Water Purification by the Water Plant Trapa japonica artificially Seeded in at Detention Pond at a Karima River Aria in Hokkaido
宮下, 洋平 ,
小林, 淳希 田中, 邦明 ,
109 , 2015-08-20 , 北海道大学大学院水産科学研究院
Lake Ohnuma in famous for the beautiful landscape in Hokkaido. However, lake Ohnuma has long been suffering from the serious cyanobacterial blooms in summer. Therefore, there is urgent needs to reduce cyanobacterial blooms. The aim of this study is to find a way to improving the water quality using a floating plant Trapa japonica Flerow. We set two different investigation spots where different densities of T. japonica were seeded. The following environmental parameters were monitored from June to November in 2014 : water temperature, pH, chlorophyll a and pheophytin, and nutrient concentrations. Water samples were examined under an inverted microscope, and the number of microalgaes was counted. The values of pH tended to be lower at high seed density spot after August. High seed density spot exhibited lower DIN than that of low seed density spot especially in June. The concentrations of phosphate and silicate were lower in high seed density spot than those of low seed density spot. As for microalgae diatoms occupied the substantial numbers and densites increased from June and showed the maximum in October for both water and biofilm samples. These results indicate that the more T. japonica is planted, the less nutrient concentrations were observed.