Showing papers in "Boreal Environment Research in 2014"

Methods for determining particle size distribution and growth rates between 1 and 3 nm using the Particle Size Magnifier

Abstract: The most important parameters describing the atmospheric new particle formation process are the particle formation and growth rates. These together determine the amount of cloud condensation nuclei attributed to secondary particle formation. Due to difficulties in detecting small neutral particles, it has previously not been possible to derive these directly from measurements in the size range below about 3 nm. The Airmodus Particle Size Magnifier has been used at the SMEAR II station in Hyytiälä, southern Finland, and during nucleation experiments in the CLOUD chamber at CERN for measuring particles as small as about 1 nm in mobility diameter. We developed several methods to determine the particle size distribution and growth rates in the size range of 1–3 nm from these data sets. Here we introduce the appearance-time method for calculating initial growth rates. The validity of the method was tested by simulations with the Ion-UHMA aerosol dynamic model.

Trends in atmospheric new-particle formation: 16 years of observations in a boreal-forest environment

Abstract: New-particle formation (NPF) is globally an important source of climatically-relevant atmospheric aerosols. Here we explore the inter-annual variability and trends in sources and sinks of atmospheric nanoparticles in a boreal forest environment. We look into the precursor vapors leading to the aerosol formation, NPF frequency, as well as the formation and growth rates of the freshly-formed particles. The analysis is based on 16 years of data acquired from the Station for Measuring Ecosystem–Atmosphere Relations (SMEAR II) in Hyytiälä, Finland. The results indicate that the probability of NPF is connected to both air mass origin, explaining a large part of the year-to-year variability in the number of NPF events, and concentrations of low-volatile vapours. The probability of NPF increases with increasing gaseous sulphuric acid concentrations, but even better association is found between the NPF probability and product of sulphuric acid and low-volatile organic vapour (proxy) concentrations. While the concentrations of both sulphuric acid (evaluated by proxy) and sulphuric-acid precursor sulphur dioxide decreased over the 16-year measurement period, the new-particle formation and growth rates slightly increased. On the other hand, the proxy concentrations of oxidized organics increased in all seasons except in winter. The contribution of sulphuric acid to the particle growth was minor, and the growth rate had a clear connection with the ambient temperature due to higher emissions of biogenic volatile organic compounds at higher temperatures. For a given sulphuric acid concentration evaluated by proxy, particle formation rates tended to be higher at higher temperatures.

Patterns in airborne pollen and other primary biological aerosol particles (PBAP), and their contribution to aerosol mass and number in a boreal forest

Abstract: 1) Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland (*corresponding author’s e-mail: hanna.manninen@helsinki.fi) 2) Institute of Physics, University of Tartu, Ulikooli 18, EE-50090 Tartu, Estonia 3) Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland 4) Department of Chemistry and Biochemistry, University of Denver, 2190 E. Illif Ave., Denver, CO 80208, USA 5) Max Planck Institute for Chemistry, P.O. Box 3060, D-55020 Mainz, Germany 6) Department of Biology, FI-20014 University of Turku, Finland 7) Department of Environmental Biology, University of Huelva, ES-21071 Huelva, Spain

CO2-induced terrestrial climate feedback mechanism: From carbon sink to aerosol source and back

Abstract: Feedbacks mechanisms are essential components of our climate system, as they either increase or decrease changes in climate-related quantities in the presence of external forcings. In this work, we provide the first quantitative estimate regarding the terrestrial climate feedback loop connecting the increasing atmospheric carbon dioxide concentration, changes in gross primary production (GPP) associated with the carbon uptake, organic aerosol formation in the atmosphere, and transfer of both diffuse and global radiation. Our approach was to combine process-level understanding with comprehensive, long-term field measurement data set collected from a boreal forest site in southern Finland. Our best estimate of the gain in GPP resulting from the feedback is 1.3 (range 1.02-1.5), which is larger than the gains of the few atmospheric chemistry-climate feedbacks estimated using large-scale models. Our analysis demonstrates the power of using comprehensive field measurements in investigating the complicated couplings between the biosphere and atmosphere on one hand, and the need for complementary approaches relying on the combination of field data, satellite observations model simulations on the other hand.

