DOI: 10.5443/11459
title: Recent changes in carbon source-sink relationships and greenhouse gas emissions in forest and peatland ecosystems along the Mackenzie Valley region of Canada

description: Recognizing that permafrost distributions are largely controlled by topography and climate, our IPY study documents local C cycling processes and GHG emissions as associated with vegetation, soil and permafrost environments along a climatic gradient from the Isolated Patches Permafrost Zone, in northern Alberta, to the Continuous Permafrost Zone at Inuvik, NWT. In order to understand variation in vegetation, soils, and permafrost, an extensive network of 26 sites has been established over the summers of 2007 and 2008, with four of these sites intensively monitored, from 2007 to the present, for C cycling and GHG exchange. Each NWT site encompasses a gradient from upland to peatland, including areas of permafrost-affected peatlands (peat plateaux), areas of permafrost thaw within the peat plateau matrix (collapse scars), and nearby forests occurring on mineral soils (upland forests). The northern Alberta site is entirely permafrost free, containing peatland plots in a bog, an internal lawn (area of permafrost thaw within an unfrozen bog matrix), and an adjacent upland forest. Preliminary data indicate that vegetation primarily varies from upland forest to peat plateau to collapse scar, with collapse scars having the most distinct plant communities. Permafrost zonation is a strong secondary gradient, with greatest differences between plant communities of the Continuous Permafrost Zone and those of either the Sporadic or Extensive Discontinuous Permafrost Zones. The CH4 release/consumption within the study area is intricate and highly variable, fluctuating with the local soil water and corresponding vegetation. Significant surface CH4 production, essentially by microbial methyl-type fermentation, occurs only in submerged parts, and hence most reducing parts of the soil profile. Contrary to initial expectations, CH4 production is greatest during the warmest months and is insignificant during the spring thaw. Carbon dioxide emissions and net ecosystem CO2 exchange (NEE) measurements at the ground surface decreases from south to north and are mainly affected by soil temperature and the presence of permafrost. Topographic position affects soil respiration rate, which is significantly greater in uplands than peatlands, while plant uptake of CO2 by photosynthesis also varies with landscape position, accounting for over half of NEE in peatlands but less than a quarter in uplands.
description: Purpose: Permafrost is a critical component of northern landscapes, not only directly affecting soil processes, but its indirect affect on soil water and active layer depths (depth of surface soil thaw in the summer) also has a substantial influence on the ecosystem. Because of the vast carbon (C) reserves present in peatlands, thawing of peatland permafrost can potentially mobilize this C, leading to enhanced emissions of greenhouse gasses (GHGs) to the atmosphere and substantially augmenting the global atmospheric C cycle. The relationship between vegetation and permafrost is particularly interesting in northern ecosystems, with plant communities both affected by changes in permafrost conditions, yet also able to influence the permafrost environment. This project was designed to improve our understanding of the potential impacts of recent climate change, as well as anthropogenic and natural disturbances, on the total C storage and source-sink relationships of forest and peat ecosystems of the Mackenzie Valley. The four main objectives of the study include: 1. across the regional gradient, assess possible changes in the distribution and composition of forest and peatland ecosystems due to recent climatic changes, permafrost melting, and human impacts and to determine present and recent past changes in C storage; 2. develop regional and site level estimates of C storage as well as recent changes in C storage in Boreal and Subarctic ecoclimatic regions of the Mackenzie Valley; 3. characterize the GHG emissions by assessing interannual and seasonal variation, and key processes controlling CO2, CH4 and N2O dynamics along the latitudinal gradient of ecosystems along Mackenzie Valley; 4. develop models of C storage and associated dynamics in order to predict future changes in the C source-sink relationship due to climate change, and other natural and anthropogenic disturbances in forest and peatland ecosystems. This project is linked nationally to IPY Climate Change Impacts on Canadian Arctic Tundra Ecosystems Project (Project 2006-SR1CC-096) and internationally to the Global Carbon Project (GCP), the International Permafrost Association's Soil Carbon Project (CAPP) and The North American Carbon Budget and Implications for the Global Carbon Cycle Project (SOCCR).
description: Summary: A network of 26 sites has been established to monitor carbon cycling and greenhouse gas emissions in the Mackenzie Valley in northwestern Canada. This is an area where significant warming is expected to cause equally significant changes in forests and peatlands. Peatlands in the North store a vast amount of carbon that could potentially be released, along with other greenhouse gases, through the thawing of permafrost. This work is providing insight into how climate change is affecting these processes, information that will be fed into models to predict changes in the plant communities and permafrost zones of the Arctic.