For two years, we quantified the exchange of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) at two different large-scale Sphagnum farming sites. At both, peat extraction left a shallow layer of highly decomposed peat and low hydraulic conductivities. One site was characterized by preceding multi-annual inundation and irrigated by ditches, while the other one was inoculated directly after peat extraction and irrigated by ditches and drip irrigation. Further, GHG emissions from an irrigation polder and the effect of harvesting Sphagnum donor material at a near-natural reference site were determined. GHG mitigation potentials lag behind the results of less decomposed sites, although our results were also affected by the extraordinary hot and dry summer 2018. CO2 exchanges ranged between -0.6 and 2.2 t CO2-C ha−1 y−1 and were mainly influenced by low water table depths. CH4 emissions were low with the exception of plots with higher Eriophorum covers, while fluctuating water tables and poorly developing plant covers led to considerable N2O emissions at the ditch irrigation site. The removal of the upper vegetation at the near-natural site resulted in increased CH4 emissions and, on average, lowered CO2 emissions. Overall, best plant growth and lowest GHG emissions were measured at the previously inundated site. At the other site, drip irrigation provided more favourable conditions than ditch irrigation. The size of the area needed for water management (ditches, polders) strongly affected the areal GHG balances. We conclude that Sphagnum farming on highly decomposed peat is possible but requires elaborate water management.
Aims Drained peatlands are a major source of greenhouse gases (GHG). Paludiculture is the production of biomass under wet and peat preserving conditions. Despite the growing recognition as GHG mitigation measure, the potential influence of climate warming on paludiculture is still unknown. Methods For two years, we quantified the exchange of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) using manual chambers and surveyed the vegetation composition of warmed and control sites at a near-natural bog and two Sphagnum farming areas in North-Western Germany. Passive warming was achieved using Open Top Chambers (OTC). Results OTCs significantly increased air and soil temperatures, while soil moisture, humidity and light availability differed only marginally. The latter was considered when calculating gross primary production. Warming tended to increase vascular plant cover, but differences to the control plots were still small after two years. Emissions of CO2 and CH4 increased with warming, dominated by CH4 at the near-natural bog and by CO2 at the paludiculture areas, where vegetation was in a successional stage and topsoils temporarily dried out during summer. N2O emissions were negligible at the near-natural bog and ceased with increasing biomass at the paludiculture sites. Interannual variability was high due to a heatwave in the second measurement year. Conclusions Climate warming could increase GHG emissions from near-natural bogs and Sphagnum farming. In the latter case, this puts even more emphasis on water management systems ensuring high water table depths during dry periods. Further, control of vascular plants might both reduce CH4 emissions and improve biomass quality.
<p>Drained organic soils are large sources of anthropogenic greenhouse gases (GHG) in many European and Asian countries. In Germany, they account for more than 7% of the national GHG emissions. Carbon dioxide (CO<sub>2</sub>) forms the vast majority of emissions from these soils and is thus the main target for mitigation measures. Bog peatlands are mainly found in North-Western Germany and frequently used for high-intensity grassland use. Further, former peat extraction areas are restored for nature protection. While restoration has decades of tradition, paludiculture and active water management in agriculture are comparatively new.</p> <p>Here, we will compile data on GHG exchange of bog peatlands and highlight recent results on water management by ditch blocking and subsurface irrigation, on <em>Sphagnum</em> paludiculture and on restored bog peatlands. Groundwater levels are usually considered as the major control for both CO<sub>2</sub> and methane (CH<sub>4</sub>) emissions. The effects of water management on CO<sub>2</sub> emissions are strongly depending on the site. Surprisingly, raising the groundwater level by subsurface irrigation in a grassland under bog peat to levels considered as acceptable even in restoration projects did not only fail to reduce CO<sub>2</sub> emissions, but raised them compared to deeply drained control parcel. These results might be explained by an interaction of increased soil moisture in the topsoil and improved nutrient retention during phases of high soil temperatures and, at the same time, by limitations of microbial activity due to low soil moisture at the control parcels. However, at a second grassland site with subsurface irrigation, this did not occur, but a combination with grassland renewal caused extremely high nitrous oxide emissions. In contrast, both re-wetting for restoration purposes and <em>Sphagnum</em> farming reliably reduce GHG emission or may even lead to a carbon sink. Here, the effects of the groundwater level on CO<sub>2</sub> and, even more, on CH<sub>4</sub> emissions in a <em>Sphagnum</em> farming experiment were partially overridden by vegetation development dynamics.</p>
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