Ruokolainen, L., Lilley, T. M., Tammi, M. & Vuorinen, I. 2006: Zooplankton in relation to cyanobacteria across a geographic gradient in Archipelago Sea, northern Baltic. Boreal Env. Res. 11: 1–11.

Toxic cyanobacterial blooms are known to be a growing problem in many types of water bodies. Cyanobacteria are also known to affect zooplankton community structure. In this study, we assessed the possible impact of cyanobacterial blooms on zooplankton species composition. Altogether 20 locations on a geographical gradient were sampled in the Archipelago Sea in the northern Baltic during late summer 2003. We analyzed the data using multivariate methods and linear regression. The Mantel test of matrix correspondence revealed a statistically significant relationship between zooplankton species composition and cyanobacterial composition in July. The regression analysis showed a strong negative relationship between the cyanobacterial and copepod abundances. No relationship was found between cladocerans and cyanobacteria. A clear positive relationship was observed between rotifers and cyanobacteria. In conclusion, negative interactions may occur between certain zooplankton taxa and cyanobacteria in the Archipelago Sea, at least in midsummer. These interactions seemed to be associated with geographic zones within the archipelago.

Ådjers, K., Appelberg, M., Eschbaum, R., Lappalainen, A., Minde, A., Repe<ka, R. & Thoresson, G. 2006: Trends in coastal fish stocks of the Baltic Sea. Boreal Env. Res. 11: 13–25.

Coastal fish monitoring with multi-mesh gill nets and gill net series is carried out in eleven areas around the Baltic Sea. The purpose of the monitoring is to reveal population status and elucidate long-term trends of fish population and community development. Time series cover 9–20 years of annual monitoring, the last year being 2002. Significant increasing trends of perch and roach catches were observed in the archipelago region of the Sea of Åland and Archipelago Sea. A possible reason for these trends was ongoing coastal eutrophication. Significant trends with opposite directions appeared in two areas in the Gulf of Bothnia and two areas at the Swedish coast of the Baltic Proper. The Curonian Lagoon is severely affected by anthropogenic impact, structuring the local fish community. Indications of decreased eutrophication were noted in the Gulf of Riga. High fishing pressure during the 1990s in the West-Estonian archipelago and the following collapse of coastal fish stocks was apparent in the monitoring catches.

Huttunen, J. T., Väisänen, T. S., Hellsten, S. K. & Martikainen, P. J. 2006: Methane fluxes at the sediment–water interface in some boreal lakes and reservoirs. Boreal Env. Res. 11: 27–34.

Methane (CH₄) fluxes at the sediment–water interface were studied during summer in six lakes and two reservoirs in Finland. The oxygen penetration in the sediments of these boreal mesotrophic–hypereutrophic freshwater ecosystems varied from 0 to 8 mm, and the CH₄ concentrations within the uppermost 10 cm from 17 to 51000 ppm(v). The diffusive methane fluxes to the overlying water column ranged from 0.44 to 105 mg m^–2 d^–1 and correlated negatively (R² = 0.68) with the oxygen penetration in the sediment. This demonstrated that the CH₄ concentration and the diffusive CH₄ fluxes in the lake sediments are closely related to the O₂ conditions, which regulate both CH4 production and CH₄ oxidation in the sediment. The comparison between the diffusive CH₄ fluxes at the sediment–water interface and CH₄ fluxes at the water–air interface previously measured in situ in one lake and two reservoirs showed that the sediment CH₄ fluxes poorly predict the CH4 release from the water surface to the atmosphere. This indicates that the CH₄ oxidation in water column, advective transport of CH₄ and CH₄ ebullition have importance in the net CH₄ release to the atmosphere. The increased CH₄ concentration in water column close to the sediment is an indicator of serious oxygen depletion within sediment.

Lepistö, L., Holopainen, A.-L., Vuoristo, H. & Rekolainen, S. 2006: Phytoplankton assemblages as a criterion in the ecological classification of lakes in Finland. Boreal Env. Res. 11: 35–44.

