ISSN 1239-6095 (print),   ISSN 1797-2469 (online)
© Boreal Environment Research 2014

Contents of Volume 19 no. 5–6

Rimkus, E., Kažys, J., Butkutė, S. & Gečaitė, I. 2014: Snow cover variability in Lithuania over the last 50 years and its relationship with large-scale atmospheric circulation. Boreal Env. Res. 19: 337–351.
Abstract
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Trump, E. R., Riipinen, I. & Donahue, N. M. 2014: Interactions between atmospheric ultrafine particles and secondary organic aerosol mass: a model study. Boreal Env. Res. 19: 352–362.
Abstract
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Gea-Izquierdo, G., Bergeron, Y., Huang, J. G., Lapointe-Garant, M. P., Grace, J. & Berninger, F. 2014: The relationship between productivity and tree-ring growth in boreal coniferous forests. Boreal Env. Res. 19: 363–378.
Abstract
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Rohtla, M., Vetemaa, M., Svirgsden, R., Taal, I., Saks, L., Kesler, M., Verliin, A. & Saat, T. 2014: Using otolith 87Sr:86Sr as a natal chemical tag in the progeny of anadromous Baltic Sea pike (Esox lucius) — a pilot study. Boreal Env. Res. 19: 379–386.
Abstract
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Seitola, T. & Järvinen, H. 2014: Decadal climate variability and potential predictability in the Nordic region: a review. Boreal Env. Res. 19: 387–407.
Abstract
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Thorstad, E. B., Foldvik, A., Lo, H., Bjørnâ, T. & Stensli, J. H. 2014: Effects of handling adult sea trout (Salmo trutta) in a fishway and tagging with external radio transmitters. Boreal Env. Res. 19: 408–416.
Abstract
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Kim, Y., Roulet, N. T, Peng, G., Li, C., Frolking, S., Strachan, I. B. & Tremblay, A. 2014: Multi-year carbon dioxide flux simulations for mature Canadian black spruce forests and ombrotrophic bogs using Forest-DNDC. Boreal Env. Res. 19: 417–440.
Abstract
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Snickars, M., Rinne, H., Salovius-Laurén, S., Arponen, H. & O'Brien, K. 2014: Disparity in the occurrence of Fucus vesiculosus in two adjacent areas of the Baltic Sea — current status and outlook for the future. Boreal Env. Res. 19: 441–451.
Abstract
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Enno, S.-E., Post, P., Briede, A. & Stankunaite, I. 2014: Long-term changes in the frequency of thunder days in the Baltic countries. Boreal Env. Res. 19: 452–466.
Abstract
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Rimkus, E., Kažys, J., Butkutė, S. & Gečaitė, I. 2014: Snow cover variability in Lithuania over the last 50 years and its relationship with large-scale atmospheric circulation. Boreal Env. Res. 19: 337–351.

In this study, the snow cover dynamics in Lithuania from 1961 to 2010 is analyzed. The spatial distribution of snow cover parameters, as well as intra-seasonal variability and long-term changes are evaluated. Snow survey results in the open field and the forest are compared. The Hess-Brezowski circulation form classification is used to link heavy snow cover accumulation or ablation events in Lithuania with the synoptic situations. The long-term variability of the number of days with snow cover and its connection with large-scale atmospheric circulation patterns (AO and NAO) is also investigated. The decrease in the number of days with snow cover during the study period is determined throughout the whole territory of Lithuania. Meanwhile, changes in the maximum snow depth are not so unambiguous. The study results also show that large-scale atmospheric patterns strongly influence the snow cover regime.
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Trump, E. R., Riipinen, I. & Donahue, N. M. 2014: Interactions between atmospheric ultrafine particles and secondary organic aerosol mass: a model study. Boreal Env. Res. 19: 352–362.

