Ecological function and functional diversity of aquatic plant vegetation

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In order to evaluate an influence that aquatic plant communities contribute to denitrification activities in littoral zone, in-situ experiment system was developed and seasonal changes of denitrification activities were discussed in Lake Kasumigaura.An acrylic chamber (1180 mm, 320 mm φ) for the experiment was manufactured. This chamber has measuring sensors for pH, oxidation-reduction potential (ORP), dissolved oxygen (DO) and air temperature. An air fun and a pump were also settled. The chambers were set at the depth of 700mm of the experiment site.A denitrification estimating method adopted acetylene inhibition technique (Yoshinari et al., 1977). Two experiment sites were established : the chambers with and without vegetation (reed maces, Typha latifolia), and the chamber with and without addition of acetylene gas. Added acetylene gas was 10%v of air + liquid phase of the chamber. As a matrix for denitrification bacteria, NaNO_3 solution was added to become 1 mg L^<-1> as NO_3^- - N … More in the liquid phase of each chamber. The denitrification activities were measured for 24 or 48 hours.The use of acetylene inhibition technique was applicable to this experiment system, since higher N_2O concentration was found in the chamber with acetylene gas addition than without. Compared with bare site, high N_2O concentration was detected in vegetation site (In May ; vegetation site : 6.0 mg N m^<-2> day^<-1>, bare site : 1.8 mg N m^<-2> day^<-1>). Therefore, it was confirmed that the denitrification activities in vegetation site was higher than in bare site. The denitrification activities varied with season, with the order : Nov. > Jul. > May. >Apr. Furthermore, NO_3^- removal ratio caused by the denitrification showed in the same change with the denitrification activities. There was high correlation between the denitrification activities and oxidative-reduced conditions in liquid phase.These results suggested that withered plants played an important role for the denitrification activity : withered plants increased in autumn and winter provided available organic matter and habitats for the bacteria. It was concluded that aquatic plant communities in littoral zone were very important for nitrogen elimination in lakes and marshes. Less