Implementation of the Water Framework Directive requires the formulation of lake types and classification of the lakes within each type using biological quality elements. In this study phytoplankton was used to test the lake typology of 32 non-impacted lakes belonging to eight of the ten lake types described in the preliminary Finnish typology. Phytoplankton did not accurately define these types, as only five lake groups were clustered in the DCA ordination analysis. The ecological status was preliminarily established for 23 impacted lakes using total phytoplankton biomass and the number of taxa. Impacted oligo-humic lakes were tentatively classified to a lower ecological status than in the general water quality classification carried out in the 1990s. Even more variation was observed when assessing the ecological status of humic impacted lakes. The number of taxa, on the other hand, appeared to overestimate the ecological status of the lakes, obviously due to the preliminary boundary classes used in this study.

Niva, M., Hernesmaa, A., Haahtela, K., Salkinoja-Salonen, M., Sivonen, K. & Haukka, K. 2006: Actinobacterial communities of boreal forest soil and lake water are rich in mycobacteria. Boreal Env. Res. 11: 45–53.

The actinobacterial communities present in two Finnish lakes and in the surrounding conifer forest soil were investigated using DNA based methods. The dominant actinobacteria in the soil were found to belong to genus Mycobacterium. Therefore specific primers were designed and tested to study the mycobacterial communities in boreal environment more closely. The denaturing gradient gel electrophoresis (DGGE) and sequencing analysis showed that the microbial populations in lakes were different from those in the surrounding soil. Thus, each of the environments had their own actinobacterial and mycobacterial populations. The majority of the obtained mycobacterial sequences were closely related to the described species of environmental mycobacteria, some of which are pathogenic. However, several sequences were not closely related to any presently known species. The chemical characteristics of boreal forest soil seem to favour proliferation of mycobacteria, many of which still remain to be isolated.

Arst, H., Erm, A., Kangro, K., Nõges, T. & Nõges, P. 2006: Comparison of spectral and broad-band models for computing photosynthetically absorbed radiation in turbid waters. Boreal Env. Res. 11: 55–65.

A comparison of values of photosynthetically absorbed radiation calculated with spectral and broad-band models was performed. Special attention was paid to turbid lake waters (Secchi depth ranging from 0.3 to 3 m). Ten measurement series of bio-optical characteristics were carried out in June and August 2003 at three Estonian lakes, Peipsi, Võrtsjärv and Harku. Photosynthetically absorbed radiation was calculated from measured quantum irradiance and a radiation model. The results obtained showed that in case of moderately clear waters (Secchi depth about 3 m) it is especially important to use a correct spectral model, as the errors of the broad-band model can be more than 40%–50%. For very turbid waters these errors usually do not exceed 20%. In our measurement results there was a rather remarkable variability of the bio-optical characteristics of the lakes. The relationships between depth-averaged assimilation number and primary production and between depth-integrated primary production and chlorophyll concentration could be described by polynomial functions with intercept = 0.

Nõges, P. & Nõges, T. 2006: Indicators and criteria to assess ecological status of the large shallow temperate polymictic lakes Peipsi (Estonia/Russia) and Võrtsjärv (Estonia). Boreal Env. Res. 11: 67–80.

Pressure-based approach, morphoedaphic index and historical data were used in deriving reference conditions and classification criteria for the Estonian large lakes: Peipsi and Võrtsjärv. The comparison of the measured total phosphorus with the reference level based on the morphoedaphic index, shows that the water quality could be estimated as 'moderate' in lake Peipsi and 'good' in Võrtsjärv despite that the measured TP values were higher in the latter. Comparing the changes observed in different quality elements with the normative definitions for quality classes given in the Water Framework Directive yielded quality estimates from 'high' to 'moderate' for both lakes. Applying the "one-out all-out" principle according to which the ecological status is determined by the biological quality element, which shows the greatest anthropogenic disturbance, both lakes fall unequivocally into the 'moderate' category. Averaging the quality estimates for lakes Peipsi and Võrtsjärv no matter whether on a quality element level or a single parameter level would indicate good status in both lakes that is close to the subjective cognitive expert opinion of the authors.