Browsing by Subject "Physical Geography"

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  • Farstad, Miia (Helsingin yliopisto, 2021)
    Due to the harsh conditions in high latitude alpine and arctic regions, climate or land use changes make them very vulnerable. Thus, it is vital to study the habitats of these regions and increase our understanding of what factors impact species distributions. Species distribution modelling can be used to predict possible habitats for species and further inspect the relationships between different environmental variables and species. Generally, these species distribution models have been created using variables describing the topographical and climatic conditions of the study area. Recently there has been more evidence supporting the inclusion of biotic variables to species distribution models at all scales. Including biotic variables can be difficult, as these relationships can be challenging to quantify. This study uses the Normalized Difference Vegetation Index (NDVI) as a surrogate for plant biomass, thus representing biotic interactions. This study aims to answer what are the relationships between environmental variables and the predicted distributions and will including a biotic variable improve the species distribution models. The study data includes observational data from 683 arctic and alpine plant species from Norway, Sweden, and Finland. The observation data were collected from the three national databanks of Norway, Sweden and Finland and completed with observations from the Global Biodiversity Information Facility and observation data collected by the BioGeoClimate Modelling Lab. The cohesive study area was outlined with the biogeographical regions defined by the European Environment Agency. Overall, six environmental variables are used in this study: annual mean temperature, the maximum temperature of the warmest month, annual precipitation, elevation difference in a cell, bedrock class, and NDVI. The NDVI data was gathered by NASA’s MODIS sensors. The observations and the environmental variables were projected into a grid consisting of 1 x 1 km cells covering the whole study area. This study uses the ensemble modelling technique with four individual modelling methods: generalized linear models (GLM), generalized additive models (GAM), generalized boosted models (GBM) and random forests (RF). The modelling process consisted of two modelling rounds so that the impact of NDVI could be evaluated. The first modelling round included all the environmental variables except NDVI (the topoclimate model) and the second modelling round included all the environmental variables (the full model). The two temperature variables, annual mean temperature and the maximum temperature of the warmest month, had the highest mean variable importance values. With the topoclimate model, annual precipitation ranked third with the rest of the climate variables, but when NDVI was added to the models, it rose above annual precipitation. Overall, among the studied arctic and alpine species, the variable importance values of both the edaphic and topographical variables were low. In general, both the topoclimate models and full models performed very well. The mean AUC- and TSS-values were all higher for the full models, indicating that including a biotic variable improved the models. When the binary predictions of both modelling rounds were compared, it was clear that NDVI refined the projected distributions for most species. The results from this study confirm the discovery that including a biotic variable, such as NDVI, has the potential to increase the predictive power of species distribution models. One of the main problems with including biotic variables in species distribution models has been the difficulty of quantifying biotic interactions. NDVI can thus be a promising tool to overcome these difficulties, as it is one of the most direct variables to describe ecosystem productivity, can be acquired at various scales, and as remotely sensed data, it can also cover areas that are difficult to access.
  • Heikkinen, Janne (Helsingin yliopisto, 2020)
    Subarctic ponds are important habitats for many freshwater species. The recent increase in global temperatures have stressed on the study of these habitats as rising water temperatures may have severe consequences to these cold and harsh ecosystems. Despite its importance, this topic has been largely overlooked in scientific research. Diatoms are microscopic, single-celled benthic algae, which are important indicators for environmental quality. Elevation is one of the main environmental variables controlling the composition and richness of diatom species as it shapes communities through several environmental variables such as temperature and water chemistry. The aim of this thesis was to illustrate the variability in diatom species richness and community composition along an elevational gradient in Kilpisjärvi and reveal the most important environmental drivers. As an additional focus, the applicability of the BenthoTorch sampling device was tested in measuring benthic algae biomass. Field and laboratory measurements were done using universal standards. Statistical analyses included multiple univariate and multivariate data analysis techniques. It was found that water pH, aluminium concentration and air temperature explained the variation in species richness and community composition the most. Elevation had only a secondary, non-significant role in shaping the diatom communities in subarctic ponds. Nearby sites showed similar compositions in terms of water chemistry and diatom communities. Biotope characterisation did not provide any further insight into the differences or similarities of diatom community composition or species richness. There were some differences in how genera responded to environmental variables. The centre of distributional range of many taxa was below the mid-point of the elevational gradient but species often occupied the whole elevational gradient. Rare taxa appeared at the ends of the elevational spectrum. The amount of singleton taxa was high (25.8%) and can be expected to increase with climate change. The BenthoTorch did provide reasonable results for benthic algae in the subarctic when compared to previous literature, but further research is required to grasp its full potential. More examination into the relationship between explanatory variables can be suggested (e.g. total phosphorus and ion balance) to gain better understanding on the changes in diatom species richness and community composition along elevational gradients.
