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  • 901.
    Wojcik, Robin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Palmtag, Juri
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Hugelius, Gustaf
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Weiss, Niels
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Kuhry, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Land cover and landform-based upscaling of soil organic carbon stocks on the Brogger Peninsula, Svalbard2019Ingår i: Arctic, Antarctic and Alpine research, ISSN 1523-0430, E-ISSN 1938-4246, Vol. 51, nr 1, s. 40-57Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study we assess the total storage, landscape distribution, and vertical partitioning of soil organic carbon (SOC) stocks on the Brogger Peninsula, Svalbard. This type of high Arctic area is underrepresented in SOC databases for the northern permafrost region. Physico-chemical, elemental, and radiocarbon (C-14) dating analyses were carried out on thirty-two soil profiles. Results were upscaled using both a land cover classification (LCC) and a landform classification (LFC). Both LCC and LFC approaches provide weighted mean SOC 0-100 cm estimates for the study area of 1.0 +/- 0.3 kg C m(-2) (95% confidence interval) and indicate that about 68 percent of the total SOC storage occurs in the upper 30 cm of the soil, and about 10 percent occurs in the surface organic layer. Furthermore, LCC and LFC upscaling approaches provide similar spatial SOC allocation estimates and emphasize the dominant role of vegetated area (4.2 +/- 1.6 kg C m(-2)) and solifluction slopes (6.7 +/- 3.6 kg C m(-2)) in SOC 0-100 cm storage. LCC and LFC approaches report different and complementary information on the dominant processes controlling the spatial and vertical distribution of SOC in the landscape. There is no evidence for any significant SOC storage in the permafrost layer. We hypothesize, therefore, that the Brogger Peninsula and similar areas of the high Arctic will become net carbon sinks, providing negative feedback on global warming in the future. The surface area that will have vegetation cover and incipient soil development will expand, whereas only small amounts of organic matter will experience increased decomposition due to active-layer deepening.

  • 902.
    Wood, Heather
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    EU tree density limits in wooded pastures and their effects on bat populations within traditional agricultural landscapes2016Självständigt arbete på avancerad nivå (masterexamen), 40 poäng / 60 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The European Union’s Common Agricultural Policy (CAP) recommends subsidies are only granted for wooded pastures with less than 100 trees per hectare. This arbitrary guidance exists despite these habitats being among the most biodiverse in rural Europe. To date, most biodiversity research in agricultural landscapes has focused on plants, birds and invertebrates. Bats are also important bio-indicators of agricultural landscapes, but to my knowledge no study has explicitly focused on bat diversity in relation to this policy. In this thesis, I investigate how bat activity, foraging and species richness is affected in twenty-six wooded pastures along a gradient of tree density, from open to dense pastures. In parallel, nearby open fields and deciduous woodlands were sampled, creating a triplet of habitats being surveyed simultaneously. Bat species were divided into feeding guilds to explore how functional diversity affects response to habitat and landscape configuration. The overall contribution of wooded pastures to the species pool of bats within a heterogeneous, low intensity agricultural landscape was also explored. I found a consistent increase in bat activity and species richness within wooded pastures along the tree density gradient and across most feeding guilds. This in combination with shrub density was the strongest predictor of total bat activity and foraging; whilst structural diversity of pastures was most strongly correlated with species richness. Wooded pastures contributed more to total species richness than forested habitats. Interestingly, higher activity levels of forest feeding specialists were observed in pastures compared to forests. At the landscape level, amount of water and deciduous forest were the strongest predictors of bat activity. This study demonstrates that tree density within wooded pastures is not a limiting factor of bat activity and that other habitat and landscape parameters are important. Wooded pastures may also be an important component of current landscapes with little remaining deciduous forest. In conclusion, focusing solely on tree density limits will not help to preserve the ecological requirements for bats within agricultural landscapes.

  • 903.
    Wood, Heather
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Lindborg, Regina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Jakobsson, Simon
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    European Union tree density limits do not reflect bat diversity in wood-pastures2017Ingår i: Biological Conservation, ISSN 0006-3207, E-ISSN 1873-2917, Vol. 210, s. 60-71Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The European Union's Common Agricultural Policy (CAP) recommends subsidies are only granted for wood-pastures with < 100 trees/ha. This guidance exists despite these habitats being among the most biodiverse in boreal Europe and currently under threat due to land conversion. Bats are important bio-indicators of agricultural landscapes, but bat diversity has not explicitly been studied in relation to this policy. We investigate how bat activity, foraging, species richness and functional groups are affected in twenty-six wood-pastures along a gradient of tree density, from open to dense. In parallel, open fields and deciduous forests were sampled and the effect of the surrounding landscape configuration was explored. Our results show a consistent increase in total bat activity, foraging activity and species richness within wood-pastures along the tree density gradient. We find optimal tree densities within wood-pastures are higher than values reported in previous studies, and suggest thresholds might depend on the landscape context. Shrub density was a strong predictor of total bat activity and foraging; whilst structural variation of tree size in wood-pastures was most strongly correlated with species richness. We show that wood-pastures are an important habitat and in comparison to forests they contribute to higher bat species richness and activity levels. Interestingly, higher activity levels of forest feeding specialists were observed in wood-pastures compared to forests. At the landscape level, amount of water in the landscape was the strongest predictor of bat activity whilst deciduous forest mostly influenced foraging activity. This study demonstrates that tree density within wood-pastures is not a limiting factor of bat activity and foraging and that other habitat and landscape parameters are important. Thereby focusing solely on tree density limits will not help to promote the ecological requirements for bats. Instead we suggest that a results based approach to CAP payments would be preferable.

