| 1. |
- Roth, Florian, et al.
(författare)
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High spatiotemporal variability of methane concentrations challenges estimates of emissions across vegetated coastal ecosystems.
- 2022
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Ingår i: Global change biology. - : Wiley. - 1365-2486 .- 1354-1013. ; 28:14, s. 4308-4322
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Tidskriftsartikel (refereegranskat)abstract
- Coastal methane (CH4 ) emissions dominate the global ocean CH4 budget and can offset the "blue carbon" storage capacity of vegetated coastal ecosystems. However, current estimates lack systematic, high-resolution, and long-term data from these intrinsically heterogeneous environments, making coastal budgets sensitive to statistical assumptions and uncertainties. Using continuous CH4 concentrations, δ13 C-CH4 values, and CH4 sea-air fluxes across four seasons in three globally pervasive coastal habitats, we show that the CH4 distribution is spatially patchy over meter-scales and highly variable in time. Areas with mixed vegetation, macroalgae, and their surrounding sediments exhibited a spatiotemporal variability of surface water CH4 concentrations ranging two orders of magnitude (i.e., 6-460 nM CH4 ) with habitat-specific seasonal and diurnal patterns. We observed (1) δ13 C-CH4 signatures that revealed habitat-specific CH4 production and consumption pathways, (2) daily peak concentration events that could change >100% within hours across all habitats, and (3) a high thermal sensitivity of the CH4 distribution signified by apparent activation energies of ~1 eV that drove seasonal changes. Bootstrapping simulations show that scaling the CH4 distribution from few samples involves large errors, and that ~50 concentration samples per day are needed to resolve the scale and drivers of the natural variability and improve the certainty of flux calculations by up to 70%. Finally, we identify northern temperate coastal habitats with mixed vegetation and macroalgae as understudied but seasonally relevant atmospheric CH4 sources (i.e., releasing ≥ 100 μmol CH4 m-2 day-1 in summer). Due to the large spatial and temporal heterogeneity of coastal environments, high-resolution measurements will improve the reliability of CH4 estimates and confine the habitat-specific contribution to regional and global CH4 budgets.
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| 2. |
- Cheung, Henry Lok Shan, et al.
(författare)
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Denitrification, anammox, and DNRA in oligotrophic continental shelf sediments
- 2024
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Ingår i: Limnology and Oceanography. - 1939-5590 .- 0024-3590.
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Tidskriftsartikel (refereegranskat)abstract
- Continental shelf sediments are considered hotspots for nitrogen (N) removal. While most investigations have quantified denitrification in shelves receiving large amounts of anthropogenic nutrient supply, we lack insight into the key drivers of N removal on oligotrophic shelves. Here, we measured rates of N removal through denitrification and anammox by the revised-isotope pairing technique (r-IPT) along the Northeastern New Zealand shelf. Denitrification dominated total N2 production at depths between 30 and 128 m with average rates (± SE) ranging from 65 ± 28 to 284 ± 72 μmol N m−2 d−1. N2 production by anammox ranged from 3 ± 1 to 28 ± 11 μmol N m−2 d−1 and accounted for 2–19% of total N2 production. DNRA was negligible in these oligotrophic settings. Parallel microbial community analysis showed that both Proteobacteria and Planctomycetota were key taxa driving denitrification. Denitrification displayed a negative correlation with oxygen penetration depth, and a positive correlation with macrofauna abundance. Our denitrification rates were comparable to oligotrophic shelves from the Arctic, but were lower than those from nutrient-rich Pacific and Atlantic shelves. Based on our results and existing IPT measurements, the global shelf denitrification rate was reassessed to be 53.5 ± 8.1 Tg N yr−1, equivalent to 20 ± 2% of marine N removal. We suggest that previous estimates of global shelf N loss might have been overestimated due to sampling bias toward areas with high N loads in the Northern Hemisphere.
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| 3. |
- Sobek, Anna, et al.