  • Jokinen, Ari-Pekka (Helsingin yliopisto, 2021)
    Glaciers and ice caps (GICs) excluding Greenland and Antarctic ice sheets account for large proportion of potential future sea level rise and are losing great amount of their mass in high confidence by 2100. Glacier elevation change observations covering whole Greenland’s GICs are limited to the 21st century and regional geodetic mass balance estimates are scarce. Recent development of photogrammetric software and rediscovery of old aerial photographs has been increasingly used to extend temporal resolution of glacier change studies. Besides for extended mass balance observations, historical photographs may be used in observing glacier surge events to improve their coverage in glacier inventories. In this study, 320 historical aerial photographs from 1953/1954 were photogrammetrically processed to create new digital elevation model (DEM) of the 1953 surface. Comparing the 1953 DEM with 1985 and 2016 DEMs extended the geodetic mass balance records on Nuussuaq peninsula to 63 years. Moreover, differenced DEMs were used with orthophotomosaics to identify glacier surface changes and advances and their possible relation to glacier surges. The study also explored the usage of Open Global Glacier Model (OGGM) with user defined input data for simulating future glacier changes in small scale regional setting. The geodetic mass balance results showed clear change from near equilibrium mass balance in 1953-1985 to overall mass loss in 1985-2016. Glacier surface lowering was found to shift to higher elevations along with the change to negative mass balance and occurred throughout the elevation range in 1985-2016. In contrast to generally retreating glaciers, advancing and/or surface elevation increases at the glacier fronts with glaciomorphological evidence of surging were observed on 5 glaciers. OGGM model is easily applicable for smaller regions but correcting the OGGM calibration with a fit to the geodetic mass balance data didn’t provide explicit result of the re-calibration efficiency. Historical photographs provide source to extend geodetic mass balance estimates and means to observe past glacier changes in more detail. Therefore, their incorporation in glacier change studies should be continued and create consistent datasets over larger regions. More research is needed with additional reference data to assess the reliability of the OGGM performance on a region without the reference data from default reference glacier network and the effect of re-calibrating with geodetic fit.
  • Kärppä, Mai (Helsingin yliopisto, 2020)
    Arctic peatlands are globally extensive and long-lasting storages of carbon and are therefore important ecosystems controlling global carbon cycling. Changes in climate affect peatlands’ ability to accumulate carbon through changes in hydrology and water table level, vegetation, soil temperature and permafrost thaw. As climate warming is projected mostly to northern and arctic regions, it may change the peatlands’ capacity to sequester and release carbon as carbon dioxide and methane. In this Master’s Thesis I studied how the past climate changes are reflected in carbon accumulation rates over the past millennia. Known climate anomalies, such as the Medieval Climate Anomaly, Little Ice Age and the last rapid warming starting from 1980, and their impact on average long-term apparent rate of carbon accumulation were studied from the peat proxies. 15 peat cores were collected from northern subarctic Swedish Lapland and from North-East European Russia. Cores were collected from the active peat layer above permafrost that is known to be sensitive to climate warming. Cores were dated with radiocarbon (14C) and lead (210Pb) methods and peat properties and accumulation patterns were calculated for one centimeter thick subsamples based on chronologies. The Little Ice Age and the last rapid warming affected the carbon accumulation rate considerably whereas for Medieval Climate Anomaly period the peat records did not show very distinctive response. During the Little Ice Age the carbon accumulation rates were low (median 10,5 g m-2v-1) but during the post-Little Ice Age and especially during the last warm decades after 1980 carbon accumulation rates have been high (median 48,5 g m-2v-1). Medieval Climate Anomaly had only a minor positive effect on accumulation rates. On average, the long-term apparent rate of carbon accumulation during the past millennia was 43,3 g m-2v-1 which is distinctly higher than the previously studied rate of 22,9 g m-2v-1 for northern peatlands (p-value 0,0003). Based on results it can be concluded that warm climate periods accelerated the carbon accumulation rate whereas during cold periods accumulation decelerated. Warm climate prolongs the growth period and accelerates the decomposition of peat; cold climate shortens the period of plant growth and thickens the permafrost layer in peatlands, respectively. However, peat layers that are formed after the Little Ice Age are incompletely decomposed which amplifies the carbon accumulation rate partly. Nevertheless, permafrost thawing has been shown to increase accumulation rates, as well. Studying past carbon accumulation rates helps to understand the peatland and carbon cycling dynamics better. Even though accumulation rates reveal a lot about carbon sequestration capabilities of peat, it does not indicate whether a peatland has been a carbon sink or a source.
  • Hanhirova, Elisa (Helsingin yliopisto, 2021)
    Large amounts of carbon is stored in the soil and vegetation of the tundra ecosystem. Carbon dioxide is stored in the vegetation in photosynthesis and is released into atmosphere from the soil and vegetation in ecosystem respiration. Rising temperatures can cause considerable changes to the delicate tundra ecosystem and create new potential feedbacks to global warming as the environment changes. There are several factors regulating carbon dioxide fluxes and their interactions and temporal changes are not yet fully known. Understanding carbon dioxide fluxes and the factors contributing to them is important in order to study and predict temporal and local changes. This research focuses on describing changes in net ecosystem exchange, primary production, and ecosystem respiration in the tundra as well as the factors contributing to them. The measurements were made with the chamber method in Saana fell, Kilpisjärvi in Finnish Lapland. This study includes 14 nivations with a total of 84 study points that were measured three times during the growing season in the summer of 2019. In addition to flux the measurements, information about controlling environmental variables were collected. These included vegetation, air temperature, soil moisture and soil temperature. The impact of the explanatory variables on fluxes at different times in the growing season was studied using mixed effects model and an estimated carbon budget was calculated for the region. The largest fluxes were measured mid-July during the peak growing season. Ecosystem respiration and primary production declined from the peak of the growing season in August towards the end of the growing season, but net ecosystem exchange increased slightly due to imbalances in the other two fluxes. Vegetation was an important explanatory variable (p ≤ 0,001) in every flux and during different times of the growing season. Air temperature had the greatest impact on net ecosystem exchange and ecosystem respiration, but the intensity of its response varied during different periods of the growing season. In both of these fluxes, higher temperatures increased the flux into the atmosphere. In primary production, the response changed in the middle of the growing season from positive to negative due to high temperatures. Soil moisture had a positive effect especially on ecosystem respiration, but its significance varied during the growing season (p = 0,0012; 0,02; < 0,001) and the response increased towards the end of the growing season. Also in primary production, response intensity and significance (p = 0,02) increased at the end of the growing season and in net ecosystem exchange the response changed from negative to positive at the end of the growing season. The response of soil temperature increased with all fluxes from the beginning of the growing season and decreased with ecosystem respiration and net ecosystem exchange towards the end of the growing season. Soil temperature was only significant in the second measurement campaign for net ecosystem exchange (p = 0,01) and ecosystem respiration (p = 0,005). During the growing season, carbon dioxide fluxes changed considerably and their explanatory factors also varied in time. The responses to soil moisture and air temperatures also turned negative or positive during the growing season. These changes and studying them is very important to understanding the processes behind different fluxes. The change in carbon dioxide fluxes and the variables that affect them in the tundra environment affects the region's carbon budget.
