Kopáček J., Cudlín P., Fluksová H., Kaňa J., Picek T., Šantrůčková H., Svoboda M. & Vaněk D. 2015: Dynamics and composition of litterfall in an unmanaged Norway spruce (Picea abies) forest after bark-beetle outbreak. Boreal Env. Res. 20: 305–323.
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Niemi R.M., Heiskanen I. & Saarnio S. 2015: Weak impacts of biochar amendment on soil enzyme activities in mesocosms in bare or Phleum pratense soil. Boreal Env. Res. 20: 324–334.
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Solberg S., Aamlid D., Tveito O.E. & Lystad S. 2015: Increased needlefall and defoliation in Norway spruce induced by warm and dry weather. Boreal Env. Res. 20: 335–349.
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Tuovinen H., Vesterbacka D., Lempinen J., Pohjolainen E., Read D., Solatie D. & Lehto J. 2015: Radionuclide and heavy metal redistribution at the former pilot-scale apatite plant in Sokli, northern Finland. Boreal Env. Res. 20: 350–362.
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Coleman K.A., Palmer M.J., Korosi J.B., Kokelj S.V., Jackson K., Hargan K.E., Courtney Mustaphi C.J., Thienpont J.R., Kimpe L.E., Blais J.M., Pisaric M.F.J. & Smol J.P. 2015: Tracking the impacts of recent warming and thaw of permafrost peatlands on aquatic ecosystems: a multi-proxy approach using remote sensing and lake sediments. Boreal Env. Res. 20: 363–377.
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Kraufvelin P. & Díaz E.R. 2015: Sediment macrofauna communities at a small mussel farm in the northern Baltic proper. Boreal Env. Res. 20: 378–390.
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Piirimäe K., Loigu E., Pachel K. & Iital A. 2015: Virtual mapping of reference conditions of pollutant load in waterbodies: phosphorus in the Lake Peipsi basin. Boreal Env. Res. 20: 391–402.
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Růžička V., Zacharda M., Šmilauer P. & Kučera T. 2015: Can paleorefugia of cold-adapted species in talus slopes resist global warming? Boreal Env. Res. 20: 403–412.
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Pajusalu L., Martin G., Põllumäe A., Torn K. & Paalme T. 2015: Direct effects of increased CO₂ concentrations in seawater on the net primary production of charophytes in a shallow, coastal, brackish-water ecosystem. Boreal Env. Res. 20: 413–422.
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Kozlov M.V. 2015: Insect herbivory on two willow species in northern Europe is independent of pollution load. Boreal Env. Res. 20: 423–430.
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Kopáček J., Cudlín P., Fluksová H., Kaňa J., Picek T., Šantrůčková H., Svoboda M. & Vaněk D. 2015: Dynamics and composition of litterfall in an unmanaged Norway spruce (Picea abies) forest after bark-beetle outbreak. Boreal Env. Res. 20: 305–323.

We investigated litterfall chemistry and fluxes, and cellulose decomposition in litter floor in mature, unmanaged Norway spruce stands in the catchments of Plešné and Čertovo lakes (Czech Republic) during 2003–2013. The Plešné forest was infested by the bark beetle (Ips typographus) in 2004, and 88%–99% of trees had died by 2011. Total litterfall and its composition were similar in both catchments in 2003. The litterfall increased from 5.4 to 42 t ha^–1 yr^–1 after the infestation and remained relatively high (5.0 t ha^–1 yr^–1) until the end of the study even though > 52% of trees were already broken. The chemical composition of most spruce litter categories changed after infestation, with the most pronounced trends in C (decrease) and Ca (increase) concentrations. Moreover, Mg, K, and P concentrations increased in the total Plešné litter due to an increasing proportion of rowan litter. Cellulose decomposition increased in the litter floor after infestation.

Niemi R.M., Heiskanen I. & Saarnio S. 2015: Weak impacts of biochar amendment on soil enzyme activities in mesocosms in bare or Phleum pratense soil. Boreal Env. Res. 20: 324–334.

Addition of biochar to soil is studied for the sustainable agriculture. We studied the impact of biochar addition on soil enzyme activities in bare soil and in soil with growing Phleum pratense during one season in two experiments, each with different soil types. Enzyme activities were monitored in mesocosms after germination (dry period) and, with fully grown plants, during dry and wet periods. Enzyme activities were high in wet conditions in both soils with growing plants, with or without biochar. Bare soils with or without biochar yielded low activities. In sandy till, alanine and leucine aminopeptidase activities decreased in biochar-treated soil, but not in the medium-fine sand. β-N-acetyl-D-glucosaminidase and phosphomonoesterase activities were enhanced in biochar-treated medium-fine sand. The effects of plant, season and soil type on the enzyme activities were clear and frequently observed, whereas the effects of biochar were only few and weak.

