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

在夏季和冬季复冰季节重复采样和CTD观测。正如去年观察到的那样，温水从湖底供应，很快就被混合了。冬季底层水冷却至2℃，密度小于最大水密度。人们认识到，即使在冬季，对流仍在继续，并形成了异常的温度廓线。对10多条流入河流和1条流出河流(久路河)进行了流量测量和采样。在一名志愿者的帮助下，开始每月对库什罗河进行采样和观测。2004年8月，人们找回了2003年9月停泊在库沙罗湖最深处的水温、电导率、叶绿素和浊度的记录仪。结果表明，在秋季和春季混合期，湖水在整个水柱中混合，然后水温在最大水密度温度下连续变化而不稳定。在冰川融化后不久，叶绿素浓度增加。水温和电导率测定仪停泊在汤川县河口，该河口是酸性和富含离子组分的地方，也是计算酸平衡的最重要的场所。结果，通过精确的测量，离子组分的浓度略有下降，碱度的浓度有所增加。由于目前碱度没有下降，库沙罗湖不会再酸化。另一方面，春季的叶绿素水华可能是富营养化的触发因素或症状。要发现库沙罗湖营养阶段的变化，需要对营养物质进行持续观察和利用公共监测数据。

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.