ISSN 1239-6095 (print),   ISSN 1797-2469 (online)
© Boreal Environment Research 2015

Contents of Volume 20 no. 4

Lohila A., Penttilä T., Jortikka S., Aalto T., Anttila P., Asmi E., Aurela M., Hatakka J., Hellén H., Henttonen H., Hänninen P., Kilkki J., Kyllönen K., Laurila T., Lepistö A., Lihavainen H., Makkonen U., Paatero J., Rask M., Sutinen R., Tuovinen J.-P., Vuorenmaa J. & Viisanen Y. 2015: Preface to the special issue on integrated research of atmosphere, ecosystems and environment at Pallas. Boreal Env. Res. 20: 431–454.
Abstract
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Aurela M., Lohila A., Tuovinen J.-P., Hatakka J., Penttilä T. & Laurila T. 2015: Carbon dioxide and energy flux measurements in four northern-boreal ecosystems at Pallas. Boreal Env. Res. 20: 455–473.
Abstract
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Lohila A., Tuovinen J.-P., Hatakka J., Aurela M., Vuorenmaa J., Haakana M. & Laurila T. 2015: Carbon dioxide and energy fluxes over a northern boreal lake. Boreal Env. Res. 20: 474–488.
Abstract
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Pearson M., Penttilä T., Harjunpää L., Laiho R., Laine J., Sarjala T., Silvan K. & Silvan N. 2015: Effects of temperature rise and water-table-level drawdown on greenhouse gas fluxes of boreal sedge fens. Boreal Env. Res. 20: 489–505.
Abstract
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Tsuruta A., Aalto T., Backman L., Peters W., Krol M., van der Laan-Luijkx I.T., Hatakka J., Heikkinen P., Dlugokencky E.J., Spahni R. & Paramonova N.N. 2015: Evaluating atmospheric methane inversion model results for Pallas, northern Finland. Boreal Env. Res. 20: 506–525.
Abstract
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Lihavainen H., Hyvärinen A., Asmi E., Hatakka J. & Viisanen Y. 2015: Long-term variability of aerosol optical properties in northern Finland. Boreal Env. Res. 20: 526–541.
Abstract
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Hellén H., Kouznetsov R., Anttila P. & Hakola H. 2015: Increasing influence of easterly air masses on NMHC concentrations at the Pallas-Sodankylä GAW station. Boreal Env. Res. 20: 542–552.
Abstract
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Ruoho-Airola T., Anttila P., Hakola H., Ryyppö T. & Tuovinen J.-P. 2015: Trends in the bulk deposition and atmospheric concentration of air pollutants in the Finnish Integrated Monitoring catchment Pallas during 1992–2012. Boreal Env. Res. 20: 553–569.
Abstract
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Lohila A., Penttilä T., Jortikka S., Aalto T., Anttila P., Asmi E., Aurela M., Hatakka J., Hellén H., Henttonen H., Hänninen P., Kilkki J., Kyllönen K., Laurila T., Lepistö A., Lihavainen H., Makkonen U., Paatero J., Rask M., Sutinen R., Tuovinen J.-P., Vuorenmaa J. & Viisanen Y. 2015: Preface to the special issue on integrated research of atmosphere, ecosystems and environment at Pallas. Boreal Env. Res. 20: 431–454.

The Pallas area in northern Finland has served as a meteorological monitoring site for 80 years and, more recently, as a platform for atmospheric, ecological and hydrological research. Currently, Pallas comprises one of the most important research infrastructures in Finland and in the wider circumpolar region. Moreover, it is a successful example of the benefits obtained from scientific cooperation and integration among disciplines. This paper is an introduction to a special issue that collates studies related to greenhouse gas fluxes and concentrations, atmospheric aerosols and air pollutants, which were presented at the Fourth Pallas Symposium held in 2013. We give an overview of the historical and current research activities within the Pallas area, outline the most important infrastructure projects and list the recent literature that has originated from the various scientific programs and projects. The results of these activities are illustrated in this paper with examples of long-term data sets on variations in soil, lake and river water, air quality and greenhouse gas concentrations.
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Aurela M., Lohila A., Tuovinen J.-P., Hatakka J., Penttilä T. & Laurila T. 2015: Carbon dioxide and energy flux measurements in four northern-boreal ecosystems at Pallas. Boreal Env. Res. 20: 455–473.

