University of Oulu

Environmental factors and aquatic macrophytes in the littoral zone of regulated lakes : causes, consequences and possibilities to alleviate harmful effects

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Author: Hellsten, Seppo1
Organizations: 1University of Oulu, Faculty of Science, Department of Biology
Format: ebook
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.9 MB)
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Language: English
Published: 2000
Publish Date: 2000-05-18
Thesis type: Doctoral Dissertation
Defence Note: Academic Dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in Kuusamonsali (Auditorium YB 210), Linnanmaa, on June 29th, 2000, at 12 noon.
Reviewer: Professor Georg A. Janauer
Professor Christer Nilsson


Water level regulation for purposes of hydropower production has caused notable changes in the littoral zones of regulated lakes in northern Finland. Marked geomorphological changes have taken place in the lakes with a raised water level. Lowering of the ice cover during the winter has also caused rapid changes in the littoral. Changes in the environmental conditions and aquatic macrophyte communities were studied largely by comparing the regulated Lake Ontojärvi and the unregulated Lake Lentua in the Kainuu area. The general aims of the study were to analyse environmental effects, to produce information of ecological relationships for remedial measures on the littoral and to apply the restoration methods in the management of regulated lakes.

The most obvious effect of regulation was the expanded area of extending ice, which caused an almost complete disappearance of large ice-sensitive isoetids (Isoetes lacustris L., Lobelia dortmanna L.). These species were largely replaced by small erosion resistant isoetids (Ranunculus reptans L., Eleocharis acicularis (L.) Roem. & Schult.). Another significant change was the decreased frequency of large helophytes due to increased erosion. A model based on environmental factors was able to predict roughly the main vegetation types. Permanent plot studies showed no significant differences in the stability of the vegetation between the research lakes, which means that the species pool had adapted to the harsh environment.

Restoration techniques based on mechanical protection of shorelines and revegetation were applied to Lake Ontojärvi. The hostile environmental conditions caused a rapid decline of the planted species, but tall Salix phylicifolia L. seedlings and Carex rostrata Stokes were able to survive, although in low abundance. More significant remedial measures were provided by the Ecologically-based Regulation Practices (ERP), which have been applied to several lakes under hydropower production. This procedure, which was largely based on the results of the Kainuu studies, offers a simple way to illustrate the differences between various regulation practices. Two case studies showed that an exceptional year with extremely high or low water levels can largely abolish the positive succession achieved by ERP. The huge financial losses caused by ERP for hydropower production have also promoted the use of other conventional restoration measures.

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Series: Acta Universitatis Ouluensis. A, Scientiae rerum naturalium
ISSN-E: 1796-220X
ISBN: 951-42-5671-9
ISBN Print: 951-42-5670-0
Issue: 348
Copyright information: © University of Oulu, 2000. This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited.