Browsing by master's degree program "Nordic Master Programme in Environmental Changes at Higher Latitudes"

Atmospheric aerosols are solid or liquid phase particles which are suspended in ambient air. These particles have an impact on the climate through direct and indirect radiative forcing, and their measurement presents challenges in high latitude environments where concentrations may fall under the detection limit of the responsible instruments. In order to both qualify and quantify the contribution of aerosol particles to environmental change at higher latitudes, it is important to understand their microphysical and optical properties, which control their interaction with visible wavelength radiation. This thesis focuses on the characterisation of the aforementioned aerosol properties in a High Arctic environment, Villum Research Station (Northeast Greenland), during two six-month observation periods in 2020 and 2021. The parameters presented in the analysis are particle total number concentration and size distribution in the 0.3 - 10 μm size range, particle scattering coefficients σsp, particle absorption coefficients σap, and Ångström exponents describing the wavelength dependence of both optical coefficients. The seasonal variability and distribution of these properties was analysed, and case studies of exceptional particle number concentration identified as particle transport events to evaluate the contribution of local and long-distance source regions to the overall aerosol population at the station. The results of the analysis show that there is a notable seasonality to both number concentration and optical characteristics of aerosol particles at Villum Research Station, with median values for these parameters at their highest in the winter, followed by the autumn and then the summer. The dominant species during episodes of exceptional particle number concentrations were found to be dust, Elemental Carbon/Organic Carbon (EC/OC) and mixed aerosols, with source regions across continental Greenland, the Canadian Archipelago and Arctic Ocean.

Biological soil crust, biocrust, is a significant contributor to biogeochemical cycles through nitrogen and carbon cycling. Further, it stabilizes soil, facilitates water infiltration, and mitigates soil erosion. The global biocrust cover is believed to decrease by about 25-40% in the next 60 years due to climate change and intensification in land use. Research on biocrust in arctic and subarctic regions is limited, much of the knowledge comes from lower latitudes in arid and semiarid ecosystems. Cold-adapted biocrust might respond differently to increasing temperatures when compared with warm-adapted biocrust. Therefore, it is fundamental to research biocrust in arctic and subarctic regions when looking at how fast the climate is changing in the Northern hemisphere. Temporal variations of soil respiration in subarctic biocrust have not been studied systematically before. This research project focuses on the effects of warming on soil respiration in biocrust, on a diurnal and a seasonal scale. It also focuses on species composition changes of vascular plants in the warming experiment where warming was induced with open-top chambers (OTCs). Soil respiration, temperature, soil water content, as well as plant species composition changes were measured during three field trips that each lasted four days during the growing season of 2021. The results show that soil respiration was lower in September when compared with measurements done in June and July. The highest values of soil respiration were observed during mid-day and the lowest during evenings and nights. The temperatures of OTC plots were, on average, 1.16 °C higher than control plots, and OTC plots had significantly lower soil water content than control plots. During this research, the soil respiration increased with higher temperature but was not different between control and OTC plots during any time of day or month measured. Soil water content did not affect soil respiration significantly, while temperature did. These findings might be explained by less soil water content within warmer plots, but warmth and moisture have been shown to increase soil respiration. In other words, less soil water content might countereffect the increase of soil respiration due to warming. Some vascular plant species were more likely to be found within or outside the warming plots. Dwarf willow, Salix herbacea, decreased in cover within OTC plots. Previous research has shown that warming significantly reduces pollen shed and time of pollen shedding for S. herbacea, which might decrease its abundance within OTC plots. Alpine bistort, Bistorta vivipara, increased in cover within OTC plots compared to control plots. Warming experiments on B. vivipara have shown positive effects on reproductive parameters, which might increase its abundance within warmed OTC plots. Sheep also prefer grazing on B. vivipara. Therefore, it might have less cover in control plots, given that OTCs exclude grazing and that many sheep roam the studied site during the growing season. Vascular plant cover was greater within control plots when compared with warmed plots. Previous results at the same site after one year of warming, from summer 2019, showed more vascular plant cover within the OTC plots when compared with control plots. The results of this research might indicate that vascular plants are gradually affected by the warming and are transitioning towards a new equilibrium. The results of this research are ground for further studies on subarctic ecosystems dominated by biocrust. Many biotic and abiotic factors affect carbon cycles. For future modelling of predicted effects of climate change, having better knowledge on how subarctic ecosystems respond to warming is essential for a better understanding of the functions and feedbacks in a global context.

