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Preprints
https://doi.org/10.5194/bg-2020-230
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-230
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  02 Jul 2020

02 Jul 2020

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A revised version of this preprint is currently under review for the journal BG.

Sub-soil irrigation does not lower greenhouse gas emission from drained peat meadows

Stefan Theodorus Johannes Weideveld1, Weier Liu2, Merit van den Berg1, Leon Peter Maria Lamers1, and Christian Fritz1 Stefan Theodorus Johannes Weideveld et al.
  • 1Aquatic Ecology and Environmental Biology, Institute for Water and Wetland Research, Radboud University, Heyendaalseweg 135, 6525, AJ, Nijmegen, the Netherlands
  • 2Integrated Research on Energy, Environment and Society,University of Groningen, Nijenborgh 6, 9747 AG, Groningen, the Netherlands

Abstract. Current water management in drained peatlands to facilitate agricultural use, leads to soil subsidence and strongly increases greenhouse gas (GHG) emission. High-density, sub-soil irrigation/drainage systems have been proposed as a potential climate mitigation measure, while maintaining high biomass production. In summer, sub-soil irrigation can potentially reduce peat decomposition by preventing groundwater tables to drop below −60 cm. In 2017–2018, we evaluated the effects of sub-soil irrigation on GHG emissions (CO2, CH4, N2O) for four dairy farms on drained peat meadows in the Netherlands. Each farm had a treatment site with perforated pipes at 70 cm below soil level spacing 5–6 m to improve both drainage (winter- spring) and irrigation (summer) of the subsoil, and a control site drained only by ditches (ditch water level −60/−90 cm, 100 m distance between ditches). GHG emissions were measured using closed chambers (0.8 x 0.8 m) every 2–4 weeks. C inputs by manure and C export by grass yields were accounted for. Unexpectedly, sub-soil irrigation hardly affected ecosystem respiration (Reco) despite raising summer groundwater tables (GWT) by 6–18 cm, and even up to 50 cm during drought. Only when the groundwater table of sub-soil irrigation sites was substantially higher than the control value (> 20 cm), Reco was significantly lower (p<0.01), indicating a small effect of irrigation on C turnover. During wet conditions sub-soil pipes lowered water levels by 1–20 cm, without a significant effect on Reco. As a result, Reco differed little (>3 %) between sub-soil irrigation and control sites on an annual base. CO2 fluxes were high at all locations, exceeding 45 t CO2 ha−1a−1, even where peat was covered by clay (25–40 cm). Despite extended drought episodes and lower water levels in 2018, we found lower annual CO2 fluxes than in 2017 indicating drought stress for microbial respiration. Contrary to our expectation, there was no difference between the yearly greenhouse balance of the sub-soil irrigated (64 t CO2–eq ha−1yr−1 in 2017, 53 in 2018) and control sites (61 t CO2–eq ha−1 yr−1 in 2017, 51 in 2018). Emissions of N2O were lower (3 ± 1 t CO2–eq ha−1 yr−1) in 2017 than in 2018 (5 ± 2 t CO2–eq ha−1 yr−1), without treatment effects. The contribution of CH4 to the total GHG budget was negligible (<0.1 %), with lower GWT favoring CH4 oxidation over its production. Even during the 2018 drought, sub-soil irrigation had only little effect on yields (9.7 vs. 9.1 t DM ha−1yr−1), suggesting that increased GWT failed to increase plant water supply. This indicates that peat oxidation is hardly affected, probably because GWT increase only takes place in deeper soil layers (60–120 cm depth). We conclude that, although our field-scale experimental research revealed substantial differences in summer GWT and timing/intensity of irrigation and drainage, sub-soil irrigation fails to lower annual GHG emission and is 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.

Stefan Theodorus Johannes Weideveld et al.

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Stefan Theodorus Johannes Weideveld et al.

Stefan Theodorus Johannes Weideveld et al.

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Short summary
Raising the groundwater table trough sub-soil irrigation does not lead to a reduction of GHG emissions from drained peat meadows, even though there was a clear increase in GWT during summer. Most likely, the largest part of the peat oxidation takes place in the top 70 cm of the soil, which stays above the groundwater table with the use of sub-soil irrigation. We conclude that the use of sub-soil irrigation is ineffective as a mitigation measure to sufficiently lower peat oxidation rates.
Raising the groundwater table trough sub-soil irrigation does not lead to a reduction of GHG...
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