We use dynamic mass-balance equations to treat the role of organic composition in driving net condensation to atmospheric particles. We consider the growth of newly formed nanoparticles that may have very different composition (volatility) than the pre-existing aerosol. Production of vapors much less volatile than the background aerosol enhances the growth of nanoparticles by the re-partitioning of semi-volatile vapors to the growing nanoparticles. In contrast, production of more-volatile vapors suppresses the growth of nanoparticles because the background aerosol draws down the semi-volatile gas-phase concentrations. The background aerosol thus serves as either a source or a sink of additional organic material. For fresh nanoparticles, the implication is that net condensation depends significantly on any imbalance between the produced organic vapors and their equilibrium (vapor) distribution over the background aerosol. This phenomenon may be important during nucleation and growth events, where relatively rapid growth of newly formed particles is difficult to explain.
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Gea-Izquierdo, G., Bergeron, Y., Huang, J. G., Lapointe-Garant, M. P., Grace, J. & Berninger, F. 2014: The relationship between productivity and tree-ring growth in boreal coniferous forests. Boreal Env. Res. 19: 363–378.

Ecosystem productivity estimated with a model calibrated with eddy-covariance data was related to tree-ring growth of two different boreal conifers along a latitudinal gradient. The relationship between ecosystem productivity and growth changed with species and site. Greater photosynthesis in spring and summer increased annual anomalies of radial growth in both species, and the response of growth to productivity was earlier in warmer southern stands particularly for pine. Radial growth of jack pine increased in the long-term with higher productivity, whereas this relationship was more reduced in black spruce. This could express species-specific differences in carbon allocation strategies but likely it is a consequence of the limiting marginal soils where spruce is found in the south. Only tree-rings of jack pine at some sites showed certain potential as direct proxies for ecosystem productivity at the low and high-frequency responses.
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Rohtla, M., Vetemaa, M., Svirgsden, R., Taal, I., Saks, L., Kesler, M., Verliin, A. & Saat, T. 2014: Using otolith 87Sr:86Sr as a natal chemical tag in the progeny of anadromous Baltic Sea pike (Esox lucius) — a pilot study. Boreal Env. Res. 19: 379–386.

Otolith 87Sr:86Sr were quantified in 54 young-of-the-year pike (Esox lucius) collected from five west-Estonian freshwater sites to investigate the potential use of 87Sr:86Sr as a natural site-specific tag. Significant differences were found among the selected study sites. Pair-wise comparisons revealed that only two sites were statistically indistinguishable from one another. Our results stress the need for understanding the migratory biology of the study species if significant early-life movements (e.g. seaward migration) occur. During the chemical analysis, maternally-influenced region (i.e. the core) should also be avoided or its data excluded. Based on our results and data from other studies we suggest that otolith 87Sr:86Sr is a powerful, yet underused marker to study the natal origins of freshwater spawning Baltic Sea fish at local (e.g. between neighbouring rivers) and regional scale (e.g. between drainage basins).
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Seitola, T. & Järvinen, H. 2014: Decadal climate variability and potential predictability in the Nordic region: a review. Boreal Env. Res. 19: 387–407.

This paper reviews decadal climate variability and predictability and its potential implications for adaptation decisions with emphasis on the Nordic region. In the North Atlantic sector, there is strong decadal to multi-decadal climate variability. The most prominent internal mechanisms explaining the variability are the North Atlantic oscillation (NAO) and the Atlantic meridional overturning circulation (AMOC). These affect also the climate variability in the Nordic region, but their impacts vary depending on local and regional conditions. The published studies also indicate that there appears to be potential for predictability of the decadal climate variations in the North Atlantic sector, mainly due to the AMOC variations. This also contributes to the predictability in the Nordic region, especially in the coastal areas adjacent to North Atlantic. The conclusions are uncertain at the moment, despite the fact that new knowledge is rapidly accumulating. Potential decadal predictability may generally be reduced due to global warming which is the largest over the high latitude oceans. For instance, weakening of the AMOC is generally noted in warmer world simulations. This may have consequences also on climate in the Nordic region, although the response is still uncertain.
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Thorstad, E. B., Foldvik, A., Lo, H., Bjørnâ, T. & Stensli, J. H. 2014: Effects of handling adult sea trout (Salmo trutta) in a fishway and tagging with external radio transmitters. Boreal Env. Res. 19: 408–416.