  • Lilja, Jiri (Helsingin yliopisto, 2021)
    Korkeuden vaikutusta eliöiden esiintymiseen on tutkittu eri alueilla jo 1800-luvulta lähtien, mutta vasta viimeisten vuosikymmenien aikana korkeuden vaikutuksen on tunnistettu olevan monimutkainen. Eri eliöryhmien lajirunsaushuiput saavutetaan korkeusgradientin eri vyöhykkeissä eri alueilla. Lintuihin korkeuden ja lajirunsauden välille on tunnistettu neljä toisistaan poikkeavaa trendiä. Korkeuden vaikutusta on tutkittu pääosin lauhkeilla ja trooppisilla alueilla, kun taas korkeiden leveyspiirien alueilta on tutkimusta vähän. Korkeuden lisäksi elinympäristöjen on todettu vaikuttavan merkittävällä tavalla lintujen esiintymiseen, mutta elinympäristöjen vaikutusta on tutkittu lähinnä metsissä, maatalousympäristöissä ja kaupungeissa. Ilmastonmuutos vaikuttaa pohjoisten alueiden elinympäristöihin erityisen voimakkaasti, mikä tekee näistä alueista tärkeitä tutkimuskohteita. Tämän tutkielman tarkoituksena on selvittää, miten korkeus ja elinympäristöt vaikuttavat lintujen esiintymiseen ja runsauteen tunturiympäristössä. Korkeuden ja elinympäristöjen vaikutusta tutkittiin tuottamalla alueellisia malleja kahdella eri mallinnusmenetelmällä (GLM ja GAM) lintuaineiston, korkeuden ja elinympäristöjen välille. Lintuaineisto kerättiin kesän 2019 aikana pistelaskennalla 420 tutkimuspisteeltä Pohjois-Norjassa Rásttigáisá-tunturin ympäristössä noin 180 km² kokoiselta alueelta. Lintuaineiston lajit luokiteltiin taksonomian mukaan lintulahkoihin varpuslintuihin, rantalintuihin, kanalintuihin ja päiväpetolintuihin. Tutkimuspisteet luokiteltiin viiteen eri elinympäristöluokkaan (metsä, metsänraja, kuiva avotunturi, kostea avotunturi, karukko) NDVI-aineiston ja ilmakuvien perusteella. Lintulajeille laskettiin Shannonin habitaatti diversiteetti-indeksi (SHDI), jonka avulla tutkittiin lajien esiintymistä eri elinympäristöissä. Sekä korkeus että elinympäristöt selittävät lintujen esiintymistä tunturiympäristössä. Korkeuden ja elinympäristöjen välillä havaittiin merkittävä suhde ja elinympäristöt sijoittuvat verrattain selvästi korkeusgradientille. Korkeuden ja lajirunsauden suhteen todettiin olevan huipukas, korkeimmat lajirunsaudet havaittiin 300–500 metrissä metsänrajalla ja sen yläpuolella. Korkeus selitti 30,3 % kokonaislajirunsauden, 30,8 % varpuslintujen ja 28,0 % rantalintujen lajirunsauden vaihtelusta (GAM). Elinympäristöluokat selittivät korkeutta paremmin etenkin esiintymisen muutoksia 50 metrin skaalalla. SHDI-arvon mukaan elinympäristöön erikoistuneimmat linnut ovat kosteiden avotuntureiden rantalintuja, kun taas varpuslinnuissa esiintyy enemmän generalistilajeja. Elinympäristöluokat selittivät tarkan skaalan lisäksi erityisen hyvin elinympäristöön erikoistuneiden rantalintujen lajirunsautta (35,5 %). Tulevat muutokset ilmastossa uhkaavat etenkin avotunturissa esiintyviä lajeja, joista monet esiintyvät vain tietyssä elinympäristössä. Korkeuden ja elinympäristöjen vaikutusten syvempään ja tarkempaan ymmärtämiseen tarvitaan lisää tutkimusta. Jatkotutkimusta tarvitaan useammalta korkeusgradientilta ja tarkemmalla elinympäristöluokituksella.
