Acta Botanica Croatica, Vol. 32 No. 1, 1973.
Original scientific paper
The Influence of Grass-carp Population (Ctenopharyngodon idella Val.) on the Vegetation and Ecosystem Lake Trakošćan
Milan Meštrov
; Hrvatska
Ljudevit Ilijanić
; Hrvatska
Vlatka Tavčar
; Hrvatska
Josip Koprek
; Hrvatska
Abstract
In this study we present the results of the research into the influence of a phytophagous fish, the grass-carp (Ctenopharyngodon idella), upon the vegetation and changes of the ecosystem of Lake Trakoscan. The artificial lake was made by putting up a flood-gate on the Ce- mernica stream beneath the castle. The area of the lakes is 17,1 ha and the total affluent complex, the territory previously coverd by forests is 10,73 square km.
Along with the increased quantity of mire, the lake was intensively overgrown by aquatic macrovegetation, which made it unatractive as a tourist and recreation resort.
The Lake with its surroundings (parks and the castle of Trakoscan) is the most beautiful landscape of the north-west Croatia and it would be essential to protect the Lake and find a complex solution to the whole problem.
According to the results of investigations of Lake Trakoscan, presented in this study, we can conclude as follows:
The Lake is choked by mud so that the mud content rises to 37°/o of total volume. The main cause of muddiness is an alluviation of deposited mineral due to erosion of affluente beds.
Abundant macrovegetation supports the sedimentation of inorganic and organic matter and causes a rise of the bottom. A large quantity of anaerobic microoorganisms in mud, made the anaerobic process possible over a great part of the Lake. Distinctive decline in the quantity of dissolved oxygen has been noted every summer.
The characteristic of the lake is its betamezosaprobity especially toward the bottom (alphamezosaprobity).
The radical decrease in macrovegetation in 1971 caused by the semce of the grass-carp, resulted in essential alteration of physicochemical features of the water as well as in quantitative and qualitative changes in plankton community (Table 1, Fig. 1 and 2).
The disappearance of the dominant kinds of macrovegetation caused elimination of the main consumer of C02) followed by vigorous augmentation of dissolved carbon dioxide in water. At the same time, in 1971 particularly in August, a decline was noticed in the quantity of dissolved oxygen.
Strong fluctuation in quantitative composition of zoo- and phytoplankton in 1971 indicate a disordered balance in the ecosystem caused by the presence of planted fish.
A serious recover will require the cleaning of the lake by remowing the mud and the construction of a retaining-sedimentary storage-pond.
The planting of grass-carp or other kinds of fish should be done seriously and its effect will have to be controled as some interventions may be necessary.
Keywords
Hrčak ID:
157270
URI
Publication date:
31.12.1973.
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