  • 904. Wu, Zhendong
    et al.
    Hugelius, Gustaf
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Stanford University, USA.
    Luo, Yiqi
    Smith, Benjamin
    Xia, Jianyang
    Fensholt, Rasmus
    Lehsten, Veiko
    Ahlström, Anders
    Approaching the potential of model-data comparisons of global land carbon storage2019Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, artikel-id 3367Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon storage dynamics in vegetation and soil are determined by the balance of carbon influx and turnover. Estimates of these opposing fluxes differ markedly among different empirical datasets and models leading to uncertainty and divergent trends. To trace the origin of such discrepancies through time and across major biomes and climatic regions, we used a model-data fusion framework. The framework emulates carbon cycling and its component processes in a global dynamic ecosystem model, LPJ-GUESS, and preserves the model-simulated pools and fluxes in space and time. Thus, it allows us to replace simulated carbon influx and turnover with estimates derived from empirical data, bringing together the strength of the model in representing processes, with the richness of observational data informing the estimations. The resulting vegetation and soil carbon storage and global land carbon fluxes were compared to independent empirical datasets. Results show model-data agreement comparable to, or even better than, the agreement between independent empirical datasets. This suggests that only marginal improvement in land carbon cycle simulations can be gained from comparisons of models with current-generation datasets on vegetation and soil carbon. Consequently, we recommend that model skill should be assessed relative to reference data uncertainty in future model evaluation studies.

  • 905. Xu, Guobao
    et al.
    Liu, Xiaohong
    Wu, Guoju
    Chen, Tuo
    Wang, Wenzhi
    Zhang, Qiong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Zhang, Youfu
    Zeng, Xiaomin
    Qin, Dahe
    Sun, Weizhen
    Zhang, Xuanwen
    Tree ring O-18's indication of a shift to a wetter climate since the 1880s in the western Tianshan Mountains of northwestern China2015Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, nr 13, s. 6409-6425Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Central Asian droughts have drastically and significantly affected agriculture and water resource management in these arid and semiarid areas. Based on tree ring O-18 from native, dominant Schrenk spruce (Picea schrenkiana Fisch. et Mey.), we developed a 300year (1710-2010) standard precipitation-evaporation index (SPEI) reconstruction from January to August for China's western Tianshan Mountains. The regression model explained 37.6% of the variation in the SPEI reconstruction during the calibration period from 1950 to 2010. Comparison with previous drought reconstructions confirmed the robustness of our reconstruction. The 20th century has been a relatively wet period during the past 300years. The SPEI showed quasi 2, 5, and 10year cycles. Several pluvials and droughts with covariability over large areas were revealed clearly in the reconstruction. The two longest pluvials (lasting for 12years), separated by 50years, appeared in the 1900s and the 1960s. The most severe drought occurred from 1739 to 1761 and from 1886 to 1911 was the wettest period since 1710. Compared to previous investigations of hydroclimatic changes in the western Tianshan Mountains, our reconstruction revealed more low-frequency variability and indicated that climate in the western Tianshan Mountains shifted from dry to wet in 1886. This regime shift was generally consistent with other moisture reconstructions for the northeastern Tibetan Plateau and northern Pakistan and may have resulted from a strengthened westerly circulation. The opposite hydrological trends in the western Tianshan Mountains and southeastern Tibetan Plateau reveal a substantial influence of strengthened westerlies and weakening of the Indian summer monsoon.

  • 906. Xu, Guobao
    et al.
    Liu, Xiaohong
    Zhang, Qiong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Zhang, Qiang
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Hudson, Amy
    Trouet, Valerie
    Century-scale temperature variability and onset of industrial-era warming in the Eastern Tibetan Plateau2019Ingår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 53, nr 7-8, s. 4569-4590Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To improve our understanding of climate variability in the Tibetan Plateau (TP) and its sensitivity to external forcings, recent temperature changes need to be placed in a long-term historical context. Here, we present two tree-ring based temperature reconstructions: a 1003-year (1000-2002 CE) annual temperature reconstruction for the northeastern TP (NETP) based on seven series and a 522-year (1489-2010 CE) summer (June-July-August) temperature reconstruction for the southeastern TP (SETP) based on 11 series. Our reconstructions show six centuries of generally warm NETP temperatures (1000-1586 CE), followed by a transition to cooler temperatures (1587-1887 CE for NETP and 1588-1930 CE for SETP). The transition from the Medieval Climate Anomaly to the Little Ice Age thus happened in the 1580s in NETP and SETP, which is about 150 years later than in larger-scale (e.g. Asia and the Northern Hemisphere) temperature reconstructions. We found that TP temperature variability, especially in SETP, was influenced by the Atlantic multi-decadal oscillation and that the twentieth century was the warmest on record in NETP and SETP. Our reconstructions and climate model simulations both show industrial-era warming trends, the onset of which happened earlier in NETP (1812 CE) compared to SETP (1887 CE) and other temperature reconstructions for Western China, East Asia, Asia, and the Northern Hemisphere. The early NETP onset of industrial-era warming can likely be explained by NETP's faster warming rate and by local feedback factors (i.e., ice-snow cover-albedo). Comparisons between climate model simulations and our reconstructions reveal that cooler TP temperatures from 1600 to 1800 CE might be related to land-use and land-cover change.

