Water chemistry of Lake Ladoga and Russian-Finnish intercalibration of analyses

As part of the Russian-Finnish research studies on Lake Ladoga, joint expeditions were organized in 1992 and 1993. Water samples were collected for intercalibration of chemical analysis methods and to monitor the chemical quality of the lake water.In August of 1992 water samples were taken from northern Lake Ladoga for intercalibration of Russian and Finnish analysis methods. In August 1993 water samples were collected from 23 sampling stations in all parts of the lake; some of these were also used for intercalibration purposes.The oxygen, colour and COD_Mn results were at the same level in the intercalibration. In 1993, the P_tot results obtained were acceptable. In N_tot, Fe and Mn analysis there seemed to be systematic and random errors between some results.The Secchi depth ranged from 1.5 m to 3.3 m. The average concentrations for the total phosphorus ranged from 15 µg 1^–1 to 29 µg 1^–1. The total nitrogen values were from 620 µg 1^–1 to 690 µg 1^–1. The N:P ratio varied from 24 to 40. The concentration of phosphorus indicated mesotrophic or even eutrophic conditions in the lake. Phosphorus seemed to be the limiting nutrient to bacteria and algae.     

Changes in diatom assemblages in the profundal sediments of two large oligohumic lakes in eastern Finland

Sedimentary diatom assemblages in two large oligotrophic clear-water lakes were analysed, to assess their present ecological state and possible eutrophication due to diffuse nutrient loading. The lakes Pyhäjärvi and Puruvesi (Finnish lake district) are proportionally large for their catchment areas which accounts for their long retention times (ca 7 and 11 yr) and oligohumic character. Pyhäjärvi was studied by pairwise comparison of surface sediment diatom assemblages collected in 1985 and 1990 at 12 sites from different parts of the lake. In Puruvesi, the stratigraphy of diatoms was analysed in two short cores from 8 m and 32 m depths.The diatom assemblages of the two lakes are rather similar, and quite distinct from the assemblages of the mesohumic large lakes of the area. Cyclotella kuetzingiana is the most common planktonic dia- tom, but Aulacoseira ambigua abounds in Pyhäjärvi at sites with local sources of eutrophication. A diverse assemblage of benthic forms, especially Fragilaria and Achnanthes spp. characterizes the shallow bottoms in both lakes.There was little change within the short-core diatom profiles of Puruvesi, but the floral composition of the 8-m and 32-m sites differed markedly. The 8-m site, with 60–70% of benthic forms, represents illuminated bottom, on which much of the buried algae have lived in situ, while the deeper site is true profundal, dominated by sedimented planktonic algae.In Pyhäjärvi there was a slight increase in the benthic diatoms from 1985 to 1990, coinciding with increased phosphorus and chlorophyll concentrations as well as Secchi depth lowering. We interprete this observation as a very early step of eutrophication, of which first the sessile algal communities of the illuminated bottom areas have benefited.     

State of Lake Sysmäjärvi,Eastern Finland,after loading with mine water and municipal waste water for several decades

Hydrobiologia - The deep mining of copper and nickel at Outokumpu, Eastern Finland, lasted from 1910 to the late 1980s, during which period metalliferous waste water of high conductivity and...     

Spatiotemporal and long-term variation in phytoplankton communities in the oligotrophic Lake Pyhäjärvi on the Finnish-Russian border

As part of the joint Finnish-Russian research and development project “Assessment of the ecological state of the transboundary waters”, seasonal and spatial variations in the phytoplankton communities of Lake Pyhäjärvi were studied in order to identify possible long-term (1963–2002) changes and to present recent data (since 2002) on phytoplankton biomass and species composition. Some changes in both phytoplankton biomass and species composition, particularly in the littoral zone and northern basins of the lake, were obvious at the end of the 1980s; in particular, the density of blue-greens increased during that period. Biomasses increased five-fold in 1980, decreased after 1990 and have remained low (0.14 mg l^?l) to the present time. The effective water protection measures applied, especially reducing the phosphorus load from municipal wastewaters and airborne pollution, can now be seen to have improved the water quality. Although no significant temporal differences were found in phytoplankton biomass during the intensive biweekly sampling in 2002, considerable spatial variation was seen within the lake. An obvious change in the species composition of phytoplankton and an increase in biomass were seen even in the loaded parts of the lake. Despite the spatial differences in phytoplankton biomass and community structure, the changed species composition in the northern part of the lake indicated a clear recovery from the blue-green and Chrysophyceae dominated high biomass of the 1980s.     

Water currents and spreading of river load in Lake Pyhäselkä, Saimaa, Finland

During the summers of 1989–1990, the pattern of water flow and the water quality in Lake Pyhäselkä, Finland, were studied using field observations and a 3-dimensional model. The lake receives its major point-source loading, including pulp mill effluents, via the Pielisjoki River in the northeastern part of the lake, where the water is slightly eutrophic. The flow pattern was measured with three types of recording current meters, two of which were conventional mechanical meters and the third a new acoustic current profiler. The profiler was used in direct reading mode on a research vessel and also in self-contained mode on a float installed in the deep basin of the lake. The water-quality part of the model simulates oxygen, BOD, total phosphorus, AOX, and phytoplankton biomass. The three-dimensional model applied here simulates accurately the flow pattern of the water in Lake Pyhäselkä. The results of this study made it possible to detect different flow patterns in the lake. The main load is clearly affected by the wind-induced pattern of flow.