Solberg S., Aamlid D., Tveito O.E. & Lystad S. 2015: Increased needlefall and defoliation in Norway spruce induced by warm and dry weather. Boreal Env. Res. 20: 335–349.

Analyses of a time-series of needlefall data showed enhanced needlefall due to unusually warm and dry weather in southeastern Norway during 1986–2000. Needlefall was sampled routinely in ten stands of older Picea abies as part of long-term forest monitoring. Mixed linear models were developed for brown and green needlefall separately. Both the brown and the green needlefall had clear seasonal variations, peaking in October and May, respectively. In addition, the needlefall was correlated with weather conditions. Unusually dry summers were followed by increased brown needlefall in the autumns and winters, and unusually high temperatures were accompanied by increased amounts of green needlefall, in particular in the winter. Using the models, we found that unusually warm and dry weather during these 15 years likely caused an overall surplus of needlefall. Even though the brown needlefall was the dominant fraction of the needlefall, the surplus of green needlefall was of larger magnitude. The results suggest that unusually warm winters and dry summers were the main cause of increased crown defoliation during these years.

Tuovinen H., Vesterbacka D., Lempinen J., Pohjolainen E., Read D., Solatie D. & Lehto J. 2015: Radionuclide and heavy metal redistribution at the former pilot-scale apatite plant in Sokli, northern Finland. Boreal Env. Res. 20: 350–362.

A new phosphate mine is being planned at Sokli in northern Finland. In the late 1970s, pilot-scale mining and mineral processing took place at the site. The mobilisation of radionuclides and heavy metals from the mill tailings was examined in order to assess the potential environmental impact of past and future mining activities. Given the considerable amount of apatite still present, the waste material does not represent true tailings. Variations in abundance probably represent material discharges to the tailings rather than mobilization of the elements from the tailings themselves. No indication of heavy-metal migration was found. Extraction results suggest that only a small proportion of cadmium is in exchangeable form. Elements that are partly soluble under weakly-acidic conditions include copper, zinc, cadmium, uranium and lead. However, most of the elements are tightly bound to the sample matrix and therefore not easily released to the environment.

Coleman K.A., Palmer M.J., Korosi J.B., Kokelj S.V., Jackson K., Hargan K.E., Courtney Mustaphi C.J., Thienpont J.R., Kimpe L.E., Blais J.M., Pisaric M.F.J. & Smol J.P. 2015: Tracking the impacts of recent warming and thaw of permafrost peatlands on aquatic ecosystems: a multi-proxy approach using remote sensing and lake sediments. Boreal Env. Res. 20: 363–377.

Regions within the discontinuous permafrost zone of the southern Northwest Territories (Canada) are experiencing accelerated thaw of permafrost as a result of recent warming. We used remotely-sensed imagery (1947–2012) to track changes in the extent of peat plateau collapse around two study lakes: KAK-1 and TAH-7. Subfossil diatoms were analyzed from sediment cores to reconstruct limnological changes over the past ~300 years and assess whether peatland subsidence affected lake ecology. Extensive peat plateau collapse was evident in catchments between 1970 and present day. In TAH-7, diatom assemblages indicated a substantial increase in coloured dissolved organic carbon coincident with the time of peat collapse, suggesting that permafrost thaw has resulted in increased transport of terrestrial organic matter to the lake. At KAK-1, while also tracking changes linked to climate warming, no changes in diatom assemblages could be linked to peat plateau collapse. Using our combined approaches, we conclude that collapsing peat plateaus may significantly alter aquatic ecosystems, but the impacts of permafrost thaw on aquatic ecosystems in the sporadic discontinuous permafrost zone are complex.

Kraufvelin P. & Díaz E.R. 2015: Sediment macrofauna communities at a small mussel farm in the northern Baltic proper. Boreal Env. Res. 20: 378–390.

The use of blue mussel farming in the Baltic Sea for mitigating eutrophication through nutrient bioextraction has recently been under debate, with emphasis on potential local negative effects induced by farmed mussels, based on theoretical scenarios. Here, we broaden the discussion by presenting an assessment of the faunal community around a non-commercial mussel farm, after two years of operation in a relatively well-oxygenated water area. It is the first large-sized farm (25 tonnes) in the northern Baltic proper. The biotic conditions at this mussel farm did not deviate negatively from the surrounding reference areas. The total abundance and species richness of sediment-dwelling fauna were higher at the farm site, which also showed a distinct zoobenthic species composition including many bioturbators which may provide extra protection against hypoxia. A snapshot view of water quality indicated relatively low P and chlorophyll-a concentrations at the farm. We caution against drawing conclusions from our study that are too far-reaching primarily because the mussel farm in question being smaller than those referred to in the debate. However, the study presents an important initial assessment of the functioning of a pilot mussel farm in the Baltic proper and provides baselines for future investigations and guidelines for improved sampling design.

