Abstract:
Wetland ecosystems and water quality are largely changing due to human activities. A
large amount of nutrients are accumulated in wetland ecosystem in a lake, due to activities such as
land reclamations, intensive agriculture and eutrophication. Some areas around the Biwa Lake (the
biggest lake in Japan), are covered by snow in winter but many alien species including water hyacinth
and water lettuce can survive, due to increasing temperature (average temperature increase about 2°c).
In the recent 20 years, it was concerned about global warming for vegetation. Japanese farmers, until
today, control the nature by cutting grass and tree, burning, and collect water plants for fertilizing.
During last 5 years, Japanese farmer’s population has been decreased by 20 % and the farmer’s
average age was about 66 years old. Now, the same condition happens in the field of fishery and
forestry. In near future, the lake area will become marsh, and wetland will become swamp forest and
consequently, evaporation range will be increased. Thus we can not keep more water in small ponds
and wetlands.
