Anna-Liisa Holopainen

Seasonal succession, vertical distribution and long term variation of phytoplankton communities in two shallow forest lakes in eastern Finland

Two pristine forest lakes have been sampled for 12 years in order to follow the long term variation of phytoplankton biomass and species composition together with environmental parameters. The lakes Iso Hietajärvi and Pieni Hietajärvi are shallow headwater lakes situated in the Patvinsuo National Park, eastern Finland. Lake Iso Hietajärvi was weakly stratified during the open water season in 1988–2001, in contrast to Lake Pieni Hietajärvi, which was always strongly stratified mainly because of its wind-sheltered location and dark water. During the long study period, the main changes in water quality have been slight increases of alkalinity and pH-value and also some decrease of the nitrate content. The phytoplankton (wet) biomass in surface water varied from 0.07 to 0.51 mg l−1 in Lake Iso Hietajärvi and from 0.18 to 0.60 mg l−1 in Lake Pieni Hietajärvi in 1991, during the intensive weekly sampling. The biomass was mainly composed of Cryptophyceae, Chrysophyceae and Bacillariophyceae in Lake Iso Hietajärvi, and Cryptophyceae in Lake Pieni Hietajärvi. In Lake Iso Hietajärvi, the differences in the vertical distribution of phytoplankton biomass and species composition were small and the productive layer reached down to 4 m, whereas in the dark coloured Lake Pieni Hietajärvi the productive layer was shallow, ≤1 m. When the whole productive water column is considered, the unstratified clear water Lake Iso Hietajärvi is more productive than the stratified dark coloured Lake Pieni Hietajärvi. The seasonal succession of phytoplankton species composition is different in these adjacent lakes; more variation was found in the unstratified Lake Iso Hietajärvi compared to the smaller stratified lake.

Effects of mining industry waste waters on a shallow lake ecosystem in Karelia, north-west Russia

The mining company Karelian Pellet in NW Russia extracts iron ore and processes it locally into iron pellets. The production operations have effects on the environment in the form of air pollution (SO2 and dust) and waste water emissions. The waste waters from the process and the mining pits are let out into a dammed basin, formerly the natural Lake Kostomuksha. This basin flows north-east through several small lakes (e.g., Poppalijärvi, Kento) to the larger lake Middle Kuito and the White Sea. For these small lakes an exceptionally high mineral content, high pH value, and high concentrations of potassium, lithium and nitrogen in the water have been characteristic. However, the total phosphorus content (6–9 μg l−1) is slightly lower than in the Lake Upper Kuito (11–13 μg l−1) which acts as a reference lake. Biota from bacteria to fish were quantitatively sampled in August 2000 and 2001. Our results suggest a twice higher biomass of both phytoplankton (mainly picoalgae) and fish (biomass per unit effort) in the lakes downstream from the mine in comparison to the reference lake. Zooplankton and zoobenthos biomass both peak in L. Kento, the lake in the middle of the outflow series. The fish fauna (seven to eight species caught) is the same in all lakes and is dominated by perch and roach. Both grow well and roach show best growth in L. Poppalijärvi, next to the waste basin. Perch gills show some histopathological changes which do not, however, appear to affect either growth or reproduction.

Liming of the Acidic Lake Valkealampi in Eastern Finland: Effects on Water Chemistry and Phytoplankton

Lake Valkealampi, an acidic lake in eastern Finland, was limed with CaCO3 in July 1983. Prior to liming, its water was clear and acidic (median pH 4.91) with no alkalinity and low levels of Ca, Ptot and chlorophyll a. pH, alkalinity and Ca increased most markedly after liming. CODMn, colour, γ25, SO4, Ntot and Ptot in the surface water were also significantly greater after liming, whereas Altot in the whole water body remained constant. Liming was followed by a decrease in the abundance of Peridinae and an increase in chlorophycean and chrysophycean species. This change persisted for at least 4 years. The number of phytoplankton taxa increased from 5 to 17 in the third year after liming. The trophic status of the lake in terms of chlorophyll a levels, became mesotrophic for 2 years after liming, and although the chlorophyll a level subsequently seemed to diminish, the lake had not yet reached its pre-treatment state after 5.5 years.

