Analysis of the growth mechanisms of a species causing freshwater red tide in a reservoir using in situ microcosms

甲藻Ceratium hirundinella(O.F.Muller)Bergh经常在水库引起淡水赤潮。然而，由于难以从实验室培养中获得其生理特性，对水库中的毛状念珠藻生长机制的研究很少。本研究的目的是通过原位微宇宙培养实验，寻找影响水库中毛状毛藻生长的因素。此外，还进行了实地调查和实验室实验。主要研究结果如下：1.在水温为20ﾟC的水温条件下，不同深度的底泥中均可观察到含有绒毛藻包囊的微宇宙。浅层营养细胞较多，0.5m处的出苗率为2%。未发现深度大于30m1的营养细胞。从实验室培养的包囊来看，最适水温为20ﾟC和25ﾟC，此时的出水率为2%。未观察到低于10ﾟC.3的收缩。根据前述结果1和结果2，预测出露期为5~9月，出露地为储集层的最高部位。田间调查结果表明，可溶性有机磷有利于毛壳藻的生长。添加PO4-P和NO3-N的微生态比不添加这些营养物质的微生态含有更高浓度的可溶性有机磷和毛状念珠藻。微宇宙实验还表明，可溶性有机磷是一种有利于毛状藻生长的因素。

The dinoflagellate Ceratium hirundinella (O. F. Muller) Bergh often causes freshwater red tide in reservoirs. There has been, however, little investigation on the growth mechanisms of C. hirundinella in a reservoir due to the difficulty in obtaining its physiological characteristics from laboratory cultures.The purpose of this study was to find the factors for the excystment and growth of C. hirundinella in a reservoir by culture experiments using microcosms in situ. In addition, field surveys and laboratory experiments were also carried out. The main results obtained were as follows:1. Microcosms containing bottom mud with cysts of C. hirundinella were suspended at several depths when the water temperature was 20 ﾟC at all depths. More vegetative cells were found in the shallower depths and the excystment rate was 2 % at 0.5 m deep. No vegetative cells were found deeper than 30 m.2. From the laboratory culture of the cysts, the optimum water temperature for excystment was 20 ﾟC and 25 ﾟC, here the excystment rate was 2 %. No excystment was observed lower than 10 ﾟC.3. The period of excystment was predicted to be from May to September and the place for excystment to be the head of the reservoir, according to results 1 and 2 mentioned above.4. It was suggested from a field survey that soluble organic phosphorus favors the growth of C. hirundinella.5. Microcosms with PO_4-P and NO_3-N added contained higher concentrations of soluble organic phosphorus and C. hirundinella compared with microcosms without the addition of those nutrients. The microcosm experiment also suggested that soluble organic phosphorus was a factor favoring the growth of C. hirundinella.