Rumyantsev, V., Viljanen, M. & Slepukhina, T. 1999. The present state of Lake Ladoga, Russia — a review. Boreal Env. Res. 4: 201–214.
Abstract
Full text (pdf format)
Holopainen, A.-L. & Letanskaya, G. I. 1999. Effects of nutrient load on species composition and productivity of phytoplankton in Lake Ladoga. Boreal Env. Res. 4: 215–227.
Abstract
Full text (pdf format)
Karjalainen, J., Rahkola, M., Holopainen, A.-L., Huttula, T., Jurvelius, J., Viljanen, M., Avinski, V., Letanskaya, G. & Telesh. I. 1999. Trophic gradients and associated changes in the plankton community in two bays of Lake Ladoga. Boreal Env. Res. 4: 229–238.
Abstract
Full text (pdf format)
Viljanen, M., Holopainen, A.-L. & Silvennoinen, R. 1999. Fluorometer measurements and transmission of light in different parts of Lake Ladoga. Boreal Env. Res. 4: 239–244.
Abstract
Full text (pdf format)
Rahkola, M., Avinski, V., Holopainen, A.-L., Jurvelius, J., Karjalainen, J. & Viljanen, M. 1999. Interacting in the dark: a study of the diel vertical migrations of pelagic plankton and fish in Lake Ladoga. Boreal Env. Res. 4: 245–255.
Abstract
Full text (pdf format)
Telesh, I.V. 1999. Species diversity and spatial distribution of the summer rotifer assemblages in Lake Ladoga. Boreal Env. Res 4. 257–262.
Abstract
Full text (pdf format)
Kapustina, L. 1999. Recent dynamics of bacterioplankton in Lake Ladoga. Boreal Env. Res. 4: 263–267.
Abstract
Full text (pdf format)
Davydova, N.N., Kukkonen, M., Simola, H. & Subetto, D.A. 1999. Human impact on Lake Ladoga as indicated by long-term changes of sedimentary diatom assemblages. Boreal Env. Res. 4: 269–275.
Abstract
Full text (pdf format)
Ilyashuk, B.P. 1999. Littoral oligochaete (Annelida: Oligochaeta) communities in neutral and acidic lakes in the Republic of Karelia, Russia. Boreal Env. Res. 4: 277–284.
Abstract
Full text (pdf format)
Rumyantsev, V., Viljanen, M. & Slepukhina, T. 1999. The present state of Lake Ladoga, Russia — a review. Boreal Env. Res. 4: 201–214.
Holopainen, A.-L. & Letanskaya, G. I. 1999. Effects of nutrient load on species composition and productivity of phytoplankton in Lake Ladoga. Boreal Env. Res. 4: 215–227.
Karjalainen, J., Rahkola, M., Holopainen, A.-L., Huttula, T., Jurvelius, J., Viljanen, M., Avinski, V., Letanskaya, G. & Telesh. I. 1999. Trophic gradients and associated changes in the plankton community in two bays of Lake Ladoga. Boreal Env. Res. 4: 229–238.
Viljanen, M., Holopainen, A.-L. & Silvennoinen, R. 1999. Fluorometer measurements and transmission of light in different parts of Lake Ladoga. Boreal Env. Res. 4: 239–244.
Rahkola, M., Avinski, V., Holopainen, A.-L., Jurvelius, J., Karjalainen, J. & Viljanen, M. 1999. Interacting in the dark: a study of the diel vertical migrations of pelagic plankton and fish in Lake Ladoga. Boreal Env. Res. 4: 245–255.
Telesh, I.V. 1999. Species diversity and spatial distribution of the summer rotifer assemblages in Lake Ladoga. Boreal Env. Res 4. 257–262.
Kapustina, L. 1999. Recent dynamics of bacterioplankton in Lake Ladoga. Boreal Env. Res. 4: 263–267.
Davydova, N.N., Kukkonen, M., Simola, H. & Subetto, D.A. 1999. Human impact on Lake Ladoga as indicated by long-term changes of sedimentary diatom assemblages. Boreal Env. Res. 4: 269–275.
Ilyashuk, B.P. 1999. Littoral oligochaete (Annelida: Oligochaeta) communities in neutral and acidic lakes in the Republic of Karelia, Russia. Boreal Env. Res. 4: 277–284.