Public participation in monitoring programmes as a tool for lakeshore monitoring: the example of Lake Pyhäjärvi, Karelia, Eastern Finland

Abstract Lake Pyhajarvi, on the border between Finland and Russia in Karelia, is a very valuable clear-water lake of the Lobelia type. It belongs to the European Unions Natura 2000 programme in Finland, and has been included in regional and national monitoring programmes since the 1960s. The main monitoring station is situated near the outlet of the lake. Deterioration of its water quality was suspected already in the 1980s because of decreasing Secchi depths (transparency) and increasing chlorophyll a. The occurrence of algal blooms on the lakeshores is monitored weekly during each summer at one site on Lake Pyhajarvi (site 1). This is a part of nationwide intensive algae monitoring programme organised by the environmental authorities together with voluntary observers at some 270 lake sites in Finland since 1998. Since 1997, Secchi depth observations have been carried out by volunteers biweekly or monthly at 17 sites on the lake. In the vicinity of one of these transparency observation sites (station 100), intensive monitoring of algae has been carried out. At this lakeshore monitoring site 69 algal observations were made, ten of which recorded algal blooms during the study period 1998–2002. The observed algal blooms were caused by algae of the Anabaena species, mainly by Anabaena lemmermannii. At Lake Pyhajarvi the number of algal bloom observations received from the public have decreased from the 1990s to the 2000s. The range of Secchi disc transparency was 5.0–8.4 m with a mean value of 6.2 m at station 100 and 4.3–7.7 m (mean 6.1 m) at the main monitoring station 2 during the open water periods in 1998–2002. During this study period, the maximum values at site 100 seem to have increased slightly, which might indicate some improvement in the water quality due to decreased point source loading. We conclude that the intensive algal monitoring results of 5 years at the lakeshore site and the transparency results — both compiled by trained volunteers — reflect an improvement in the state of Lake Pyhajarvi in Karelia. This conclusion is in accordance with the long-term water quality and short-core studies of sedimentary diatoms in Lake Pyhajarvi. We suggest that the intensive algal observations and transparency measurements are both suitable methods for the monitoring of lakeshores and lakes, and that both are suitable for voluntary monitoring. We found public participation a good tool for monitoring lakes and lakeshores.

Temporal and spatial variation in pelagic phytoplankton and zooplankton in the central basin of a large lake, Finland

Spatial heterogeneity is a common feature of ecosystems and is the product of many interacting physical, chemical, and biological processes (PINEL-ALLOUL 1995). The spatial distribution of zooplankton is usually highly aggregated (GEORGE 1981, MALONE & McQuEEN 1983, URABE 1990, VILJANEN & KARJALAINEN 1993, CARTER et al. 1995, KARJALAINEN et al. 1996a), with densities being mainly controlled by the feeding regimes of planktivorous fish (SARVALA et al. 1998). Physical processes such as wind (JONES et al. 1995), wind-induced currents (THACKERAY et al. 2004, RINKE et al. 2007), water temperature and stability (PINEL-ALLOUL et al. 1999), and inshore-offshore temperature gradients (JoHANSsoN et al. 1991) are thought to have a dominant influence on the large-scale spatial distribution of organisms. On smaller scales, however, there are various biological processes that serve to decouple organisms from the direct effects o f many physical processes, notably predation, competition, swarming and avoidance behaviour, reproductive behaviour, size of plankton, food resources (PINEL-ALLOUL et al. 1988, JoHANSSON et al. 1991, VILJANEN & KARJALAINEN 1993, LACROIX & LESCHER-MouTouE 1995). The combined action of wind-induced water movements and organism behaviour can result in large-scale spatial heterogeneity (PINEL-ALLOUL 1995, TuACKERAY et al. 2004). We examined spatial and temporal heterogeneity in the plankton community of a moderately large 1ake, Lake Pyhãselkã, in July of 2 years and revealed and verified short-interval day-to-day temporal and spatial distribution pattems among pelagic plankton. We also analysed the influence of the short time interval, place, depth, temperature, and water currents on phytoplankton and zooplankton.

