Browsing by Subject "biogeochemistry"

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  • Forsius, Martin; Posch, Maximilian; Holmberg, Maria; Vuorenmaa, Jussi; Kleemola, Sirpa; Augustaitis, Algirdas; Beudert, Burkhard; Bochenek, Witold; Clarke, Nicholas; de Wit, Heleen A.; Dirnböck, Thomas; Frey, Jane; Grandin, Ulf; Hakola, Hannele; Kobler, Johannes; Krám, Pavel; Lindroos, Antti-Jussi; Löfgren, Stefan; Pecka, Tomasz; Rönnback, Pernilla; Skotak, Krzysztof; Szpikowski, Józef; Ukonmaanaho, Liisa; Valinia, Salar; Váňa, Milan (Elsevier, 2021)
    Science of The Total Environment 753 (2021), 141791
    Anthropogenic emissions of nitrogen (N) and sulphur (S) compounds and their long-range transport have caused widespread negative impacts on different ecosystems. Critical loads (CLs) are deposition thresholds used to describe the sensitivity of ecosystems to atmospheric deposition. The CL methodology has been a key science-based tool for assessing the environmental consequences of air pollution. We computed CLs for eutrophication and acidification using a European long-term dataset of intensively studied forested ecosystem sites (n = 17) in northern and central Europe. The sites belong to the ICP IM and eLTER networks. The link between the site-specific calculations and time-series of CL exceedances and measured site data was evaluated using long-term measurements (1990–2017) for bulk deposition, throughfall and runoff water chemistry. Novel techniques for presenting exceedances of CLs and their temporal development were also developed. Concentrations and fluxes of sulphate, total inorganic nitrogen (TIN) and acidity in deposition substantially decreased at the sites. Decreases in S deposition resulted in statistically significant decreased concentrations and fluxes of sulphate in runoff and decreasing trends of TIN in runoff were more common than increasing trends. The temporal developments of the exceedance of the CLs indicated the more effective reductions of S deposition compared to N at the sites. There was a relation between calculated exceedance of the CLs and measured runoff water concentrations and fluxes, and most sites with higher CL exceedances showed larger decreases in both TIN and H+ concentrations and fluxes. Sites with higher cumulative exceedance of eutrophication CLs (averaged over 3 and 30 years) generally showed higher TIN concentrations in runoff. The results provided evidence on the link between CL exceedances and empirical impacts, increasing confidence in the methodology used for the European-scale CL calculations. The results also confirm that emission abatement actions are having their intended effects on CL exceedances and ecosystem impacts.
  • Tison, J. -L.; Schwegmann, S.; Dieckmann, G.; Rintala, J. -M.; Meyer, H.; Moreau, S.; Vancoppenolle, M.; Nomura, D.; Engberg, S.; Blomster, L. J.; Hendrickx, S.; Uhlig, C.; Luhtanen, A. -M.; de Jong, J.; Janssens, J.; Carnat, G.; Zhou, J.; Delille, B. (2017)
    Sea ice is a dynamic biogeochemical reactor and a double interface actively interacting with both the atmosphere and the ocean. However, proper understanding of its annual impact on exchanges, and therefore potentially on the climate, notably suffer from the paucity of autumnal and winter data sets. Here we present the results of physical and biogeochemical investigations on winter Antarctic pack ice in the Weddell Sea (R. V. Polarstern AWECS cruise, June-August 2013) which are compared with those from two similar studies conducted in the area in 1986 and 1992. The winter 2013 was characterized by a warm sea ice cover due to the combined effects of deep snow and frequent warm cyclones events penetrating southward from the open Southern Ocean. These conditions were favorable to high ice permeability and cyclic events of brine movements within the sea ice cover (brine tubes), favoring relatively high chlorophyll-a (Chl-a) concentrations. We discuss the timing of this algal activity showing that arguments can be presented in favor of continued activity during the winter due to the specific physical conditions. Large-scale sea ice model simulations also suggest a context of increasingly deep snow, warm ice, and large brine fractions across the three observational years, despite the fact that the model is forced with a snowfall climatology. This lends support to the claim that more severe Antarctic sea ice conditions, characterized by a longer ice season, thicker, and more concentrated ice are sufficient to increase the snow depth and, somehow counterintuitively, to warm the ice.
  • Kettunen, Ilkka Henrikki (Helsingin yliopisto, 2022)
    Aim of this study is to develop biogeochemical exploration methods for cobalt. Several different samples were collected from study area, analyzed, and compared to each other. This study took place at Rautio village at North Ostrobothnia and more accurately over the Jouhineva mineralization. Jouhineva is well-known high-grade cobalt-copper-gold mineralization. Elements examined in this study are cobalt, copper, arsenic, zinc, selenium, and cadmium. Samples were collected from three different study profiles from the area. From these three profiles samples collected are: soil, pine, lingonberry, birch, rowan, and juniper. Water samples were collected around the study area from every location possible. Soil samples were analyzed with four different methods: Ionic leaching, aqua regia, weak leaching and pXRF. Ionic leaching and aqua regia had both elevated concentrations of cobalt, but in different locations depending on study profile. Ionic leaching detects rising ions from the ore and therefore elevated concentrations are found at different locations compared to aqua regia. Aqua regia results proved how different orientation of study profile, direction of the ore and glacial flow can affect to the anomalies of elemental concentration. Profile-2 was oriented differently to ore and glacial flow than Profile-1, and therefore elevated concentrations of cobalt and copper were not drifted away from the ore on Profile-2 like they were on Profile-1. Aqua regia and pXRF have very similar copper, arsenic and zinc results. Pine and lingonberry turn out to be the most promising plant species applied for cobalt exploration, and rowan appears to be most suitable for copper exploration. Lower detection limit could significantly improve pine analyses as exploration method and more extensive sampling could remove some of the uncertainties about the method. Lingonberry samples have elevated concentration of copper and arsenic. Birch and juniper produced somewhat unclear results. Despite this, cobalt and copper concentrations in birch leaves were elevated when compared to concentrations found in other studies. In addition to this birch is suitable for arsenic exploration. Juniper had elevated copper concentration in the study area compared to other studies. Water samples collected from the Jouhineva area yielded concentrations of cobalt, copper and arsenic that were above the average concentration in the Kalajoki area waters. Copper and arsenic were above the average concentration of the Kalajoki area in every sample collected from the study area. Cobalt was above the average concentration in all samples that were not collected directly from the pond formed in the old test mine. Zinc concentration was below the average limit in all samples collected from the area. Zinc concentration in the water samples collected from the pond is significantly lower compared to the other samples collected from the area.
  • Tupek, Boris (Helsingin yliopisto, 2020)
    Process-based soil carbon models can simulate small short-term changes in soil organic carbon (SOC) by reconstructing the response of soil CO2 and CH4 emissions to simultaneously changing environmental factors. However, the models still lack a unifying theory on the effects of soil temperature, moisture, and nutrient status on the boreal landscape. Thus, even a small systematic error in modelled instantaneous soil CO2 emissions and CH4 emissions may increase bias in the predicted long-term SOC stock. We studied the environmental factors that control CO2 and CH4 emissions in Finland in sites along a continuum of ecosystems (forest-mire ecotone) with increasing moisture and SOC (I and II); soil CO2 emissions and SOC in four forest sites in Finland (III); and SOC sequestration at the national scale using 2020 forest sites from the Swedish national forest soil inventory (IV). The environmental controls of CO2 and CH4 emissions, and SOC were evaluated using non-linear regression and correlation analysis with empirical data and by soil C models (Yasso07, Q and CENTURY). In the upland forest-mire ecotone, the instantaneous variation in soil CO2 emissions was mainly explained by soil temperature (rather than soil moisture), but the SOC stocks were correlated with long-term moisture. During extreme weather events, such as prolonged summer drought, soil CO2 emissions from the upland mineral soil sites and CH4 emissions from the mire sites were significantly reduced. The transition from upland forest to mire did not act as a hot spot for CO2 and CH4 emissions. The CO2 emissions were comparable between forest/mire types but the CH4 emissions changed from small sinks in forests to relatively large emissions in mires. However, the CH4 emissions in mires did not offset their CO2 sinks. In the Swedish data, upland forest SOC stocks clearly increased with higher moisture and nutrient status. The soil carbon models reconstructed SOC stocks well for mesotrophic soils but failed for soils of higher fertility and wetter soils with a peaty humus type. A comparison of measured and modelled SOC stocks and the seasonal CO2 emissions from the soil showed that the accuracy of the estimates varied greatly depending on the mathematical design of the model’s environmental modifiers of decomposition, and their calibration. Inaccuracies in the modelling results indicated that soil moisture and nutrients are mathematically underrepresented (as drivers of long-term boreal forest soil C sequestration) in process-based models, resulting in a mismatch for both SOC stocks and seasonal CO2 emissions. Redesigning these controls in the models to more explicitly account for microbial and enzyme dynamics as catalysts of decomposition would improve the reliability of soil carbon models to predict the effects of climate change on soil C.