On-line field measurements of BVOC emissions from Norway spruce (Picea abies) at the hemiboreal SMEAR-Estonia site under autumn conditions

Abstract: We investigated biogenic volatile organic compound (BVOC) emissions from a Norway spruce (Picea abies) in a hemiboreal mixed forest in autumn. Measurements were performed at the SMEAR-Estonia forest station, using PTR-MS techniques and a dynamic branch enclosure system. Parallel to BVOC measurements, atmospheric (CO2, CH4, H2O, CO) and meteorological (temperature, relative humidity, global radiation, wind speed, precipitation) parameters were monitored in the ambient atmosphere and inside the enclosure (temperature, relative humidity, ozone). Prior to the measuring period, a new inlet line consisting of 19.4 m of heated and isolated glass tube was constructed. The new inlet system allowed the on-line detection and calculation of sesquiterpene (SQT) emission rates for the first time for a hemiboreal forest site. In total, 12 atmospherically relevant BVOCs were continuously monitored during the measurement campaign and the emission rates of terpenoid species and predominant oxygenated VOCs were estimated, with monoterpenes to be emitted the most, followed by acetone, acetaldehyde and sesquiterpenes.

Responses of zooplankton to long-term environmental changes in a small boreal lake

Abstract: 1) University of Helsinki, Lammi Biological Station, FI-16900 Lammi, Finland (*corresponding author’s e-mail: lauri.arvola@helsinki.fi) 2) Department of Biological and Environmental Sciences/Aquatic sciences, P.O. Box 65, FI-00014 University of Helsinki, Finland 3) Finnish Game and Fisheries Research Institute, Evo Fisheries Research Station, Rahtijärventie 291, FI-16970 Evo, Finland 4) Department of Biology, FI-20014 University of Turku, Finland 5) Finnish Environmet Institute, P.O. Box 140, FI-00251 Helsinki, Finland

Water quality of a small headwater lake reflects long-term variations in deposition, climate and in-lake processes

Abstract: 1) Finnish Environment Institute, P.O. Box 140, FI-00251 Helsinki, Finland (*corresponding author’s e-mail: jussi.vuorenmaa@ymparisto.fi) 2) University of Helsinki, Lammi Biological Station, Pääjärventie 320, FI-16900 Lammi, Finland 3) Department of Biological and Environmental Science, P.O. Box 35, FI-40014 University of Jyväskylä, Finland 4) Finnish Game and Fisheries Research Institute, Evo Fisheries Research Station, Rahtijärventie 291, FI-16970 Evo, Finland 5) Centre for Economic Development, Transport and the Environment for Häme, Vesijärvenkatu 11 A, FI-15140 Lahti, Finland

Fingerprints of the urban particle number size distribution in Helsinki, Finland: Local versus regional characteristics

Abstract: 1) Department of Physics, P.O. Box 48, FI-00014 University of Helsinki, Finland 2) The University of Jordan, Department of Physics, Amman 11942, Jordan 3) Finnish Meteorological Institute, P.O. Box 503, FI-00101 Helsinki, Finland 4) Technische Universität Braunschweig, Institute of Geoecology, Climatology and Environmental Meteorology, Langer Kamp 19c, D-38106 Braunschweig, Germany 5) University of Duisburg-Essen, Faculty of Biology, Department of Applied Climatology and Landscape Ecology, Campus Essen, D-45141 Essen, Germany 6) Politecnico di Milano, DIIAR Environmental Engineering Section, P.za L. da Vinci n°32, IT-20133 Milano, Italy

The projected 21st century forest-fire risk in Finland under different greenhouse gas scenarios

