• Energy Research

Large areas of peatlands have worldwide been drained to facilitate agriculture, which has adverse effects on the environment and the global climate. Agriculture on rewetted peatlands (paludiculture) provides a sustainable alternative to drainage-based agriculture. One form of paludiculture is the cultivation of Sphagnum moss, which can be used as a raw material for horticultural growing media. Under natural conditions, most Sphagnum mosses eligible for paludiculture typically predominate only in nutrient-poor wetland habitats. It is unknown, however, how the prevailing high nutrient levels in rewetted agricultural peatlands interfere with optimal Sphagnum production. We therefore studied the effect of enriched nutrient conditions remaining even after top soil removal and further caused by external supply of nutrient-rich irrigation water and (generally) high inputs of atmospheric nitrogen (N) to habitat biogeochemistry, biomass production and nutrient stoichiometry of introduced Sphagnum palustre and S. papillosum in a rewetted peatland, which was formerly in intensive agricultural use. Airborne N was responsible for the major supply of N. Phosphorus (P) and potassium (K) were mainly supplied by irrigation water. The prevailing high nutrient levels (P and K) are a result of nutrient-rich irrigation water from the surroundings. Peat porewater (10 cm below peatmoss surface) CO2 concentrations were high, bicarbonate concentrations low, and the pH was around 4.2. Provided that moisture supply is sufficient and dominance of fast-growing, larger graminoids suppressed (in order to avoid outshading of Sphagnum mosses), strikingly very high biomass yields of 6.7 and 6.5 t DW ha(-1) yr(-1) (S, palustre and S. papillosum [including S. fallax biomass], respectively) were obtained despite high N supply and biomass N concentrations. Despite high P and K supply and uptake, N:P and N:K ratios in the Sphagnum capitula were still low. Sphagnum mosses achieved high nutrient sequestration rates of 34 kg N, 17 kg K and 4 kg P ha(-1) yr(-1) from May 2013 to May 2014, which shows that the site acted as an active nutrient sink. Nutrient management still needs further improvement to reduce the competitive advantage of fast growing peatmoss species (cf. S. fallax) at the expense of slower growing but preferred peatmosses as horticultural substrate (S. palustre and S. papillosum) to optimize the quality of biomass yields. In conclusion, Sphagnum farming is well able to thrive under high N input provided that there is a simultaneous high input of P and K from irrigation water, which facilitates high production rates. Due to the lack of suitable, nutrient poor sites, it seems to be useful to remove the topsoil (mainly P removal) prior to start growing Sphagnum mosses. In addition, bicarbonate concentrations have to stay sufficientlylow to ensure a low pH, CO2 supply from the peat soil should be sufficiently high to prevent C limitation, and graminoids should be mown regularly. (C) 2016 Elsevier B.V. All rights reserved.

Large areas of peatlands have worldwide been drained to facilitate agriculture, which has adverse effects on the environment and the global climate. Agriculture on rewetted peatlands (paludiculture) provides a sustainable alternative to drainage-based agriculture. One form of paludiculture is the cultivation of Sphagnum moss, which can be used as a raw material for horticultural growing media. Under natural conditions, most Sphagnum mosses eligible for paludiculture typically predominate only in nutrient-poor wetland habitats. It is unknown, however, how the prevailing high nutrient levels in rewetted agricultural peatlands interfere with optimal Sphagnum production. We therefore studied the effect of enriched nutrient conditions remaining even after top soil removal and further caused by external supply of nutrient-rich irrigation water and (generally) high inputs of atmospheric nitrogen (N) to habitat biogeochemistry, biomass production and nutrient stoichiometry of introduced Sphagnum palustre and S. papillosum in a rewetted peatland, which was formerly in intensive agricultural use. Airborne N was responsible for the major supply of N. Phosphorus (P) and potassium (K) were mainly supplied by irrigation water. The prevailing high nutrient levels (P and K) are a result of nutrient-rich irrigation water from the surroundings. Peat porewater (10 cm below peatmoss surface) CO2 concentrations were high, bicarbonate concentrations low, and the pH was around 4.2. Provided that moisture supply is sufficient and dominance of fast-growing, larger graminoids suppressed (in order to avoid outshading of Sphagnum mosses), strikingly very high biomass yields of 6.7 and 6.5 t DW ha(-1) yr(-1) (S, palustre and S. papillosum [including S. fallax biomass], respectively) were obtained despite high N supply and biomass N concentrations. Despite high P and K supply and uptake, N:P and N:K ratios in the Sphagnum capitula were still low. Sphagnum mosses achieved high nutrient sequestration rates of 34 kg N, 17 kg K and 4 kg P ha(-1) yr(-1) from May 2013 to May 2014, which shows that the site acted as an active nutrient sink. Nutrient management still needs further improvement to reduce the competitive advantage of fast growing peatmoss species (cf. S. fallax) at the expense of slower growing but preferred peatmosses as horticultural substrate (S. palustre and S. papillosum) to optimize the quality of biomass yields. In conclusion, Sphagnum farming is well able to thrive under high N input provided that there is a simultaneous high input of P and K from irrigation water, which facilitates high production rates. Due to the lack of suitable, nutrient poor sites, it seems to be useful to remove the topsoil (mainly P removal) prior to start growing Sphagnum mosses. In addition, bicarbonate concentrations have to stay sufficientlylow to ensure a low pH, CO2 supply from the peat soil should be sufficiently high to prevent C limitation, and graminoids should be mown regularly. (C) 2016 Elsevier B.V. All rights reserved.