Survival and behavioural effects of handling and transport related to a fishway in a natural waterfall was examined for radio-tagged sea trout (Salmo trutta, n = 39) during their upstream migration to spawning grounds. Main aims were to examine (1) if handling and transport impacted their subsequent survival, (2) whether they remained above the waterfall and resumed upstream migration, or migrated downstream again below the waterfall, and (3) if migration behaviour differed between fish tagged with small and large external transmitters. A high survival rate (at least 97% of the fish), fast upstream movement after release above the waterfall (average 6 km during the 6 first days), no recorded downstream movements during the entire study period, and wide-ranging migration before the spawning period (average 25–27 km upstream of the release sites), indicated that handling, tagging and transport of the sea trout did not greatly impact their subsequent survival and behaviour. The results did not differ between two release sites (0 and 9 km upstream from the waterfall) and did not depend on fish body size or sex. Fish with large, external radio transmitters had covered a shorter distance before spawning than fish with small transmitters. Our results indicate that the use of external transmitters may reduce the migration distance and affect the distribution of fish during the spawning period. Hence, we recommend using as small external transmitters as possible in watersheds where fish have to negotiate waterfalls and river stretches with strong currents. A low determination coefficient of the model (r2 = 0.22) indicates that other factors than the external transmitters largely affect the migration distance among individuals.
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Kim, Y., Roulet, N. T, Peng, G., Li, C., Frolking, S., Strachan, I. B. & Tremblay, A. 2014: Multi-year carbon dioxide flux simulations for mature Canadian black spruce forests and ombrotrophic bogs using Forest-DNDC. Boreal Env. Res. 19: 417–440.

Ecosystem modelling is a useful tool for gaining insight and quantifying the carbon exchange between the atmosphere and terrestrial ecosystems. This study examines how well Forest-DNDC (a process-based biogeochemical model for forests/wetlands) estimates carbon dioxide (CO2) fluxes from Canadian boreal forests and peatlands. We also evaluate the appropriateness in using Forest-DNDC to establish the baseline conditions of CO2 fluxes before land-use change. Two mature black spruce forests and two ombrotrophic bogs were selected for comparisons between modelled and measured CO2 fluxes. Two vegetation parameters in Forest-DNDC were optimized, and a hydrologic parameter was calibrated for the CO2 flux simulations. The daily GPP (gross primary production) and ER (ecosystem respiration) simulations from all the study sites were in close agreement with the observations (r2 for GPP and ER equal 0.79–0.86 and 0.86–0.87, respectively). The results of this study show that Forest-DNDC is useful in establishing baseline exchanges for boreal ecosystems prior to land-use change.
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Snickars, M., Rinne, H., Salovius-Laurén, S., Arponen, H. & O'Brien, K. 2014: Disparity in the occurrence of Fucus vesiculosus in two adjacent areas of the Baltic Sea — current status and outlook for the future. Boreal Env. Res. 19: 441–451.

The occurrence of the habitat-forming macroalgae Fucus vesiculosus has generally decreased in many Baltic Sea areas. Parallel to eutrophication, water temperature has increased, enhancing pelagic primary production, light absorption and sedimentation, affecting phytobenthic communities. We studied the occurrence of F. vesiculosus (> 3400 drop-video observations) and long-term environmental changes in two adjacent areas (Archipelago Sea, Bothnian Sea). Fucus vesiculosus has not recovered from its disappearance from the outer Archipelago Sea that was reported in the late 1970s. In the Bothnian Sea, it was six times more common and grew deeper and denser. Temperature, total phosphorus concentration and chlorophyll a have increased since the 1970s in both areas but from lower initial levels in the Bothnian Sea. We suggest that if the trends of these variables continue, the water quality of the Bothnian Sea will deteriorate within two to three decades and reach levels that may lead to major losses of F. vesiculosus.
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Enno, S.-E., Post, P., Briede, A. & Stankunaite, I. 2014: Long-term changes in the frequency of thunder days in the Baltic countries. Boreal Env. Res. 19: 452–466.

Long-term changes in the thunderstorm climate of the Baltic countries and their relations with circulation weather types (CWT) during the period 1950–2004 were analyzed. The study area was located in northeastern Europe and encompassed Estonia, Latvia and Lithuania. Thunderstorm day (TD) data series collected by of observers at 40 meteorological stations were carefully checked for artificial inhomogeneities and used as the data source. During the study period, the average annual number of TDs decreased by about 24% in the Baltic countries with a rate of 0.9 TDs per decade. The maximum in thunderstorm frequency was observed during the period 1953–1963, and the minimum during 1990–1994. A long-term decrease in the TD frequency was accompanied by an increased frequency of northerly CWTs that are unfavorable for thunderstorm development. Meanwhile, the frequency of southerly and easterly CWTs that are favorable to thunderstorm formation decreased.
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