The Baltic Sea is undergoing changes due to climate change, including an increase in its temperature. This may in turn lead to changes in the traits of the species that inhabit it, including non-endemic, invasive species. Palaemon elegans is a species native to the Atlantic Ocean that has been present in the Baltic Sea since the beginning of this century. Abilities such as high thermal tolerance make it successful in colonising new ecosystems like the brackish waters of this sea. However, less is known about the behavioural traits’ adaptions to these changes. This study aims then to find out how climate change may affect the behaviour of this species. To do so, five behaviours expressed by this species were observed and analysed to see how temperature change, seabed composition and body size influence their expression. The behaviours analysed were aggressiveness, movement frequency, reaction to food stimulus, number of feeding interactions and shelter-seeking. Analyses were conducted using ten-minute videos with ten specimens of P. elegans placed in water tanks and interacting in ecosystems representations with elements typical of the seabed where this species lives, both vegetation and rocks. Student's t-tests in R were then performed to test the significance of possible differences between the behaviours studied and the three parameters that may influence their expression. The results obtained show that the increase in water temperature might indeed lead to an increase in the frequency of the five behaviours studied except in aggressiveness. On the other hand, it was found that the composition of the ecosystem does not have a significant influence overall, while body size has a major influence on feeding related behaviours. Therefore,knowing more about changes in the behavior of species susceptible to climate change can be helpful to understand how biodiversity and its distribution will vary in the not so distant and changing future and what consequences it may generate at the ecosystem level.

This thesis investigates the impact of the energy crisis on air quality in the Po Valley, Italy, with a focus on the effect of changes in methane consumption over the potential changes in wood burning consumption. The study employs the WRF-CHIMERE model to simulate the consequences of varying wood burning consumption on air quality. Observational data of benzo[a]pyrene and PM2.5 concentrations in the Po Valley are also analyzed. The results indicate that meteorological conditions have a significant influence on air quality, overshadowing the potential effects of emission changes resulting from the energy crisis. However, we observed a model’s bias correlated to the planetary boundary layer height, which could have influenced this result. Further investigation is necessary to correct this bias and comprehensively understand the relationship between energy consumption, air quality, and meteorology in the Po Valley.

Boreal peatlands are major constituents of the global carbon (C) and water cycles and therefore important climate regulators. These cycle dynamics are strongly determined by plant phenology (e.g., vascular plant photosynthesis and seasonality) and evapotranspiration (ET), next to other abiotic factors. While it is evident that climate change affects these networks of interactions, it is only poorly understood to what extent, as site-specific empirical evidence over multiple decades is lacking. This study investigates the role of phenology (leaf area index: LAI) for peatland C (net ecosystem exchange: NEE) and water fluxes (ET and water table: WT) by combining inter-annual and seasonal observations at the ecosystem level, in Siikaneva fen, Finland (2005-2007, 2014-2022). Interactions with temperature (T), vapor pressure deficit (VPD), photosynthetically active radiation (PAR) and rain were included and tested with various statistical methods (trend- and correlation-analysis, commonality analysis, time lag testing, stepwise multiple-regression, and structural equation modelling). Significant trends were found for LAI (increasing) and WT (decreasing), suggesting ongoing changes in the ecosystem (climate change signal). Within this system LAI provided substantial effects on NEE, less so on ET. These relationships differed seasonally: the greenup season showed the strongest effects of LAI on NEE and ET (and other interactions). However, e.g., PAR and VPD became more relevant for NEE and ET in the later seasons. A time lag analysis suggested that effects (e.g., LAI on NEE) can be delayed at the scale of weeks. Inconclusive evidence was found for the LAI effect on ET and WT (via ET). It is assumed that ET is a limited measure to differentiate between evaporation (E) and transpiration (T) by leaves or the ground, as they might cancel each other out. A shading of increasing LAI over the season might shade moss-ET (and photosynthesis). The applied methods provided complementary information with differing suitability to reveal certain parts of complex network dynamics. A consistent, while seasonally changing, importance of plant phenology for peatland NEE can be concluded. Phenology showed clear correlation with ET, however, the effect size could not be quantified conclusively. Future studies should partition E and T or incorporate the contribution of mosses to both ET and NEE for a more comprehensive understanding. Collectively, this study highlights the role of phenology for peatland C and water fluxes and provides evidence for climate change induced alterations of biotic-abiotic interactions at the ecosystem scale.

The behaviour of Greenland's tidewater glaciers is crucial for the understanding of the Greenland Ice Sheet. The retreat of those marine-terminating glaciers has far-reaching implications, impacting not only the regional hydrography but also the diverse fjord ecosystems. Here, this study investigated the rapid retreat of Narsap Sermia (NS), a tidewater glacier located in Southwest Greenland. Between 1987 and 2022, the volume of ice discharged from NS increased by 45%, a rate more than double the Greenlandic mean. This destabilization led to retreat events occurring in three distinct episodes: 2004-2005, 2010-2012, and 2019-2021. The study identified that changes in subglacial hydrology were pivotal in triggering and sustaining these retreats. Drainage of ice-dammed lakes or increased meltwater resulting from heatwaves over the ice sheet suddenly increased subglacial freshwater discharge, subsequently instigating these retreat events. Once initiated, exposure to elevated ocean temperatures or retreat into a glacial trough further sustained ice loss at the terminus, eventually resulting in a collapse of the glacial front. As of the summer of 2023, Narsap Sermia is still retreating, and the study anticipates that further retreat of approximately 3 kilometers is inevitable. Subsequently, should air and ocean temperatures continue to rise, Narsap Sermia is poised to retreat further for 30 km, dramatically transitioning into a land-terminating glacier. This drastic transformation could occur in as little as 30 years, with profound consequences for local eco-hydrology and nearby communities.