| 61. |
- Sawakuchi, Henrique Oliveira, et al.
(författare)
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Phosphorus Regulation of Methane Oxidation in Water From Ice-Covered Lakes
- 2021
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Ingår i: Journal of Geophysical Research - Biogeosciences. - : Wiley-Blackwell Publishing, Inc.. - 2169-8953 .- 2169-8961. ; 126:9
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Tidskriftsartikel (refereegranskat)abstract
- Winter methane (CH4) accumulation in seasonally ice-covered lakes can contribute to large episodic emissions to the atmosphere during spring ice melt. Biological methane oxidation can significantly mitigate such CH4 emissions, but despite favorable CH4 and O2 concentrations, CH4 oxidation appears constrained in some lakes for unknown reasons. Here we experimentally test the hypothesis that phosphorus (P) availability is limiting CH4 oxidation, resulting in differences in ice-out emissions among lakes. We observed a positive relationship between potential CH4 oxidation and P concentration across 12 studied lakes and found an increase in CH4 oxidation in response to P amendment, without any parallel change in the methanotrophic community composition. Hence, while an increase in sedimentary CH4 production and ebullitive emissions may happen with eutrophication, our study indicates that the increase in P associated with eutrophication may also enhance CH4 oxidation. The increase in CH4 oxidation may hence play an important role in nutrient-rich ice-covered lakes where bubbles trapped under the ice may to a greater extent be oxidized, reducing the ice-out emissions of CH4. This may be an important factor regulating CH4 emissions from high latitude lakes.
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| 62. |
- Temnerud, Johan, et al.
(författare)
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Spatial patterns of some trace elements in four Swedish stream networks
- 2013
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 10, s. 1407-1423
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Tidskriftsartikel (refereegranskat)abstract
- Four river basins in southern Sweden, with catchment sizes from 0.3 to 127 km(2) (median 1.9), were sampled in October 2007. The 243 samples were analysed for 26 trace elements (Ag, As, Au, Ba, Be, Bi, Cd, Co, Cr, Cu, Ga, Ge, In, La, Li, Mo, Ni, Pb, Sb, Se, Sn, Tl, Ti, U, V and Zn) to identify spatial patterns within drainage networks. The range and median of each element were defined for different stream orders, and relationships to catchment characteristics, including deposition history, were explored. The sampling design made it possible to compare the differences along 40 stream reaches, above and below 53 stream junctions with 107 tributaries and between the 77 inlets and outlets of 36 lakes. The largest concentration differences (at reaches, junctions and lakes) were observed for lakes, with outlets usually having lower concentration compared to the inlets for As, Ba, Be, Bi, Cd, Co, Cr, Ga, Ge, Ni, Pb, Sn, Ti, Tl, U, V and Zn. Significantly lower concentrations were observed for Cd and Co when comparing headwaters with downstream sites in each catchment. Common factor analysis (FA) revealed that As, Bi, Cr, Ga, Ge, Tl and V co-vary positively with Al, Fe and total organic carbon (TOC) and negatively with La, Li and pH. The strong removal of a large number of trace elements when passing through lakes is evident though in the FA, where lake surface coverage plots opposite to many of those elements. Forest volume does not respond in a similar systematic fashion and, surprisingly, the amount of wetland does not relate strongly to either Fe or TOC at any of the rivers. A better understanding of the quantitative removal of organic carbon and iron will aid in understanding trace element fluxes from landscapes rich in organic matter and iron.
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| 63. |
- Omstedt, Anders, 1949, et al.
