Book excerpt: This book offers a comprehensive guide to microcosms (N-systems) in multiple-species testing and aquatic ecosystem risk assessment. It provides standardized methods for creating the microbial ecosystem, and proposes a standardized microcosm system for environmental impact risk assessments. The book will be of interest to students and educators, researchers, government authorities, developers and manufacturers engaged in ecosystem preservation, water quality management personnel at sewage treatment or industrial effluent treatment facilities, and anyone involved in education, management and analysis evaluation for environmental standards and waste water quality standards.