The effect of biomass harvesting on greenhouse gas emissions from a rewetted temperate fen

Abstract

The growing demand for bioenergy increases pressure on peatlands. The novel strategy of wet peatlands agriculture (paludiculture) may permit the production of bioenergy from biomass while avoiding large greenhouse gas emissions as occur during conventional crop cultivation on drained peat soils. Herein, we present the first greenhouse gas balances of a simulated paludiculture to assess its suitability as a biomass source from a climatic perspective. In a rewetted peatland, we performed closed-chamber measurements of carbon dioxide, methane, and nitrous oxide exchange in stands of the potential crops Phragmites australis, Typha latifolia, and Carex acutiformis for two consecutive years. To simulate harvest, the biomass of half of the measurement spots was removed once per year. Carbon dioxide exchange was close to neutral in all tested stands. The effect of biomass harvest on the carbon dioxide exchange differed between the 2 years. During the first and second year, methane emissions were 13-63 g m À2 a À1 and 2-5 g m À2 a À1, respectively. Nitrous oxide emissions lay below our detection limit. Net greenhouse gas balances in the study plots were close to being climate neutral during both years except for the Carex stand, which was a source of greenhouse gases in the first year (in CO 2 -equivalents: 18 t ha À1 a À1). Fifteen years after rewetting the net greenhouse gas balance of the study site was similar to those of pristine fens. In addition, we did not find a significant short-term effect of biomass harvest on net greenhouse gas balances. In our ecosystem,~17 t ha À1 a À1 of CO 2 -equivalent emissions are saved by rewetting compared to a drained state. Applying this figure to the fen area in northern Germany, emission savings of 2.8-8.5 Mt a À1CO 2 -equivalents could possibly be achieved by rewetting; this excludes additional savings by fossil fuel replacement.

High net CO<sub>2</sub> and CH<sub>4</sub> release at a eutrophic shallow lake on a formerly drained fen

“…Furthermore, the soil of emergent vegetation stands is generally only temporarily and partly inundated and the water table decreased additionally during the unusual warm and dry summer 2013, probably resulting in a lower rate of anaerobic decomposition to CH 4 and a higher rate of CH 4 oxidation in the aerated top soil. This in turn might be a reason that in comparison to other sites dominated by Typha (rewetted wetlands, lake shores and freshwater marshes; see Table 4) the emergent vegetation at our site is at the lower limit of reported CH 4 release rates and best comparable to closed chamber measurements of Typha latifolia microsites at another rewetted fen site in NE Germany (Günther et al, 2015).…”

“…We could not observe a considerable decrease of the spatial extent of the open water body as emergent vegetation mainly covers the shallower edges of the water body. The effect of water table lowering at Typha sites due to dry conditions is also shown by Günther et al (2015) and Chu et al (2015): relative increase of R eco rates, resulting in net CO 2 release. This might be of special interest in terms of climate change, as a temperature increase and significantly less precipitation in summer are expected for NE Germany and meteorological conditions are more frequently characterised as "unusually" warm and dry.…”

“…In comparison to the decreasing CH 4 emissions at this site, Waddington and Day (2007) report enhancing CH 4 release for a Canadian peatland in the first 3 years after rewetting. A third rewetted fen site in NE Germany with water levels close to the soil surface was reported as weak GHG source 14-15 years after rewetting (Günther et al, 2015).…”

Water level, vegetation composition, and plant productivity explain greenhouse gas fluxes in temperate cutover fens after inundation

“…The importance of water level was also evident for a Phragmites australis site in a rewetted former grassland fen in NE Germany that sequestrated 83 g CO 2 −C m −2 yr −1 and emitted 11 g CH 4 −C m −2 yr −1 in an exceptionally wet year (WL at surface) but released 68 g CO 2 −C m −2 yr −1 and only 1 g CH 4 −C m −2 yr −1 in a typical year (WL below surface; Günther et al, 2014). Annual methane and CO 2 fluxes from floating tall sedge -Typha latifolia reeds are not reported in the literature.…”

Effect of reed canary grass cultivation on greenhouse gas emission from peat soil at controlled rewetting

“…In order to reduce the large emissions of CO 2 from drained peatlands, extensive rewetting projects have been implemented in Europe and North America (Höper et al, 2008), and rewetted organic soils have been included in the guidelines for national greenhouse gas (GHG) inventories by the Intergovernmental Panel on Climate Change (IPCC, 2014). In addition, agricultural use of wet and rewetted peatlands for crop growth (paludiculture) is considered as a possible land use option that may indirectly reduce the CO 2 emissions by biomass production for energy purposes (Joosten et al, 2012;Günther et al, 2014).…”