  • 907. Yang, Haijun
    et al.
    Zhao, Yingying
    Liu, Zhengyu
    Li, Qing
    He, Feng
    Zhang, Qiong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Heat Transport Compensation in Atmosphere and Ocean over the Past 22,000 Years2015Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, artikel-id 16661Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Earth's climate has experienced dramatic changes over the past 22,000 years; however, the total meridional heat transport (MHT) of the climate system remains stable. A 22,000-year-long simulation using an ocean-atmosphere coupled model shows that the changes in atmosphere and ocean MHT are significant but tend to be out of phase in most regions, mitigating the total MHT change, which helps to maintain the stability of the Earth's overall climate. A simple conceptual model is used to understand the compensation mechanism. The simple model can reproduce qualitatively the evolution and compensation features of the MHT over the past 22,000 years. We find that the global energy conservation requires the compensation changes in the atmosphere and ocean heat transports. The degree of compensation is mainly determined by the local climate feedback between surface temperature and net radiation flux at the top of the atmosphere. This study suggests that an internal mechanism may exist in the climate system, which might have played a role in constraining the global climate change over the past 22,000 years.

  • 908.
    Yang, Heng
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. China Institute of Water Resources and Hydropower Research, China.
    Zhao, Yong
    Wang, Jian-Hua
    Xiao, Wei-Hua
    Jarsjö, Jerker
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Huang, Ya
    Liu, Yang
    Wu, Jia-Peng
    Wang, He-jia
    Urban closed lakes: Nutrient sources, assimilative capacity and pollutant reduction under different precipitation frequencies2020Ingår i: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 700, artikel-id UNSP 134531Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many natural and man-made urban lakes have been developed under urbanization. A unique feature of these lakes is the lack of an outlet; thus, they are defined as urban closed lakes (UCLs). UCLs are facing unexpected eutrophication under climate change and human activities. Our study assessed the trophic state, assimilative capacity (AC) and pollutant reduction of UCLs under different precipitation frequencies in Wuhan, China based on Carlson's Trophic State Index, assimilative capacity modelling, field investigations and observed data. The UCLs in Wuhan are nearly eutrophic in summer. Three primary nutrient sources are atmospheric deposition, pollutants carried in rainfall and nutrients released by sediments. TN and TP in the UCL water column are primarily contributed by surface runoff. The ACs of TN and TP in 2015 for Lingjiao Lake, Yue Lake, and Houxianghe Lake were 3472.07 kg, 13,800.99 kg, and 2805.58 kg, respectively, and 641.66 kg, 8386.79 kg, and 800.14 kg, respectively. The ACs of TN and TP were much higher at a 25% precipitation frequency (wet year) compared with a 50% frequency, and the lowest AC was observed at a 75% precipitation frequency (dry year). A comparison of the pollution load and AC showed that TN and TP reduction was highest in the dry and wet years, respectively. We found that specific meteorological conditions in the early stage led to the algal bloom. These results can facilitate governmental decision making in the future.

  • 909. Yu, Lin
    et al.
    Zanchi, Giuliana
    Akselsson, Cecilia
    Wallander, Håkan
    Belyazid, Salim
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Modeling the forest phosphorus nutrition in a southwestern Swedish forest site2018Ingår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 369, s. 88-100Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, a phosphorus (P) module containing the biogeochemical P cycle has been developed and integrated into the forest ecosystem model ForSAFE. The model was able to adequately reproduce the measured soil water chemistry, tree biomass (wood and foliage), and the biomass nutrient concentrations at a spruce site in southern Sweden. Both model and measurements indicated that the site showed signs of P limitation at the time of the study, but the model predicted that it may return to an N-limited state in the future if N deposition declines strongly. It is implied by the model that at present time, the plant takes up 0.50 g P m(-2) y(-1) of which 80% comes from mineralization and the remainder comes from net inputs, i.e. deposition and weathering. The sorption/desorption equilibrium of P contributed marginally to the supply of bioavailable P, but acted as a buffer, particularly during disturbances.

  • 910.
    Zandén Ljungmark, Mimi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Razna National Park: - a selection of excursion destinations2012Självständigt arbete på grundnivå (högskoleexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Different areas in Latvias youngest National Park Rāzna has been visited and analyzed. One objectivewas to find out if ecotourism is a possibility and what improvements need to be made. Latvia has avery old history of nature conservation. Objectives to protect valuable species and habitats for thefuture are influenced by factors such as economy and politics. The laws and regulations concerningenvironmental care are dependent on the processes and conditions that have contributed to formingthem. What is considered normality in Sweden can be completely different in Latvia eventhough theintentions and wished results are the same. The conclusion is that there is potential for ecotourism,although many factors must be considered and disadvantageous situations be avoided in the natureprotecting process.