(författare)
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Future changes in the Baltic Sea acid-base (pH) and oxygen balances
- 2012
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 64
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Tidskriftsartikel (refereegranskat)abstract
- Possible future changes in Baltic Sea acid–base (pH) and oxygen balances were studied using a catchment–sea coupled model system and numerical experiments based on meteorological and hydrological forcing datasets and scenarios. By using objective statistical methods, climate runs for present climate conditions were examined and evaluated using Baltic Sea modelling. The results indicate that increased nutrient loads will not inhibit future Baltic Sea acidification; instead, the seasonal pH cycle will be amplified by increased biological production and mineralization. All examined scenarios indicate future acidification of the whole Baltic Sea that is insensitive to the chosen global climate model. The main factor controlling the direction and magnitude of future pH changes is atmospheric CO2 concentration (i.e. emissions). Climate change and land-derived changes (e.g. nutrient loads) affect acidification mainly by altering the seasonal cycle and deep-water conditions. Apart from decreasing pH, we also project a decreased saturation state of calcium carbonate, decreased respiration index, and increasing hypoxic area – all factors that will threaten the marine ecosystem. We demonstrate that substantial reductions in fossil-fuel burning are needed to minimize the coming pH decrease and substantial reductions in nutrient loads are needed to reduce the coming increase in hypoxic and anoxic waters.
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| 64. |
- Wang, Tongmei, et al.
(författare)
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Stable Water Isotopologues in the Stratosphere Retrieved from Odin/SMR Measurements
- 2018
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 10:2
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Tidskriftsartikel (refereegranskat)abstract
- Stable Water Isotopologues (SWIs) are important diagnostic tracers for understanding processes in the atmosphere and the global hydrological cycle. Using eight years (2002-2009) of retrievals from Odin/SMR (Sub-Millimetre Radiometer), the global climatological features of three SWIs, (H2O)-O-16, HDO and (H2O)-O-18, the isotopic composition D and O-18 in the stratosphere are analysed for the first time. Spatially, SWIs are found to increase with altitude due to stratospheric methane oxidation. In the tropics, highly depleted SWIs in the lower stratosphere indicate the effect of dehydration when the air comes through the cold tropopause, while, at higher latitudes, more enriched SWIs in the upper stratosphere during summer are produced and transported to the other hemisphere via the Brewer-Dobson circulation. Furthermore, we found that more (H2O)-O-16 is produced over summer Northern Hemisphere and more HDO is produced over summer Southern Hemisphere. Temporally, a tape recorder in (H2O)-O-16 is observed in the lower tropical stratosphere, in addition to a pronounced downward propagating seasonal signal in SWIs from the upper to the lower stratosphere over the polar regions. These observed features in SWIs are further compared to SWI-enabled model outputs. This helped to identify possible causes of model deficiencies in reproducing main stratospheric features. For instance, choosing a better advection scheme and including methane oxidation process in a specific model immediately capture the main features of stratospheric water vapor. The representation of other features, such as the observed inter-hemispheric difference of isotopic component, is also discussed.
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| 65. |
- Podgrajsek, Eva, et al.
(författare)
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Methane fluxes from a small boreal lake measured with the eddy covariance method
- 2016
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 61:Supplement 1, s. S41-S50
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Tidskriftsartikel (refereegranskat)abstract
- Fluxes of methane, CH4, were measured with the eddy covariance (EC) method at a small boreal lake in Sweden. The mean CH4 flux during the growing season of 2013 was 20.1 nmol m(-2) s(-1) and the median flux was 16 nmol m(-2) s(-1) (corresponding to 1.7 mmol m(-2) d(-1) and 1.4 mmol m(-2) d(-1)). Monthly mean values of CH4 flux measured with the EC method were compared with fluxes measured with floating chambers (FC) and were in average 62% higher over the whole study period. The difference was greatest in April partly because EC, but not FC, accounted for fluxes due to ice melt and a subsequent lake mixing event. A footprint analysis revealed that the EC footprint included primarily the shallow side of the lake with a major inlet. This inlet harbors emergent macrophytes that can mediate high CH4 fluxes. The difference between measured EC and FC fluxes can hence be explained by different footprint areas, where the EC system sees the part of the lake presumably releasing higher amounts of CH4. EC also provides more frequent measurements than FC and hence more likely captures ebullition events. This study shows that small lakes have CH4 fluxes that are highly variable in time and space. Based on our findings we suggest to measure CH4 fluxes from lakes as continuously as possible and to aim for covering as much of the lakes surface as possible, independently of the selected measuring technique.
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| 66. |
- Thorsson, Sofia, 1972, et al.
