STUDY ON WATER QUALITY IMPROVEMENT BY BIOMANIPULATION

(1)鱼类对蓝藻优势度的影响利用6个相同进水氮磷浓度、不同鱼(金鱼)密度的室外实验池塘进行了13个月的试验，研究了夏季蓝藻优势度的影响因素。一般来说，鱼塘中以蓝绿藻为主，而无鱼池塘中则以绿藻为主。8月下半月以后，蓝藻开始大量繁殖，P0_4-P浓度降至10微克V^-1以下。鱼塘和无鱼池塘的优势浮游植物数量的差异可以用总磷的减少以及随后鱼粪及其生长对池塘水中P_4-P的消耗来解释，这一条件有利于蓝藻的生长。此外，叶绿素a在鱼塘和无鱼池塘中的分解过程也不同。(2)水生系统生产力和呼吸的现场测量采用新开发的箱式孵化和自由水法，连续几天每小时测定希穆纳湖和广岛湾的生产力和群落呼吸速率的变化。暗箱的设计包括光箱和暗箱，在光箱和暗箱中同时测量水的温度、DO和pH，暗箱中的水定期与外部水交换。(3)有无大型植物灌溉池塘水环境的研究大型植物生物量是由湖泊尺度(表面积和深度)决定的，对浮游植物与营养物质的比例、有机污染物和沉积物的季节变化规律有很大影响。

(1) Influence of fish on dominance of blue-green algaeExperiments using six outdoor experimental ponds equipped with a continuous flow-through system of the same influx nitrogen and phosphorus concentrations and with different fish (goldfish) densities were conducted for 13 months to investigate the factors influencing the dominance of blue-green algae in summer. In general, blue-green algae predominated in fish ponds, in contrast to green algae in fishless ponds. Blue-green algae started to flourish after the latter half of August, when P0_4-P concentrations decreased to less than 10 ug V^-^1. The difference in dominated phytoplankton between fish and fishless ponds could be explained by the reduction of total phosphorus and subsequently the depletion of P0_4-P in pond water due to feces of fish and their growth, the condition of which is advantageous for blue-green algae than others. In addition, the decomposition processes of chlorophyll a were different between in fish ponds and in fishless ponds.(2) In-situ measurement of productivity and respiration in aquatic systemsChanges in productivity and community respiration rates were determined hourly in Lake Himuna and Hiroshima Bay for several days, using a newly developed box incubation and free water method. The design of the box included light and dark box, with simultaneous measurement of temperature, DO and pH of the water in light and dark boxes in which the water was exchanged with outside water at regular intervals. This box method is a capable one for evaluating gross and net production, and respiration in a wide variety of aquatics.(3) Study on water environment in irrigation ponds with or without macrophyteBiomass of macrophyte, which was determined by lake dimensions (surface area and depth), influenced greatly the ratio of phytoplankton to nutrient, the seasonal change pattern of organic pollution and sediments.