| 1. |
- Abbott, Benjamin W., et al.
(författare)
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We Must Stop Fossil Fuel Emissions to Protect Permafrost Ecosystems
- 2022
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Ingår i: Frontiers in Environmental Science. - : Frontiers Media SA. - 2296-665X. ; 10
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Forskningsöversikt (refereegranskat)abstract
- Climate change is an existential threat to the vast global permafrost domain. The diverse human cultures, ecological communities, and biogeochemical cycles of this tenth of the planet depend on the persistence of frozen conditions. The complexity, immensity, and remoteness of permafrost ecosystems make it difficult to grasp how quickly things are changing and what can be done about it. Here, we summarize terrestrial and marine changes in the permafrost domain with an eye toward global policy. While many questions remain, we know that continued fossil fuel burning is incompatible with the continued existence of the permafrost domain as we know it. If we fail to protect permafrost ecosystems, the consequences for human rights, biosphere integrity, and global climate will be severe. The policy implications are clear: the faster we reduce human emissions and draw down atmospheric CO2, the more of the permafrost domain we can save. Emissions reduction targets must be strengthened and accompanied by support for local peoples to protect intact ecological communities and natural carbon sinks within the permafrost domain. Some proposed geoengineering interventions such as solar shading, surface albedo modification, and vegetation manipulations are unproven and may exacerbate environmental injustice without providing lasting protection. Conversely, astounding advances in renewable energy have reopened viable pathways to halve human greenhouse gas emissions by 2030 and effectively stop them well before 2050. We call on leaders, corporations, researchers, and citizens everywhere to acknowledge the global importance of the permafrost domain and work towards climate restoration and empowerment of Indigenous and immigrant communities in these regions.
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| 2. |
- A'Campo, Willeke, et al.
(författare)
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Arctic Tundra Land Cover Classification on the Beaufort Coast Using the Kennaugh Element Framework on Dual-Polarimetric TerraSAR-X Imagery
- 2021
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 13:23
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Tidskriftsartikel (refereegranskat)abstract
- Arctic tundra landscapes are highly complex and are rapidly changing due to the warming climate. Datasets that document the spatial and temporal variability of the landscape are needed to monitor the rapid changes. Synthetic Aperture Radar (SAR) imagery is specifically suitable for monitoring the Arctic, as SAR, unlike optical remote sensing, can provide time series regardless of weather and illumination conditions. This study examines the potential of seasonal backscatter mechanisms in Arctic tundra environments for improving land cover classification purposes by using a time series of HH/HV TerraSAR-X (TSX) imagery. A Random Forest (RF) classification was applied on multi-temporal Sigma Nought intensity and multi-temporal Kennaugh matrix element data. The backscatter analysis revealed clear differences in the polarimetric response of water, soil, and vegetation, while backscatter signal variations within different vegetation classes were more nuanced. The RF models showed that land cover classes could be distinguished with 92.4% accuracy for the Kennaugh element data, compared to 57.7% accuracy for the Sigma Nought intensity data. Texture predictors, while improving the classification accuracy on the one hand, degraded the spatial resolution of the land cover product. The Kennaugh elements derived from TSX winter acquisitions were most important for the RF model, followed by the Kennaugh elements derived from summer and autumn acquisitions. The results of this study demonstrate that multi-temporal Kennaugh elements derived from dual-polarized X-band imagery are a powerful tool for Arctic tundra land cover mapping.
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| 3. |
- Beer, C., et al.