  • Jilbert, Tom; Gustafsson, Bo G.; Veldhuijzen, Simon; Reed, Daniel C.; Helmond, Niels A. G. M.; Hermans, Martijn; Slomp, Caroline P. (2021)
    Hypoxia has occurred intermittently in the Baltic Sea since the establishment of brackish-water conditions at similar to 8,000 years B.P., principally as recurrent hypoxic events during the Holocene Thermal Maximum (HTM) and the Medieval Climate Anomaly (MCA). Sedimentary phosphorus release has been implicated as a key driver of these events, but previous paleoenvironmental reconstructions have lacked the sampling resolution to investigate feedbacks in past iron-phosphorus cycling on short timescales. Here we employ Laser Ablation (LA)-ICP-MS scanning of sediment cores to generate ultra-high resolution geochemical records of past hypoxic events. We show that in-phase multidecadal oscillations in hypoxia intensity and iron-phosphorus cycling occurred throughout these events. Using a box model, we demonstrate that such oscillations were likely driven by instabilities in the dynamics of iron-phosphorus cycling under preindustrial phosphorus loads, and modulated by external climate forcing. Oscillatory behavior could complicate the recovery from hypoxia during future trajectories of external loading reductions.
  • Campbell, Karley; Matero, Ilkka; Bellas, Christopher; Turpin-Jelfs, Thomas; Anhaus, Philipp; Graeve, Martin; Fripiat, Francois; Tranter, Martyn; Landy, Jack Christopher; Sanchez-Baracaldo, Patricia; Leu, Eva; Katlein, Christian; Mundy, C. J; Rysgaard, Søren; Tedesco, Letizia; Haas, Christian; Nicolaus, Marcel (Royal Swedish Academy of Sciences, 2022)
    Sea ice continues to decline across many regions of the Arctic, with remaining ice becoming increasingly younger and more dynamic. These changes alter the habitats of microbial life that live within the sea ice, which support healthy functioning of the marine ecosystem and provision of resources for human-consumption, in addition to influencing biogeochemical cycles (e.g. air–sea CO2 exchange). With the susceptibility of sea ice ecosystems to climate change, there is a pressing need to fill knowledge gaps surrounding sea ice habitats and their microbial communities. Of fundamental importance to this goal is the development of new methodologies that permit effective study of them. Based on outcomes from the DiatomARCTIC project, this paper integrates existing knowledge with case studies to provide insight on how to best document sea ice microbial communities, which contributes to the sustainable use and protection of Arctic marine and coastal ecosystems in a time of environmental change.