  • 911. Zhang, Haicheng
    et al.
    Goll, Daniel S.
    Manzoni, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Ciais, Philippe
    Guenet, Bertrand
    Huang, Yuanyuan
    Modeling the effects of litter stoichiometry and soil mineral N availability on soil organic matter formation using CENTURY-CUE (v1.0)2018Ingår i: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 11, nr 12, s. 4779-4796Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Microbial decomposition of plant litter is a crucial process for the land carbon (C) cycle, as it directly controls the partitioning of litter C between CO2 released to the atmosphere versus the formation of new soil organic matter (SOM). Land surface models used to study the C cycle rarely considered flexibility in the decomposer C use efficiency (CUEd) defined by the fraction of decomposed litter C that is retained as SOM (as opposed to be respired). In this study, we adapted a conceptual formulation of CUEd based on assumption that litter decomposers optimally adjust their CUEd as a function of litter substrate C to nitrogen (N) stoichiometry to maximize their growth rates. This formulation was incorporated into the widely used CENTURY soil biogeochemical model and evaluated based on data from laboratory litter incubation experiments. Results indicated that the CENTURY model with new CUEd formulation was able to reproduce differences in respiration rate of litter with contrasting C: N ratios and under different levels of mineral N availability, whereas the default model with fixed CUEd could not. Using the model with flexible CUEd, we also illustrated that litter quality affected the long-term SOM formation. Litter with a small C: N ratio tended to form a larger SOM pool than litter with larger C: N ratios, as it could be more efficiently incorporated into SOM by microorganisms. This study provided a simple but effective formulation to quantify the effect of varying litter quality (N content) on SOM formation across temporal scales. Optimality theory appears to be suitable to predict complex processes of litter decomposition into soil C and to quantify how plant residues and manure can be harnessed to improve soil C sequestration for climate mitigation.

  • 912. Zhang, Peng
    et al.
    Linderholm, Hans W.
    Gunnarson, Björn E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Björklund, Jesper
    Chen, Deliang
    1200 years of warm-season temperature variability in central Scandinavia inferred from tree-ring density2016Ingår i: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 12, nr 6, s. 1297-1312Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Despite the emergence of new high-resolution temperature reconstructions around the world, only a few cover the Medieval Climate Anomaly (MCA). Here we present C-Scan, a new Scots pine tree-ring density-based reconstruction of warm-season (April-September) temperatures for central Scandinavia back to 850aEuro-CE, extending the previous reconstruction by 250aEuro-years. C-Scan is based on samples collected in a confined mountain region, adjusted for their differences in altitude and local environment, and standardised using the new RSFi algorithm to preserve low-frequency signals. In C-Scan, the warm peak of MCA occurs ca. 1000-1100aEuro-CE, and the Little Ice Age (LIA) between 1550 and 1900aEuro-CE. Moreover, during the last millennium the coldest decades are found around 1600aEuro-CE, and the warmest 10 and 30aEuro-years occur in the most recent century. By comparing C-Scan with other millennium-long temperature reconstructions from Fennoscandia, regional differences in multi-decadal temperature variability, especially during the warm period of the last millennium are revealed. Although these differences could be due to methodological reasons, they may indicate asynchronous warming patterns across Fennoscandia. Further investigation of these regional differences and the reasons and mechanisms behind them are needed.

  • 913.
    Zhang, Qiong
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Holmgren, Karin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Sundqvist, Hanna
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Decadal Rainfall Dipole Oscillation over Southern Africa Modulated by Variation of Austral Summer Land-Sea Contrast along the East Coast of Africa2015Ingår i: Journal of Atmospheric Sciences, ISSN 0022-4928, E-ISSN 1520-0469, Vol. 72, nr 5, s. 1827-1836Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A rainfall dipole mode characterized by negative correlation between subtropical southern Africa and equatorial eastern Africa is identified in instrumental observation data in the recent 100 years. The dipole mode shows a pronounced oscillation signal at a time scale of about 18 years. This study investigates the underlying dynamical mechanisms responsible for this dipole pattern. It is found that the southern African rainfall dipole index is highly correlated to the land-sea contrast along the east coast of Africa. When the land-sea thermal contrast strengthens, the easterly flow toward the continent becomes stronger. The stronger easterly flow, via its response to east coast topography and surface heating, leads to a low pressure circulation anomaly over land south of the maximum easterly flow anomalies and thus causes more rainfall in the south. On a decadal time scale, an ENSO-like SST pattern acts to modulate this land-sea contrast and the consequent rainfall dipole. During a wet in the south and dry in the north dipole, there are warm SSTs over the central Indian Ocean and cold SSTs over the western Indian Ocean. The cold SSTs over the western Indian Ocean further enhance the land-sea contrast during austral summer. Moreover, these cold western Indian Ocean SSTs also play an important role in regulating land temperature, thereby suppressing clouds and warming the land via increased shortwave radiation over the less-cloudy land. This cloud-SST coupling acts to further strengthen the land-sea contrast.