  • Takala, Tuure (Helsingin yliopisto, 2021)
    Urban stormwater systems effectively connect harmful substances from urban areas to more natural waters. The goal of this study was to determine whether stormwater sumps served as purifying elements of urban waters or whether urban stormwater and its harmful substance load passes through the system into nature. In addition, the study examined if significant quantities of harmful heavy metals are deposited in the stormwater sump sediment traps, and if the intensity of land use affects the quality of sediment in these traps. The study analyzed sediment samples from 30 stormwater sump traps in Helsinki, Finland. The stormwater sumps were selected from areas representing different land use intensities. For each sump, a catchment area and the magnitude of built area were determined by using geoinformatic data. From the sediment samples taken from the stormwater sump traps, metal concentrations (Al, P, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Pb and U), susceptibility, organic matter as well as dry matter and grain size distribution were analyzed. The study looked at the statistical significance of correlations between different variables. All measured variables were also studied by primary component analysis. The differences in metal concentrations of land use classes were assessed by one-way variance analysis. The harmfulness of the sediments in the stormwater sump traps was assessed based on the regulations of the Ministry of the Environment’s degraded soil and sediment slapping guidelines. The results show that stormwater sump traps had harmful concentrations of heavy metals. Concentrations of nickel, copper, and zinc harmful to water nature were found in the sediment samples. In addition, concentrations of zinc and copper exceeding the soil pollution limits were found. Metal concentrations in sediments were generally highest in the stormwater sump traps in traffic areas. Statistically highly significant correlations were observed with the increase in land use intensity and the concentrations of heavy metals. As land use intensity increased, concentrations of metals referring to human activity increased in stormwater sump traps. However, the metal concentrations in the sediments of the stormwater sump traps were not higher than the metal concentrations in stream sediments studied in the Helsinki region. The minor amount of fine sediment present in the stormwater sump traps also suggests that the particles that move with stormwater do not sediment into the sump traps in large quantities. This study indicates that stormwater sumps in the Helsinki region could have significant amounts of harmful metals. Based on the results of this study, when draining stormwater sumps, sediment treatment should be considered prior to its possible deployment into the watershed or reuse as filling soil or mull. In particular, reusing untreated sediments from stormwater sumps in traffic areas can be detrimental to nature. The fine material sedimentation capacity of stormwater sumps should be improved to minimize the load of harmful substances passing through the stormwater system into nature. More research is needed on the sedimentation processes of stormwater sumps suitable for Finnish conditions.
  • Kukkonen, Tommi (Helsingin yliopisto, 2020)
    The Arctic is warming with an increased pace, and it can affect ecosystems, infrastructure and communities. By studying periglacial landforms and processes, and using improved methods, more knowledge on these changing environmental conditions and their impacts can be obtained. The aim of this thesis is to map studied landforms and predict their probability of occurrence in the circumpolar region utilizing different modelling methods. Periglacial environments occur in high latitudes and other cold regions. These environments host permafrost, which is frozen ground and responds effectively to climate warming, and underlays areas that host many landform types. Therefore, landform monitoring and modelling in permafrost regions under changing climate can provide information about the ongoing changes in the Arctic and landform distributions. Here four landform/process types were mapped and studied: patterned ground, pingos, thermokarst activity and solifluction. The study consisted of 10 study areas across the circumpolar Arctic that were mapped for their landforms. The study utilized GLM, GAM and GBM analyses in determining landform occurrences in the Arctic based on environmental variables. Model calibration utilized logit link function, and evaluation explained the deviance value. Data was sampled to evaluation and calibration sets to assess prediction abilities. The predictive accuracy of the models was assessed using ROC/AUC values. Thermokarst activity proved to be most abundant in studied areas, whereas solifluction activity was most scarce. Pingos were discovered evenly throughout studied areas, and patterned ground activity was absent in some areas but rich in others. Climate variables and mean annual ground temperature had the biggest influence in explaining landform occurrence throughout the circumpolar region. GBM proved to be the most accurate and had the best predictive performance. The results show that mapping and modelling in mesoscale is possible, and in the future, similar studies could be utilized in monitoring efforts regarding global change and in studying environmental and periglacial landform/process interactions.
  • Määttä, Tiia (Helsingin yliopisto, 2020)
    Methane (CH4) is a greenhouse gas with a great impact on global climate. In the soil, it is produced in anoxic and consumed in oxic conditions by microbes. Together with different methane transport mechanisms, methane production and consumption directly regulate the resulting soil methane flux. Boreal upland forests are generally considered to act as methane sinks due to high methane consumption. However, some studies have shown a boreal upland forest soil turning from a methane sink to a source after long-term abundant precipitation. This study aimed to examine the effects of soil moisture on CH4 flux from simulated increase in rainfall in a northern boreal upland forest soil, and how simultaneous soil temperature increase, organic litter addition and organic litter and root exclusion affect the temporal changes in flux. The study was conducted in Kenttärova forest in Kittilä, Finland in summer 2018. Split-plot design was used in the experiment with soil moisture being the main treatment variable and soil warming (T), organic litter addition (A) and organic litter and root exclusion (E) subtreatment variables. The design included two main plots: irrigation (I) and control (C), within which each subtreatment was replicated three times. In addition to the T, A and E manipulations, plots without additional manipulations (O) were included for the assessment of the effect of only soil moisture increase, and were replicated four times within both main plots. Methane flux was measured at least once a week using chamber method. Soil moisture and temperature were also continuously measured. The treatment effects were analysed using both autoregressive heterogeneous and autoregressive two-way analyses of variance, TukeyHSD method, variable correlations and Generalized Linear Models. The soil did not turn into a methane source but the results showed significant differences between the irrigation and control site, indicating a strong decreasing effect of soil moisture on soil CH4 sink in all treatment levels. All treatments had lowest uptake rates in August, possibly as a result from highest soil moisture levels. IA treatment was the most effective in producing low uptake rates possibly due to the reduction in gas diffusion. E treatments had contrasting results, IE showing increases in uptake rate by increases in soil moisture but the causes remained unsolved and the results were highly uncertain. T treatment had no effect on uptake likely due to a failure to create soil temperature differences and thus the interactions were not reliably analysed. The results suggest that the changes may have been more related to changes in methane consumption than production. Further research is needed especially for examining the combined effect of litter addition, soil moisture and soil temperature increase on methane flux with multiple temporal replications of the experiment.
