Ecosystem development in different types of littoral enclosures |
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Authors: | Vermaat J E Hootsmans M J M van Dijk G M |
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Institution: | (1) Dept. of Nature Conservation, Agricultural University, Ritzema Bosweg 32a, 6703 AZ Wageningen, The Netherlands;(2) Present address: International Institute for Hydraulic and Environmental Engineering, Oude Delft 95, P.O. Box 3015, 2601 DA Delft, The Netherlands |
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Abstract: | Macrophyte growth was studied in two enclosure types (gauze and polythene) in a homogeneousPotamogeton pectinatus bed in Lake Veluwe (The Netherlands). The gauze was expected to allow for sufficient exchange with the lake to maintain similar
seston densities, the polythene was expected to exclude fish activity and most water exchange. Polythene enclosures held higher
totalP. pectinatus biomass (ash-free dry weight, AFDW) than the lake, gauze enclosures were intermediate. The enclosures had a higher abundance
of other macrophyte species (Chara sp.,Potamogeton pusillus) than the lake. Seston ash content was not but seston AFDW, periphyton ash content and AFDW were lower in polythene than
in gauze enclosures. The difference in plant biomass between gauze and polythene may be attributed to a difference in periphyton
density and in seston AFDW due to zooplankton grazing (Rotatoria andDaphnia densities were higher in polythene enclosures). Since seston and periphyton AFDW and ash content were similar in lake and
gauze enclosures, the intermediate macrophyte biomass in the gauze enclosures may be explained by reduced wave action and
mechanical stress. Alternatively, phytoplankton inhibition by allelopathic excretions from the macrophytes may have caused
the high macrophyte biomass in the polythene, and an absence of sediment-disturbing fish the intermediate biomass in the gauze
enclosures. Creation of sheltered areas may favour macrophyte growth through both mechanisms and we conclude that this can
be an important tool in littoral biomanipulation. |
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Keywords: | enclosures Potamogeton pectinatus wave-action turbidity lake-restoration |
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