ALBERT

Description: We present the first high-resolution (500 m × 500 m) gridded methane (CH4) emission inventory for Switzerland, which integrates the national emission totals reported to the United Nations Framework Convention on Climate Change (UNFCCC) and recent CH4 flux studies conducted by research groups across Switzerland. In addition to anthropogenic emissions, we also include natural and semi-natural CH4 fluxes, i.e., emissions from lakes and reservoirs, wetlands, wild animals as well as uptake by forest soils. National CH4 emissions were disaggregated using detailed geostatistical information on source locations and their spatial extent and process- or area-specific emission factors. In Switzerland, the highest CH4 emissions in 2011 originated from the agricultural sector (150 Gg CH4/yr), mainly produced by ruminants and manure management, followed by emissions from waste management (15 Gg CH4/yr) mainly from landfills and the energy sector (12 Gg CH4/yr), which was dominated by emissions from natural gas distribution. Compared to the anthropogenic sources, emissions from natural and semi-natural sources were relatively small (6 Gg CH4/yr), making up only 3 % of the total emissions in Switzerland. CH4 fluxes from agricultural soils were estimated to be not significantly different from zero (between -1.5 and 0 Gg CH4/yr), while forest soils are a CH4 sink (approx. -2.8 Gg CH4/yr), partially offsetting other natural emissions. Estimates of uncertainties are provided for the different sources, including an estimate of spatial disaggregation errors deduced from a comparison with a global (EDGAR v4.2) and a European CH4 inventory (TNO/MACC). This new spatially-explicit emission inventory for Switzerland will provide valuable input for regional scale atmospheric modeling and inverse source estimation.

Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Visser, A., Wankel, S. D., Niklaus, P. A., Byrne, J. M., Kappler, A. A., & Lehmann, M. F. Impact of reactive surfaces on the abiotic reaction between nitrite and ferrous iron and associated nitrogen and oxygen isotope dynamics. Biogeosciences, 17(16), (2020): 4355-4374, doi:10.5194/bg-17-4355-2020.

Description: Anaerobic nitrate-dependent Fe(II) oxidation (NDFeO) is widespread in various aquatic environments and plays a major role in iron and nitrogen redox dynamics. However, evidence for truly enzymatic, autotrophic NDFeO remains limited, with alternative explanations involving the coupling of heterotrophic denitrification with the abiotic oxidation of structurally bound or aqueous Fe(II) by reactive intermediate nitrogen (N) species (chemodenitrification). The extent to which chemodenitrification is caused (or enhanced) by ex vivo surface catalytic effects has not been directly tested to date. To determine whether the presence of either an Fe(II)-bearing mineral or dead biomass (DB) catalyses chemodenitrification, two different sets of anoxic batch experiments were conducted: 2 mM Fe(II) was added to a low-phosphate medium, resulting in the precipitation of vivianite (Fe3(PO4)2), to which 2 mM nitrite (NO−2) was later added, with or without an autoclaved cell suspension (∼1.96×108 cells mL−1) of Shewanella oneidensis MR-1. Concentrations of nitrite (NO−2), nitrous oxide (N2O), and iron (Fe2+, Fetot) were monitored over time in both set-ups to assess the impact of Fe(II) minerals and/or DB as catalysts of chemodenitrification. In addition, the natural-abundance isotope ratios of NO−2 and N2O (δ15N and δ18O) were analysed to constrain the associated isotope effects. Up to 90 % of the Fe(II) was oxidized in the presence of DB, whereas only ∼65 % of the Fe(II) was oxidized under mineral-only conditions, suggesting an overall lower reactivity of the mineral-only set-up. Similarly, the average NO−2 reduction rate in the mineral-only experiments (0.004±0.003 mmol L−1 d−1) was much lower than in the experiments with both mineral and DB (0.053±0.013 mmol L−1 d−1), as was N2O production (204.02±60.29 nmol L−1 d−1). The N2O yield per mole NO−2 reduced was higher in the mineral-only set-ups (4 %) than in the experiments with DB (1 %), suggesting the catalysis-dependent differential formation of NO. N-NO−2 isotope ratio measurements indicated a clear difference between both experimental conditions: in contrast to the marked 15N isotope enrichment during active NO−2 reduction (15εNO2=+10.3 ‰) observed in the presence of DB, NO−2 loss in the mineral-only experiments exhibited only a small N isotope effect (〈+1 ‰). The NO−2-O isotope effect was very low in both set-ups (18εNO2 〈1 ‰), which was most likely due to substantial O isotope exchange with ambient water. Moreover, under low-turnover conditions (i.e. in the mineral-only experiments as well as initially in experiments with DB), the observed NO−2 isotope systematics suggest, transiently, a small inverse isotope effect (i.e. decreasing NO−2 δ15N and δ18O with decreasing concentrations), which was possibly related to transitory surface complexation mechanisms. Site preference (SP) of the 15N isotopes in the linear N2O molecule for both set-ups ranged between 0 ‰ and 14 ‰, which was notably lower than the values previously reported for chemodenitrification. Our results imply that chemodenitrification is dependent on the available reactive surfaces and that the NO−2 (rather than the N2O) isotope signatures may be useful for distinguishing between chemodenitrification catalysed by minerals, chemodenitrification catalysed by dead microbial biomass, and possibly true enzymatic NDFeO.

