ISSN 1239-6095
© Boreal Environment Research 2006

Contents of Volume 11 Number 3

Peltola, P. & Wikström, E. 2006: Tyre stud derived tungsten carbide particles in urban street dust. Boreal Env. Res. 11: 161–168.
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Jaagus, J. 2006: Trends in sea ice conditions in the Baltic Sea near the Estonian coast during the period 1949/1950–2003/2004 and their relationships to large-scale atmospheric circulation. Boreal Env. Res. 11: 169–183.
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Tulonen, T., Pihlström, M., Arvola, L. & Rask, M. 2006: Concentrations of heavy metals in food web components of small, boreal lakes. Boreal Env. Res. 11: 185–194.
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Valpola, S. E. & Ojala, A. E. K. 2006: Post-glacial sedimentation rate and patterns in six lakes of the Kokemäenjoki upper watercourse, Finland. Boreal Env. Res. 11: 195–211.
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Rankinen, K., Kenttämies, K., Lehtonen, H. & Nenonen, S. 2006: Nitrogen load predictions under land management scenarios for a boreal river basin in northern Finland. Boreal Env. Res. 11: 213–228.
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Northcote, T. G. & Hammar, J. 2006: Feeding ecology of Coregonus albula and Osmerus eperlanus in the limnetic waters of Lake Mälaren, Sweden. Boreal Env. Res. 11: 229–246.
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Peltola, P. & Wikström, E. 2006: Tyre stud derived tungsten carbide particles in urban street dust. Boreal Env. Res. 11: 161–168.

In countries where studded winter tyres are used they contribute to the generation of street dust by grinding the road surface and traction sand into finer particles. At the same time the hard metal tips of the studs, made out of tungsten carbide (WC), wear to finer particles dispersed into the environment. Elevated tungsten concentrations in different sampling media, probably caused by the use of studded tyres, have also been reported. In this study three size fractions of street dust sampled in Turku, Finland, were investigated. Tungsten and various other element concentrations were determined with ICP-MS after total dissolution, pseudo total concentration (aqua regia) and a weaker extraction (1M NH4Ac). A visual analysis was made with a SEM-EDX to study the presence and size fraction of WC particles, which has not been studied before. The total concentrations (median values) of tungsten in the fractions were 9.2 g g–1 (100 µm–2 mm), 21 µg g–1 (45 m–100 m) and 39 g g–1 (< 45 µm). As expected, tungsten showed a tendency to accumulate into the finer size fractions. However, more surprising was the result that out of all elements determined, tungsten had the greatest (median values) relative enrichment in the fine fraction. In the SEM-EDX analysis particles consisting of tungsten were identified and ruled out to be WC abraded from tyre studs. The WC particles occurred either separately or in clusters with size range of 0.1–1.4 µm.
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Jaagus, J. 2006: Trends in sea ice conditions in the Baltic Sea near the Estonian coast during the period 1949/1950–2003/2004 and their relationships to large-scale atmospheric circulation. Boreal Env. Res. 11: 169–183.

In this paper, I study changes in the sea ice regime near the Estonian coast in 1949/1950–2003/2004. The trends in the dates of the first appearance of sea ice and final disappearance of sea ice, as well as in the number of days with sea ice, were analysed and related to the trends in air temperature and atmospheric circulation characteristics. The dependence of sea ice trends on circulation changes was estimated with the conditional Mann-Kendall test. The results revealed no similar trends in sea ice parameters in different areas of Estonia. I found a significant shift towards a later date in the first appearance of sea ice on the western Estonian coast of the inland sea, but not on the coasts of the Gulf of Finland and the Baltic Proper. This trend could not be explained by the trends in the circulation parameters. The date of the final disappearance of sea ice has shifted earlier by more than a month. The largest change has occurred at the westernmost stations and the smallest change was typical for the Gulf of Finland. This variable had a close correlation with the intensity of westerlies during the whole winter. The correlation coefficient between the date of the final disappearance of sea ice, NAO and AO indices and the frequency of the zonal circulation type W during the winter season (December–March) lay between –0.56 and –0.73. Concerning single months, the circulation in February plays a key role. The number of days with sea ice, as the main characteristic of the iciness, has decreased significantly in all the stations, except in Kunda and Narva-Jõesuu located on the southern coast of the Gulf of Finland. The most substantial decrease was observed at the westernmost stations located on the open coast of the Baltic Proper. This change was also induced by an increase in the intensity of winter westerlies.
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Tulonen, T., Pihlström, M., Arvola, L. & Rask, M. 2006: Concentrations of heavy metals in food web components of small, boreal lakes. Boreal Env. Res. 11: 185–194.

