抄録
Field surveys were conducted in Osaka-Nanko Sakishima Canal from May to October 2006, to clarify the water quality and causative organisms of the deteriorated scenery. Steady increase of pH was observed with decreasing salinity at the inner part of the canal due to the inflow of rainwater and/or underground water. Concentrations of dissolved oxygen were high in the bottom water of the canal compared with the surface one in May 2006. This phenomena result from the active photosynthesis of a green alga, Chaetomorpha sp. on the bottom sediment. Nutrient concentrations in the bottom water changed from 0.2 to 1.0mg/L for total nitrogen and from 25 to 50μg/L for total phosphorus in June, July, and September 2006. A marked decline in nutrient concentration was observed below 3m in depth near a sluice gate of the canal. The facts obtained from the present investigations suggest that putting lower the water level in the canal, setting lower the vertical level of the sluice gate, together with enhancement of water exchange are effective for the improvement of water quality and for the depression of algal blooms.
