Conventional subsoil irrigation techniques do not lower carbon emissions from drained peat meadows

Abstract

Abstract. The focus of current water management in drained peatlands is to facilitate optimal drainage, which has led to soil subsidence and a strong increase in greenhouse gas (GHG) emissions. The Dutch land and water authorities proposed the application of subsoil irrigation (SSI) system on a large scale to potentially reduce GHG emissions, while maintaining high biomass production. Based on model results, the expectation was that SSI would reduce peat decomposition in summer by preventing groundwater tables (GWTs) from dropping below −60 cm. In 2017–2018, we evaluated the effects of SSI on GHG emissions (CO2, CH4, N2O) for four dairy farms on drained peat meadows in the Netherlands. Each farm had a treatment site with SSI installation and a control site drained only by ditches (ditch water level −60 / −90 cm, 100 m distance between ditches). The SSI system consisted of perforated pipes −70 cm from surface level with spacing of 5–6 m to improve drainage during winter–spring and irrigation in summer. GHG emissions were measured using closed chambers every 2–4 weeks for CO2, CH4 and N2O. Measured ecosystem respiration (Reco) only showed a small difference between SSI and control sites when the GWT of SSI sites were substantially higher than the control site (> 20 cm difference). Over all years and locations, however, there was no significant difference found, despite the 6–18 cm higher GWT in summer and 1–20 cm lower GWT in wet conditions at SSI sites. Differences in mean annual GWT remained low (< 5 cm). Direct comparison of measured N2O and CH4 fluxes between SSI and control sites did not show any significant differences. CO2 fluxes varied according to temperature and management events, while differences between control and SSI sites remained small. Therefore, there was no difference between the annual gap-filled net ecosystem exchange (NEE) of the SSI and control sites. The net ecosystem carbon balance (NECB) was on average 40 and 30 t CO2 ha−1 yr−1 in 2017 and 2018 on the SSI sites and 38 and 34 t CO2 ha−1 yr−1 in 2017 and 2018 on the control sites. This lack of SSI effect is probably because the GWT increase remains limited to deeper soil layers (60–120 cm depth), which contribute little to peat oxidation. We conclude that SSI modulates water table dynamics but fails to lower annual carbon emission. SSI seems unsuitable as a climate mitigation strategy. Future research should focus on potential effects of GWT manipulation in the uppermost organic layers (−30 cm and higher) on GHG emissions from drained peatlands.

Farm-Level Effects of Emissions Tax and Adjustable Drainage on Peatlands

“…A study by Weideveld et al ( 2021 ) evaluated the effects of subsoil-irrigation systems on GHG emissions (CO 2 , CH 4 , and N 2 O) for four dairy farms on drained peat meadows in the Netherlands in 2017–2018. The system prevented the groundwater table dropping below −60 cm.…”

Responsible agriculture must adapt to the wetland character of mid‐latitude peatlands

“…It is a simple measure, which cannot capture site‐specific differences in moisture content, oxygen concentration and C density in the unsaturated zone. Variables such as average summer WTD (Weideveld et al, 2021) and hydrograph skewness (Tiemeyer et al, 2016) may offer more nuance. However, average annual WTD has been widely used in the literature to date and data are more often available.…”

“…Traditional drainage ditch networks were designed for removal of excess water in winter and are usually unsuitable for precise WTD control. Submerged drainage systems involve the installation of drainage pipes within the peat layer to improve drainage in winter and limit WTD drawdown in summer (Weideveld et al, 2021; Figure 4a and b). This can provide a more stable WTD over the course of the year, facilitating both sub‐irrigation of crops and winter vehicle access.…”

Effect of freezing on the microstructure of a highly decomposed peat material close to water saturation when used prior to X-ray micro computed tomography

“…However, the short-and long-term modelling of peatland functioning, and in particular the impact of anthropogenic warming and direct human disturbance on atmospheric CO 2 , CH 4 and N 2 O, requires detailed knowledge of the peat structure and of both water and gas flow with respect to the groundwater table level (e.g. Gharedaghloo et al, 2018;Zhao et al, 2020;Glaser et al, 2021;Muller & Fortunat, 2021;Swinnen et al, 2021;Wiedeveld et al, 2021). To achieve this, X-ray Computed Tomography, which is widely used in science as a non-invasive technique for the study of internal 2D and 3D structures, appears to be a promising technique to perform new analyses of the structure of peats and of their physical properties.…”