The concentrations of heavy metals in different food web components, such as zooplankton, benthic invertebrates and fish, were examined in small humic lakes from southern Finland. Variation in metal concentrations in zooplankton was observed between different lakes and in benthic invertebrates between different animal groups. We found a significant relationship between lakewater pH and Cd concentration in isopods (Asellus aquaticus), while no relationship between the humic content of lakewater and Cd or Hg concentrations was observed. Annual variation in Cd, studied over a six-year period, was correlated with the amount of discharge, which indicated the importance of the annual loading of Cd from the catchment in determining accumulation in isopods. The metal concentrations in perch (Perca fluviatilis) were higher in a humic and acid lake than in a slightly humic lake and may partly be explained by the varying dietary regime of perch.
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Valpola, S. E. & Ojala, A. E. K. 2006: Post-glacial sedimentation rate and patterns in six lakes of the Kokemäenjoki upper watercourse, Finland. Boreal Env. Res. 11: 195–211.

Sediment distribution and accumulation in a chain of five lakes and Pääjärvi, southern Finland for the last ca. 10 000 years were investigated using acoustic sounding profiles. Lake bathymetry, catchment relief, geology and locations of input creeks and ditches have a critical effect on sedimentary dynamics in the study lakes. These factors cause considerable within-lake variation in the sediment depositions. Typically, the majority of accumulating matter and nutrients are removed from the flow system in sedimentation pools, which are seldom evident on bottom topography alone. However, detailed geological study can provide this information. The physical properties of long sediment sequences from each lake were investigated and dated using a palaeomagnetic dating method. The long-term sediment composition in the study lakes appeared to be more dependent on regional environmental factors, i.e. climate, whereas the rate of sedimentation was connected with soil types and land use in the immediate catchment area.
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Rankinen, K., Kenttämies, K., Lehtonen, H. & Nenonen, S. 2006: Nitrogen load predictions under land management scenarios for a boreal river basin in northern Finland. Boreal Env. Res. 11: 213–228.

In Finland municipal and industrial waste water purification has effectively decreased nutrient emissions from point sources leading to improved water quality. No clear effects of decreasing non-point loading (atmospheric deposition, agriculture, forestry) are found, however, and nitrate concentrations are increasing in some rivers. The aim of this study was to determine the origin and timing of inorganic nitrogen loading to the Simojoki using the dynamic, semi-distributed INCA-N model. The simulation results showed that, at the river outlet, only about half of the inorganic nitrogen load originated from anthropogenic sources. The inorganic nitrogen load largely depended on runoff and half of the annual load was centred around the snowmelt period in April–May. There was a risk of increasing nitrogen load due to changes in agricultural land use. Water protection measures at all diffuse sources could decrease the anthropogenic part of the inorganic N load to the sea, but individual measures would only result in small reductions.
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Northcote, T. G. & Hammar, J. 2006: Feeding ecology of Coregonus albula and Osmerus eperlanus in the limnetic waters of Lake Mälaren, Sweden. Boreal Env. Res. 11: 229–246.

A large block of unpublished information from the late 1960s on the interactive ecology of two highly zooplanktivorous fishes — vendace (Coregonus albula) and smelt (Osmerus eperlanus) — in Lambarfjärden of Lake Mälaren, Sweden, was used to demonstrate quantitatively diel and seasonal changes in their limnetic feeding distribution, to compare their trophic structures, and to examine their selective use of some 20 different zooplanktonic taxa with those pelagically present by species, size, abundance and vertical distribution. Although there were significant differences in gillraker number, as well as spacing and structure between vendace and smelt, these did not seem to be strongly reflected in selection or use of major zooplanktonic prey taxa during the summer–autumn seasons. While small cladocerans dominated the prey choice of both species during June–September, large-sized calanoid copepods dominated in October. Schoener's overlap indices were high for both vertical distribution and prey taxa use by the two species, suggesting the possibility of strong competitive interaction between their planktivorous stages, though alternative explanations are explored. Their joint use of pelagic space and prey, changing seasonally, may offer a partial explanation for the marked year class fluctuations and periodic failures of vendace recruitment known to occur in Lambarfjärden, and other lakes where the two species coexist. In addition, the comparisons support the image of the environmental cul-de-sac position of vendace as an extreme zooplankton specialist, with a very narrow diet spectrum and habitat range, whereas smelt seem to express a more opportunistic ecology.
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