  • 914. Zhang, Quan
    et al.
    Ficklin, Darren L.
    Manzoni, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Wang, Lixin
    Way, Danielle
    Phillips, Richard P.
    Novick, Kimberly A.
    Response of ecosystem intrinsic water use efficiency and gross primary productivity to rising vapor pressure deficit2019Ingår i: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 14, nr 7, artikel-id 074023Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Elevated vapor pressure deficit (VPD) due to drought and warming is well-known to limit canopy stomatal and surface conductance, but the impacts of elevated VPD on ecosystem gross primary productivity (GPP) are less clear. The intrinsic water use efficiency (iWUE), defined as the ratio of carbon (C) assimilation to stomatal conductance, links vegetation C gain and water loss and is a key determinant of how GPP will respond to climate change. While it is well-established that rising atmospheric CO2 increases ecosystem iWUE, historic and future increases in VPD caused by climate change and drought are often neglected when considering trends in ecosystem iWUE. Here, we synthesize long-term observations of C and water fluxes from 28 North American FLUXNET sites, spanning eight vegetation types, to demonstrate that ecosystem iWUE increases consistently with rising VPD regardless of changes in soil moisture. Another way to interpret this result is that GPP decreases less than surface conductance with increasing VPD. We also project how rising VPD will impact iWUE into the future. Results vary substantially from one site to the next; in a majority of sites, future increases in VPD (RCP 8.5, highest emission scenario) are projected to increase iWUE by 5%-15% by 2050, and by 10%-35% by the end of the century. The increases in VPD owing to elevated global temperatures could be responsible for a 0.13% year(-1) increase in ecosystem iWUE in the future. Our results highlight the importance of considering VPD impacts on iWUE independently of CO2 impacts.

  • 915. Zhang, Quan
    et al.
    Katul, Gabriel G.
    Oren, Ram
    Daly, Edoardo
    Manzoni, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Yang, Dawen
    The hysteresis response of soil CO2 concentration and soil respiration to soil temperature2015Ingår i: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 120, nr 8, s. 1605-1618Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Diurnal hysteresis between soil temperature (T-s) and both CO2 concentration ([CO2]) and soil respiration rate (R-s) were reported across different field experiments. However, the causes of these hysteresis patterns remain a subject of debate, with biotic and abiotic factors both invoked as explanations. To address these issues, a CO2 gas transport model is developed by combining a layer-wise mass conservation equation for subsurface gas phase CO2, Fickian diffusion for gas transfer, and a CO2 source term that depends on soil temperature, moisture, and photosynthetic rate. Using this model, a hierarchy of numerical experiments were employed to disentangle the causes of the hysteretic [CO2]-T-s and CO2 flux T-s (i.e., F-T-s) relations. Model results show that gas transport alone can introduce both [CO2]-T-s and F-T-s hystereses and also confirm prior findings that heat flow in soils lead to [CO2] and F being out of phase with T-s, thereby providing another reason for the occurrence of both hystereses. The area (A(hys)) of the [CO2]-T-s hysteresis near the surface increases, while the A(hys) of the R-s-T-s hysteresis decreases as soils become wetter. Moreover, a time-lagged carbon input from photosynthesis deformed the [CO2]-T-s and R-s-T-s patterns, causing a change in the loop direction from counterclockwise to clockwise with decreasing time lag. An asymmetric 8-shaped pattern emerged as the transition state between the two loop directions. Tracing the pattern and direction of the hysteretic [CO2]-T-s and R-s-T-s relations can provide new ways to fingerprint the effects of photosynthesis stimulation on soil microbial activity and detect time lags between rhizospheric respiration and photosynthesis.

  • 916. Zhang, Quan
    et al.
    Phillips, Richard P.
    Manzoni, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Scott, Russell L.
    Oishi, A. Christopher
    Finzi, Adrien
    Daly, Edoardo
    Vargas, Rodrigo
    Novick, Kimberly A.
    Changes in photosynthesis and soil moisture drive the seasonal soil respiration-temperature hysteresis relationship2018Ingår i: Agricultural and Forest Meteorology, ISSN 0168-1923, E-ISSN 1873-2240, Vol. 259, s. 184-195Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In nearly all large-scale terrestrial ecosystem models, soil respiration is represented as a function of soil temperature. However, the relationship between soil respiration and soil temperature is highly variable across sites and there is often a pronounced hysteresis in the soil respiration-temperature relationship over the course of the growing season. This phenomenon indicates the importance of biophysical factors beyond just temperature in controlling soil respiration. To identify the potential mechanisms of the seasonal soil respiration-temperature hysteresis, we developed a set of numerical models to demonstrate how photosynthesis, soil moisture, and soil temperature, alone and in combination, affect the hysteresis relationship. Then, we used a variant of the model informed by observations of soil respiration, soil temperature, photosynthesis, and soil moisture from multiple mesic and semi-arid ecosystems to quantify the frequency of hysteresis and identify its potential controls. We show that the hysteresis can result from the seasonal cycle of photosynthesis (which supplies carbon to rhizosphere respiration), and soil moisture (which limits heterotrophic respiration when too low or too high). Using field observations of soil respiration, we found evidence of seasonal hysteresis in 9 out of 15 site-years across 8 diverse biomes. Specifically, clockwise hysteresis occurred when photosynthesis preceded seasonal soil temperature and counterclockwise hysteresis occurred when photosynthesis lagged soil temperature. We found that across all sites, much of the respiration-temperature lag was explained by the decoupling of photosynthesis and temperature, highlighting the importance of recently assimilated carbon to soil respiration. An analysis of observations from 129 FLUXNET sites revealed that time lags between gross primary productivity (a proxy for canopy photosynthesis) and soil temperature were common phenomena, which would tend to drive counterclockwise hysteresis at low-latitude sites and clockwise hysteresis at high-latitude sites. Collectively, our results show that incorporating photosynthesis and soil moisture in the standard exponential soil respiration-temperature model (i.e., Q(10) model) improves the explanatory power of models at local scales.