(författare)
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Present and projected future mean radiant temperature for three European cities
- 2017
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Ingår i: International Journal of Biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254. ; 61:9
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 The Author(s)Present-day and projected future changes in mean radiant temperature, Tmrt in one northern, one mid-, and one southern European city (represented by Gothenburg, Frankfurt, and Porto), are presented, and the concept of hot spots is adopted. Air temperature, Ta, increased in all cities by 2100, but changes in solar radiation due to changes in cloudiness counterbalanced or exacerbated the effects on Tmrt. The number of days with high Tmrt in Gothenburg was relatively unchanged at the end of the century (+1 day), whereas it more than doubled in Frankfurt and tripled in Porto. The use of street trees to reduce daytime radiant heat load was analyzed using hot spots to identify where trees could be most beneficial. Hot spots, although varying in intensity and frequency, were generally confined to near sunlit southeast-southwest facing walls, in northeast corner of courtyards, and in open spaces in all three cities. By adding trees in these spaces, the radiant heat load can be reduced, especially in spaces with no or few trees. A set of design principles for reducing the radiant heat load is outlined based on these findings and existing literature.
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| 67. |
- Mattsson, Eskil, 1981, et al.
(författare)
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Quantification of carbon stock and tree diversity of homegardens in a dry zone area of Moneragala District, Sri Lanka
- 2015
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Ingår i: Agroforestry Systems. - : Springer Science and Business Media LLC. - 1572-9680 .- 0167-4366. ; 89:3, s. 435-445
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Tidskriftsartikel (refereegranskat)abstract
- Homegarden agroforestry systems are suggested to hold a large potential for climate change mitigation and adaptation. This is due to their multifunctional role in providing income, food and ecosystem services while decreasing pressure on natural forests and hence saving and storing carbon. In this paper, above-ground biomass carbon and tree species diversity of trees was quantified in homegardens around two villages in the dry south-eastern part of Moneragala district of Sri Lanka. A total of 45 dry zone homegardens were sampled on size, diameter at breast height, tree height and species diversity. Using allometric equations, we find a mean above-ground biomass stock of 13 mega grams of carbon per hectare (Mg C ha−1) with a large range among homegardens (1–56 Mg C ha−1, n = 45) due to a variation of tree diversity and composition between individual homegardens. Mean above-ground carbon stock per unit area was higher in small homegardens (0.2 ha, 26 Mg C ha−1, n = 11) and statistically different compared to medium (0.4–0.8 ha, 9 Mg C ha−1, n = 27) and large (1.0–1.2 ha, 8 Mg C ha−1, n = 7) homegardens. In total, 4,278 trees were sampled and 70 tree species identified and recorded. The Shannon Wiener index were used to evaluate diversity per homegarden and ranged from 0.76 to 3.01 with a mean value of 2.05 ± 0.07 indicating a medium evenly distributed diversity of sampled tree species. The results show a vast heterogeneity in terms of carbon stock and tree diversity within the less studied dry zone homegardens; results that contribute to more knowledge of their expansion potential as well as climate mitigation and adaptation potential. The results are also useful for whether homegardens should be considered to be included as an activity to enhance natural forest cover within Sri Lanka’s newly commenced UN-REDD National Programme.
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| 68. |
- Orgel, Csilla, et al.
(författare)
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Gridmapping the Northern Plains of Mars: A New Overview of Recent Water‐ and Ice‐Related Landforms in Acidalia Planitia.