Abstract: We evaluated forest fire potential at four locations in Finland in the current climate and in projected future climates under the B1, A1B and A2 greenhouse-gas (GHG) emission scenarios. In evaluating the forest fire danger potential, the Canadian fire weather index (FWI) system was used. Using the results of the earlier experimental ignition studies, we further estimated the number of fire danger days in different forest stands typical to the northern boreal zone. By the end of the current century, the annual median number of days with elevated forest fire risk is projected to increase by 10%–40%, depending on the GHG scenario. In different forest stands, approximately 5–10 additional fire risk days were found annually based on the A1B and A2 scenarios. Substantially smaller changes are projected under the low-emission B1 scenario. However, there is great inter-annual variability in the forest fire potential which, in the nearest future, largely overwhelms the projected change.

Plankton metabolism and sedimentation in a small boreal lake - a long-term perspective

Abstract: We used weekly or biweekly data from the years 1990–2009 to analyse variation in primary production (PP), chlorophyll a (Chl) and respiration (R) of plankton, and organic matter sedimentation (S) in a small boreal lake with intense water colour. PP and S had a decreasing trend over the study period while no trend was found in Chl and R. PP and R were in balance except during the last five years when R > PP. The results indicated that light limited PP, while occasionally phosphorus, nitrogen and/or dissolved inorganic carbon could also act as limiting factors. The decrease in S coincided with that of PP although during the last five years allochthonous organic matter load seemed to compensate for the decrease in PP. Weather and hydrological conditions were the key drivers in modifying the properties of the lake while the metabolic processes were intercorrelated, and R correlated strongly with water temperature.

Climate variability and trends in the Valkea-Kotinen region, southern Finland: comparisons between the past, current and projected climates

Abstract: extended abstract, figure captions and tables

Population dynamics and growth of perch in a small, humic lake over a 20-year period - importance of abiotic and biotic factors

Abstract: Population dynamics and growth of perch (Perca fluviatilis) were studied over a 20-year period in a small, humic, boreal lake (Valkea-Kotinen). The annual estimated total population size of perch (> 8 cm, total length) varied from 2700–13 400 and the biomass from 16.1–44.2 kg ha–1. Strong year-classes were born at four-year intervals between 1991 and 2003. A decreasing trend was recorded in the growth of 1and 2-year-old perch, whereas a slight increase appeared in the yearly growth of 4and 5-year-old fish. Our view is that the decrease in the early growth was caused by negative effects of increased organic carbon loads on water colour and hence on light conditions and the general productivity of the plankton community. These changes outweighed the expected positive effect of increasing temperature for young perch but not for the older fish.

The effect of granulated wood-ash fertilization on soil properties and greenhouse gas (GHG) emissions in boreal peatland forests.

Abstract: The amount of wood ash produced in power plants is increasing with increasing use of forest biomass in energy production Wood ash can be recycled as fertilizer especially in boreal peatland forests naturally rich in nitrogen Improved nutrient availability and increases in soil pH can enhance microbial activities, decomposition of organic matter and greenhouse gas (GHG) emissions We studied the effects of granulated wood-ash on soil chemical properties, vegetation characteristics, decomposition rate and fluxes of nitrous oxide (N2O) and methane (CH4) in boreal peatland forests In addition to the field measurements, we conducted laboratory experiments Wood-ash fertilization changed soil chemical properties, altered understory vegetation, increased tree growth and decomposition rate but there were no significant changes in the N2O and CH4 fluxes in situ, whereas in laboratory incubations ash decreased the N2O production rate The results show that there is no major risk of increasing GHG emissions after granulated wood-ash fertilization in boreal peatland forests

Winter to spring transition and diurnal variation of vocs in Finland at an urban background site and a rural site