Until the early 1960s, Lake Ladoga was oligotrophic and characterized by good water quality, but within the past 20–30 years, as a result of human impact, the ecological state seems to have deteriorated. Especially since the 1970s, its trophic state has changed to mesotrophic, with elevated nutrient concentrations and decreased transparency. Conditions at some of the worst polluted sites have actually improved in recent years, due to closing down of some sources of industrial pollution, but there are alarming signs of general eutrophication of the main body of water. The total concentration of phosphorus has increased 2–5-fold since the 1960s. During the last decades, several planktonic, benthic and fish species sensitive for eutrophication have disappeared. The present species composition and the biomass of the plankton and zoobenthos typify different trophic conditions in different parts of the lake. Primary production, phytoplankton and zooplankton biomass and species composition display mesotrophic and eutrophic conditions in the coastal regions, whereas the pelagial areas are mainly oligo-mesotrophic. The species composition of the macrobenthos and its small biomass characterize the deep central part of Lake Ladoga as oligotrophic.
Back to the top
As part of the joint Russian-Finnish evaluation of human impact on Lake Ladoga, we studied the phytoplankton species composition, biomass, chlorophyll a content and primary production in the lake in order to estimate the state of eutrophication. Samples were collected from 9–31 sampling stations in August 1992–95. In the surface water, the phytoplankton biomass varied from 0.3 to 6.6 g m–3 fresh weight, chlorophyll a from 1.7 to 18.6 mg m–3 and the primary productivity of phytoplankton from 33 to 471 mg C m–3 d–1. The biomass was lowest close to the western shore and highest in the Sortavala Bay. Blue-green and green algae were abundant inshore and small cryptophyceans (Rhodomonas lacustris, Cryptomonas spp.) offshore. In the most nutrient-rich parts of Lake Ladoga (Volkhov, Sortavala and Svir bays) the phytoplankton communities were dominated mainly by blue-greens and cryptomonads. Areas close to the Vuoksa and Burnaya rivers were dominated by diatoms (Diatoma tenuis, Asterionella formosa, Tabellaria fenestrata, Aulacoseira italica, A. granulata, Melosira varians, Fragilaria crotonensis, Stephanodiscus binderanus and Synedra actinastroides). In the 1970s and 1980s eutrophication was seen not only as changes in species composition of phytoplankton but also as growing biomass and algal primary productivity. The maximum mean total phosphorus content (26 mg m–3) was attained during the late 1970s when the mean biomass of algae was six times and the maximum values 20 times those in the 1960s. In the 1990s the tendency has been towards decreasing phosphorus content (1992–95 mean 18 mg m–3), but the changes in phytoplankton productivity between years were connected mainly with temperature. On the basis of phytoplankton biomass, chlorophyll a content and primary production, Lake Ladoga can presently be classified as a mesotrophic lake. The most eutrophicated areas are found in the northern archipelago and in areas influenced by large rivers.
Back to the top
Simultaneous analyses of water quality parameters, and the composition of phytoplankton, crustacean and rotifer assemblages were done at two sampling areas in Lake Ladoga: the Sortavala Archipelago (August 1994 and 1995) and the Bay of Volkhov (August 1994). The samples were taken at stations located at different distances from the main nutrient-loading points in both areas. The plankton communities in the two study areas differed due to differing hydrological conditions and also with respect to the waste water influence. The effect of nutrient loading on the plankton community is evident along the Bay of Sortavala. However, wind-induced currents from the pelagic zone to the bay also affect the structure of the plankton community. In the Bay of Volkhov, high discharge and turbidity as well as the waste waters appear to decrease phyto- and zooplankton biomasses in comparison to those in the Bay of Sortavala.
Back to the top
A fluorometer and multispectral underwater photodetector was used in different parts of Lake Ladoga during a joint Russian-Finnish expedition in 1995 to measure in vivo fluorescence and the intensity of solar and sky radiation. The spectral distribution of radiation at various depths in the water column and penetration of photosynthetically active radiation (PAR) were measured using an underwater multispectral photodetector (420–670 nm). The results were compared with Secchi disk and temperature measurements. The fluorometer values were highest in the pelagic zone of the lake and smallest in areas close to the Burnaya River and in the Volkhov Bay. Light absorption by algae and other suspended matter effectively reduced light penetration especially in the Volkhov Bay. Deepest transmission of light in water and relatively low fluorometer values were found in the western areas of the lake, where light (at 1% level of surface radiation) was transmitted more than six metres. Pulp mill waste waters seemed to decrease the photosynthetic activity in the NE part of the lake.