(författare)
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Carbon dioxide release from retrogressive thaw slumps in Siberia
- 2023
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Ingår i: Environmental Research Letters. - 1748-9326. ; 18:10
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Tidskriftsartikel (refereegranskat)abstract
- Thawing of ice-rich permafrost soils in sloped terrain can lead to activation of retrogressive thaw slumps (RTSs) which make organic matter available for decomposition that has been frozen for centuries to millennia. Recent studies show that the area affected by RTSs increased in the last two decades across the pan-Arctic. Combining a model of soil carbon dynamics with remotely sensed spatial details of thaw slump area and a soil carbon database, we show that RTSs in Siberia turned a previous quasi-neutral ecosystem into a strong source of carbon dioxide of 367 ± 213 gC m-1 a-1. On a global scale, recent CO2 emissions from Siberian thaw slumps of 0.42 ± 0.22 Tg carbon per year are negligible so far. However, depending on the future evolution of permafrost thaw and hence thaw slump-affected area, such hillslope processes can transition permafrost landscapes to become a major source of additional CO2 release into the atmosphere.
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| 4. |
- Beer, Christian, et al.
(författare)
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Vertical pattern of organic matter decomposability in cryoturbated permafrost-affected soils
- 2022
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 17:10
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Tidskriftsartikel (refereegranskat)abstract
- Permafrost thaw will release additional carbon dioxide into the atmosphere resulting in a positive feedback to climate change. However, the mineralization dynamics of organic matter (OM) stored in permafrost-affected soils remain unclear. We used physical soil fractionation, radiocarbon measurements, incubation experiments, and a dynamic decomposition model to identify distinct vertical pattern in OM decomposability. The observed differences reflect the type of OM input to the subsoil, either by cryoturbation or otherwise, e.g. by advective water-borne transport of dissolved OM. In non-cryoturbated subsoil horizons, most OM is stabilized at mineral surfaces or by occlusion in aggregates. In contrast, pockets of OM-rich cryoturbated soil contain sufficient free particulate OM for microbial decomposition. After thaw, OM turnover is as fast as in the upper active layer. Since cryoturbated soils store ca. 450 Pg carbon, identifying differences in decomposability according to such translocation processes has large implications for the future global carbon cycle and climate, and directs further process model development.
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| 5. |
- Chadburn, Sarah E., et al.
(författare)
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Modeled Microbial Dynamics Explain the Apparent Temperature Sensitivity of Wetland Methane Emissions
- 2020
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 34:11
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Tidskriftsartikel (refereegranskat)abstract
- Methane emissions from natural wetlands tend to increase with temperature and therefore may lead to a positive feedback under future climate change. However, their temperature response includes confounding factors and appears to differ on different time scales. Observed methane emissions depend strongly on temperature on a seasonal basis, but if the annual mean emissions are compared between sites, there is only a small temperature effect. We hypothesize that microbial dynamics are a major driver of the seasonal cycle and that they can explain this apparent discrepancy. We introduce a relatively simple model of methanogenic growth and dormancy into a wetland methane scheme that is used in an Earth system model. We show that this addition is sufficient to reproduce the observed seasonal dynamics of methane emissions in fully saturated wetland sites, at the same time as reproducing the annual mean emissions. We find that a more complex scheme used in recent Earth system models does not add predictive power. The sites used span a range of climatic conditions, with the majority in high latitudes. The difference in apparent temperature sensitivity seasonally versus spatially cannot be recreated by the non-microbial schemes tested. We therefore conclude that microbial dynamics are a strong candidate to be driving the seasonal cycle of wetland methane emissions. We quantify longer-term temperature sensitivity using this scheme and show that it gives approximately a 12% increase in emissions per degree of warming globally. This is in addition to any hydrological changes, which could also impact future methane emissions.
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| 6. |
- Ciais, Philippe, et al.
