Jurvelius, J. & Marjomäki, T. J. 2004: Vertical distribution and swimming speed of pelagic fishes in winter and summer monitored in situ by acoustic target tracking. Boreal Env. Res. 9: 277–284.

We studied the swimming speed and vertical distribution of fish under ice from March to April and in open water in August. Fish were surveyed with a downward facing stationary 120 kHz split beam echo-sounder in a boreal lake. A commercial trace tracking software was used to estimate the depth, speed and size of fish. Most fish in the study area were smelt (Osmerus eperlanus) and vendace (Coregonus albula). In March and April, fish were detected under the ice around the clock, whereas in August only a few fish were detected during daytime. Fish were typically detected between 12 and 19 m depth and they swam from 5 to 50 cm s^–1 i.e. 0.5 to 3 body lengths s^–1. The effect of sunrise and sunset on the under-ice swimming depth and speed became more marked with increasing day length. In summer, the effect on depth was not so evident. In March–April there was a shift towards day activity, which persisted in August. Changing illumination seemed to account for most variation in the swimming depth and speed of fish.

Kiiskinen, P., Huuskonen, H., Hyvärinen, H. & Piironen, J. 2004: Smolting of two-year-old lower and upper size class of Saimaa landlocked salmon (Salmo salar m. sebago Girard) under fish farm conditions. Boreal Env. Res. 9: 285–293.

Smolt development was assessed in two-year-old lower and upper size class of hatchery-reared Saimaa landlocked salmon during January–July and late April–July, respectively. The fish in both size classes showed increased gill Na⁺,K⁺-ATPase during the spring suggesting smolting of these fish. The fish in the lower size class showed also a smolting-associated decrease in lipid content of muscle as spring progressed whereas the lipid content in upper-size-class fish appeared to increase during late April–May. The differences in lipid content of muscle as well as in gill Na⁺,K⁺-ATPase activity between the groups may indicate the presence of non-smolting individuals among the fish sampled from upper size class. However, variation in these as well as other parameters was small. Thus, it is suggested that each class of juvenile Atlantic salmon shows a distinct developmental pattern of ionoregulation.

Nilsson, J., Andersson, J., Karås, P. & Sandström, O. 2004: Recruitment failure and decreasing catches of perch (Perca fluviatilis L.) and pike (Esox lucius L.) in the coastal waters of southeast Sweden. Boreal Env. Res. 9: 295–306.

In the early 1990s, commercial and recreational fishermen in the Kalmar Sound of the Baltic Sea reported decreasing stocks of Eurasian perch (Perca fluviatilis) and northern pike (Esox lucius). Test fishing surveys confirmed regionally declining abundances of both species. Both pike and perch spawning were observed annually, but virtually no young-of-the-year were captured in surveys from 1997–1999. The rapid decrease of the stocks was probably a result of the widespread recruitment failure. Studies of potential causes of the recruitment failure were conducted in 1998–2000. Field experiments excluded suboptimal water quality in brackish water recruitment areas as regulatory factor. Laboratory tests did not indicate reproductive disturbances in parental fish that could be related to chronic toxicity or endocrine disruptions, as hatching success and yolk-sac larvae survival were not negatively affected. Exposure to filamentous algae (Pilayella sp.) and diatoms, common in the spawning areas, had only a slight negative effect on pike egg hatchability. Two hypotheses that could not be rejected are food deficiency during the post hatching period and egg predation.

Linderholm, H. W. & Linderholm, K. 2004: Age-dependent climate sensitivity of Pinus sylvestris L. in the central Scandinavian Mountains. Boreal Env. Res. 9: 307–317.

