Cascading trophic interactions from fish to bacteria and nutrients after reduced sewage loading: An 18-year study of a shallow hypertrophic lake

被引:132
作者
Jeppesen, E
Sondergaard, M
Jensen, JP
Mortensen, E
Hansen, AM
Jorgensen, T
机构
[1] Natl Environm Res Inst, Dept Lake & Estuarine Ecol, DK-8600 Silkeborg, Denmark
[2] Arhus Cty, Environm Off, DK-8230 Hojbjerg, Denmark
关键词
recovery; top-down control; bottom-up control; loading reduction; internal loading; fish; zooplankton; phytoplankton; ciliates; bacteria; size distribution; production;
D O I
10.1007/s100219900020
中图分类号
Q14 [生态学(生物生态学)];
学科分类号
071012 ; 0713 ;
摘要
The effects of major reductions in organic matter, total phosphorus (TP), and total nitrogen (TN) loading on the chemical environment, trophic structure, and dynamics of the hypertrophic, shallow Lake Sobygard were followed for 18 years. After the reduction in organic matter loading in 1976, the lake initially shifted from a summer clear-water state, most likely reflecting high grazing pressure by large Daphnia species, to a turbid state with extremely high summer mean chlorophyll a (up to 1400 mu g L-1), high pH (up to 10.2), and low zooplankton grazing. Subsequently, a more variable stale with periodically high grazing rates on phytoplankton and bacteria was established. Changes in zooplankton abundance and grazing could be attributed to variations in cyprinid abundance due to a fish kill (probably as a consequence of oxygen depletion) and pi-I-induced variations in fish recruitment and fry survival. The results suggest strong cascading effects of fish on the abundance and size of zooplankton and phytoplankton and on phytoplankton production. A comparatively weak cascading effect on ciliates and bacterioplankton is suggested. Due to high internal loading, only minor changes were observed in lake-water TP after a reduction in external TP loading of approximately 80% in 1982; net retention of TP was still negative 13 years after the loading reduction, despite a short hydraulic retention time of a few weeks. TN, however, decreased proportionally to the TN-loading reduction in 1987, suggesting a fast N equilibration. Only minor improvement in the environmental state of the lake has been observed. We suggest that another decade will be required before the lake is in equilibrium with present external P loading.
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页码:250 / 267
页数:18
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