STUDY ON WATER QUALITY IMPROVEMENT BY BIOMANIPULATION

(1)鱼类对蓝藻优势度的影响在6个室外实验池塘中，设置了相同进水氮、磷浓度、不同鱼类（金鱼）密度的连续流通系统，对夏季蓝藻优势度的影响因素进行了为期13个月的研究。一般来说，蓝绿色藻类占主导地位的鱼塘，相反，绿色藻类在无鱼池塘。8月下旬，当P0_4-P浓度降至10 ug V^-^1以下时，蓝绿藻开始大量繁殖。有鱼池塘与无鱼池塘浮游植物优势种的差异可能是由于鱼的排泄和生长导致池塘水体中总磷的减少和P0_4-P的消耗，而这种条件对蓝藻有利。此外，有鱼池和无鱼池中叶绿素a的分解过程也不同。(2)利用新开发的箱培养和自由水方法，在冰名湖和广岛湾连续几天每小时测定一次生产力和群落呼吸速率的变化。箱的设计包括明箱和暗箱，同时测量明箱和暗箱中的水的温度、DO和pH，其中水与外部水定期交换。这种箱法是一种有能力的评估毛和净生产力，呼吸在各种各样的水生动物。(3)有、无水生植物灌溉池塘水环境研究水生植物生物量的大小决定于湖泊的尺度（表面积和深度），它对浮游植物与营养盐的比值、有机污染物的季节变化规律和沉积物有重要影响。

(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.