(författare)
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Organic matter degradation causes enrichment of organic pollutants in hadal sediments
- 2023
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Ingår i: Nature Communications. - 2041-1723. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- Burial of persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) in deep-sea sediments contributes to 60% of their historical emissions. Yet, empirical data on their occurrence in the deep-ocean is scarce. Estimates of the deep-ocean POP sink are therefore uncertain. Hadal trenches, representing the deepest part of the ocean, are hotspots for organic carbon burial and decomposition. POPs favorably partition to organic carbon, making trenches likely significant sinks for contaminants. Here we show that PCBs occur in both hadal (7720–8085 m) and non-hadal (2560–4050 m) sediment in the Atacama Trench. PCB concentrations normalized to sediment dry weight were similar across sites while those normalized to sediment organic carbon increased exponentially as the inert organic carbon fraction of the sediment increased in degraded hadal sediments. We suggest that the unique deposition dynamics and elevated turnover of organic carbon in hadal trenches increase POP concentrations in the deepest places on Earth.
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| 4. |
- Vestin, Patrik, et al.
(författare)
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Impacts of stump harvesting on carbon dioxide, methane and nitrous oxide fluxes
- 2022
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Ingår i: Iforest-Biogeosciences and Forestry. - : Italian Society of Sivilculture and Forest Ecology (SISEF). - 1971-7458. ; 15, s. 148-162
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Tidskriftsartikel (refereegranskat)abstract
- During 2010-2013, we investigated the effects of stump harvesting on greenide (N2O) with the flux-gradient technique at four experimental plots in a hemiboreal forest in Sweden. All plots were clear-cut and soil scarified and two of the plots were additionally stump harvested. The two clear-cut plots served as control plots. Due to differences in topography, we had one wetter and one drier plot of each treatment. All plots exhibited substantial emissions of GHGs and we noted significant effects of wetness on CO2, CH4 and N2O fluxes within treatments and significant effects of stump harvesting on CO2 and N2O fluxes at the dry plots. The CO2 emissions were lower at the dry stump harvested plot than at the dry control, but when estimated emissions from the removed stumps were added, total CO2 emissions were higher at the stump harvested plot, indicating a small enhancement of soil respiration. In addition, we noted significant emissions of N2O at this plot. At the wet plots, CO2 emissions were higher at the stump harvested plot, also suggesting a treatment effect but differences in wetness and vegetation cover at these plots make this effect more uncertain. At the wet plots, we noted sustained periods (weeks to months) of net N2O uptake. During the year with simultaneous measurements of the abovementioned GHGs, GHG budgets were 1.224??103 and 1.442??103 gm-2 of CO2-equivalents at the wet and dry stump harvested plots, respectively, and 1.070??103 and 1.696??103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. CO2 fluxes dominated GHG budgets at all plots but N2O contributed with 17% at the dry stump harvested plot. For the full period 2010-2013, total carbon (CO2+CH4) budgets were 4.301??103 and 4.114??103 g m-2 of CO2-eqvivalents at the wet and dry stump harvest plots, respectively and 4.107??103 and 5.274??103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. Our results support recent studies suggesting that stump harvesting does not result in substantial increase in CO2 emissions but uncertainties regarding GHG fluxes (especially N2O) remain and more long-term measurements are needed before robust conclusions can be drawn.
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| 5. |
- Omstedt, Anders, 1949
(författare)
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The Development of Climate Science of the Baltic Sea Region
- 2017
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Ingår i: Oxford Research Encyclopedia of Climate Science. - : Oxford University Press.
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Dramatic climate changes have occurred in the Baltic Sea region caused by changes in orbital movement in the earth–sun system and the melting of the Fennoscandian Ice Sheet. Added to these longer-term changes, changes have occurred at all timescales, caused mainly by variations in large-scale atmospheric pressure systems due to competition between the meandering midlatitude low-pressure systems and highpressure systems. Here we follow the development of climate science of the Baltic Sea from when observations began in the 18th century to the early 21st century. The question of why the water level is sinking around the Baltic Sea coasts could not be answered until the ideas of postglacial uplift and the thermal history of the earth were better understood in the 19th century and periodic behavior in climate related time series attracted scientific interest. Herring and sardine fishing successes and failures have led to investigations of fishery and climate change and to the realization that fisheries themselves have strongly negative effects on the marine environment, calling for international assessment efforts. Scientists later introduced the concept of regime shifts when interpreting their data, attributing these to various causes. The increasing amount of anoxic deep water in the Baltic Sea and eutrophication have prompted debate about what is natural and what is anthropogenic, and the scientific outcome of these debates now forms the basis of international management efforts to reduce nutrient leakage from land. The observed increase in atmospheric CO and its effects on global warming have focused the climate debate on trends and generated a series of international and regional assessments and research programs that have greatly improved our understanding of climate and environmental changes, bolstering the efforts of earth system science, in which both climate and environmental factors are analyzed together.
