Large differences in CO2 emissions from two dairy farms on a drained peatland driven by contrasting respiration rates during seasonal dry conditions

David I Campbell; Georgie L Glover-Clark; Jordan P Goodrich; Christopher P Morcom; Louis A Schipper; Aaron M Wall

doi:10.1016/j.scitotenv.2020.143410

Large differences in CO₂ emissions from two dairy farms on a drained peatland driven by contrasting respiration rates during seasonal dry conditions

Sci Total Environ. 2021 Mar 15:760:143410. doi: 10.1016/j.scitotenv.2020.143410. Epub 2020 Nov 7.

Authors

David I Campbell¹, Georgie L Glover-Clark², Jordan P Goodrich², Christopher P Morcom², Louis A Schipper², Aaron M Wall²

Affiliations

¹ School of Science, Environmental Research Institute, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand. Electronic address: david.campbell@waikato.ac.nz.
² School of Science, Environmental Research Institute, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand.

PMID: 33213925
DOI: 10.1016/j.scitotenv.2020.143410

Abstract

Drained peatlands are major sources of CO₂ to the atmosphere, yet the effects of land management and hydrological extremes have been little-studied at spatial scales relevant to agricultural enterprises. We measured fluxes of CO₂ using the eddy covariance (EC) technique at two adjacent dairy farms on a drained peatland in Aotearoa New Zealand with remaining peat depths 5.5-8 m. One site (SD) had shallow surface drains and mean water table depth (WTD) -657 mm, while the other site (BD) had deep field border drains and mean WTD -838 mm. Net ecosystem CO₂ production (NEP) was similar at the two sites when the soils were moist but diverged during late-summer drying, with site BD having 4.56 t C ha^-1 greater CO₂ emission than site SD over the four-month dry period. Soil drying reduced gross primary production (GPP) at both sites, while ecosystem respiration (ER) was reduced at site SD but not at site BD. The low dry season respiration rates at site SD contributed to near-zero annual NEP, while higher respiration rates at site BD led to annual CO₂ loss of -4.95 ± 0.59 t C ha^-1 yr^-1. Accounting for other imports and exports of carbon, annual net ecosystem carbon balances were -2.23 and -8.47 t C ha^-1 yr^-1 at sites SD and BD, respectively. It is likely that the contrasting dry season respiration rates resulted from differences in soil physical properties affecting soil moisture vertical redistribution and availability to plants and microbes rather than from the relatively small differences in WTD. These differences could be caused by soil physical disturbances during pasture renewal or paddock recontouring, or time since initial drainage. Therefore, improved soil management might provide practical mitigation against excessive CO₂ emissions during dry conditions, including droughts.

Keywords: Capillary zone; Drainage; Drought; Eddy covariance; Net ecosystem carbon balance; Peat respiration.