  • 917.
    Zheng, Jianqiu
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. University of Science and Technology of China, China; Nanjing University of Information Science and Technology, China.
    Zhang, Qiong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Li, Qiang
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Zhang, Qiang
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Cai, Ming
    Contribution of sea ice albedo and insulation effects to Arctic amplification in the EC-Earth Pliocene simulation2019Ingår i: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 15, nr 1, s. 291-305Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work, we simulate the Pliocene climate with the EC-Earth climate model as an equilibrium state for the current warming climate induced by rising CO2 in the atmosphere. The simulated Pliocene climate shows a strong Arctic amplification featuring pronounced warming sea surface temperature (SST) over the North Atlantic, in particular over the Greenland Sea and Baffin Bay, which is comparable to geological SST reconstructions from the Pliocene Research, Interpretation and Synoptic Mapping group (PRISM; Dowsett et al., 2016). To understand the underlying physical processes, the air-sea heat flux variation in response to Arctic sea ice change is quantitatively assessed by a climate feedback and response analysis method (CFRAM) and an approach similar to equilibrium feedback assessment. Given the fact that the maximum SST warming occurs in summer while the maximum surface air temperature warming happens during winter, our analyses show that a dominant ice albedo effect is the main reason for summer SST warming, and a 1% loss in sea ice concentration could lead to an approximate 1.8Wm(-2) increase in shortwave solar radiation into open sea surface. During the winter months, the insulation effect induces enhanced turbulent heat flux out of the sea surface due to sea ice melting in previous summer months. This leads to more heat released from the ocean to the atmosphere, thus explaining why surface air temperature warming amplification is stronger in winter than in summer.

  • 918. Zhou, Guoyi
    et al.
    Xu, Shan
    Ciais, Philippe
    Manzoni, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Fang, Jingyun
    Yu, Guirui
    Tang, Xuli
    Zhou, Ping
    Wang, Wantong
    Yan, Junhua
    Wang, Gengxu
    Ma, Keping
    Li, Shenggong
    Du, Sheng
    Han, Shijie
    Ma, Youxin
    Zhang, Deqiang
    Liu, Juxiu
    Liu, Shizhong
    Chu, Guowei
    Zhang, Qianmei
    Li, Yuelin
    Huang, Wenjuan
    Ren, Hai
    Lu, Xiankai
    Chen, Xiuzhi
    Climate and litter C/N ratio constrain soil organic carbon accumulation2019Ingår i: National Science Review, ISSN 2095-5138, Vol. 6, nr 4, s. 746-757Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Soil organic carbon (SOC) plays critical roles in stabilizing atmospheric CO2 concentration, but the mechanistic controls on the amount and distribution of SOC on global scales are not well understood. In turn, this has hampered the ability to model global C budgets and to find measures to mitigate climate change. Here, based on the data from a large field survey campaign with 2600 plots across China's forest ecosystems and a global collection of published data from forested land, we find that a low litter carbon-to-nitrogen ratio (C/N) and high wetness index (P/PET, precipitation-to-potential-evapotranspiration ratio) are the two factors that promote SOC accumulation, with only minor contributions of litter quantity and soil texture. The field survey data demonstrated that high plant diversity decreased litter C/N and thus indirectly promoted SOC accumulation by increasing the litter quality. We conclude that any changes in plant-community composition, plant-species richness and environmental factors that can reduce the litter C/N ratio, or climatic changes that increase wetness index, may promote SOC accumulation. The study provides a guideline for modeling the carbon cycle of various ecosystem scales and formulates the principle for land-based actions for mitigating the rising atmospheric CO2 concentration.

  • 919. Zhu, Dan
    et al.
    Ciais, Philippe
    Krinner, Gerhard
    Maignan, Fabienne
    Puig, Albert Jornet
    Hugelius, Gustaf
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Controls of soil organic matter on soil thermal dynamics in the northern high latitudes2019Ingår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, artikel-id 3172Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Permafrost warming and potential soil carbon (SOC) release after thawing may amplify climate change, yet model estimates of present-day and future permafrost extent vary widely, partly due to uncertainties in simulated soil temperature. Here, we derive thermal diffusivity, a key parameter in the soil thermal regime, from depth-specific measurements of monthly soil temperature at about 200 sites in the high latitude regions. We find that, among the tested soil properties including SOC, soil texture, bulk density, and soil moisture, SOC is the dominant factor controlling the variability of diffusivity among sites. Analysis of the CMIP5 model outputs reveals that the parameterization of thermal diffusivity drives the differences in simulated present-day permafrost extent among these models. The strong SOC-thermics coupling is crucial for projecting future permafrost dynamics, since the response of soil temperature and permafrost area to a rising air temperature would be impacted by potential changes in SOC.