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| 6. |
- Björk, Mats, 1960-, et al.
(författare)
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Methane emissions from macrophyte beach wrack on Baltic seashores
- 2023
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Ingår i: Ambio. - : Springer Nature. - 0044-7447 .- 1654-7209. ; 52:1, s. 171-181
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Tidskriftsartikel (refereegranskat)abstract
- Beach wrack of marine macrophytes is a natural component of many beaches. To test if such wrack emits the potent greenhouse gas methane, field measurements were made at different seasons on beach wrack depositions of different ages, exposure, and distance from the water. Methane emissions varied greatly, from 0 to 176 mg CH4-C m−2 day−1, with a clear positive correlation between emission and temperature. Dry wrack had lower emissions than wet. Using temperature data from 2016 to 2020, seasonal changes in fluxes were calculated for a natural wrack accumulation area. Such calculated average emissions were close to zero during winter, but peaked in summer, with very high emissions when daily temperatures exceeded 20 °C. We conclude that waterlogged beach wrack significantly contributes to greenhouse gas emissions and that emissions might drastically increase with increasing global temperatures. When beach wrack is collected into heaps away from the water, the emissions are however close to zero.
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| 7. |
- Myers-Smith, Isla H., et al.
(författare)
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Complexity revealed in the greening of the Arctic
- 2020
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Ingår i: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 10:2, s. 106-117
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Tidskriftsartikel (refereegranskat)abstract
- As the Arctic warms, vegetation is responding, and satellite measures indicate widespread greening at high latitudes. This ‘greening of the Arctic’ is among the world’s most important large-scale ecological responses to global climate change. However, a consensus is emerging that the underlying causes and future dynamics of so-called Arctic greening and browning trends are more complex, variable and inherently scale-dependent than previously thought. Here we summarize the complexities of observing and interpreting high-latitude greening to identify priorities for future research. Incorporating satellite and proximal remote sensing with in-situ data, while accounting for uncertainties and scale issues, will advance the study of past, present and future Arctic vegetation change.
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| 8. |
- Broman, Elias, 1985-, et al.
(författare)
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Biotic interactions between benthic infauna and aerobic methanotrophs mediate methane fluxes from coastal sediments
- 2024
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Ingår i: The ISME journal. - 1751-7370 .- 1751-7362. ; 18:1
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Tidskriftsartikel (refereegranskat)abstract
- Coastal ecosystems dominate oceanic methane (CH4) emissions. However, there is limited knowledge about how biotic interactions between infauna and aerobic methanotrophs (i.e. CH4 oxidizing bacteria) drive the spatial-temporal dynamics of these emissions. Here, we investigated the role of meio- and macrofauna in mediating CH4 sediment-water fluxes and aerobic methanotrophic activity that can oxidize significant portions of CH4. We show that macrofauna increases CH4 fluxes by enhancing vertical solute transport through bioturbation, but this effect is somewhat offset by high meiofauna abundance. The increase in CH4 flux reduces CH4 pore-water availability, resulting in lower abundance and activity of aerobic methanotrophs, an effect that counterbalances the potential stimulation of these bacteria by higher oxygen flux to the sediment via bioturbation. These findings indicate that a larger than previously thought portion of CH4 emissions from coastal ecosystems is due to faunal activity and multiple complex interactions with methanotrophs.
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| 9. |
- Li, Jun, et al.