(författare)
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Definitions and methods to estimate regional land carbon fluxes for the second phase of the REgional Carbon Cycle Assessment and Processes Project (RECCAP-2)
- 2022
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 15:3, s. 1289-1316
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Tidskriftsartikel (refereegranskat)abstract
- Regional land carbon budgets provide insights into the spatial distribution of the land uptake of atmospheric carbon dioxide and can be used to evaluate carbon cycle models and to define baselines for land-based additional mitigation efforts. The scientific community has been involved in providing observation-based estimates of regional carbon budgets either by downscaling atmospheric CO2 observations into surface fluxes with atmospheric inversions, by using inventories of carbon stock changes in terrestrial ecosystems, by upscaling local field observations such as flux towers with gridded climate and remote sensing fields, or by integrating data-driven or process-oriented terrestrial carbon cycle models. The first coordinated attempt to collect regional carbon budgets for nine regions covering the entire globe in the RECCAP-1 project has delivered estimates for the decade 2000–2009, but these budgets were not comparable between regions due to different definitions and component fluxes being reported or omitted. The recent recognition of lateral fluxes of carbon by human activities and rivers that connect CO2 uptake in one area with its release in another also requires better definitions and protocols to reach harmonized regional budgets that can be summed up to a globe scale and compared with the atmospheric CO2 growth rate and inversion results. In this study, using the international initiative RECCAP-2 coordinated by the Global Carbon Project, which aims to be an update to regional carbon budgets over the last 2 decades based on observations for 10 regions covering the globe with a better harmonization than the precursor project, we provide recommendations for using atmospheric inversion results to match bottom-up carbon accounting and models, and we define the different component fluxes of the net land atmosphere carbon exchange that should be reported by each research group in charge of each region. Special attention is given to lateral fluxes, inland water fluxes, and land use fluxes.
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| 7. |
- Fluet-Chouinard, Etienne, et al.
(författare)
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Extensive global wetland loss over the past three centuries
- 2023
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 614:7947, s. 281-286
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Tidskriftsartikel (refereegranskat)abstract
- Wetlands have long been drained for human use, thereby strongly affecting greenhouse gas fluxes, flood control, nutrient cycling and biodiversity1,2. Nevertheless, the global extent of natural wetland loss remains remarkably uncertain3. Here, we reconstruct the spatial distribution and timing of wetland loss through conversion to seven human land uses between 1700 and 2020, by combining national and subnational records of drainage and conversion with land-use maps and simulated wetland extents. We estimate that 3.4 million km2 (confidence interval 2.9–3.8) of inland wetlands have been lost since 1700, primarily for conversion to croplands. This net loss of 21% (confidence interval 16–23%) of global wetland area is lower than that suggested previously by extrapolations of data disproportionately from high-loss regions. Wetland loss has been concentrated in Europe, the United States and China, and rapidly expanded during the mid-twentieth century. Our reconstruction elucidates the timing and land-use drivers of global wetland losses, providing an improved historical baseline to guide assessment of wetland loss impact on Earth system processes, conservation planning to protect remaining wetlands and prioritization of sites for wetland restoration4.
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| 8. |
- Guasconi, Daniela, 1992-, et al.
(författare)
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Climate-dependent responses of root and shoot biomass to drought duration and intensity in grasslands–a meta-analysis
- 2023
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Ingår i: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 903
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the effects of altered precipitation regimes on root biomass in grasslands is crucial for predicting grassland responses to climate change. Nonetheless, studies investigating the effects of drought on belowground vegetation have produced mixed results. In particular, root biomass under reduced precipitation may increase, decrease or show a delayed response compared to shoot biomass, highlighting a knowledge gap in the relationship between belowground net primary production and drought. To address this gap, we conducted a meta-analysis of nearly 100 field observations of grassland root and shoot biomass changes under experimental rainfall reduction to disentangle the main drivers behind grassland responses to drought. Using a response-ratio approach we tested the hypothesis that water scarcity would induce a decrease in total biomass, but an increase in belowground biomass allocation with increased drought length and intensity, and that climate (as defined by the aridity index of the study location) would be an additional predictor. As expected, meteorological drought decreased root and shoot biomass, but aboveground and belowground biomass exhibited contrasting responses to drought duration and intensity, and their interaction with climate. In particular, drought duration had negative effects on root biomass only in wet climates while more intense drought had negative effects on root biomass only in dry climates. Shoot biomass responded negatively to drought duration regardless of climate. These results show that long-term climate is an important modulator of belowground vegetation responses to drought, which might be a consequence of different drought tolerance and adaptation strategies. This variability in vegetation responses to drought suggests that physiological plasticity and community composition shifts may mediate how climate affects carbon allocation in grasslands, and thus ultimately carbon storage in soil.
