Nitrogen and Phosphorus Metabolism in Lake Water/Mud Ecosystems and Ecological Succession as Factors responsible for Cyanobacterial Bloom.

通过野外调查和营养强化培养，揭示了碧洼湖富营养化蓝藻水华发生的可能因素，特别是湖泊水/泥相互作用系统的氮磷代谢和浮游植物群落的演替相互作用。在前人研究底泥营养物质再生对蓝藻种群发展的积极作用的基础上，野外调查重点研究了湖水和浮游植物中氮、磷的动态变化。从春末到仲夏，随着水温的升高，硝酸盐浓度显著下降，颗粒氮和蓝藻丰度显著增加。这些发现和溶解有机氮的平行下降表明，夏季蓝藻种群的发展可能受到镍…的支持。在硝酸盐水平最低的情况下，通过微生物活动从溶解的有机物中再生出更多的氮素。最低的硝酸盐条件也有效地限制了其他藻类的生长，并允许蓝藻的生长。在北盆湖表层富营养化养殖中，蓝藻种群在较高温度和外加磷的条件下对藻类生长有显著的正效应，绿藻在富氮条件下对藻类的生长有显著的正向影响，而硅藻在较低的温度下对藻类的生长有显著的促进作用。这些结果表明，较高的温度和较低的硝酸盐环境对蓝藻种群的竞争发展是必不可少的，在这种环境下向水体提供外部磷供应应该会刺激蓝藻的生长。琵琶湖滨海带的湖水/沉积物生态系统夏季温度较高，沉积物中磷的释放受到刺激，应为蓝藻水华的频繁发育提供场所。较少

Field surveys and nutrient enrichment cultures were conducted for the North Basin to reveal the possible factors responsible for the development of cyanobacterila bloom in oligotrophic Lake Biwa, with a special reference to the nitrogen and phosphorus metabolism at lake water/mud interaction system and successional interaction in phytoplankton community.Based on my previous studies on the positive role of nutrients regeneration from the bottom sediments on development of cyanobacterial population, the field survey was focused on the sequential changes s of nitrogen and phosphorus in both lake water and phytoplankton. Pronounced decrease in nitrate concentration and noticeable increases in particulate nitrogen and cyanobacterial abundance were observed in association with increasing water temperature from late spring toward mid summer. These findings and a parallel decrease of dissolved organic nitrogen suggest the summer development of cyanobacterial population could be supported by ni … More trogen regeneration from dissolved organic matter through microbial activity at the lowest level of nitrate. Lowest nitrate condition is also effective to limit the growth of other algal species and permits the growth of cyanobacteria. In the nutrient enrichment cultures using the lake waters from the surface of the North Basin, significant positive effects on algal growth were observed for cyanobacterial population at higher temperature and external phosphorus enrichment, for green algae at nitrogen enrichment and for diatoms at lower temperature.These results imply that higher temperature and lower nitrate environment could be essential for the competitive development of cyanobacterial population and an external phosphorus supply to the water under this environment should stimulate the cyanobacterial growth. Lake water/sediments ecosystem at littoral zone of Lake Biwa is characterized by higher temperature and stimulated phosphorus liberation from the sediments during summer, and hence should provide the sites with frequent development of cyanobacterial bloom. Less