海跡湖の湖岸低地および沿岸帯における環境変化  [in Japanese] Environmental changes at the lacustrine lowlands and littoral zone of the coastal lakes in Japan  [in Japanese]

日本における海跡湖では, 近年周辺地域における都市域の拡大, 都市化の進展を背景に, 湖岸地域の多面的活用や湖水位の人為的変動を伴う水質源の効率的利用が志向されている。そのため, とくに関東地方以西の海跡湖では, 湖岸の人工化や湖岸低地での都市的土地利用の割合が高い。本研究では, まず顕著な人工改変が行われる以前の海跡湖の湖岸地帯の地形構造や景観を明らかにし, ついで1970年以降, 湖および周辺部での開発が高度に進められてきた霞ヶ浦を例に, 湖岸低地と沿岸帯における人工改変の実態を定量的に把握した。その結果, 湖岸低地の人工改変に比較して, 沿岸帯での堤防・舟溜り・養殖施設などの人工施設の構築・設置, 砂利採取など様々な人間活動の度合いが大きく, それによって湖沼の水質保全や生態系, 景観にとって重要な機能を有している挺水植物群落地が, 過去10年以上にわたって減少していることが明らかになった。

In the coastal lowlands in Japan we can find over 30 lakes whose basins are each more than 4 km^2. Among these coastal lakes, those which are situated near some big cities are faced with serious environmental changes. Around these coastal lakes, rapid urbanization has occurred and the inhabitants in each drainage basin have increased during the last few decades. Consequently, some ecological changes and water pollution have been brought about in and around such lakes. This paper is to discussthe influences of human activities on the environmental changes at lake shore. The author researched into the types of land use and land transformation in the lacustrine lowlands and littoral zones on the basis of geomorphological land classification. As a result, recently several types of urban land use accompanied with land transformation in littoral zones have become apparent at some coastal lakes. Aquatic plants, especially the emerged plant community which plays very important parts in the ecosystem in the coastal lakes and improves the water quality, has gradually diminished or vanished. The landscape at lake front also has been spoiled lately. We should pay more attention to the environmental changes in and around the coastal lakes and consider how to preserve natural ecosystems and desirable landscapes from the urbanization of the area.