This module introduces students to freshwater ecosystems while reinforcing and extending knowledge of basic ecological concepts. Physical and chemical properties of water and of different freshwater ecosystems are used as a springboard for understanding biotic patterns. These focus primarily on lotic systems but also encompass lentic and other freshwater ecosystems. The diversity of species at each trophic level is investigated and their roles explored. This module also investigates human impacts on freshwaters and examines various ways in which these ecosystems can be monitored.