Abstract: We measured volatile organic compound (VOC) volume mixing ratios (VMRs) using a quadrupole proton-transfer-reaction mass spectrometer, and investigated the differences between winter and spring VMRs and sources at an urban background site in Helsinki (2006) and a rural site in Hyytiala (2007) utilizing a receptor model EPA Unmix. In Helsinki, VMRs of VOCs were typically higher,and their diurnal variations were more pronounced than at the rural site. At both sites, monoterpenes have anthropogenic influence in winter, while in spring biogenic influence is dominating. At the urban background site, the main aromatic hydrocarbon source was traffic, which also explained most of the oxidated VOCs during the urban winter. At other times and at the rural location most of oxidated VOCs originated mainly from distant sources. At the rural site, traffic and distant sources contributed equally to the aromatics in winter but in spring the distant source dominated.

The relationship between productivity and tree-ring growth in boreal coniferous forests

Abstract: 1) Centre d’Étude de la Forêt (CEF), Département des Sciences Biologiques, Université du Québec à Montreal, CP 8888 Succ. Centre Ville, Montreal (Qc), H3P 3P8, Canada (*corresponding author’s e-mails: gea-izquierdo@cerege.fr; guigeiz@gmail.com) 2) CEREGE UMR 7330, CNRS/Aix-Marseille Université, Europole de l’Arbois, BP 80, F-13545 Aix-enProvence Cedex 4, France 3) Université du Québec en Abitibi-Témiscamingue, 445 Boulevard de l’Université, Rouyn-Noranda, Québec, J9X 5E4, Canada 4) School of GeoSciences, The University of Edinburgh, The King’s Buildings, West Mains Road, Edinburgh EH9 3JN, UK 5) Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland 6) South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China

Influence of hypoxia on silicate concentrations in the Baltic Proper (Baltic Sea)

Abstract: Silica (Si) is a key nutrient for diatoms. Over the last century, Si concentrations within the Baltic Sea decreased significantly. This is mainly attributed to ongoing eutrophication, increased production and subsequent deposition and accumulation of organic matter including biogenic silica. As a consequence of the eutrophication, hypoxic and anoxic bottom waters have spread affecting nutrient cycling. This paper looks at the potential impact of oxygen on dissolved silica (DSi). It presents a statistical analysis of the relationship between DSi concentrations and oxygen conditions (O-2) in the deep water of the Baltic Proper. The idea is not new, but this is the first time it is studied in more detail in this area. Regression analysis shows that DSi concentrations decrease significantly with O-2 concentrations, and that the major intrusion of saline water in 1993 strengthened this relationship. Increased hypoxia will significantly affect the cycling of Si in the Baltic Sea.

Simulated snowmelt and infiltration into frozen soil affected root growth, needle structure and physiology of Scots pine saplings

Abstract: Climate warming scenarios predict a decreased snow cover and more rain instead of snow in boreal areas in winter. These conditions may affect soil freezing processes. We studied how watering of the soil before and after soil thawing affects fine roots and shoots of Scots pine saplings during the follow-up season. A growth chamber experiment was carried out with four treatments. During the dormancy water was applied onto frozen soil three times (3¥FROSOIL) or once (1¥FROSOIL) whereas in the beginning of the growing season the watering was started when the soil temperature reached +9 (START+9) and +15 °C (START+15). Fine root damage was noted in 3¥FROSOIL, and on a smaller scale also in 1¥FROSOIL. The root growth did not recover during the follow-up season. Due to the root damage, in 3¥FROSOIL there was a reduced transport of water in the saplings, which induced xeromorphic features in the needles developed after the treatment. The fine root damage in 3¥FROSOIL was most probably caused by mechanical breakage after the applied water froze in the soil. Our results suggest that even established saplings may suffer root damage if the climatic and soil conditions favour infiltration and freezing cycles of water, which induce frost heaving.

