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応用生態工学 4(1), 81-86, 2001

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ミニ特集: 健全な河川とは? MINI-FEATURE: WHAT IS RIVER HEALTH
総説 REVIEW

ECEロゴマーク

河川の健康を守る−人間の健康維持の実戦経験から学ぶ

James R. KARR1), Eriko MORISHITA ROSSANO2): Applying Public Health Lessons to Protect River Health Ecol. Civil. Eng. 4(1), 3-18, 2001.

1) School of Aquatic and Fisheries Sciences, University of Washington, Box 355020, Seattle WA 98195-5020 USA
2) Institute of Freshwater Biology, 2-11-22-402, Miyahara, Yodogawa-ku, Osaka, 532-0003, Japan

Abstract:Revealing, and indeed exacerbating, the globe's present water crisis is the failing ecological health of rivers. Those who would protect and restore river health can learn important lessons from humanity's continual fight against disease. We discuss four of these lessons, including their applicability to river issues : (1) recognize and respond to changing challenges, (2) avoid unintended consequences, (3) employ both cure and prevention, and (4) take a systematic approach. The overarching message from human health science is that we need to view human actions and their consequences for river health in an integrated way. In an effort to construct such a view of river degradation, we suggest that human actions jeopardize river health in five major ways : (1) altering physical habitat, (2) modifying seasonal flow of water, (3) changing the food base of the system, (4) changing interactions within the river biota, and (5) polluting with chemical contaminants. Another key lesson of human health science is the need for a commonly understood and robust measure of river condition, or health. Biological monitoring and assessment using the index of biological integrity for Japanese streams (IBI-J) provides a rigorous measure of river condition as well as guidance on the causes of river degradation. Examples of the index's use in Japan illustrate the importance of various stressors responsible for degradation, such as amount and types of effluent, proximity of dams and other structural alterations, and riparian condition. They also show the dangers of management driven solely by narrow water quality measures such as biochemical oxygen demand (BOD). We conclude that biological measures are important because they provide a strong scientific framework to inform the largely cultural process of deciding how humans treat rivers.

Key words: biological integrity, biological monitoring, public health, IBI, river health

摘要

河川環境は人間の活動によって大きく変化する.原因を取り除き,健康な河川に戻すことが大きな課題である.この課題へのアプローチを,河川が抱えている問題をこれまで人間が長く対処してきた健康維持の実践経験にあてはめて考えた.すなわち,1) 次々に変化する健康への脅威を理解し対処する,2) 二次感染など予期しなかった病原の発生を食い止める,3) 予防と治療を大切にする,4) 病気の克服には包括的にかつ系統だった対策を講ずることが考えられる.これらから,人間活動とそれによってひきおこされる河川の健康状態の変化を総括的にとらえる視点が必要であることが教訓として得られる.そのために,人間活動が河川の健康状態を改変する視点として,次の5点:生息場所の構造,流量の季節変化,食物源,生物間の関係,水質汚濁(Fig. 1)を取り上げた.さらに,河川がどの程度健康であるかを診断するための,解りやすくかつ強力な手法の開発も必要である.水環境カルテ(index of biological integrity for Japanese streams, IBI-J)は,河川の状態を総括的に測り,健康状態を損なう原因を提案する指標である.IBI-Jを使った研究例から,河川の健康状態を損なう要因として,排水の量と種類,ダムなどの構造物との距離,河畔植生の有無などが重要であることが示唆された.これらは,生物化学的酸素要求量(BOD)などの単一の視点だけに立脚して河川管理を進めることの危険性を指し示す(Fig. 6).IBI-Jのような生物学的環境評価法は,人間が河川をどう扱うかを決める際の多分に文化的な過程に対して科学的な情報提供をするための枠組みとして重要である.

line Recived 16 March 2001 ; Accepted 31 May 2001
e-mail: jrkarr@u.washington.edu line
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