  • Kohli, Juliana (Helsingin yliopisto, 2021)
    Boreal forests are an important storage of carbon (C), representing over one-third of terrestrial C stocks. The continuity of C storage in boreal forests and forest soils is critical to mitigate climate change. Climate change will likely increase the fire season length and the frequency of forest fires in Finland, of which surface fires are the dominant type. Fire affects C dynamics by modifying biotic (SOM, vegetation, microbial activity) and abiotic (soil temperature, moisture, chemistry) components of the forest ecosystem. These fire-induced effects will depend on the intensity of the fire (duration, flame temperature) and the site characteristics, ultimately resulting in either the persistence of, or in a net C loss, which has implications on both a local and global scale. There is a lack of existing research regarding the short-term impacts of surface forest fires and comparisons between different fire intensities. Subsequently, this thesis describes an experimental burn conducted in an even-aged Pinus sylvestris forest in southern Finland and the short- term post-fire impacts on soil biogeochemical processes (June-October 2020). The aims of this study were: (1) to study the effects of low- (200-300 oC) and high- (500-600 oC) intensity surface fires on soil temperature, moisture and soil surface CO2 fluxes straight after fire and through four months after experimental fire; (2) to study the effects of low- and high-intensity surface fires on plant (above and below ground) biomass immediately and four months after fire; (3) to identify the most important factors driving soil CO2 effluxes shortly after the fire. Eight sample plots (225 m2 each) were used, divided between high and low biomass loads to achieve high- and low-intensity fires. Continuous soil temperature and moisture measurements, vegetation inventories, soil sampling (0-30 cm), and soil CO2 efflux measurements were obtained using portable chambers. The results of this study showed that some soil physical and chemical properties were significantly altered due to the experimental surface fire (vegetation, temperature, moisture, root biomass, C, N (nitrogen), C/N), whereas some remained unchanged (pH, humus thickness). Soil moisture was the only variable, which increased as a result of higher fire intensity. Fires at both intensities resulted in the mortality of ground vegetation whilst trees did not experience mortality by the end of the monitoring period. Soil CO2 fluxes decreased in burned areas compared to unburned plots over time, but this change was not significantly different between burning intensities. Future research should investigate the mechanisms of C and N translocation through the soil profile following the addition of water, the relationship between post-fire soil temperature and soil CO2 efflux, how burning different biomass components changes the composition of ash, and how larger differences in burning intensities affect soil properties and soil CO2 effluxes. If trees experience mortality after the time period encompassed by this study, the site could become a potential C source; further monitoring of the study site could account for delayed indirect impacts such as these.
  • Marttila, Hannu; Lohila, Annalea; Ala-Aho, Pertti; Noor, Kashif; Welker, Jeffrey M.; Croghan, Danny; Mustonen, Kaisa; Meriö, Leo-Juhani; Autio, Anna; Muhic, Filip; Bailey, Hannah; Aurela, Mika; Vuorenmaa, Jussi; Penttilä, Timo; Hyöky, Valtteri; Klein, Eric; Kuzmin, Anton; Korpelainen, Pasi; Kumpula, Timo; Rauhala, Anssi; Kløve, Bjørn (2021)
    Subarctic ecohydrological processes are changing rapidly, but detailed and integrated ecohydrological investigations are not as widespread as necessary. We introduce an integrated research catchment site (Pallas) for atmosphere, ecosystems, and ecohydrology studies in subarctic conditions in Finland that can be used for a new set of comparative catchment investigations. The Pallas site provides unique observational data and high-intensity field measurement datasets over long periods. The infrastructure for atmosphere- to landscape-scale research in ecosystem processes in a subarctic landscape has recently been complemented with detailed ecohydrological measurements. We identify three dominant processes in subarctic ecohydrology: (a) strong seasonality drives ecohydrological regimes, (b) limited dynamic storage causes rapid stream response to water inputs (snowmelt and intensive storms), and (c) hydrological state of the system regulates catchment-scale dissolved carbon dynamics and greenhouse (GHG) fluxes. Surface water and groundwater interactions play an important role in regulating catchment-scale carbon balances and ecosystem respiration within subarctic peatlands, particularly their spatial variability in the landscape. Based on our observations from Pallas, we highlight key research gaps in subarctic ecohydrology and propose several ways forward. We also demonstrate that the Pallas catchment meets the need for sustaining and pushing the boundaries of critical long-term integrated ecohydrological research in high-latitude environments.