AbstractWetlands are the largest natural source of global atmospheric methane (CH4). Despite advances to our understanding of changes in temperature and precipitation extremes, their impacts on carbon‐rich ecosystems such as wetlands, remain significantly understudied. Here, we quantify the impacts of extreme temperature, precipitation, and dry events on wetland CH4 dynamics by investigating the effects of both compound and discrete extreme‐events. We use long‐term climate data to identify extreme‐events and 45 eddy covariance sites data sets sourced from the FLUXNET‐CH4 database and Ameriflux project to assess impacts on wetland CH4 emissions. These findings reveal that compound hot + dry extreme‐events lead to large increases in daily CH4 emissions. However, per event, discrete dry‐only extreme‐events cause the largest total decrease in CH4 emissions, due to their long duration. Despite dry‐only extreme‐events leading to an overall reduction in CH4 emissions, enhanced fluxes are often observed for the first days of dry‐only extreme‐events. These effects differ depending on wetland type, where marsh sites tend to be sensitive to most types of extreme‐events. Lagged impacts are significant for at least the 12 months following several types of extreme‐events. These findings have implications for understanding how extreme‐event impacts may evolve in the context of climate change, where changes in the frequency and intensity of temperature and precipitation extreme‐events are already observed. With increasing occurrences of enhanced CH4 fluxes in response to hot‐only extreme‐events and hot + wet extreme‐events and fewer occurrences of reduced CH4 fluxes during cold‐only extreme‐events, the impact of wetland CH4 emissions on climate warming may be increasing.

AbstractWetlands are the largest natural source of global atmospheric methane (CH4). Despite advances to our understanding of changes in temperature and precipitation extremes, their impacts on carbon‐rich ecosystems such as wetlands, remain significantly understudied. Here, we quantify the impacts of extreme temperature, precipitation, and dry events on wetland CH4 dynamics by investigating the effects of both compound and discrete extreme‐events. We use long‐term climate data to identify extreme‐events and 45 eddy covariance sites data sets sourced from the FLUXNET‐CH4 database and Ameriflux project to assess impacts on wetland CH4 emissions. These findings reveal that compound hot + dry extreme‐events lead to large increases in daily CH4 emissions. However, per event, discrete dry‐only extreme‐events cause the largest total decrease in CH4 emissions, due to their long duration. Despite dry‐only extreme‐events leading to an overall reduction in CH4 emissions, enhanced fluxes are often observed for the first days of dry‐only extreme‐events. These effects differ depending on wetland type, where marsh sites tend to be sensitive to most types of extreme‐events. Lagged impacts are significant for at least the 12 months following several types of extreme‐events. These findings have implications for understanding how extreme‐event impacts may evolve in the context of climate change, where changes in the frequency and intensity of temperature and precipitation extreme‐events are already observed. With increasing occurrences of enhanced CH4 fluxes in response to hot‐only extreme‐events and hot + wet extreme‐events and fewer occurrences of reduced CH4 fluxes during cold‐only extreme‐events, the impact of wetland CH4 emissions on climate warming may be increasing.

Abstract Siberia experienced a prolonged heatwave in the spring of 2020, resulting in extreme summer drought and major wildfires in the North-Eastern Siberian lowland tundra. In the Arctic tundra, plants play a key role in regulating the summer land surface energy budget by contributing to land surface cooling through evapotranspiration. Yet we know little about how drought conditions impact land surface cooling by tundra plant communities, potentially contributing to high air temperatures through a positive plant-mediated feedback. Here we used high-resolution land surface temperature and vegetation maps based on drone imagery to determine the impact of an extreme summer drought on land surface cooling in the lowland tundra of North-Eastern Siberia. We found that land surface cooling differed strongly among plant communities between the drought year 2020 and the reference year 2021. Further, we observed a decrease in the normalized land surface cooling (measured as water deficit index) in the drought year 2020 across all plant communities. This indicates a shift towards an energy budget dominated by sensible heat fluxes, contributing to land surface warming. Overall, our findings suggest significant variation in land surface cooling among common Arctic plant communities in the North-Eastern Siberian lowland tundra and a pronounced effect of drought on all community types. Based on our results, we suggest discriminating between functional tundra plant communities when predicting the drought impacts on energy flux related processes such as land surface cooling, permafrost thaw and wildfires.

Abstract Siberia experienced a prolonged heatwave in the spring of 2020, resulting in extreme summer drought and major wildfires in the North-Eastern Siberian lowland tundra. In the Arctic tundra, plants play a key role in regulating the summer land surface energy budget by contributing to land surface cooling through evapotranspiration. Yet we know little about how drought conditions impact land surface cooling by tundra plant communities, potentially contributing to high air temperatures through a positive plant-mediated feedback. Here we used high-resolution land surface temperature and vegetation maps based on drone imagery to determine the impact of an extreme summer drought on land surface cooling in the lowland tundra of North-Eastern Siberia. We found that land surface cooling differed strongly among plant communities between the drought year 2020 and the reference year 2021. Further, we observed a decrease in the normalized land surface cooling (measured as water deficit index) in the drought year 2020 across all plant communities. This indicates a shift towards an energy budget dominated by sensible heat fluxes, contributing to land surface warming. Overall, our findings suggest significant variation in land surface cooling among common Arctic plant communities in the North-Eastern Siberian lowland tundra and a pronounced effect of drought on all community types. Based on our results, we suggest discriminating between functional tundra plant communities when predicting the drought impacts on energy flux related processes such as land surface cooling, permafrost thaw and wildfires.