The fluxes of carbon dioxide and energy were measured by the eddy covariance method for four contrasting ecosystems within the Pallas area in northern Finland: Kenttärova spruce forest, open Lompolojänkkä wetland, treeless top of Sammaltunturi fell, and Pallasjärvi which is a lake. Clear differences in carbon and energy exchange were found among these ecosystems, in both the instantaneous fluxes and the related longer-term balances. The available solar energy and its partitioning into sensible and latent heat fluxes differed markedly among the sites. The characteristics of the CO2 exchange at individual sites varied in terms of the maximum uptake and emission capacity and the associated responses to environmental drivers. The highest instantaneous fluxes were observed over wetland and forest. The mean annual balance showed a considerable net uptake at the wetland, while the balances of the fell top and the forest were both close to zero. The lake, on the other hand, was estimated to be a relatively large source of carbon dioxide. An upscaling exercise based on the actual land-use map of the surroundings demonstrated the importance of including all the major ecosystems in the landscape CO2 balance.
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Lohila A., Tuovinen J.-P., Hatakka J., Aurela M., Vuorenmaa J., Haakana M. & Laurila T. 2015: Carbon dioxide and energy fluxes over a northern boreal lake. Boreal Env. Res. 20: 474–488.

We present a data set covering three months of carbon dioxide (CO2) and energy fluxes measured by the eddy covariance method over a northern boreal lake that collects waters from a surrounding catchment dominated by upland forest and wetlands. The data period comprises more than half of the open-water period of 2013. The 30-min averages of CO2 fluxes ranged from –0.02 to 0.05 mg m–2 s–1. The monthly CO2 balances varied from 20 to 30 g m–2 (emission) between July and September, and decreased in October. A small daytime uptake of CO2, probably caused by the aquatic plants growing near the measurement mast, was observed from July to September. In September, we observed a temporary enhancement of CO2 efflux, which was attributed to both high wind speed and rapid cooling of the water and subsequent water column overturn. This peak was accompanied by a period of high sensible heat flux (SHF) from the water to the atmosphere, which is known to enhance the mixing of the water. The seasonal CO2 flux during the open-water period from the shallow part of the lake was estimated to be 120 g m–2 yr–1, which corresponds to a loss of approximately 25 g m–2 yr–1 from the terrestrial part of the catchment, assuming that the observed lake CO2 emissions result from the decomposition of the imported carbon. At midday, the net energy received by the lake was used mostly to heat the water, and only a minor part of it was converted to SHF and latent heat flux (LHF), with more energy used for the latter. While the SHF showed a clear diurnal cycle with a peak early in the morning and no flux in the afternoon, the diurnal pattern of LHF was more even, with evaporation occurring throughout the day until the freezing of the lake. Our data from this northern lake highlight the importance of thermal water mixing in the air–lake CO2 flux dynamics and imply that this flux constitutes a significant part of the annual catchment-scale carbon budget.
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Pearson M., Penttilä T., Harjunpää L., Laiho R., Laine J., Sarjala T., Silvan K. & Silvan N. 2015: Effects of temperature rise and water-table-level drawdown on greenhouse gas fluxes of boreal sedge fens. Boreal Env. Res. 20: 489–505.

As potential outcomes of climate change, we examined the effects of environmental warming and drying on instantaneous CO2, CH4 and N2O fluxes in three sedge fens situated in the northern and middle boreal zones. Warming was induced by means of open top chambers (OTCs) and drying through drainage via ditching. OTCs raised the air temperature by 0.2–2 °C, whereas short-term drainage dropped the water-table level (WTL) by 5–10 cm and long-term drainage by 10–30 cm. The impact of simulated warming was rather negligible as warmer and drier conditions caused net ecosystem exchange (NEE) to decrease only at one of the two mid-boreal sites. Otherwise, the temperature rise alone or paired with WTL drawdown did not alter gas fluxes at any of the sites. Instead, the drainage effect overrode that of warming. Primarily WTL drawdown accounted for the differences in fluxes detected, but this was more apparent at the mid-boreal sites than our northern-boreal one. Notably, the northernmost Lompolojänkkä sedge fen, which was both the coolest and wettest of the three sites, was least sensitive to temperature rise and drainage; there, only CH4 emissions were affected by WTL drawdown.
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Tsuruta A., Aalto T., Backman L., Peters W., Krol M., van der Laan-Luijkx I.T., Hatakka J., Heikkinen P., Dlugokencky E.J., Spahni R. & Paramonova N.N. 2015: Evaluating atmospheric methane inversion model results for Pallas, northern Finland. Boreal Env. Res. 20: 506–525.

