Anthropogenic changes in Finnish lakes during the past 150 years inferred from benthic invertebrates and their sedimentary remains

Abstract

Järvien kuormitus-, rehevöitymis- ja palautumishistoria on ollut monivaiheinen ja pitkäkestoinen. Monet teollisuuden ja asumajätevesien kuormittamista järvistämme olivat lähes luonnontilaisia vielä 1900-luvun alussa, likaantuivat myöhemmin voimakkaasti, mutta ovat sittemmin alkaneet elpyä. Hajakuormituksesta kärsivissä järvissä rehevöityminen sen sijaan on edelleenkin jatkunut. Tämä selviää Juhani Hynysen vesistöjen ympäristöhistoriaa käsittelevässä väitöskirjassa, jossa hän on tutkinut puunjalostusteollisuuden kuormituksen, asumajätevesien sekä hajakuormituksen vaikutuksia suurten järvien biologisen tilan kehitykseen noin 1800-luvun puolivälistä nykypäivään.

This thesis focuses on two themes concerning the anthropogenic impacts on Finnish lakes during the past 150 years. The effects of pulp mill discharges, municipal wastewaters and diffuse loading on the ecosystems of large lakes were studied from macroinvertebrate samples and from short-core paleolimnological samples. The response of benthic invertebrates to acidification and the patterns of recovery were studied from the littoral macrozoobenthos of acid-sensitive headwater lakes. The long-term responses of lacustrine chironomids to the changing degree of acidification were studied from paleolimnological samples. Based on the physical and chemical properties and biological remains in the sediment, several developmental phases were distinguished in the ecological status of the loaded lakes. These phases differed from each other on the basis of changing ecological disturbance affecting the lake ecosystems. The sediment profiles covered the time from the pre-industrial phase to the phase of severe pollution and, later on, to the phase of recovery. The lakes exposed to point loading from industrial and municipal sources revealed recent biological recovery patterns, while the lakes suffering from diffuse loading still revealed an ongoing eutrophication process. The study of acidic headwater lakes revealed many acid-sensitive benthic taxa, but also taxa tolerant of acidification. Recent chemical recovery was accompanied by a slight biological recovery in the most acidified lakes. Sedimentary chironomid assemblages of acidified lakes revealed only slight changes during the past centuries. Possible future trends and threats to the biological recovery of loaded lakes are discussed.