| 著者 |
阿部, 薫
駒田, 充生
大熊, 哲仁
荒城, 雅昭
田中, 幸一
楠本, 良延
安田, 耕司
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内容記述 |
A constructed wetland and a biotope were constructed by converting paddy fields in the campus of Koibuchi College of Agriculture and Nutrition, Mito, Ibaraki Prefecture, Japan, in 2004. The constructed wetland consists of a shallow, 500-m^2, free-water-surface flow type and planted with Zizania latifolia for advanced treatment of wastewater. The biotope with an area of 1500 m^2 consists of ponds and water canals for providing habitats of organisms. The secondary effluent from a dormitory in the campus flowed into the wetland. To assess the potential of wetland to polish the effluent from the dormitory, we measured the efficiencies of removal of N, P, and Zn by the wetland for about 5 years. Inorganic N, PO_4-P, and dissolved Zn were the principal forms of N, P, and Zn removed by the constructed wetland system but sedimentation of particulates did not proceed well. The wetland effectively removed not only nutrient salts but also Zn from the secondary effluent throughout the 5-year study period. The mass balance data suggest that N was removed mainly by denitrification and secondarily by adsorption to soil and by plant uptake; P was removed mainly by adsorption to soil and secondarily by plant uptake; and Zn was removed mainly by adsorption to soil. The average removal rates for N, P, and Zn were 0.29 g m^<-2> d^<-1>, 0.033 g m^<-2> d^<-1>, 0.69 mg m^<-2> d^<-1>, respectively. To assess the suitability of the biotope as a habitat for organisms, we surveyed plants, insects and soil nematodes in this biotope. Focusing on biotope for habitat of plants, we show the suitable maintenance method of school biotope by field vegetation survey from the point of biodiversity. As a result of vegetation survey, we recorded the plant of 150 species of 55 families, including several endangered species and rare species. Many native plants had invaded into the biotope from the adjoining pond with the natural forest(Alnus japonica forest). It was suggested that distance from source of seed supply was important about the choice of biotope creation site. In addition, the biotope with a variety of flora needs moderate human disturbance. We suggest the dredging management once in 2-3 years in wetland of the biotope. To assess the biotope for insects, we surveyed the populations of odonate adults and aquatic insects (coleopterans, hemipterans, and odonate nymphs) in the biotope during 2006–2011. We observed 31 odonate species and at least 41 species of aquatic insects during this period. The observed species richness, i.e., the number of species, was similar to that in species-rich ponds in Ibaraki Prefecture. Thus, this biotope may provide a profitable habitat for these insects. The species richness of odonates and aquatic insects increased until 2007, and then decreased in 2008. This decrease may be attributed to the accumulation of mud at the bottom of the water bodies. To recover habitat quality, we dredged up mud from the bottom of the water bodies in December 2008. Following 2009, the species richness of odonates and aquatic insects increased again. We estimate the process and factors responsible for the changes in the species richness of odonates and aquatic insects, and discuss some approaches for managing the biotope. Furthermore, a genus-level, a part family-level, list of soil nematodes found from biotope and paddy fields in were presented. Total 64 taxa were distinguished. Damp environment such as paddy fields, artificial marsh and pond sediments had an aquatic fauna consisted of Chronogaster, Tobrilus, Tripyla, Cryptonchus, Mononchus and Dorylaimus etc., whereas grassland around biotope pond mainly contained terrestrial nematodes with abundant dorylaimid fauna including Discomyctus longicaudatus(Imamura,1931) etc. |
niaes_report_No33p1-24p.pdf (1.3 MB)
