Effects of submerged plants on water quality and biota in large-scale experimental ponds |
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Authors: | Keigo Nakamura Yuichi Kayaba Jun Nishihiro Noriko Takamura |
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Institution: | (1) River Restoration Team, Public Works Research Institute, 1-6 Minamihara, Tsukuba 305-8516, Japan;(2) Aqua Restoration Research Center, Public Works Research Institute, Kawashima-Kasada, Kakamigahara, Gifu 501-6021, Japan;(3) Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-8657, Japan;(4) Biodiversity Conservation Research Project, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba 305-8506, Japan |
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Abstract: | We quantitatively studied the effect of submerged plants on water quality and biota under fish-free conditions for 3 weeks
in four large freshwater experimental ponds (533 m3 per pond) at the Aqua Restoration Research Center, Japan. Two artificially harvested ponds with scant vegetation were used
as “harvested ponds” (H1, H2), and the other two ponds, which were naturally dominated by Hydrilla verticillata, were used as “vegetated ponds” (V1, V2). The PVI (percent water volume infested with macrophytes) was employed as an index
of vegetation abundance. Vegetated ponds had much clearer water than harvested ponds. The water quality in H2 (PVI 10%) was
better than in H1 (PVI 3%), whereas the water quality did not differ significantly between the two vegetated ponds (V1, PVI
38% and V2, PVI 84%). Therefore, the threshold between clear water and turbidity was between 10 and 38% in PVI. Our result
also showed that a turbid water state was created shortly after harvest. Green algae were abundant in the harvested ponds,
and diatoms were dominant in the vegetated ponds. Rotifers were stably dominant in the harvested ponds. Aquatic worms were
more abundant in the harvested ponds than in the vegetated ponds. Unexpectedly, zooplanktons were much less abundant in the
vegetated ponds; therefore, zooplankton grazing was not the main mechanism behind the cleaner water in our experiment. These
results are physical evidence that the presence of dense macrophytes was the main factor in the creation of a clear water
state. |
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Keywords: | Submerged macrophytes Aquatic plants Shallow lake Alternative stable state PVI |
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