Eutrophication and recovery of Lake Vesijärvi (south Finland): Diatom frustules in varved sediments over a 30-year period

Liukkonen, Mikko; Kairesalo, Timo; Keto, Juha

doi:10.1007/978-94-017-3622-0_42

Cited by 14 publications

(21 citation statements)

References 13 publications

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“…Small Stephanodiscus diatoms have been found typical of eutrophic and phosphorus‐replete conditions (Stoermer et al ; Anderson ). According to the sediment records from Enonselkä (Liukkonen et al ; Liukkonen et al ), they have been a dominant component of the spring phytoplankton maximum in Enonselkä for decades of its eutrophic history. Mechanical mixing did not seem to affect the species composition of the diatom assemblage, which is not surprising, because natural convection overrode mechanical mixing in late spring.…”

Section: Discussionmentioning

confidence: 99%

Regular build-up of the spring phytoplankton maximum before ice-break in a boreal lake

Salmi

Salonen

2015

Limnol. Oceanogr.

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The development of phytoplankton biomass and composition in a eutrophic boreal lake was studied during the evolution of under‐ice convection in spring. The results from 8 yr showed that, within a few weeks before ice‐break, phytoplankton biomass regularly increased by up to two or three orders of magnitude, reaching or exceeding the biomass in summer. Accordingly, this may be the most significant single annual phytoplankton episode in the lake. The development of phytoplankton was closely coupled with that of convection created by solar radiation at water temperatures < 4°C. In addition to vertical convection which keeps phytoplankton suspended, there was also horizontal convection which transported water with likely higher abundance of phytoplankton from the shallow lake margins. The effect of mechanical mixing, which was meant to prevent anoxia in the deep water layers of the study basin, was overridden by natural convection. Stochastic variations in weather played a key role controlling light penetration into the lake and hence the abundance and composition of under‐ice phytoplankton. After snow melt the proportion of motile algae was at first higher, sometimes with a maximum nearest to the ice, but later diatoms flourished throughout the convection layer. Only in the years of the shortest convection period did the proportion of motile algae remain high until the end of ice cover. More detailed information about the interaction between littoral and pelagial water masses under different mixing regimes is needed for a more profound understanding of the development of phytoplankton under‐ice.

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Section: Discussionmentioning

confidence: 99%

Regular build-up of the spring phytoplankton maximum before ice-break in a boreal lake

Salmi

Salonen

2015

Limnol. Oceanogr.

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“…More detailed descriptions of the eutrophication history of Lake Vesijärvi, as well as methods for analyses used, are given by Keto (1982), Keto & Sammalkorpi (1988), Liukkonen et al (1993) and Kairesalo et al (1998a). This paper presents the ecological basis for the present and future management of Lake Vesijärvi.…”

Section: Introductionmentioning

confidence: 99%

Direct and indirect mechanisms behind successful biomanipulation

Kairesalo

Laine

Luokkanen

et al. 1999

The Ecological Bases for Lake and Reservoir Management

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Lake Vesijärvi is a relatively large (length 25 km; total area 110 km 2 ), shallow (mean depth 6 m), but stratified lake in southern Finland. The Enonselkä basin (26 km 2 ), surrounded by the city of Lahti, received its sewage effluent, and changed from a clear water basin with flourishing fisheries from the 1940-50s to one of the most eutrophic lake systems in Finland thereafter. In 1976, the sewage effluent was diverted, resulting in a temporary recovery of water quality. However, in the 1980s, massive surface scums of cyanobacteria degraded the water quality and arrested the recovery of the lake. A restoration strategy providing an ecologically sound basis for the management of the lake was initiated in 1987. This strategy involved biomanipulation (mass removal of coarse fish) together with conventional pollution control measures on discharges to the lake. Biomanipulation was chosen instead of much more expensive chemical and/or technical methods, such as chemical treatment or dredging of the profundal sediment. The large-scale biomanipulation trial was carried out in the Enonselkä basin during 1989-93. Following the mass removal of coarse fish (1000 metric tons of fish; mainly roach and smelt), the biomass of cyanobacteria collapsed concomitantly with a decline of total phosphorus concentration from 45 to 35 mg P m −3 , and with an increase of Secchi depth from 1 m to 3.5 m. These observed improvements in the water quality were matched with a large decline in roach-mediated phosphorus movement from littoral to pelagial, from 100 mg P m −2 in 1989 to 15 mg P m −2 in 1993. Year-to-year variation within the littoral communities, and in the recruitment of fish, could in this way cause large oscillations in the whole ecosystem. The involvement of local people (fishermen, farmers etc.) in controlling non-point nutrient loading and fish stock development, is of prime importance for the long term success of lake restoration.

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“…In the Enonselka basin the annual sedimentation rate has been c . 1 .5 cm (Liukkonen et al ., 1993) . This is obviously one very important reason for high smelt, roach and perch density, and low vendace (Coregonus albula (L .))…”

Section: Discussionmentioning

confidence: 99%

Hydroacoustic monitoring of the distribution, density and the mass-removal of pelagic fish in a eutrophic lake

Jurvelius¹,

Sammalkorpi²

1995

Hydrobiologia

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A large scale biomanipulation of pelagic fish by trawling was started in the eutrophic Enonselka basin (26 km 2 ) of Lake Vesijdrvi to improve the water quality which had remained poor in spite of the termination of nutrient loading . The distribution and density of the fish were studied by hydroacoustics before and during the removal . The initial annual fish density varied between 13 000-21 000 fish ha -' in the study area in August 1984-89 . The mass-removal of the fish by pelagic trawling took place in 1989-1992 . The catch varied annually between 64 and 92 kg ha -1 . Roach (Rutilus rutilus (L.)) and smelt (Osmerus eperlanus (L .)) accounted for c . 85% of the weight of the catch . The mass-removal decreased the pelagic fish density in the Enonselka basin during the trawling . An increase in the density was observed after the trawling ceased in these years, and the initial density level was reached within one month . The density level after mass-removal remained high compared with oligotrophic lakes . The pelagic fish had a diurnal ascending trend with the decreasing light intensity in August, and the fish were significantly (p < 0 .01) higher in the water mass in temperature non-stratified water in autumn than in stratified water in summer. The fish were somewhat deeper in the years of mass-removal than before it . Mass-removal did not affect the individual length of the echosurveyed fish . Fish smaller than c . 15 cm (TS < -44 dB ; mainly smelt) were numerically dominant throughout the whole study period .

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Eutrophication and recovery of Lake Vesijärvi (south Finland): Diatom frustules in varved sediments over a 30-year period

Cited by 14 publications

References 13 publications

Regular build-up of the spring phytoplankton maximum before ice-break in a boreal lake

Regular build-up of the spring phytoplankton maximum before ice-break in a boreal lake

Direct and indirect mechanisms behind successful biomanipulation

Hydroacoustic monitoring of the distribution, density and the mass-removal of pelagic fish in a eutrophic lake

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