Description: This research has been supported by the Deutsche Forschungsgemeinschaft (DFG; grant no. GRK 1708, “Molecular principles of bacterial survival strategies”) and the University of Basel, Switzerland.

Description: Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land \nuse and climate have considerably reduced the scale of this system1 \n. Remote-sensing \nestimates to quantify carbon losses from global forests2\xe2\x80\x935 \n are characterized by \nconsiderable uncertainty and we lack a comprehensive ground-sourced evaluation to \nbenchmark these estimates. Here we combine several ground-sourced6 \n and satellitederived approaches2,7,8 \n to evaluate the scale of the global forest carbon potential \noutside agricultural and urban lands. Despite regional variation, the predictions \ndemonstrated remarkable consistency at a global scale, with only a 12% diference \nbetween the ground-sourced and satellite-derived estimates. At present, global forest \ncarbon storage is markedly under the natural potential, with a total defcit of 226\xe2\x80\x89Gt \n(model range\xe2\x80\x89=\xe2\x80\x89151\xe2\x80\x93363\xe2\x80\x89Gt) in areas with low human footprint. Most (61%, 139\xe2\x80\x89Gt\xe2\x80\x89C) \nof this potential is in areas with existing forests, in which ecosystem protection can \nallow forests to recover to maturity. The remaining 39% (87\xe2\x80\x89Gt\xe2\x80\x89C) of potential lies in \nregions in which forests have been removed or fragmented. Although forests cannot \nbe a substitute for emissions reductions, our results support the idea2,3,9 \n that the \nconservation, restoration and sustainable management of diverse forests ofer \nvaluable contributions to meeting global climate and biodiversity targets.

Description: Understanding what controls global leaf type variation in trees is crucial for \ncomprehending their role in terrestrial ecosystems, including carbon, water \nand nutrient dynamics. Yet our understanding of the factors infuencing \nforest leaf types remains incomplete, leaving us uncertain about the global \nproportions of needle-leaved, broadleaved, evergreen and deciduous \ntrees. To address these gaps, we conducted a global, ground-sourced \nassessment of forest leaf-type variation by integrating forest inventory \ndata with comprehensive leaf form (broadleaf vs needle-leaf) and habit \n(evergreen vs deciduous) records. We found that global variation in leaf \nhabit is primarily driven by isothermality and soil characteristics, while leaf \nform is predominantly driven by temperature. Given these relationships, \nwe estimate that 38% of global tree individuals are needle-leaved evergreen, \n29% are broadleaved evergreen, 27% are broadleaved deciduous and \n5% are needle-leaved deciduous. The aboveground biomass distribution \namong these tree types is approximately 21% (126.4\xe2\x80\x89Gt), 54% (335.7\xe2\x80\x89Gt), 22% \n(136.2\xe2\x80\x89Gt) and 3% (18.7\xe2\x80\x89Gt), respectively. We further project that, depending \non future emissions pathways, 17\xe2\x80\x9334% of forested areas will experience \nclimate conditions by the end of the century that currently support a \ndiferent forest type, highlighting the intensifcation of climatic stress on \nexisting forests. By quantifying the distribution of tree leaf types and their \ncorresponding biomass, and identifying regions where climate change will \nexert greatest pressure on current leaf types, our results can help improve \npredictions of future terrestrial ecosystem functioning and carbon cycling.