(författare)
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Hygroscopicity and Ice Nucleation Properties of Dust/Salt Mixtures Originating from the Source of East Asian Dust Storms
- 2022
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Ingår i: Frontiers in Environmental Science. - : Frontiers Media SA. - 2296-665X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Dust storms are common meteorological events that occur frequently in the late spring and early summer in arid and semi-arid areas. The resulting lofted dust and salt mixtures can impact atmospheric chemistry and climate systems through the many pathways represented by aerosol-cloud-climate interactions. In this study, dust/salt samples were collected from important sources of the East Asian dust storm, including the Badain Jaran Desert, the Tengger Desert and the Ulan Buh Desert in northwestern China. Ion chromatography (IC) measurements were performed to determine the concentrations of cations and anions. The ionic concentrations, pH and dissolvable fractions of sand samples show a positive correlation, indicating that the dissolved content is rich in alkaline ions. A positive matrix factorization (PMF) receptor model was employed to analyze the IC results, and from the PMF solutions non-obvious connections to local geography emerge. The results of hygroscopic experiments of sand samples which were measured by a vapor sorption analyzer indicate that the hygroscopicity may be related to the soluble content of samples, and the observed hygroscopic behavior can be well described by a thermodynamic model. The morphology of individual particles was chemically mapped by the synchrotron-based scanning transmission X-ray microscopy, and needle-shaped CaCO3 particles were observed to adhere to more irregular high K-containing particles. Moreover, a continuous flow diffusion chamber was used to investigate the ice nucleation abilities of typical salts, with both homogeneous freezing and deposition nucleation being observed. The results indicate that the salts primarily act as cloud condensation nuclei but can also act as ice nucleating particles at low temperatures.
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| 10. |
- Wang, Y. J., et al.
(författare)
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The formation of nitro-aromatic compounds under high NOx and anthropogenic VOC conditions in urban Beijing, China
- 2019
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:11, s. 7649-7665
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Tidskriftsartikel (refereegranskat)abstract
- Nitro-aromatic compounds (NACs), as important contributors to the light absorption by brown carbon, have been widely observed in various ambient atmospheres; however, their formation in the urban atmosphere was little studied. In this work, we report an intensive field study of NACs in summer 2016 at an urban Beijing site, characterized by both high-NO(x)and anthropogenic VOC dominated conditions. We investigated the factors that influence NAC formation (e.g., NO2, VOC precursors, RH and photolysis) through quantification of eight NACs, along with major components in fine particulate matter, selected volatile organic compounds, and gases. The average total concentration of the quantified NACs was 6.63 ng m(-3), higher than those reported in other summertime studies (0.14-6.44 ng m(-3)). 4-Nitrophenol (4NP, 32.4 %) and 4-nitrocatechol (4NC, 28.5 %) were the top two most abundant NACs, followed by methyl-nitrocatechol (MNC), methyl-nitrophenol (MNP), and dimethyl-nitrophenol (DMNP). The oxidation of toluene and benzene in the presence of NOx was found to be a more dominant source of NACs than primary biomass burning emissions. The NO2 concentration level was found to be an important factor influencing the secondary formation of NACs. A transition from low- to high-NOx regimes coincided with a shift from organic- to inorganic-dominated oxidation products. The transition thresholds were NO2 similar to 20 ppb for daytime and NO2 similar to 25 ppb for nighttime conditions. Under low-NOx conditions, NACs increased with NO2, while the NO3 concentrations and (NO3-)/NACs ratios were lower, implying organic-dominated products. Under high-NOx conditions, NAC concentrations did not further increase with NO2, while the NO3- concentrations and (NO3-)/NACs ratios showed increasing trends, signaling a shift from organic- to inorganic-dominated products. Nighttime enhancements were observed for 3M4NC and 4M5NC, while daytime enhancements were noted for 4NP, 2M4NP, and DMNP, indicating different formation pathways for these two groups of NACs. Our analysis suggested that the aqueous-phase oxidation was likely the major formation pathway of 4M5NC and 3M5NC, while photo-oxidation of toluene and benzene in the presence of NO2 could be more important for the formation of nitrophenol and its derivatives. Using the (3M4NC+4M5NC) / 4NP ratios as an indicator of the relative contribution of aqueous-phase and gas-phase oxidation pathways to NAC formation, we observed that the relative contribution of aqueous-phase pathways increased at elevated ambient RH and remained constant at RH > 30 %. We also found that the concentrations of VOC precursors (e.g., toluene and benzene) and aerosol surface area acted as important factors in promoting NAC formation, and photolysis as an important loss pathway for nitrophenols.
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