Environmental monitoring detects changes in the health of an ecosystem and indicates whether conditions are improving, stable, or deteriorating. This quality, too large to gauge as a whole, is assessed by measuring indicators, which represent more complex characteristics. The concentration of sulfur dioxide , for example, is an indicator that reflects the presence of other air pollutants. The abundance of a predator indicates the health of the larger environment . Other indicators include metabolism , population, community, and landscape. All changes are compared to an ideal, pristine ecosystem. The SER (stressor-exposure-response) model, a simple but widely used tool in environmental monitoring, classifies indicators as one of three related types:

• Stressors, which are agents of change associated with physical, chemical, or biological constraints on environmental processes and …

Source: Freedman, Bill; Staicer, Cynthia. "Environmental Monitoring." Environmental Encyclopedia. 2003. Encyclopedia.com. 1 Oct. 2010 <http://www.encyclopedia.com/>.