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| 9. |
- Guasconi, Daniela, 1992-, et al.
(författare)
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Spatial and temporal variability in soil and vegetation carbon dynamics under experimental drought and soil amendments
- 2023
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Soils are the largest carbon (C) pool on the planet, and grassland soils have a particularly large C sequestration potential. Appropriate land management strategies, such as organic matter additions, can improve soil health, increase soil C stocks, and increase grassland resilience to drought by improving soil moisture retention. However, soil C dynamics are deeply linked to vegetation response to changes in both management and climate, which may also be manifested differently in roots and shoots. This study presents findings from a three-year experiment that assessed the impact of a compost amendment and of reduced precipitation on soil and vegetation C pools. Compost addition increased aboveground biomass and soil C content (%C), but because bulk density decreased, there was no significant effect on soil C stocks. Drought decreased aboveground biomass, but did not significantly affect root biomass. Overall, the soil amendment shifted C allocation to aboveground plant organs, and drought to belowground organs. We also observed significant spatial and temporal variability in vegetation biomass and soil C over the study period. These results highlight the need to consider multiple biotic and abiotic factors driving ecosystem C dynamics across spatial scales when upscaling results from field trials.
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| 10. |
- Guasconi, Daniela, 1992-
(författare)
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The hidden half of the meadow : Interactions between drought, soil carbon, roots and soil microbial communities
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Soil is a hidden ecosystem which harbours plant roots and countless microorganisms, vital for sustaining life aboveground. These belowground communities provide essential ecosystem services like soil stabilisation and organic matter decomposition. Soil is also one of the largest terrestrial carbon repositories, and land management strategies aimed at increasing organic matter inputs from plants, such as compost additions, can promote further soil carbon accumulation. Because organic carbon is important for soil water retention, this management may also help to increase resilience against more frequent and intense droughts. Although roots and microbial communities are largely acknowledged to play a key role in regulating the carbon cycle, there are still many open questions regarding the link between above- and belowground processes and ecosystem functions. Observing climate- and management-driven changes in the soil habitat is fundamental for understanding how ecosystems respond to environmental change.The aim of this thesis is to explore the relationship between soil properties, plant communities, and soil microbial communities in response to environmental changes. The research builds on a meta-analysis of drought effects on grasslands, and a multifactorial field experiment which combined three years of precipitation reduction and a compost treatment in two Swedish grasslands. We analysed the response of roots and soil microbial communities to drought and compost amendments, and identified environmental factors behind their large spatial variability. Finally, we tested the effects of compost additions on soil carbon storage and its interactions with drought.The results of the meta-analysis indicate that, on a global scale, grassland roots and shoots have diverging responses to drought duration and intensity, with long-term climate mediating that difference. At the local scale assessed in the field experiment, we observed that the spatial patterns of soil microbial communities were driven by soil properties and vegetation. Growing season drought affected roots only at trait level, but did not significantly affect microbial communities. Positive effects of compost on aboveground plant productivity and fungal growth were detectable after three years. Compost amendments also increased the percentage of total soil carbon, but no net increase in soil carbon stocks was detected. Spatial variability in roots and microbial communities was larger than the treatment effects, and was important in shaping microbial community composition and determining grassland responses to drought.Taken together, these findings suggest that roots and microbial communities are likely to be tolerant to drought a within the timescale of this experiment, but we did not observe an increase soil carbon sequestration or drought resilience when adding compost. This thesis highlights the importance of considering soil processes as complementary to aboveground observations when studying carbon dynamics, predicting ecosystem responses to environmental change, and developing sustainable land management practices.
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