BER 18(3-4), 2013

ISSN 1239-6095 (print), ISSN 1797-2469 (online)
© Boreal Environment Research 2013

Contents of Volume 18 no. 3–4

Lappalainen, M., Kukkonen, J. V. K., Piirainen, S, Sarjala, T., Setälä, H., Koivusalo, H., Finér, L. & Laurén, A. 2013: Nitrogen release in decomposition of boreal mor and peat as affected by enchytraeid worms. Boreal Env. Res. 18: 181–194.
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Tõnno, I., Kirsi, A.-L., Freiberg, R., Alliksaar, T., Lepane, V., Kõiv, T., Kisand A. & Heinsalu, A. 2013: Ecosystem changes in large and shallow Võrtsjärv, a lake in Estonia — evidence from sediment pigments and phosphorus fractions. Boreal Env. Res. 18: 195–208.
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Nevalainen, L. & Luoto, T. P. 2013: Limnological deterioration forces community and phenotypic changes in Cladocera: Tracking eutrophication of Mallusjärvi, a lake in southern Finland. Boreal Env. Res. 18: 209–222.
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Pitkänen, A., Turunen, J., Tahvanainen, T. & Simola, H. 2013: Carbon storage change in a partially forestry-drained boreal mire determined through peat column inventories. Boreal Env. Res. 18: 223–234.
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Raateoja, M. 2013: Deep-water oxygen conditions in the Bothnian Sea. Boreal Env. Res. 18: 235–249.
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Maljanen, M., Hytönen, J., Mäkiranta, P., Laine, J., Minkkinen, K. & Martikainen, P. J. 2013: Atmospheric impact of abandoned boreal organic agricultural soils depends on hydrological conditions. Boreal Env. Res. 18: 250–268.
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Dorodnikov, M., Marushchak, M., Biasi, Ch. & Wilmking, M. 2013: Effect of microtopography on isotopic composition of methane in porewater and efflux at a boreal peatland. Boreal Env. Res. 18: 269–279.
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Jönsson, O., Andersson, C., Forsberg, B. & Johansson, C. 2013: Air pollution episodes in Stockholm regional background air due to sources in Europe and their effects on human population. Boreal Env. Res. 18: 280–302.
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Prchalová, M., Peterka, J., Čech, M. & Kubečka, J. 2013: A simple proof of gillnet saturation. Boreal Env. Res. 18: 303–308.
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Ronkainen, T., Väliranta, M. & Tuittila, E.-S. 2013: Fire pattern in a drainage-affected boreal bog. Boreal Env. Res. 18: 309–316.
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Hugron, S., Poulin, M. & Rochefort, L. 2013: Organic matter amendment enhances establishment of reintroduced bryophytes and lichens in borrow pits located in boreal forest highlands. Boreal Env. Res. 18: 317–328.
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Kannosto, J., Yli-Pirilä, P., Hao, L. Q., Leskinen, J., Jokiniemi, J., Mäkelä, J. M., Joutsensaari, J., Laaksonen, A., Worsnop, D. R., Keskinen, J. & Virtanen, A. 2013: Bounce characteristics of α-pinene-derived SOA particles with implications to physical phase. Boreal Env. Res. 18: 329–340.
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Mor, slightly decomposed peat and highly decomposed peat, two soil types of each, were incubated for 154 days in the laboratory at +15 °C with and without enchytraeid worms, which functionally are the most influential faunal group in boreal forests. We quantified the release rates of organic and inorganic nitrogen (N) in dissolved and extractable forms from decomposing organic matter and explored the effects of enchytraeid worms on the release rates. About 80% of the dissolved N was released in the form of NH₄⁺-N, except in mor without worms and in slightly decomposed peat with and without worms, where the net release from soil solution was in the form of dissolved organic N (DON). The majority of DON was in the high molecular weight fraction. In the presence of worms, the mineralization rate of N was highest in mor and in the absence of worms in highly decomposed peat. The large initial DON pool may explain the high mineralization rate in highly decomposed peat. The changes in the soil-solution N pool were small compared to the changes in extractable N pool which emphasizes the importance of the adsorbed N in soil N dynamics. Because N release through decomposition is the major component of N balance in forested catchments, the results of the study can be used for improving models of catchment scale N dynamics.

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Palaeopigments, organic matter dissolved in sediment porewater (pDOM) and phosphorus fractions were analysed in a sediment core from large shallow Võrtsjärv with the aim to assess whether the trends of climate-driven and anthropogenic changes in lake trophy within the 20th century are reflected in its sediment record. In the first half of the last century, the lake was naturally slightly eutrophic as the accumulation of palaeopigments was low and the load of nutrients stable; investigated variations in palaeoparameters were induced by the regular natural water level fluctuations. Since the mid-1950s eutrophication of Võrtsjärv has accelerated — content of fossil pigments, CaCO₃ and nutrients increased, while pDOM revealed high autochthonous matter input. The increase of palaeopigment's concentrations during the last decade may be consistent with regional climate warming. Investigated palaeoindicators and water level changes had a stronger relationship in the second half of the 20th century.

