Impact of water table level on annual carbon and greenhouse gas balances of a restored peat extraction area

Järvi Järveoja,Kaido Soosaar,Ülo Mander,Kai Vellak,Martin Maddison,Edgar Karofeld,Matthias Peichl,Alar Teemusk

doi:10.5194/bg-13-2637-2016

Abstract

Abstract. Peatland restoration may provide a potential after-use option to mitigate the negative climate impact of abandoned peat extraction areas; currently, however, knowledge about restoration effects on the annual balances of carbon (C) and greenhouse gas (GHG) exchanges is still limited. The aim of this study was to investigate the impact of contrasting mean water table levels (WTLs) on the annual C and GHG balances of restoration treatments with high (ResH) and low (ResL) WTL relative to an unrestored bare peat (BP) site. Measurements of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes were conducted over a full year using the closed chamber method and complemented by measurements of abiotic controls and vegetation cover. Three years following restoration, the difference in the mean WTL resulted in higher bryophyte and lower vascular plant cover in ResH relative to ResL. Consequently, greater gross primary production and autotrophic respiration associated with greater vascular plant cover were observed in ResL compared to ResH. However, the means of the measured net ecosystem CO2 exchanges (NEE) were not significantly different between ResH and ResL. Similarly, no significant differences were observed in the respective means of CH4 and N2O exchanges. In comparison to the two restored sites, greater net CO2, similar CH4 and greater N2O emissions occurred in BP. On the annual scale, ResH, ResL and BP were C sources of 111, 103 and 268 g C m−2 yr−1 and had positive GHG balances of 4.1, 3.8 and 10.2 t CO2 eq ha−1 yr−1, respectively. Thus, the different WTLs had a limited impact on the C and GHG balances in the two restored treatments 3 years following restoration. However, the C and GHG balances in ResH and ResL were considerably lower than in BP due to the large reduction in CO2 emissions. This study therefore suggests that restoration may serve as an effective method to mitigate the negative climate impacts of abandoned peat extraction areas.

Highlights

Peatlands are widely distributed across the Northern Hemisphere covering 5–30 % of national land areas in northern Europe, North America and Russia and play a key role in the global carbon (C) cycle (Gorham, 1991; Joosten and Clarke, 2002; Vasander et al, 2003; Charman et al, 2013)
The mean water table levels (WTLs) in bare peat (BP) was −46 cm resulting in mean differences of −22 and −15 cm compared to restoration treatments with high (ResH) and ResL, respectively
Since Sphagnum mosses are generally more sensitive to drought compared to vascular plants, restoration strategies allowing the development of a diverse vegetation cover could be considered to have greater potential for limiting the CO2 loss and regaining the C sink function (Tuittila et al, 1999)

Summary

Introduction

Peatlands are widely distributed across the Northern Hemisphere covering 5–30 % of national land areas in northern Europe, North America and Russia and play a key role in the global carbon (C) cycle (Gorham, 1991; Joosten and Clarke, 2002; Vasander et al, 2003; Charman et al, 2013). Throughout the Holocene, northern peatlands have accumulated ∼ 270–450 Gt C as peat and presently store about a third of the global soil C pool (Gorham, 1991; Turunen et al, 2002). They provide a small but persistent long-term C sink (between 20 and 30 g C m−2 yr−1) (Gorham, 1991; Vitt et al, 2000; Roulet et al, 2007; Nilsson et al, 2008).

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