  • 920. Ziemann, Saskia
    et al.
    Ketzer, Daniel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Karlsruhe Institut für Technologie (KIT), Germany.
    Young, Steven B.
    Weil, Marcel
    Poganietz, Witold Roger
    Increased Lifetime and Resource Efficiency in Electric Mobility – Linking Material Flow Analysis with System Dynamics2016Ingår i: 4. Symposium Rohstoffeffizienz und Rohstoffinnovationen / [ed] Ulrich Teipel, Armin Reller, Stuttgart: Fraunhofer IRB Verlag, 2016, Vol. 4Konferensbidrag (Refereegranskat)
  • 921.
    Åberg, Amanda
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Rice yields under water-saving irrigation management: A meta-analysis2017Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Water scarcity combined with an increasing world population is creating pressure to develop new methods for producing food using less water. Rice is a staple crop with a very high water demand. This study examined the success in maintaining yields under water-saving irrigation management, including alternate wetting and drying (AWD). A meta-analysis was conducted examining yields under various types of water-saving irrigation compared to control plots kept under continuous flooding. The results indicated that yields can indeed be maintained under AWD as long as the field water level during the dry cycles is not allowed to drop below -15 cm, or the soil water potential is not allowed to drop below -10 kPa. Yields can likewise be maintained using irrigation intervals of 2 days, but the variability increases. Midseason drainage was not found to affect yield, though non-flooded conditions when maintained throughout most of the crop season appeared to be detrimental to yields. Increasingly negative effects on yields were found when increasing the severity of AWD or the length of the drainage periods. Potential benefits and drawbacks of water-saving irrigation management with regards to greenhouse gas emissions, soil quality and nutrient losses were discussed to highlight the complexity of the challenges of saving water in rice production. 

  • 922.
    Åhlén, Imenne
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Connecting Hydrological Processes to the Hypersaline Conditions of the Wetland Complex of Ciénaga Grande de Santa Marta, Colombia2016Självständigt arbete på avancerad nivå (masterexamen), 30 poäng / 45 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Wetlands and coastal wetlands are important ecosystems for many aquatic and terrestrial flora and fauna as well as for the sustainable development of humans. Unfortunately, many of the world’s wetlands and coastal wetlands are subjected to degradation due to both natural processes and human activities changing the hydrodynamics of the area. As such, many coastal wetlands have been affected by hypersaline conditions consequently contributing to the degradation of both flora and fauna. This has also been true for the wetland complex of Ciénaga Grande de Santa Marta (CGSM), Colombia, where hypersalinity has been associated to constructions reducing freshwater inputs to the lagoon. As hydrological processes build up wetlands, it is crucial to understand how these processes impact wetlands and specifically the occurrence of hypersaline conditions. At the same time, not much is known about the hydrological conditions of wetlands, which is also the case for the wetland complex of CGSM. As such, this study focuses on disentangling the hydrological processes affecting the salinity levels of the wetland complex of CGSM by analysing the seasonal salinity patterns in both time (from the year of 2000 until 2015) and space. The analysis of the temporal pattern of salinity was also analysed statistically in relation to climatological data. The results from the temporal pattern of salinity showed a minor trend in increased salinity levels for the wetland in general, and by season, throughout the studied period. A rather strong correlation between salinity and climatological factors could also be identified. Moreover, the salinity for some areas within the wetland complex were higher during the wet season for some years,  compared to the dry season. The results from the spatial patterns of salinity showed that the salinity of the wetland was generally higher further away from the fresh water sources, by the outlet to the open sea, and especially for the area of Ciénaga de Ahuyama. The salinity patterns in space changed as the rain period started creating a division of the wetland complex into a high-salinity western area (main lagoon) and a low-salinity eastern area. This could be due to the relatively higher amount of fresh water inputs from rivers fed by precipitation on the mountains of Sierra Nevada de Santa Marta, east of the wetland complex,  compared to the relative small amount of freshwater from the channel of Aguas Negras in the western part of the wetland complex. Lack of correlation between salinity and channel dredging efforts questions the effectiveness of ongoing remediation strategies in the western section of the CGSM, while salinity levels in the eastern section are mainly regulated naturally via unrestricted freshwater inputs.

  • 923.
    Åhlén, Imenne
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Hambäck, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Thorslund, Josefin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Frampton, Andrew
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Destouni, Georgia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Jarsjö, Jerker
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Wetlandscape size thresholds for ecosystem service delivery: Evidence from the Norrström drainage basin, Sweden2020Ingår i: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 704, artikel-id 135452Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Wetlands are interconnected with the larger surrounding landscape through the hydrological cycling of water and waterborne substances. Therefore, the borders of individual wetlands may not be appropriate landscape system boundaries for understanding large-scale functions and ecosystem services of wetlandscapes (wetland network - landscape systems), and how these can be impacted by climate and land-use changes. Recognizing that such large-scale behaviours may not be easily predicted by simple extrapolation of individual wetland behaviours, we here investigate properties of 15 Swedish wetlandscapes in the extensive (22 650 km(2)) Norrstrom drainage basin (NDB) comprising as many as 1699 wetlands. Results based on wetland survey data in combination with GIS-based ecohydrological analyses showed that wetlands located in wetlandscapes above a certain size (in the NDB: similar to 250 km(2)) consistently formed networks with characteristics required to support key ecosystem services such as nutrient/pollutant retention and biodiversity support. This was in contrast to smaller wetlandscapes (<250 km(2)), which had smaller and less diverse wetlands with insufficient throughflow to significantly impact large-scale flows of water and nutrients/pollutants. The existence of such wetlandscape-size thresholds is consistent with scale-dependent flow accumulation patterns in catchments, suggesting likely transferability of this result also to other regions.

