Mechanisms regulating abundance of submerged vegetation in shallow eutrophic lakes |
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Authors: | S E B Weisner John A Strand Håkan Sandsten |
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Institution: | (1) Limnology, Lund University, Ecology Building, S-223 62 Lund, Sweden fax: +46 462224536; e-mail: stefan.weisner@limnol.lu.se, SE |
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Abstract: | Shallow eutrophic lakes tend to be either in a turbid state dominated by phytoplankton or in a clear-water state dominated
by submerged macrovegetation. Recent studies suggest that the low water turbidity in the clear-water state is maintained through
direct and indirect effects of the submerged vegetation. This study examined what mechanisms may cause a recession of the
submerged vegetation in the clear-water state, and thereby a switch to the turbid state. The spatial distribution of submerged
vegetation biomass was investigated in two shallow eutrophic lakes in the clear-water state in southern Sweden. Biomass of
submerged vegetation was positively correlated with water depth and wave exposure, which also were mutually correlated, suggesting
that mechanisms hampering submerged vegetation were strongest at shallow and/or sheltered locations. The growth of Myriophyllum spicatum, planted in the same substrate and at the same water depth, was compared between sheltered and wave exposed sites in two
lakes. After 6 weeks the plants were significantly smaller at the sheltered sites, where periphyton production was about 5
times higher than at the exposed sites. Exclosure experiments were conducted to evaluate the effects of waterfowl grazing
on macrophyte biomass. Potamogeton pectinatus growth was decreased by grazing, whereas M. spicatum was not affected. The effects were greater at a sheltered than at a wave-exposed site, and also negatively related to distance
from the reed belt. These results suggest that competition from epiphytes and waterfowl grazing hamper the development of
submerged vegetation at sheltered and/or shallow locations. An increased strength of these mechanisms may cause a recession
of submerged vegetation in shallow eutrophic lakes in the clear-water state and thereby a switch to the turbid state.
Received: 24 June 1996 / Accepted: 8 September 1996 |
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Keywords: | Submerged macrophytes Alternative stable states Periphyton Wave exposure Grazing |
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