  • Saari, Petra (Helsingin yliopisto, 2021)
    Eutrophication and climate change are considered to be the worst threats to the Baltic Sea ecosystem. The goal of this work is to understand, what are the consequences of environmental change to the distribution of Fucus spp., one of the key species of the Baltic Sea. Of particular interest here is to find the role of light and water turbidity in defining Fucus spp. distribution since scenario models of the effect of water turbidity defining the distribution has yet remained less studied. Nemo-SCOBI model of physical and biogeochemical conditions of the Baltic Sea calibrated according to different eutrophication and climate change scenarios were used in species distribution modelling (SDM) to predict future distribution of Fucus spp. The SDM method that was used was a regression-tree-based machine-learning generalized boosting method (GBM). In the modelling over 30 000 species presence and absence observations and six environmental variables (temperature, salinity, light attenuation, depth attenuated wave exposition and two seafloor types) were used. Water turbidity decreased in all scenarios in the areas where Fucus spp. occur but the BSAP was more beneficial scenario than the worst case scenario. Salinity decreased more and temperature increased less in the RCP8.5 scenario than in the RCP4.5 scenario. On top of that temperature decreased in the west coast of Finland in the RCP8.5 scenario. Suitable area for Fucus spp. declined in all scenarios so that the average occurrence probability decreased 11–30 percentage points. If no climate and eutrophication objectives (the Baltic Sea Action Plan and the RCP4.5) were met the average occurrence probability declined 25 percentage points. The situation for Fucus spp. is quite alarming because even if all the objectives would be achieved the suitable environment will nevertheless decline. If no actions will be taken in order to reduce nutrients the average occurrence probability declines 11–25 percentage points. Temperature decline in the RCP8.5 scenarios is thought to be caused by increasing upwelling events in the future, which may increase nutrient amounts in the coastal waters. The weak response to light and temperature and strong response to salinity and the fact that salinity decreased in all scenarios may explain why suitable areas decreased in all scenarios. There were some inconsistencies between the results and literature since the most optimistic scenario was the RCP4.5 & worst case, where BSAP goals are not achieved. This can be due to lack of species observations in the whole environmental gradients. The prediction results in the areas where water will be clearer in the future are not reliable and presumably more positive than these results show. While the BSAP scenarios may be too pessimistic the results of worst case scenarios are more reliable.
  • Müller, Mitro (Helsingin yliopisto, 2020)
    A warming trend of annual average surface temperatures since pre-industrial times has been observed globally. High-arctic area of Svalbard, Norway is undergoing amplified change of annual average temperatures when compared to the global average. Decline of glaciers in western Svalbard has been ongoing for several decades, and in the recent past, rapid biological successions have taken place. These changes have likely had effect on regional scale carbon dynamics at Svalbard’s moss tundra areas. Possibly indicating onset of paludification process of these areas. However, palaeoecological studies from the area are scarce, and the response of high-latitude moss tundra areas to past or ongoing climate change, are still not fully understood. This thesis aimed to bring forward information of changes in recent organic matter and carbon accumulation rates at Svalbard, Norway. Soil profiles were collected from four moss tundra sites, located on coastal areas and fjords descending towards Isfjorden, on the western side of Spitsbergen island. Radiocarbon (14C) and lead (210Pb) dating methods with novel age-depth modelling and soil property analyses, were used to reconstruct recent organic matter and carbon accumulation histories from 1900 AD to 2018 AD. Accumulation histories were supported by meteorological measurements from the area. In addition, annual maximum value Normalized Difference Vegetation Indices for 1985 AD till 2018 AD period were produced, to study vegetation succession in the recent past. Lastly, possibility to predict spatiotemporal variation of soil carbon accumulation with satellite derived vegetation indices was assessed. Development from predominantly mineral soils to organic soils was distinguishable within multiple soil profiles, pointing to potential paludification. Recent apparent carbon accumulation rates showed an increasing trend. Supporting meteorological data and literature suggest that regional abiotic and biotic factors in synergy with weather and climate are contributing to this observed trend. Vegetation indices pointed to major changes in vegetation composition and productivity. However, investigation of relationship between recent carbon accumulation rates and vegetation indices did not produce reliable results. Spatiotemporal heterogeneity of carbon soil-atmosphere fluxes presently imposes large challenges for such modelling. To alleviate this problem, efforts for more efficient synergetic use of field sampling and remote sensing -based material should be undertaken, to improve modelling results.