An overview of the state of two large lakes in North Karelia, Finland

Finland has about 130 000 lakes with a surface area ofmore than 0.04km2, but only 47 ofthese lakes are large (i. e. with an area over 100 km2; MANNIO et al. 2000). Of these large lakes five are situated in North Karelia, the eastermnost province of Finland. Their water chemistry and phytoplankton have been included in both regional and national monitoring prograrnmes from the 1960s, and since 2000 they have been encompassed by the Finnish Eurowatemet (NIEMI et al. 2001). The aim of this work is to give an overview o f two o f these lakes, Lake Koitere and L. Hõytiãinen, and to discuss the long-term data on water quality and phytoplankton in respect to paleolimnological data.

Seasonal water quality variations in two pristine headwater lakes, boreal coniferous forest area, eastern Finland

There are some 30,000 lakes with surface areas >4 ha in Finland (MANNIO et al. 2000). The lakes have different catchment characteristics reflected in variable water qualiry and aquatic ecosystems. The northern European forest lakes thus provide a range of conditions to study the dynamics of water chemistry and the succession of phytoplanktic communities. Several small natural-state catchment areas have been chosen for detailed monitoring and research to assess the effectiveness of emission reductions according to international conventions in different regions in Europe. The Lakes Iso Hietajarvi and Pieni Hietajarvi, eastern Finland, have been studied as a part of an Integrated Monitoring (IM) Programme of Air Pollution Effects on Ecosystems since 1988.

Water chemistry, phytoplankton and hydrodynamics in Lake Pielinen, eastern Finland

The aim of the study was to assess the present state of a large lake in the eastern part of Finland by simultaneous collection of data on hydrodynamics, water chemistry and phytoplankton. lntegrated multidisciplinary data o f this kind are needed for environmental assessment and for planning water protection measures, and also to integrate the monitoring of network design and to assess the ecological quality of waters for the European Freshwater Monitoring Network (NIXON 1996). lnformation of this kind is also needed for the proposed EU directive on water policy (EUROPEAN UNION 1998).

Changes in the ecological state of Lake Ladoga

Although the effect of anthropogenic eutrophication was first observed at the beginning of this century, intensive srudy of this process only began in the 1950s and 1960s. Several planktonic and fish species sensitive to eutrophication have disappeared since then (RUMYANTSEV et al. 1999). The hydrochemical characteristics of Lake Ladoga have recently been srudied by Russian and Finnish scientists (e.g. PETROVA 1982, PETROVA & RAsPLETINA 1987, RAsPLETINA 1992, PETROVA & TERZHEVIK 1992, NIINIOJA et al. 1996, 1997), w ho have also discussed the eutrophication o f the lake. In the most recent developmenr, a slight decrease in rotal phosphorus concenrrations has been reported (CHERNYKH et al. 1994, NIINIOJA et al. 1997). The phytoplankron of Lake Ladoga has been studied intensively since 1975 (PETROVA 1987, LETANSKAYA & HINDAK 1992, 1994, PETROVA & TERZHEVIK 1992, RAHKOLA et al. 1994, HOLOPAINEN et al. 1996, l<ARJALAINEN et al. 1999). The aim of this paper is ro present some new results of joint Russian-Finnish investigations o n the hydrochemistry, plankron and fish of Lake Ladoga and compare these with earlier data to evaluate any changes in the ecological state and nature of h uman impact o n the lake. This study is part of a joint multidisciplinary Russian-Finnish evaluation of human impact on Lake Ladoga.