the water (bacteria, phytoplankton, pigments), and its physicochemical (profiles of temperature, pH, conductivity, dissolved O2 and nutrients) and optical characteristics (DOM fluorescence and absorbance, DOC, total suspended solids and light penetration). In 2005, we have performed trials to estimate the bacterial production and substrate limitation. To understand the pathways of carbon in these systems, we have collected stable isotope samples and have performed short-term photo- (5 ponds) and long-term bio-degradation experiments (7 ponds). We are exploring the role of viruses on DOM dynamics in 2005 biodegradation experiments. Finally, to estimate the export of carbon to the atmosphere, we have measured dissolved concentration and diurnal variations of CO2 and CH4. Preliminary results indicate a large variability in chemical conditions, microbial communities and concentration of dissolved, gas and particulate carbon. The bacterial concentration is quite high for such environments. In 2004, all ponds were oversaturated in CO2 and CH4, about 10 times more concentrated relative to the atmospheric concentration. The biodegradation experiments in 2004 indicated a different DOC loss rate depending on DOM quality (e.g., bulk DOC was lost more rapidly than was colour).
Bibliography of Canadian Geomorphology