- 2019
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Ingår i: Journal of Geophysical Research - Planets. - 2169-9100. ; 124:2, s. 454-82
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Tidskriftsartikel (refereegranskat)abstract
- We used a grid‐mapping technique to analyze the distribution of 13 water‐ and ice‐related landforms in Acidalia Planitia as part of a joint effort to study the three main basins in the northern lowlands of Mars, that is, Acidalia, Utopia, and Arcadia Planitiae. The landforms were mapped at full Context Camera resolution along a 300‐km‐wide strip from 20°N to 84°N. We identified four landform assemblages: (1) Geologically recent polar cap (massive ice), which superposes the latitude‐dependent mantle (LDM) (LA1); (2) ice‐related landforms, such as LDM, textured terrain, small‐scale polygons, scalloped terrain, large‐scale viscous flow features, and gullies, which have an overlapping distribution (LA2); (3) surface features possibly related to water and subsurface sediment mobilization (LA3; kilometer‐scale polygons, large pitted mounds, small pitted mounds, thumbprint terrain); and (4) irregularly shaped pits with raised rims on equator‐facing slopes. Pits are likely the result of an energetic release of volatiles (H2O, CO2, and CH4), rather than impact‐, volcanism‐, or wind‐related processes. LDM occurs ubiquitously from 44°N to 78°N in Acidalia Planitia. Various observations suggest an origin of air fall deposition of LDM, which contains less ice in the uppermost tens of meters in Acidalia Planitia than in Arcadia and Utopia Planitiae. However, LDM may be thicker and more extended in the past in Acidalia Planitia. The transition between LDM‐free terrain and LDM is situated further north than in Utopia and Arcadia Planitiae, suggesting different past and/or present climatic conditions among the main basins in the northern lowlands.
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| 69. |
- Pendrill, Florence, 1983
(författare)
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Felling Forests from Afar: Quantifying Deforestation Driven by Agricultural Expansion and International Trade
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Deforestation is a major source of human-caused greenhouse gas emissions and the largest threat to terrestrial biodiversity. Most forest loss is due to the expansion of agricultural land use increasingly driven by international demand for food, fuel and fibre. However, there is still limited understanding of the extent to which different agricultural commodities are contributing to deforestation. It has therefore also been difficult to evaluate the role of international trade in driving deforestation. This dissertation aims at quantifying the agricultural drivers of tropical deforestation (Papers I and II) and the associated carbon emissions (Paper III). It further assesses the role of international trade, by following the agricultural commodities with embodied deforestation through international supply chains using trade models (Papers II and III). The results show that a few commodity types, primarily cattle meat and oilseed products, account for a large part of tropical deforestation. Much (26–39%) of the embodied deforestation and concomitant emissions were found to be associated with international demand (from products and services). Looking closer at the countries that import embodied deforestation, Paper II finds that many countries that are increasing their forest cover at home, import products associated with deforestation elsewhere, thereby offsetting about a third of their forest gains. Paper III finds that imports of embodied deforestation emissions for many developed countries are similar in size to their national agricultural emissions amounting, e.g., for the EU, to around 15% of the carbon footprint of an average diet. Put together, the results add to the evidence that combating deforestation can benefit from complementing domestic policies with measures that target international demand. The results also indicate that tackling deforestation and its associated impacts at the global level is probably even more challenging than at the national level, although international trade can also provide efficiency gains by optimising land use globally.
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| 70. |
- Granath, Gustaf
(författare)
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Hydrological feedbacks in northern peatlands
- 2015
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Ingår i: Ecohydrology. - : Wiley. - 1936-0584 .- 1936-0592. ; 8, s. 113-127
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Tidskriftsartikel (refereegranskat)abstract
- Northern peatlands provide important global and regional ecosystem services (carbon storage, water storage, and biodiversity). However, these ecosystems face increases in the severity, areal extent and frequency of climate-mediated (e.g. wildfire and drought) and land-use change (e.g. drainage, flooding and mining) disturbances that are placing the future security of these critical ecosystem services in doubt. Here, we provide the first detailed synthesis of autogenic hydrological feedbacks that operate within northern peatlands to regulate their response to changes in seasonal water deficit and varying disturbances. We review, synthesize and critique the current process-based understanding and qualitatively assess the relative strengths of these feedbacks for different peatland types within different climate regions. We suggest that understanding the role of hydrological feedbacks in regulating changes in precipitation and temperature are essential for understanding the resistance, resilience and vulnerability of northern peatlands to a changing climate. Finally, we propose that these hydrological feedbacks also represent the foundation of developing an ecohydrological understanding of coupled hydrological, biogeochemical and ecological feedbacks. Copyright (c) 2014 John Wiley & Sons, Ltd.
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