What is the future of Lake Kussharo, which has been naturally recovering from acid lake of pH 4, eutrophication or acidification once again?

在夏季和冬季冰雪覆盖季节，重复进行CTD取样和观测。从湖底提供的温水很快混合在一起，正如去年观察到的那样。冬季底水冷却至2℃，密度小于水的最大密度。认识到即使在冬季对流仍在继续，形成了异常的温度剖面。对10余条入流河流和1条出流河流（钏路河）的流量进行重复测量和采样。在湖边志愿者的帮助下，钏路河开始了每月的采样和观察。从2003年9月起，在库沙罗湖最深处停泊的水温、电导率、叶绿素和浊度记录仪于2004年8月恢复。结果表明，在秋季和春季混合期，湖水在整个水柱中混合，然后水温不断变化，在最大水密度温度下不稳定。叶绿素浓度在冰融化后增加。水温和电导率记录仪系泊在汤川河口，这是酸性的，富含离子成分，是计算酸收支的最重要地点。测定碱度和离子组分。结果，通过精确的测量，发现离子组分浓度略有下降，碱度浓度略有增加。由于目前碱度没有下降，预计库沙罗湖不会再酸化。另一方面，叶绿素在春季的大量繁殖可能是富营养化的诱因或症状。要了解库沙罗湖营养阶段的变化，需要持续观测和利用公共营养监测数据。

Water sampling and observation with CTD were repeated in summer and winter ice-covered seasons. Warm water was supplied from the lake bottom and it was mixed quickly, as was observed last year. Bottom water was cooled to 2℃ in winter, whose density was lighter than the maximum density of water. It was recognized that convection continues even in winter and anormal temperature profile was formed. Flow rate measurement and sampling from more than 10 inflow rivers and one outflow river (Kushiro River) were repeated. With a help of volunteer working around the lake, monthly sampling and observation of Kushiro River started.Loggers for water temperature, conductivity, chlorophyll and turbidity moored at the deepest point of Lake Kussharo from September 2003 were recovered in August 2004. It was shown that lake water mixed throughout the water column in autumn and spring mixing periods, and then the water temperature changed continuously without stabilization at the temperature of maximum water density. Chlorophyll concentration increased just after the ice melting. The logger for water temperature and conductivity was moored at the river mouth of Yukawa, which is acidic and rich in ionic components and the most important site to calculate the acid budget.Alkalinity and ionic components were determined. As a result, slight decreases in the concentration for ionic components and increase in that of alkalinity were detected through precise measurements. For the alkalinity does not decrease at present, re-acidification of Lake Kussharo is not expected. On the other hand, chlorophyll bloom in the spring might be a trigger or symptom for the eutrophication. Continuous observation as well as utilization of public monitoring data for nutrients is required to detect the change in the trophic stage of Lake Kussharo.