Carbon and peat accumulation over the past 1200 years in a landscape with discontinuous permafrost, northwestern Canada

Abstract

Apparent recent carbon and peat accumulation rates over the past 1200 years were measured in five peat landforms in the discontinuous permafrost zone near Fort Simpson, Northwest Territories, Canada. The White River volcanic ash layer was used as a chronostratigraphic horizon to ensure a consistent time span of peat deposition among peat cores and to allow a large core sample size (n = 20 cores in each landform) without the expense of radiocarbon dating. Apparent recent carbon accumulation rates were not significantly different (p>0.05) among rich fen (13.58 ± 1.07 g C m−2yr−1), peat plateau (13.31 ± 2.20 g C m−2yr−1) and collapse fen (13.54 ± 1.50 g C m−2yr−1). Poor fen and ombrotrophic bog accumulation rates were 20.34 ± 2.86 and 21.81 ± 3.25 g C m−2yr−1, respectively, and were not significantly different from each other. Variation within the poor fen and ombrotrophic bog cores is attributed to microtopography, with hollows accumulating carbon at significantly greater rates than hummocks. Vertical peat accumulation rates vary significantly in the poor fen, with hummocks showing a greater annual vertical accumulation rate than hollows. Vertical peat accumulation rates ranged from 0.282 ± 0.052 mm yr−1in the peat plateau to 0.563 ± 0.070 mm yr−1in the ombrotrophic bog. Variations in mean core bulk density were also significant and ranged from 0.071 ± 0.011 g cm−3(collapse fen) to 0.102 ± 0.011 g cm−3(poor fen). A regional survey incorporating measurements from other parts of the southwestern Northwest Territories and the southeastern Yukon show rates similar to those near Fort Simpson. These rates are significantly lower than published rates from other parts of northern Canada, Finland, and the former Soviet Union. Low and variable summer precipitation in the region may contribute to the low carbon accumulation rates through decreased plant production and/or increased aerobic decomposition.