  • Kinnunen, Antti (Helsingin yliopisto, 2019)
    The stability of local organism communities is affected by multiple variables from historical dispersal factors of broad spatiotemporal scale to more local variables of ecosystem trophic level and disturbance variables. Streams are a very a unique living environment in this regard, as their hydrological circumstances and nutrient balance vary substantially throughout the year, disturbances reflect from upstream locations to downstream relatively fast and the dispersal created by current causes microorganism communities to resemble one another along upstream-downstream gradient. As such, stream habitats are temporally remarkably variable by their environmental conditions and on the other hand subject to continuous one-way migration from upstream sites. The population dynamics of stream micro-organisms differs greatly from lentic systems as a result. In this thesis the temporal stability of six Southern Finnish diatom communities was studied during the summer 2017. A clear gradient from urban to natural environments, characterized by their catchment’s land use variables was sought after in the initial study setting. The aim of the study was to recognize the most important variables affecting the stability of diatom communities as well as to study how the stability of communities differed between varying habitats characterized by their pwater quality and physical environment. In addition, the stability and performance of diatom indices IPS and TDI was studied. The sampling period of the study was conducted between 17th of May 2017 and 18th of October 2017, covering the majority of Southern Finnish growing period. In total eight samples were collected per site, primarily following the temporal cycle of 21 days. In addition to diatom samples the physicochemical water quality and physical environmental variables were studied from the sampling locations. These were used to recognize the central environmental variables affecting the changes observed in diatom communities. Linear regression analysis and a variety of multivariable analyses, such as non-metric multidimensional scaling (NMDS), canonical correspondence analysis (CCA) and generalized linear mixed models (GLMM) were utilized as statistical methods. The results indicated that the sampling sites differed significantly by their physicochemical water quality as well as their diatom communities. The diversity and structure of diatom communities was affected most strongly by variables representing the overall environmental stress and disturbance level, trophic level and local hydrology. The local species count was most strongly correlated with electrical conductivity, total phosphorus concentration and time elapsed since the onset of sampling period. The stability of diatom communities was mainly affected by environmental variables representing anthropogenic activity and trophic level of the ecosystem. The communities were generally most temporally stable in urban sampling locations, although they were temporally more variable than their natural habitat counterparts over short observation time span. The values of both studied diatom indices differed significantly between sampling locations. According to the results the IPS-index failed to reflect differences in physicochemical water quality. By contrast, the TDI-index was temporally relatively stable and also correlated better with physicochemical water quality variables. The results were mostly in accordance with the most crucial reference frame of the study field as well as the results of previous studies. As such, they can be seen to further reinforce the view that diatom communities are most species diverse in high trophic level and low environmental stress habitats. The temporal stability of the communities followed the same principles with the most stable communities being present in high environmental stress, low trophic level habitats.
  • Haverinen, Samuel (Helsingin yliopisto, 2021)
    Methane is an important greenhouse gas in the global atmosphere and its concentration has more than doubled compared to preindustrial times. Fresh water lakes and streams are substantial sources of methane. However, the estimations of their role in the global methane budget vary significantly and not until the 21st century has the understanding of their role as substantial methane sources increased. In the boreal zone, lakes produce as much as 30 % of the methane emissions. In this study, we examine spatial and temporal changes in methane fluxes from northern boreal lake Pallasjärvi and from a small stream located in its catchment area between June and November of 2020. We also examine the factors that explain the spatial and temporal changes in the methane fluxes, both lake and stream. Lake and stream methane fluxes were measured every other week between June and August, once a week in September, and once in the beginning of November using the chamber method. During the chamber measurements we also measured water surface temperature. Furthermore, at the stream sites we measured the water flow rate. At the lake measurement points we measured the water depth in November, which we calibrated to apply to the entire measurement period using water pressure logger. In March 2021, we measured the depth of the sediment layer at the lake sites. We also used CORINE-landcover data to model stream methane fluxes and for the lake, we used Finnish Meteorological Institute’s wind speed and direction dataset. We used these variables in order to explain the spatial and temporal variation of the lake and the stream methane fluxes using correlation analysis and linear mixed models. In this study, we find that water surface temperature, water depth, and wind were significant variables in explaining the lake methane fluxes. Respectively, landcover and surface water temperature explained the stream methane flux. From a temporal perspective, the strongest fluxes were measured between June and July at the lake sites and August and the beginning of September at the stream sites. Methane fluxes were divided spatially in two different groups at both lake and stream sites. At the lake sites, the strongest fluxes were measured in the shallow Pallaslompolo area and the weakest at the larger and deeper main basin of the lake. At the stream sites, the fluxes were also divided in two groups, the upstream’s weak fluxes and the downstream’s strong fluxes. According to the results, the temporal change of flux in the lake area is controlled by the changes in the factors underlying the methane production, and the differences in the lake basin depth control the spatial change of flux. The temporal change of stream methane flux depends on the changes in the methane production in the stream and its catchment area, while the spatial change depends on the changes in the landcover along the stream. However, more research and data are needed about the lake sediment layer temperature and oxygen levels, the water methane concentration, and stream catchments with different landcovers, which all impact the methane fluxes.