Back to the top
The diel vertical distribution of nutrients, phytoplankton, zooplankton and fish were studied simultaneously at two pelagial stations in Lake Ladoga in August 1995. At one site (Valaam) cryptophyceans dominated in phytoplankton, while at the other (Konevits) diatoms were more common. In Valaam the algae were distributed unevenly, mainly in the surface layers, while in Konevits the algae were distributed evenly throughout the entire 0–20 m layer. In Valaam a clear diel migration pattern was observed by most of studied zooplankton taxa, while in Konevits only large Cyclops and Limnocalanus migrated. The peak total density of pelagic fish was more than twice as high in Konevits as in Valaam, while the zooplankton density was three times lower in Konevits than in Valaam. In Valaam the clear surface maximum of cryptophyceans probably affected the migration pattern of most species of herbivorous zooplankton. In Konevits the lower temperature in the metalimnion, where the daytime zooplankton maximum occurred, and evenly distributed food resources may have limited zooplankton migration, despite the existing predation pressure.
Back to the top
The rotifer assemblages of Lake Ladoga were studied in samples of the 0–10 m water layer taken at 60 sampling stations in different parts of the lake in August 1994 and 1995. In general, the species composition of the pelagial assemblages was rather similar throughout the lake. However, the dominant species differed markedly between the northern part, the central area and the Volkhov Bay. The highest species diversity (Shannon index H´ = 3.03) and lowest wet weight biomass of rotifers (0.015 mg WW l–1) were recorded in the Volkhov Bay, maximum biomass (2.53 mg WW l–1) in the northern pelagic region, and lowest species diversity (H' = 0.25) in the northern archipelago. The filter-feeding microphagous rotifers Conochilus unicornis and Keratella cochlearis dominated most of the microzooplankton communities in the northern parts of the lake, while grasping phytophagous species of the genus Polyarthra predominated in the central and south-eastern parts. Species diversity, spatial distribution and the role of rotifers in the zooplankton community structure are discussed in relation to the ecological zoning of Lake Ladoga.
Back to the top
New data are presented on the dynamics of total bacterioplankton numbers (BN) and dark CO2-fixation (DCF) in 1989–1993. During this period, both BN and DCF have been much higher than in the preceding years. Summer averages of DCF and BN for the period 1985–1988 were 0.49 ug C l–1 d–1 and 0.54 x 106 cells ml–1, and for 1989–1993 they were 2.4 µg C l–1 d–1 and 1.02 x 106 cells ml–1, respectively. The summer 1992 averages of BN, 2.26 x 106 cells ml–1 in epilimnion and 1.16 x 106 cells ml–1 in hypolimnion are the highest values recorded since the beginning of bacterioplankton investigations in Lake Ladoga in 1977. The increase of DCF and BN has been accompanied with a considerable decrease (from 9 down to 6.3–8.3 mg l–1) of total organic carbon levels in Lake Ladoga.
Back to the top
Lake Ladoga is the largest lake in Europe. Eutrophication of the lake, caused by various human activities, has been noticed since the early 1960s. Besides nutrients, Lake Ladoga is also affected by industrial pollution. In order to assess patterns and trends in the aquatic environment quality, we have applied Detrended Correspondence Analysis (DCA) to surface sediment diatom assemblages, collected from different parts of the lake in 1959–60, 1978–79 and 1991–94, and from the main inflowing rivers in 1983–85. The eutrophication process is evident as a general change of the diatom assemblages between the three sampling periods, e.g. appearance of Diatoma tenuis first in the Volkhov Bay area in 1978–79 and subsequently throughout the lake. The eutrophication appears most pronounced near the discharge sites of industrial and municipal effluents and main river inflows. The river sediment assemblages reflect patterns in the riverine inflow quality related to catchment geology and effluent loading.
Back to the top
The structure of littoral oligochaete communities in relation to pH was studied in five small lakes in South-western Karelia. Among the lakes, three were affected by acidification and characterized by low pH (mean pH = 4.2–5.9). Two lakes were neutral (mean pH = 6.9 and pH = 7.1, respectively). The oligochaete communities of the acidified lakes were poorer compared to the neutral ones. Taxa richness, total biomass of the oligochaetes, their relative density and relative biomass in macroinvertebrate communities were lower in the strongly acidified lakes. Changes of major taxon proportions in the total density and biomass of the oligochaetes were recorded with lowering of pH. For the analyses, the oligochaetes were separated into three functional feeding groups, as gatherers (S) that selectively ingest mainly on the sediment surface and other substrates, gatherers (T) that selectively ingest mainly in the sediments, and predators. Total density of gatherers (T) as well as their relative density in the oligochaete assemblage and macroinvertebrate communities were lower in the acidified lakes.
Back to the top