Modelling the impact of higher temperature on the phytoplankton of a boreal lake

Abstract: We linked the models PROTECH and MyLake to test potential impacts of climate-change-induced warming on the phytoplankton community of Pyhajarvi, a lake in southwest Finland. First, we calibrated the models for the present conditions, which revealed an apparent high significance of internal nutrient loading for Pyhajarvi. We then estimated the effect of two climate change scenarios on lake water temperatures and ice cover duration with MyLake. Finally, we used those outputs to drive PROTECH to predict the resultant phytoplankton community. It was evident that cyanobacteria will grow significantly better in warmer water, especially in the summer. Even if phosphorus and nitrogen loads to the lake remain the same and there is little change in the total chlorophyll a concentrations, a higher proportion of the phytoplankton community could be dominated by cyanobacteria. The model outputs provided no clear evidence that earlier ice break would advance the timing of the diatom spring bloom.

The third Pallas Cloud Experiment: Consistency between the aerosol hygroscopic growth and CCN activity

Abstract: Measurements of aerosol chemical and hygroscopic properties and cloud condensation nuclei were carried out as a part of the third Pallas Cloud Experiment. In this study, the aerosol hygroscopicity parameter, k, was determined using data from instruments operating in the sub-saturated and supersaturated water vapour regimes, as well as from measurements of aerosol chemical composition. During the campaign, k varied from ~0.01 to ~0.37 as derived by Cloud Condensation Nuclei counter and Hygroscopic Tandem Differential Mobility analyser data, and from ~0.13 to ~0.60 as derived from Aerosol Mass Spectrometer data, the average values being 0.11 and 0.29, respectively. CCN closure calculations showed that the sub-saturated growth factor retrieved CCN concentration is lower than the measured one. Overall, at the Pallas site, aerosol hygroscopicity was size dependent with hygroscopicity increasing with size. Hence, size dependent information on composition is needed to predict CCN concentrations relevant to cloud droplet formation.

Challenges in managing inland fisheries - Using the ecosystem approach

Abstract: Inland fisheries are an important source of food and livelihood. However, the socio-economic importance of inland fisheries is often undervalued and inadequately addressed in national and international policies for development. Furthermore, while irresponsible fishing can have serious consequences, there are also many outside threats to inland fisheries. The ecosystem approach to fisheries (EAF) strives to balance a diversity of societal objectives, preserving possibilities for future generations to benefit from exploitation of aquatic ecosystems. Implementation of the approach to inland fisheries presents special challenges that arise from multiple uses of inland waters, external pressures, and difficulties in acquiring accurate information. The basic elements of an ecosystem approach include identification of relevant participants, identification of objectives of management and establishment of a monitoring system with appropriate indicators.

Spatio-temporal composition and dynamics of zooplankton in the Kalmar Sound (western Baltic Sea) in 2009-2010

Abstract: In pelagic food webs, zooplankton is the link between lower and higher trophic levels. It is thus essential to know how the zooplankton community structure varies with its environment. We investigated the seasonal and spatial variation in the zooplankton diversity and community structure during two consecutive years in the Kalmar Sound, along the Swedish east coast, an area with a strong bathymetric gradient and of high ecological importance for e.g. commercial fish species. Two zooplankton communities were identified in the area: a coastal/estuarine community in the south and an open-water community in the north. They were separated mainly by differing salinity and temperature conditions. Biodiversity increased from spring to autumn and was higher in the open waters.

Seasonal variation in the reflectance of photosynthetically active radiation from epicuticular waxes of Scots pine (Pinus sylvestris) needles

Abstract: Epicuticular waxes influence leaf reflectance, but the spatiotemporal dynamics in their reflectance properties have not been properly characterized, and its consequences remain unknown. In this study, we analysed the seasonal changes in wax reflectance of Scots pine needles. It tended to decrease with needle age and towards lower positions within the canopy. In addition, we also identified a clear seasonal pattern of variation superimposed on the of above-mentioned wax weathering effect. We conclude that spatiotemporal dynamics in wax optical properties need to be considered in studies that implicitly assume constant light absorption, particularly when different leaf age classes, canopy positions or seasons are compared, and especially in species with substantial amount of waxes. We suggest that the observed dynamics in wax reflectance could represent a new photoprotective mechanism operating at the seasonal scale as they modulate the absorption of the photosynthetically active radiation (PAR) over time.