  • Tyystjärvi, Vilna (Helsingin yliopisto, 2019)
    Soil moisture influences various environmental and climatological processes and is an important part of the hydrological cycle. The processes influencing its spatial and temporal variation are complex and linked with each other as well as influenced by soil moisture itself which makes observing them challenging. This is especially true in cold regions where soil moisture has shown strong fine scale variation and influences numerous ecosystem processes. To test different hypotheses related to soil moisture and to simulate its variation, several hydrological process-based models have been developed. Understanding how these models differ from each other and how they describe soil moisture is crucial in order to use them effectively. For this study, three process-based models representing varying model approaches and answering different research questions were chosen and used to simulate the spatial and temporal variation of soil moisture in a small study area in northwestern Finland. JSBACH is a global-scale land surface model that simulates various geophysical and geochemical processes over land and in the boundary layer between land surface and the atmosphere. SpaFHy is a catchment scale hydrological model developed to simulate water balance and evapotranspiration in boreal forests. Ecohydrotools is a hydrological model used to study fine scale spatial variation in soil hydrology. The model results show clear similarities as well as differences when compared with each other and with field measurements of soil moisture. The strongest similarities are in distinguishing wetter and drier areas in the study area, although the actual moisture content estimations vary between the models. All models show difficulties in simulating finer scale spatial variation, particularly in drier areas. Temporal variation shows more similarities between the models, although there are also clear discrepancies with measurements and the models. These simulations show that there are several things influencing a model’s capability to simulate soil moisture variation. Varying data requirements, included processes as well as model design and purpose all influence the results, leading to varying estimations of soil moisture. Improving model predictions in cold environments requires better understanding of the underlying processes as well as more detailed information on the environmental variables influencing soil moisture.
  • Manninen, Petra (Helsingin yliopisto, 2020)
    Soils are important stocks of carbon and the soil-atmosphere CO2 flux is the second largest carbon flux between ecosystems and the atmosphere. Soil respiration is in previous studies considered to be mostly controlled by soil moisture and temperature, but also the activity of soil macrofauna. In African semi-arid savannas these parameters are controlled by seasonality. Mound-building termites are abundant in these savannas and in addition to the carbon cycle, they affect soil properties when building mounds and foraging outside them. Gas exchange and heat transfer in mounds is a complex phenomenon that varies depending on mound architecture and environment variables. Mound ventilation brings the CO2 generated in termite and their nest metabolism outside the mounds. CO2 emissions of termites, especially outside their mounds, should be studied to clarify their impact on the savanna soil respiration. In attempt to understand soil respiration around termite mounds, soil respiration rates was measured from surrounding area of six mounds of fungus-growing termite species Macrotermes michaelseni and Macrotermes subhyalinus using closed static chamber method in Tsavo ecosystem, southern Kenya. Measurements were made during the three assumed rainy seasons, in November 2016, April 2017, and December 2017. Research focused whether CO2 emissions come from the soil or from termites. The effect of prevailing wind was also studied to understand the role of mound ventilation better. Soil moisture, soil temperature, and the amount of rainfall were also measured and their effect on respiration was studied. The results show that a single reason for the changes in soil respiration rates around termite mounds is difficult to find. Most of the variation between measurement sites and measurement periods were due to changes in soil moisture. Prevailing wind direction was also found to be possible reason for changes in soil respiration rates. Soil respiration rates were higher near the mounds, so termite activity or changes in soil properties caused by them are assumed to be a contributing factor. Due to limited amount of data, many of the uncertainties on the subject should be further researched.
  • Seppälä, Outi (Helsingin yliopisto, 2020)
    Arctic soils store significant amounts of carbon deposited by plants and litter. Carbon is released from the soil in respiration due to plant roots and decomposition by microbes. In the northern hemisphere, carbon inputs from photosynthesis have exceeded releases of carbon to atmosphere via respiration. Arctic soils have been a globally remarkable carbon sink due to cold and waterlogged conditions. However, rising global temperatures and changes in hydrology have caused the carbon fluxes in soil-atmosphere interface to alter. Arctic areas are considered especially vulnerable to climate change and alterations in the arctic soil carbon pools could create powerful feedbacks to warming. Furthermore, drivers controlling soil respiration flux remain poorly known, especially their contributions in different environments and their dynamics in time. Thus, understanding soil respiration as a process is vital in understanding future changes in the global carbon cycle.The aim of this study was to identify environmental drivers of soil respiration in tundra at landscape-scale and their relative importance in different stages of growing season. The study area was a valley between two fells at Kilpisjärvi, Finland. Soil respiration was measured using the chamber method in 100 study sites on the 3 x 2 km landscape three times during the summer of 2018. Environmental data on soil microclimate and vegetation properties was gathered fromthe area as well. The impact of environmental conditions to respiration flux was studied using multiple generalized linear models with different explanatory variable combinations.Results suggest that abundant vegetation causes high respiration by providing resources for belowground microbes and creating extensive root network. Highest respiration was measured in peak growing season, when elevated temperatures stimulated respiration exclusively in tundra meadows. It seems that vegetation and soil parameters also define the temperature response of respiration. The flux increased with elevated temperatures only on soils that are assumed to have adequate nutrient and carbon composition to support higher respiration. This study suggests that onlandscape-scale, the resources provided by vegetation are of bigger importance to respiration than climatic changes both spatially and temporally.Moving forward, more empiricaldata is needed in order to accurately model future changes in respiration. Intense sampling efforts from the Arctic tundra areasthatcover the large spatial and temporal variabilityof respiration are necessary.
