Carbon balance of rewetted and drained peat soils used for biomass production: a mesocosm study

Sandhya Karki,Tanka P Kandel,Lars Elsgaard,Poul Erik Lærke

doi:10.1111/gcbb.12334

Abstract

AbstractRewetting of drained peatlands has been recommended to reduce CO2 emissions and to restore the carbon sink function of peatlands. Recently, the combination of rewetting and biomass production (paludiculture) has gained interest as a possible land use option in peatlands for obtaining such benefits of lower CO2 emissions without losing agricultural land. This study quantified the carbon balance (CO2, CH4 and harvested biomass C) of rewetted and drained peat soils under intensively managed reed canary grass (RCG) cultivation. Mesocosms were maintained at five different groundwater levels (GWLs), that is 0, 10, 20 cm below the soil surface, representing rewetted peat soils, and 30 and 40 cm below the soil surface, representing drained peat soils. Net ecosystem exchange (NEE) of CO2 and CH4 emissions was measured during the growing period of RCG (May to September) using transparent and opaque closed chamber methods. The average dry biomass yield was significantly lower from rewetted peat soils (12 Mg ha−1) than drained peat soils (15 Mg ha−1). Also, CO2 fluxes of gross primary production (GPP) and ecosystem respiration (ER) from rewetted peat soils were significantly lower than from drained peat soils, but net uptake of CO2 was higher from rewetted peat soils. Cumulative CH4 emissions were negligible (0.01 g CH4 m−2) from drained peat soils but were significantly higher (4.9 g CH4 m−2) from rewetted peat soils during measurement period (01 May–15 September 2013). The extrapolated annual C balance was 0.03 and 0.68 kg C m−2 from rewetted and drained peat soils, respectively, indicating that rewetting and paludiculture can reduce the loss of carbon from peatlands.

Highlights

Natural peatlands are important ecosystems in the global carbon cycle as they sequester and store atmospheric carbon for thousands of years (Gorham, 1991; Yu et al, 2011)
The daily mean air temperature during the measurement period varied from 6 to 22°C with an average of 14.2°C and cumulative precipitation was 294 mm; this was similar to the long-term average (1970–2000) of 13.9°C and 298 mm in the study area for the period from May to September
The daily mean soil temperature at depth of 5 cm varied from 7 to 21°C (Fig. 1) with seasonal averages (May to September) of 15.4 to 15.8°C for the five groundwater levels (GWLs) treatments; lowest temperatures were at 0 cm GWL and highest were at 40 cm GWL

Summary

Introduction

Natural peatlands are important ecosystems in the global carbon cycle as they sequester and store atmospheric carbon for thousands of years (Gorham, 1991; Yu et al, 2011). Natural peatlands are net sinks of carbon dioxide (CO2), but net sources of methane (CH4) (Frolking et al, 2011). Drainage as a prerequisite for agricultural crop production reduces CH4 emissions, but changes the peatland from a net sink to large source of CO2 due to aerobic peat mineralization (Maljanen et al, 2010). It is estimated that about 1 Pg yearÀ1 of CO2 is emitted from drained peatlands globally, which is equivalent to 10% of the CO2 emissions from the entire agriculture, forestry and other land use sector (IPCC, 2014b). In recent years, rewetting of formerly drained peatlands has been a major focus

Methods

Results

Conclusion