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A 300-year sediment record was used to investigate cladoceran community and phenotypic responses under extreme eutrophication process in the clay-turbid Mallusjärvi, a lake in southern Finland. The aims were to identify reference and disturbed communities, and to assess species and functional diversity and phenotypic characteristics as indices for lake ecological quality. The results showed that the oligomesotrophic reference status is characterized by rich planktonic and littoral-benthic assemblages with high species and functional diversity. Nutrient-enrichment, caused by increased agricultural activities in the catchment, was enhanced during the 19th century, inducing gradual responses in cladoceran community composition (decreasing benthic and increasing planktonic taxa) and functioning (decreasing invertebrate and increasing fish predation, decreasing species and functional diversity), and changes in phenotypic properties (decreasing body size of Bosmina longirostris and relative ephippial production). The disturbed state was characterized by eutrophic-hypereutrophic conditions and subsequent high abundance of planktonic cladocerans and deteriorated littoral-benthic conditions. Our results suggest that cladoceran communities, and their functional and phenotypic indices, are sensitive indicators of long-term limnological deterioration and ecosystem equilibrium.

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To study the impact of forestry drainage on peat carbon storage, we cored paired quantitative peat samples from undrained and drained sides of an eccentric bog. Five pairs of 0 to ≤ 100-cm-deep surface-peat cores, and a pair of profiles representing the full peat deposit provided stratigraphic evidence of marked loss of surface peat due to drainage. For the drained side cores, we found a relative subsidence of 25–37 cm of the surface, and a loss of about 10 kg_DW m^–2, corresponding to 131 ± 28 g C m^–2 a^–1 (mean ± SE) for the post-drainage period. Similar peat loss was also found in the full deposit profiles, thus lending credibility to the whole-column inventory approach, even though the decrease (9 kg_DW m^–2) was relatively small in comparison with the total carbon storage (233 and 224 kg_DW m^–2 for the undrained and drained sides, respectively).

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Raateoja, M. 2013: Deep-water oxygen conditions in the Bothnian Sea. Boreal Env. Res. 18: 235–249.

The hydrography of the deep waters of the Bothnian Sea (BS) underwent considerable changes during the most recent two decades. Most importantly, slightly worsened deep-water oxygen (O₂) conditions followed a gradual increase in the water-column density gradient. Up to the present time, the lowest measured O₂ concentrations fell within the range 3.5–4.5 ml l^–1, 1.4 ml l^–1 being used in this work as the upper limit for hypoxia. I investigated the long-term deep-water characteristics of the BS to determine how possible it is for an hypoxic event to occur there in the near future. It appears that there is only a remote probability of this, unless profound changes take place in the hydrographic regime of the BS and/or in the anthropogenic load to the BS. The key factor behind this conclusion is the hydrodynamic regime of the Åland Sea and the ridge formations around it. This area acts as a buffering/filtration mechanism that prevents the saline and O₂-poor deep waters of the Northern Baltic Proper from entering the BS without considerable mixing and dilution. A discussion is presented of the consequences of this conclusion, taking into account the past adverse development in the Gulf of Finland, with its internal loading of phosphorus and its accelerated eutrophication. With respect to the Finnish coastal area of the BS, the stable O₂ conditions and the favourable hydrographic setup in the near-coastal area suggest that any O₂ problems will most probably be concentrated in the inner-archipelago areas.

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Drained agricultural peat soils are significant sources of carbon dioxide (CO₂) but also small sinks for methane (CH₄). Leaving these soils without any cultivation practice could be an option to mitigate GHG emissions. To test this hypothesis, we measured, over a three year period, net CO₂ exchange and fluxes of CH₄ for five agricultural peat soils that had been abandoned for 20–30 years. Annually, the sites were either small net sinks or sources of CO₂ and CH₄ (–7.8 to 530 g CO₂-C m^–2 and –0.41 to 1.8 g CH₄ m^–2). Including N₂O emissions from our previous study, the net (CH₄ + CO₂ + N₂O) emissions as CO₂ equivalents were lower than in cultivated peat soils and were lowest in the wet year. Therefore, high GHG emissions from these soils could be avoided if the water table is maintained close to the soil surface when photosynthesis is favoured over respiration.