  • Rautakoski, Helena (Helsingin yliopisto, 2021)
    As the climate warms tundra ecosystems will face changes that have an impact on their carbon cycle. Arctic tundra is already experiencing changes in plant species composition and distribution, and vegetation height expected to increase. Vegetation shifts such as shrubification can increase carbon uptake from the atmosphere to the tundra ecosystems but changes in soil microclimate and plant-microbe interactions related to vegetation shifts can also create feedbacks that increase carbon losses from the ecosystems to the atmosphere. To better understand changes in tundra carbon dioxide (CO2) fluxes related to climate change and vegetation shifts, it’s crucial to understand the factors controlling CO2 fluxes in the tundra in general and in the tundra environments that differ in their vegetation composition. We used environmental gradients created by late-lying snowbanks to collect the data and we used modelling to understand the factors controlling CO2 fluxes in the tundra and within four different vegetation types during the growing season. The vegetation types included in the study were barrens, meadow-like environments, prostrate shrub tundra (heat) and erect shrub tundra (shrub). Gross primary production (GPP) and ecosystem respiration (ER) were the highest in shrub plots, smaller in the heat and in meadow-like environments and the smallest in barrens. Net CO2 sink increased with vegetation cover and GPP, but also barrens with little vegetation were still mostly net CO2 sinks during the growing season due to low ER. The amount of vegetation measured in vegetation height and cover well explained the variation in GPP and net ecosystem exchange (NEE) in the whole data and within vegetation types. ER was also related to the amount of vegetation but was more affected by microclimate, mainly air temperature and soil moisture, than GPP and NEE. In shrub plots, variation in ER was explained by air temperature more than by vegetation cover or height. Microclimate variables were not important in explaining variation in GPP in the whole data or within vegetation types but air temperature in heath and in the whole data and soil temperature and soil moisture in barrens helped to explain variation in NEE. In the whole data, heat and shrub plots soil temperature was not related to higher ER. Depth of organic layer explained some variation in NEE and ER in the whole data and some variation in NEE in some of the vegetation types. Soil pH was not an important factor explaining CO2 fluxes, but it was related to vegetation type and vegetation distribution especially in the whole data. The main factor controlling CO2 fluxes in the tundra and within different vegetation types seemed to be the amount of vegetation. Air temperature and soil moisture help to explain the variation especially in ER. The ability of vegetation parameters to explain variation in ER may be partly because of a relatively small amount of heterotrophic respiration compared to autotrophic respiration in the system or because of a positive link between the amount of vegetation and the amount of decomposition. Drought during the field campaigns may have limited decomposition and decreased temperature sensitivity of decomposition which may partly explain the insensitivity of ER to soil temperature. In heat and in shrub plots the shading effect of vegetation lowered soil temperature and may have slowed decomposition. As the ability of vegetation, microclimate and soil variables to explain variation in CO2 fluxes differed between vegetation types, CO2 fluxes of different vegetation types may respond to changes in the tundra environment differently. The results imply that the effect of vegetation composition should be considered when estimating how tundra ecosystem CO2 fluxes will respond to climate change. Similarly, the role of factors controlling decomposition, such as drought and shading effect of shrub vegetation, may be important in determining the future carbon balance of the tundra.
  • Kivimäki, Arttu (Helsingin yliopisto, 2021)
    Wind is often difficult to include in microclimatic research due to its high spatial and temporal variability. The development of wind speed and direction measurement methods together with the increase in available surface wind models and computational resources enable wind field simulation on a high temporal and spatial resolution. Winds were measured during summer 2018 in a topographically varying landscape of mostly low vegetation in Finnish Lapland. Six ultrasonic anemometers were placed to measure wind speed and direction in positions of varying topography and vegetation. Based on June 2018 data, topography has a clear effect on wind speeds but the effect of vegetation was not visible from the data. The highest average wind speeds measured on the study area varied between 6.3 m/s – 13.2 m/s, and highest gust wind speeds between 10.1 m/s – 17.1 m/s. The anemometers' data was used in modeling wind fields with WindNinja application to study areas of both topographic and vegetational variation and also to a larger area surrounding the study site. WindNinja is a diagnostic wind model, into which the data were applied as virtual weather stations. The modeling results were compared to measured wind speeds by leave-one-out validation. Spearman correlation coefficients between measured and simulated average wind speeds varied between 0.28 – 0.59, RMSE values between 1.1 – 2.6 m/s and MAE values between 0.8 – 2.0 m/s. The respective values for gust wind simulations were 0.42 – 0.63, 1.6 – 2.7 m/s and 1.2 – 2.1 m/s. Overall WindNinja underpredicted high wind speeds and overpredicted low speeds. In modeling results, topography had a clear effect on regional and local wind fields on all modeling areas Winds were strongest on top of ridges and weakest in depressions. Vegetation had very local effects to wind speed by increasing and lowering it. The results give a good overview of the small-scale windiness variability in the modeling areas. To further examine the micro- and mesoclimatic effects of windiness, the results of this thesis should be combined with other research conducted in the area. WindNinja has potential to further use in high resolution wind modeling, which is an important factor of microclimatic research in the changing climate. However, the software’s graphical user interface is not optimal for modeling longer periods of wind data.