Integrating peatlands into the coupled Canadian Land Surface Scheme (CLASS) v3.6 and the Canadian Terrestrial Ecosystem Model (CTEM) v2.0

Yuanqiao Wu,Joe R Melton,Diana L Verseghy

doi:10.5194/gmd-9-2639-2016

Abstract

Abstract. Peatlands, which contain large carbon stocks that must be accounted for in the global carbon budget, are poorly represented in many earth system models. We integrated peatlands into the coupled Canadian Land Surface Scheme (CLASS) and the Canadian Terrestrial Ecosystem Model (CTEM), which together simulate the fluxes of water, energy, and CO2 at the land surface–atmosphere boundary in the family of Canadian Earth system models (CanESMs). New components and algorithms were added to represent the unique features of peatlands, such as their characteristic ground floor vegetation (mosses), the slow decomposition of carbon in the water-logged soils and the interaction between the water, energy, and carbon cycles. This paper presents the modifications introduced into the CLASS–CTEM modelling framework together with site-level evaluations of the model performance for simulated water, energy and carbon fluxes at eight different peatland sites. The simulated daily gross primary production (GPP) and ecosystem respiration are well correlated with observations, with values of the Pearson correlation coefficient higher than 0.8 and 0.75 respectively. The simulated mean annual net ecosystem production at the eight test sites is 87 g C m−2 yr−1, which is 22 g C m−2 yr−1 higher than the observed annual mean. The general peatland model compares well with other site-level and regional-level models for peatlands, and is able to represent bogs and fens under a range of climatic and geographical conditions.

Highlights

Peatlands represent about 20 % of the global soil carbon (C) pool and have played a critical role in regulating the global climate since the onset of the Holocene (Yu et al, 2013)
Ponded water is simulated in the model, the simulated water table depth (WTD) did not include the depth of pond above the soil surface, which appears in the observations as a negative value, for example up to −0.14 m in the SE-Faj bog during the winter
For Alberta western peatland treed fen (AB-Fen), the model overestimated the inter-annual fluctuation and did not reproduce the trend of increasing WTD seen in the observations, which was likely associated with the change in vegetation cover

Summary

Introduction

Peatlands represent about 20 % of the global soil carbon (C) pool and have played a critical role in regulating the global climate since the onset of the Holocene (Yu et al, 2013). The inhibited decomposition in waterlogged organic soil persistently sequesters C in peatlands, despite the relatively low primary production. Bryophytes, especially Sphagnum mosses, are non-vascular land plants that are able to effectively capture and store water and nutrients (Turetsky, 2003). Bryophytes and lichens are widely present, especially over tundra, boreal forest floor and desert, and are estimated to account for a net C uptake of 0.34 Gt C yr−1 on average (Porada et al, 2013), out of 5.0 (±0.9) Gt C yr−1 global net C uptake by land and oceans between 1960 and 2010 (Ballantyne et al, 2012). Bogs are dependent upon precipitation for water and nutrients while fens receive additional contributions from ground

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Conclusion