Microclimatological consequences for plant and microbial composition in Sphagnum-dominated peatlands

Abstract: In three Scandinavian peatlands we studied to what extent plant and microbial community compositions are governed by local-scale microhabitat, with a special interest in the effect of aspect (i.e. exposition of slopes). Despite differences in solar irradiance between the south- and north-facing slopes, maximum temperature was elevated in the south-facing slopes at the most northern site only. Pore-water nutrient concentrations were not affected by aspect, yet dissolved organic carbon concentrations were higher in the south-facing microhabitats. This was likely caused by higher vascular plant biomass. Plant and microbial community composition clearly differed among sites. In all three sites, microhabitat (i.e. prevailing water-table depth) affected the plant and microbial community compositions. Aspect, however, did not affect community composition, even though microclimate significantly differed between the south- and the north-facing aspects at the northernmost site. Our results highlight the complex link between plant community composition, microbial community and environmental conditions, which deserves much more attention than currently in order to fully understand the effects of climate change on peatland ecosystem function.

Biomass-burning smoke episodes in Finland from eastern European wildfires

Abstract: Biomass burning emissions from intensive wildfires in eastern Europe were observed in Finland in the spring of 2006 and in the late of summers 2006 and 2010. The smoke plumes were detected at three ground-measurement stations around Finland and in the lower troposphere after long-range transport from fire areas. The vertical extent of the smoke was estimated by flight measurements over southern Finland and the measurements were compared with CALIPSO satellite data from 29 July 2010. The history of the arriving air masses was analysed by using backward trajectories and MODIS fire detections. The smoke plumes had elevated concentrations of aerosol particle number, black carbon, CO, CO2, SO2, O3 and NOx, and the differences as compared with the background air were clear. The smoke was observed to be highly scattering, with a single-scattering albedo of 0.96 ± 0.01. The median particle size was 60%–250% larger during the plume days than during July–August on average, and the growth of smoke particles was observed even after long-range transport of several hundreds of kilometres.

labile carbon addition affects soil organisms and n availability but not cellulose decomposition in clear-cut norway spruce forests

Abstract: We assessed the effects of sucrose addition on the biological and chemical properties of organic soil in clear-cut Norway spruce forests managed with or without wood-ash fertilization and mechanical site preparation. Sucrose addition increased the abundances of enchytraeids and tardigrades and soil moisture percentage in the clear-cut areas. Sucrose also increased nematode abundance in the non-fertilized plots. Sucrose reduced the pool of waterextractable NH 4 -N in the soil in the first year, but increased it in the second year. Sucrose addition did not affect the decomposition rate of cellulose strips. The biomass of ground vegetation was not affected by sucrose. Carbohydrate addition seems to enhance N immobilization in clear-cut areas in the short term, and it is suggested that aims at reducing N loss from disturbed forest soil do not necessarily accelerate carbon loss from the forest ecosystem.

Urban nitrous-oxide fluxes measured using the eddy-covariance technique in Helsinki, Finland

Abstract: Using the eddy covariance technique, nitrous oxide (N2O) fluxes were measured at the semi-urban SMEAR III station in Helsinki, Finland, between 21 June and 27 November 2012. The measurement period covered a seasonal change from summer to autumn allowing us to examine variations in the N2O fluxes by season. Also, varying land cover around the measurement site enabled us to study the effects of different urban land covers on the N2O exchange. Overall, the measurement surroundings acted as a source of N2O with a median and quartile deviation for the campaign of 1.7 ± 2.0 μmol m–2 h–1. The net emissions were slightly higher from the direction of green areas than from the direction of roads under heavy traffic indicating that vegetation cannot be neglected in the urban N2O exchange studies. No seasonal change in the N2O flux during the measurement campaign was found.