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The application of stable isotopes is an approach to identify pathways of methanogenesis, methane (CH₄) oxidation and transport in peatlands. We measured the stable C isotopic characteristics (δ¹³C) of CH₄ in peat profiles below hummocks, lawns and hollows of a Finnish mire to study the patterns of CH₄ turnover. Porewater CH₄ concentrations ([CH₄]; at 0.5–2 m) increased with depth below all microforms. Emissions of CH₄ from hummocks were the lowest, and increased with the increasing water-saturated zone, being ~10 times higher from hollows. Thus, the microtopography of the peatland did not affect the porewater [CH₄] in the water-saturated part of the peat profile, but the CH₄ emissions were affected due to differences in the oxidative potential of the microforms. There was a decrease in δ¹³C-CH₄ with depth below all microforms indicating dominance of CO₂-reduction over acetate cleavage pathway of methanogenesis at deep peat layers. However, estimated potential portions of transported CH₄ comprised 50%–70% of the δ¹³C-CH₄ enrichment on microforms at the 0.5-m depth, hereby masking the acetate cleavage pathway of methanogenesis. Stable C composition (δ¹³C) of CH₄ proved to be a suitable (but not sufficient) tool to differentiate between types of methanogenesis in continuously water-saturated layers below microforms of a peatland. Combined flux-based and multi-isotopic approaches are needed to better understand the CH₄ turnover process.

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Using air quality measurements, we categorized air pollution according to source sectors in a rural background environment in southern Sweden based on hourly air-mass backward trajectories during 1997–2010. Concentrations of fine (PM_2.5) and sum of fine and coarse particulate matter (PM₁₀), accumulation mode particle number, black carbon and surface ozone were 4.0, 3.9, 4.5, 6.8 and 1.3 times higher, respectively, in air masses from the southeast as compared with those in air masses from the cleanest sector in the northwest, consistent with air-mass transport over areas with relatively high emissions of primary particulate matter (PM) and secondary PM precursors. The highest ultrafine particle numbers were associated with clean air from the northwest. We estimate that almost 7.8% and 0.6% higher premature human mortality is caused by PM_2.5 and ozone exposure, respectively, when air originates from the southeast as compared with that when air originates from the northwest. Reductions of emissions in eastern Europe would reduce the highest air pollution concentrations and associated health risks. However, since air masses from the southwest are more frequent, emissions in the western part of Europe are more important for annual mean premature mortality.

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Prchalová, M., Peterka, J., Čech, M. & Kubečka, J. 2013: A simple proof of gillnet saturation. Boreal Env. Res. 18: 303–308.

Gillnet saturation was assessed between standard (overnight, uninterrupted exposure) and consecutive (half or one hour exposures) sampling in two Czech reservoirs. The consecutive sampling yielded a greater number and biomass of fish as compared with those of the standard sampling. Species compositions were comparable between sampling types. Shannon’s diversity indices did not differ significantly between the two sampling approaches.

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Ronkainen, T., Väliranta, M. & Tuittila, E.-S. 2013: Fire pattern in a drainage-affected boreal bog. Boreal Env. Res. 18: 309–316.

Similarly to drainage caused by land-use change, the predicted climate warming may cause a moderate water-level drawdown in northern peatlands due to increased evapotranspiration. This is likely to alter the frequency and severity of peatland fires. We surveyed the fire pattern in drainage-affected and unmanaged parts of a boreal raised bog using three sampling transects reaching from drainage-affected area to an unmanaged bog area. Throughout the bog, dry hummock surfaces provided spreading routes for fire while hollows remained intact. Drainage promoted succession that lead to the dominance of hummock vegetation close to the drained area. Consequently, drainage succession favoured fire. The results suggest an increase in fire impact as a consequence of lowered water levels. In warmer climate with increased evapotranspiration bogs are likely to become more vulnerable to fires.

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Borrow pits, gravel and sand extraction sites, are commonly reclaimed by reintroducing vascular plants. Even after vegetation rehabilitation, recovery is slow and likely only dominated by a few plant species, often atypical of the surrounding landscape. This study aims to evaluate the short term effect of different restoration treatments for establishing diaspores of bryophytes and lichens in disturbed boreal habitats. We tested different treatments: organic matter addition (peat), straw mulch, and nitrogen and phosphorous fertilisation. We found that amending with peat was the most effective treatment in establishing bryophyte and lichen using diaspores, but only if no mulch was applied. Applying mulch had a detrimental effect on the diaspores, whereas nitrogen and phosphorous fertilisation appeared to have no effect. The lack of a fertiliser response, however, may be due to the negative effect of applying mulch, since all plots treated with fertiliser and diaspores also included the mulch treatment.

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Electrical Low Pressure Impactor (ELPI) was used to study the physical phase of fresh secondary-organic-aerosol (SOA) particles formed by the ozonolysis of pure α-pinene in a chamber. The particles bounced from smooth impactor plates towards lower impactor stages, indicating a solid physical state. These particles had a similar bouncing ability as Scots pine-derived particles in previous studies. The measured bounce factor of large particles (diameter > 40 nm) did not significantly change during the particle growth, indicating no changes in the particle solidity. For the smallest particles, the calculated bounce factor increased as the particles grew. The smallest particles were less solid (i.e. having lower viscosity) than the larger ones. The maximum value of the bounce factor decreased for consequent impactor stages. According to a simplified model, this can be explained by a combination of bounce probability and charge transfer between the particles and the impactor surface if at least 50% particles are bouncing.

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