A role of thermocline on biological activities in Lake Biwa.

叶绿素的垂直分布在1994年9月异常缺水时和1995年9月正常降雨时有所不同。1994年，表层叶绿素a含量极低，温跃层出现峰值。表层浮游植物生长中断，主要原因是入河水量不足，营养物质缺乏。因此，可用于光合作用的太阳辐射可以充分穿透温跃层。硝态氮从底层向温跃层的向上扩散逐渐提供，磷-磷的供应是通过从底层向温跃层输送浑浊水中的铁和铝吸附的磷中释放磷酸盐来实现的。1995年，含有丰富营养物质的河水流入温跃层上方，为温跃层提供营养物质。因此，浮游植物的生长与表层的光合作用相结合得到了促进。叶绿素a的垂直分布格局似乎取决于是否从河流向表层提供营养物质。

Vertical distribution of chlorophyll a differedl in the pattern between September 1994 when it was extraordinarily water shortage and September 1995 when it was a usual rain. In 1994, chlorophyll a was extremely low in the epilimnion and showed a peak in the thermocline. Phytoplankton growth was interrupted in the epilimnion because of nutrients deficiency due to shortage of river inflow. As a result, solar radiation available for photosynthesis could penetrate sufficiently into the thermocline. Nitrate-N was gradually supplied by the upward diffusion from the hypolimnion to the thermocline and phosphate-phosphorus was supplied continuously by release of phosphate from the phosphorus adsorbed with ferric iron and alminium in the turbid water transperted from share-bottom into the thermocline. In 1995, river water including rich nutrients inflowed just above the thermocline and supplied nutrients to the epilimnion. As a result, phytoplankton growth was enhanced in combination with photosynthesis in the epilimnion. Vertical distribution pattern of chlorophyll a seems to be determined by whether or not nutrients are supplied from river to the epilimnion.