Piirimäe K., Loigu E., Pachel K. & Iital A. 2015: Virtual mapping of reference conditions of pollutant load in waterbodies: phosphorus in the Lake Peipsi basin. Boreal Env. Res. 20: 391–402.

Our study proposes a novel virtual mapping method to define reference conditions in a water body that is assumed to be not affected by human activities. We applied a modified PolFlow model, a raster-GIS analysis tool, to the Lake Peipsi basin. Running 'reference conditions' scenario revealed that the mean annual reference load comprised 225 t (31%) of phosphorus while the remaining 498 t (69%) originated from anthropogenic sources. Of the total reference load, 77 t (34%) originated from the Estonian part of the catchment, while the remaining 148 t (66%) came from Russia. High variability appeared in key factors that determine the P load to the lake in Estonia and Russia. The management measures in Estonia should prioritize land use issues, such as a reduction of diffuse emissions from agriculture. In contrast, the short-term Russian policy should focus on improved municipal and industrial waste-water treatment.

Růžička V., Zacharda M., Šmilauer P. & Kučera T. 2015: Can paleorefugia of cold-adapted species in talus slopes resist global warming? Boreal Env. Res. 20: 403–412.

In central Europe, some boreal and arctic organisms can survive in low-altitude freezing talus slopes disjunct from their normal ranges far to the north. The external air temperature and the interior temperature of the talus were measured for five years at three low-elevation talus slopes in North Bohemia (Czech Republic). The year-round interplay between both temperature regimes was affected both by below-average as well as above-average climatic variations during winters 2005–2006 and 2006–2007, respectively. The total of air-freezing degree-days per year was confirmed to be the best and sufficient predictor for all considered thermal characteristics in the lower part of the talus slopes. Persistency of cold talus thermal behavior supports Nekola’s concept of paleorefugia inhabited by cold-adapted species of boreal origin. Our results suggest that the talus microclimate can be sufficiently resistant to an increase of mean annual atmospheric temperature by 3 °C, retaining a sufficient number of freezing days during the winter season.

Pajusalu L., Martin G., Põllumäe A., Torn K. & Paalme T. 2015: Direct effects of increased CO₂ concentrations in seawater on the net primary production of charophytes in a shallow, coastal, brackish-water ecosystem. Boreal Env. Res. 20: 413–422.

Charophytes are found in fresh and brackish waters across the globe and play key roles in coastal ecosystems. However, their response to increasing CO₂ is not well understood. The aim of the study was to detect the effects of elevated CO₂ on the physiology of charophyte species growing in the brackish Baltic Sea by measuring net primary production. Mesocosm experiments were conducted in the Kõiguste Bay (N Gulf of Riga) during the field season of 2012. Separate mesocosms were maintained at different p_CO2 levels: ~2000, ~1000 and ~200 µatm. The experiments were carried out with three species of charophytes: Chara aspera, C. tomentosa and C. horrida. The short-term photosynthetic responses of charophytes to different treatments were measured by the oxygen method. The results show that elevated CO₂ levels in brackish water may enhance the photosynthetic activity of charophyte species and suggest that increasing CO₂ in the Baltic Sea could have implications for interspecific competition and community structure in a future high CO₂ world.

Kozlov M.V. 2015: Insect herbivory on two willow species in northern Europe is independent of pollution load. Boreal Env. Res. 20: 423–430.

Pollution has repeatedly been suggested to increase plant susceptibility to insect attack, some diseases and severe climatic conditions. This study explored the effects of industrial pollution on leaf damage by insect herbivores (primarily defoliators) in two willow species, Salix myrsinifolia and S. caprea, growing naturally at different distances from two nickel-copper smelters (Harjavalta, SW Finland and Monchegorsk, NW Russia). The relationships between pollution load and herbivory were variable, from significantly positive to significantly negative. However, this variation was not related to the differences between polluters, willow species or study years; an overall effect of pollution on herbivory, as evaluated by meta-analysis of 12 individual data sets, did not differ from zero. This result hints that an overall increase in insect herbivory with industrial pollution, discovered in meta-analysis of published observational studies, may be an artefact caused by research and publication biases.