For the improvement of water quality and aquatic ecosystem, 2,650 ㎡ of macrophyte-vegetated floating island (MFI) was installed at Kyungan Stream in Lake Paldang at May 2000. To evaluate the effects of MFI on water qualities and aquatic ecosystems, ...
For the improvement of water quality and aquatic ecosystem, 2,650 ㎡ of macrophyte-vegetated floating island (MFI) was installed at Kyungan Stream in Lake Paldang at May 2000. To evaluate the effects of MFI on water qualities and aquatic ecosystems, temporal variations of water quality and changes of aquatic biota were surveyed at MFI and Kyungan Stream, as a control site, for two years in Lake Paldang from April 2005.
Mean depth of MFI installed area was 1.9 m. There were no differences in water temperature and conductivity between MFI installed area and Kyungan Stream. The value of pH was high at open area of Kyungan Stream where the phytoplankton grew actively up with high concentration of nutrients and sunlight. DO had been maintained at a low concentration, and became to practically anaerobic state in surface layer of MFI at mid-summer.
Comparing the water quality parameters between MFI installed area and lake water, concentrations of TP, DTP, PO₄-P, NH₄-H, BOD and POC were high in MFI installed area, but those of TN, DTN and NO₃-N were high in Kyungan Stream, respectively. Values of DOC showed similar level among survey sites.
At early May, when the macrophytes on MFI developed actively, there was remarkable differences in Chl.a concentration between MFI and Kyungan Stream. Chl.a concentration in Kyungan Stream exceeded 100 ㎎/㎥ frequently, but there was no algal bloom at inner part of MFI during survey periods. By the shade effect of MFI and grown macrophytes, the phytoplankton could not be able to multiply. However, rapid growth of phytoplankton was observed for a short period just after mid July 2006 when macrophytes was cut off.
Abundance and biomass of zooplankton at MFI were 5.6 and 16.5 times higher than those at Kyungan Stream, respectively. Abundance of zooplankton was seriously affected by heavy rainfall and seasonal fluctuation of inflow in Kyungan Stream, but that at MFI was not disturbed. This phenomenon was probably caused by the protection of turbulence with the MFI and roots of macrophytes. The biomass of zooplankton could be sustained by the high contents of organic matters and plenty of food source such as bacteria, protozoa, rotifera, etc.
Number of total bacteria had a similar values in both surveyed sites, but ratio of active bacteria to total bacteria was very high at MFI.
Totally, 26 genus, 29 species belong to 19 families of macrophytes were observed at MFI. All of them were herbaceous plant except Salix gracilistyla. Habitation area of Phragmites japonica was expanded from 25 % at 2000 to 42 % at 2006. But Zizania latifolia and Typha angustata were not adapted well, so they almost disappeared at MFI after five years of installation.
Contents of nitrogen and phosphorus per unit weight of macrophyte showed the high value at May through to June, an active growing season of aquatic plants, but nutrients contents were lowered at regrowing period after cut-off. Therefore, to remove the nutrients from water column by macrophytes of MFI, it is suitable to cut off the macrophyte before late summer, when the nutrients of shoot and leaves were transferred to rhizosphere.
In benthic macroinvertebrates, 352 individuals in 27 species belong to 3 phyla were sampled from rhizosphere and sediment under MFI, but only 30 individuals of 3 species were caught from sediment in Kyungan Stream.
Fishes, 26 genus, 29 species were captured from near MFI, which was similar level of species to natural vegetation area. But fishes caught from vegetation free area barely over the half of above sites
Based on the above results, MFI can improve the water quality through nutrients uptake by macrophytes from water column and mineralization of organic matters by various aquatic micro-biota, such as bacteria, zooplankton and aquatic insects and etc. But the effects of MFI on improvement of water quality was not conspicuous in open water where the water column is mixed rapidly with short retention time.
After MFI was installed, new aquatic ecosystem was developed. The abundances and diversities of zooplankton, benthic macro-invertebrate, fish were remarkably increased.
Littoral zone of large artificial dams area was seriously destroyed by water level fluctuation. For overcoming this problem, MFI can be a alternative choice to rehabilitate the impaired aquatic ecosystems.
，韩语论文范文，韩语论文网站 |