  • 924.
    Åhrberg, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Regionaliseringar av Afrika inom regionalgeografin: Exempel från regionalgeografiska läroböcker2017Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Early in the bachelor’s degree program in Geography, the students learn that maps should be seen as a subjective visualization of the world, rather than the actual world itself. Although this is essential forfurther analysis, especially in Geography, cartographers often commit the crime of not arguing for their choice of what is being showed; what colours are being used; what objects represents reality and why they have characterized and regionalized the areas as they have. In the studies of Regional Geography one could expect that there are discussions about this issue, since the aim of the disciplineis to split the world into smaller regions. This is especially important when it comes to studies of Africa, since it historically has been a continent that has endured regionalizations with great consequences for the understanding of its geography, from the age of colonialism to today. Therefore, this thesis examined the regionalization of Africa in textbooks used in Regional Geography, to study how Africa is regionalized today and what the motives are for these regions. The result showed that regionalizations of Africa are often made by ill-based assumptions of the continent’s geography, much like those from the colonial period. But today there is a growing focuson world religion and especially Islam, in the cartographers’ search for regions and their characteristics. Although the proportion of Christians or Muslims in different regions are true, these features often make a weak base for further geographical analysis. This is particularly troublesome when none of the books have discussions of the map as the author’s subjective view of the world. Thus, these textbooks could be used as a tool for political opinion, which should be taken into accountin the education of new geographers.

  • 925.
    Åkerström, Lisa
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    En uppdatering av årsringsvidd- och densitetskronologier vid Torneträsk till och med år 2017 och om att undvika fallgropar för divergens vid årsringsuppdatering2018Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    I arbetet har jag samlat in borrprovkärnor från 21st levande träd 218-27år gamla från en lokal nära Torneträsk, behandlat och analyserat borrprovkärnorna vad gäller ringvidd (TRW), eng. tree ring width, och densitet (MXD), eng. maximum density, samt studerat hur väl resulterande kronologier följer sommarmedeltemperaturerna från Abisko väderstation. I arbetet ges kort bakgrundsfakta om det valda geografiska områdets, Torneträsk, roll och betydelse i det aktuella forskningsområdet, dendroklimatologi, och beskrivningar av några för uppgiften viktiga aspekter och metoder och problematiken med fenomenet divergence phenomena (DP). Datat är förberett för att användas som en förlängning till den existerande kronologin. Dendrokronologin vid Torneträsk innehåller innan detta; TRW som sträcker sig över 7 400år (år 5704 f.kr. – år 2004) och MXD som sträcker sig över 1 563år (åren 441 – 2004). Vid insamlandet har unga träd inkluderats i proverna för att undvika DP vid skapandet av kronologin.

  • 926.
    Ösgård, Anton
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Vad är en Sjöstadsbo?: Platsidentitetens framväxt i ett nybyggt bostadsområde2017Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This paper examines some processes behind the creation of place identity and place attachment using a broad theoretical framework. The framework is structured around the creation of space and place, followed by theories and models on how places are given identity and finally some possible effects of place identity. These theories are then used to examine place identity formation among residents and real estate agents in Hammarby Sjöstad, a newly developed urban residential area in Stockholm, Sweden.

    A total of 5 in depth interviews were carried out with local residents in different parts of the residential area, as well as 3 in depth interviews with real estate agents active in different parts of the area. The interviews were transcribed and analysed in relation to the theoretical framework as well as documents relating to the planning of the area.

    The study shows that there has formed a local identity in Hammarby Sjöstad, not defined by the administrative borders of the area. The perceived extent of the area most probably stem from that the lake Hammarby Sjö acts as a physical barrier between the area and the rest of the inner city. This might be the reason to the evolution of a defined perceived community there. The effects of this could be a contributing factor in the segregation that is evident in urban areas, which calls for attention to the possible effects of place identity in urban planning. 

  • 927.
    Øvereng, Aurora
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    A Sustainable Future for Wind Energy in Sweden2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The 2040 governmental goal of 100 % renewable electricity in Sweden means that there will be a shift in electricity production and a phasing out of nuclear power. This nuclear power has to be replaced by some other source. Wind power is a viable alternative, thanks to its reliability and the abundance of wind in Sweden. However, wind power production requires a large amount of land and carries the risk of disrupting the landscape. Wind energy is therefore often difficult to develop, and when developed it is often in rural areas where it disturbs as few people as possible. This study presents an alternative to rural exploitation, it investigates whether it is possible to produce sufficient wind power to satisfy urban demand within 20 000 meters of the 20 largest cities in Sweden.

    Firstly, the criteria for areas where wind power can be developed were synthesised. Secondly a numerical model was used to simulate energy demand in TWh considering the future growth in demand and the phasing out of nuclear power. The demand for wind power was then translated into correlating area in km2. Finally, a GIS analysis was conducted to estimate the extent of area suitable for wind power development based on the criteria above and within a 20 000m perimeter from the 20 largest cities in Sweden. The analysis showed that only 35 % of the required area for wind power development fulfilled the criteria within the given perimeter. From the GIS analysis only 940.73 km2 was found to be suitable. From the numerical model, the results showed that for it to be sufficient, there would have to be at least 2687.1 km2 suitable land. The conclusion from this study is that in order to phase out the nuclear power, the majority of the wind power has to be located in the rural areas.

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