A state-of-the-art inverse model, CarbonTracker Data Assimilation Shell (CTDAS), was used to optimize estimates of methane (CH4) surface fluxes using atmospheric observations of CH4 as a constraint. The model consists of the latest version of the TM5 atmospheric chemistry-transport model and an ensemble Kalman filter based data assimilation system. The model was constrained by atmospheric methane surface concentrations, obtained from the World Data Centre for Greenhouse Gases (WDCGG). Prior methane emissions were specified for five sources: biosphere, anthropogenic, fire, termites and ocean, of which biosphere and anthropogenic emissions were optimized. Atmospheric CH4 mole fractions for 2007 from northern Finland calculated from prior and optimized emissions were compared with observations. It was found that the root mean squared errors of the posterior estimates were more than halved. Furthermore, inclusion of NOAA observations of CH4 from weekly discrete air samples collected at Pallas improved agreement between posterior CH4 mole fraction estimates and continuous observations, and resulted in reducing optimized biosphere emissions and their uncertainties in northern Finland.
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Lihavainen H., Hyvärinen A., Asmi E., Hatakka J. & Viisanen Y. 2015: Long-term variability of aerosol optical properties in northern Finland. Boreal Env. Res. 20: 526–541.

We studied the optical properties in continental and marine air masses, including seasonal cycles and long-term trends using 10-year data on aerosol scattering properties and 5-year data on absorption and combined aerosol optical properties. The average (median) scattering coefficient, backscattering fraction, absorption coefficient and single scattering albedo at the wavelength of 550 nm were 7.9 (4.4) Mm–1, 0.13 (0.12), 0.74 (0.35) Mm–1 and 0.92 (0.93), respectively. We observed clear seasonal cycles in these variables, the scattering coefficient having high values during summer and low in autumn, and absorption coefficient having high values during winter and low in autumn. We found that the high values of the absorption coefficient and low values of the single scattering albedo were related to continental air masses from lower latitudes. These aerosols can induce an additional effect on the surface albedo and melting of snow. We observed the signal of the Arctic haze in marine (northern) air masses during March and April. The haze increased the value of the absorption coefficient by almost 80% and that of the scattering coefficient by about 50% compared with the annual-average values. We did not observe any long-term trend in the scattering coefficient, while our analysis showed a clear decreasing trend in the backscattering fraction and scattering Ângström exponent during winter. A possible reason for this feature is the gradual change in the relative contributions of different emission sources. However, this remains to be confirmed by future studies.
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Hellén H., Kouznetsov R., Anttila P. & Hakola H. 2015: Increasing influence of easterly air masses on NMHC concentrations at the Pallas-Sodankylä GAW station. Boreal Env. Res. 20: 542–552.

Non-methane hydrocarbons (NMHCs, C2–C6) have been measured at the Pallas-Sodankylä GAW station since 1994. In 2010, evacuated stainless-steel-canister sampling was replaced by an in-situ gas chromatograph, and parallel measurements were conducted over the period of a year. Results were in good agreement for all other compounds except propene. NMHCs at Pallas show a typical seasonal variation, with the highest mixing ratios in winter and lowest in summer. Alkanes did not show any clear diurnal variation, but ethene had a maximum at midday or during the afternoon in summer. This indicated biogenic sources. i/n-Butane and n/i-pentane ratios were higher than those typically found in urban areas or in traffic emissions, indicating other sources than these (e.g. wood combustion or natural gas) having a strong effect on mixing ratios at Pallas. Trend analysis over twenty years of measurements indicated a significant decreasing trend only for ethyne, even though emissions of NMHCs in the European Union (EU) decreased by 50% during this period. No trend was found for ozone, either. This indicated that some other source areas than the EU must play a significant role at Pallas. This was confirmed by source area estimates, which showed that eastern Europe is the main source area for high mixing ratios at Pallas.
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Ruoho-Airola T., Anttila P., Hakola H., Ryyppö T. & Tuovinen J.-P. 2015: Trends in the bulk deposition and atmospheric concentration of air pollutants in the Finnish Integrated Monitoring catchment Pallas during 1992–2012. Boreal Env. Res. 20: 553–569.

The air and precipitation chemistry of 15 components was monitored within the Pallas Integrated Monitoring catchment during 1992–2012. A continuous time series of 21 years was available for the bulk deposition of acidifying compounds and base cations, whereas for the atmospheric concentration of sulphur and nitrogen compounds and ozone, the measurements covered 14–21 years. In this paper, an updated analysis of trends in these time series is presented and discussed in relation to the development in European emissions. The most notable result, a significant increase in NO3 bulk deposition since 1997, could serve as a general warning of the threats of excessive nutrient inputs to the vulnerable arctic ecosystems. There were no major changes in ozone concentrations between 1992–2012. The annually averaged source areas of gaseous SO2 and NO2 detected at Pallas were estimated using air parcel back trajectories.
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