Twentieth century climate–radial growth relationships of Pinus sylvestris L. at the central Scandinavian Mountain tree line were analyzed. Some differences in growth responses to climate were evident among age classes, where the old pines (> 250 years old) retained their climate sensitivity throughout the analysed period better than the middle-aged pines (100–250 years old). However, the pines in the oldest age class responded less to unfavourable climate than the pines in younger age classes. The pines in all the age classes displayed significant changes in climate/radial growth relationships from the 1940s and onwards. From the 1970s, pines in the youngest age class (about 35 years old) displayed a higher climate sensitivity than the older pines, in addition to which they had high growth rates not previously seen in the past five centuries. Changes in climate/radial growth relationships were related to a twentieth-century climate change. Finally our results illustrated the importance of including trees of all ages when building a tree-ring chronology for climate research.

Solantie, R. 2004: Daytime temperature sum — a new thermal variable describing growing season characteristics and explaining evapotranspiration. Boreal Env. Res. 9: 319–333.

The effective temperature sum, the sum of the positive differences between diurnal mean temperatures and 5 °C, is used in ecology, agriculture, forestry, and hydrology. It does not differentiate between day and night. However, most assimilation and evapotranspiration occurs in the daytime. A "daytime temperature sum" is presented that is better related to assimilation. First, temperatures above 7 °C were integrated during the period, starting when the sun rises five degrees above the horizon, and ending when it descends to two degrees. The sums of these values were then reduced to be, on average, equal to the traditional ones. The new variable appeared to smooth out much of the spatial variation caused by night-time temperatures. It also gives a more distinct start and end to the thermal vegetation period. When using the daytime temperature sum instead of the traditional sum in explaining evapotranspiration, a better result was obtained.

Tervahattu, H., Hongisto, M., Aarnio, P., Kupiainen, K. & Sillanpää, M. 2004: Composition and origins of aerosol during a high PM₁₀ episode in Finland. Boreal Env. Res. 9: 335–345.

We investigated the sources of a PM₁₀ episode in September 2001 on the coasts of the Gulf of Finland. The episode lasted six days with the peak phase lasting over 14 hours. The highest hourly PM₁₀ concentration was 190 ug m^–3. Exceptional meteorological conditions strongly influenced the course of the episode. Very warm air masses came from central Asia forming a stable inversion over the Gulf of Finland. Dust emissions from the Estonian and Russian oil-shale burning industrial areas near the southeastern coast of the Gulf of Finland were transported over the Gulf above the inversion layer. After reaching the northern coast the PM was mixed down by convection and partly by gravitation, and then transported westwards along the coastline. The chemical analyses by SEM/EDX and IC indicated that the particles had both the characteristics of the oil-shale burning emissions and soil dust. Windy conditions in the Kazakhstan Ryn Peski desert raised soil dust into the air. This dust was transported towards Scandinavia and mixed with the anthropogenic emissions. Such large quantities of coarse particles from foreign sources have not been observed earlier in Helsinki.

Tanskanen, N., Kareinen, T., Nissinen, A. & Ilvesniemi, H. 2004: Soil solution aluminium in disturbed and undisturbed podzolic profiles at two tilt-ploughed forest sites. Boreal Env. Res. 9: 347–355.

Podzolic soil profiles down to the illuvial (B) horizon are inverted on soil surfaces during ploughing of forest soils (as part of forestry practices). As a result, aluminium once immobilized in the horizon may begin to remobilize. In the present study, soil solution Al concentrations in ploughed podzolic profiles were compared with those of the corresponding undisturbed profiles at two forest sites tilt-ploughed 17 (K1) and 31 (K2) years ago. The soil solution was obtained from fresh soil samples, using a centrifugation drainage technique. Aluminium was fractioned to labile monomeric Al, non-labile monomeric Al and acid-soluble Al. Increased concentrations of various Al fractions were observed in the ploughed profiles at both forest sites, especially in the Bs horizons exposed to the soil surface and in the O horizon buried beneath the tilt at site K1. In those horizons where Al had increased, soil solution pH decreased while the concentration of dissolved organic carbon (DOC) increased, suggesting that remobilization of Al occurred in the ploughed profiles.