Introduction 



Worldwide concern about environmental threats and sustainable development has led to 

 increased efforts to monitor and assess status and trends in environmental condition. 

 Environmental monitoring initially focused on obvious, discrete sources of stress such as 

 chemical emissions. It soon became evident that remote and combined stressors, while 

 difficult to measure, also significantly alter environmental condition. Consequently, 

 monitoring efforts began to examine ecological receptors, since they expressed the effects 

 of multiple and sometimes unknown stressors and their status was recognized as a societal 

 concern. To characterize the condition of ecological receptors, national, state, and 

 community-based environmental programs increasingly explored the use of ecological 

 indicators. 



An indicator is a sign or signal that relays a complex message, potentially from numerous 

 sources, in a simplified and useful manner. An ecological indicator is defined here as a 

 measure, an index of measures, or a model that characterizes an ecosystem or one of its 

 critical components. An indicator may reflect biological, chemical or physical attributes of 

 ecological condition. The primary uses of an indicator are to characterize current status and 

 to track or predict significant change. With a foundation of diagnostic research, an 

 ecological indicator may also be used to identify major ecosystem stress. 



There are several paradigms currently available for selecting an indicator to estimate 

 ecological condition. They derive from expert opinion, assessment science, ecological 

 epidemiology, national and international agreements, and a variety of other sources (see 

 Noon 1998, Anonymous 1995, Cairns et al. 1993, Hunsaker and Carpenter 1990, and 

 Rapport e^ al. 1985). The chosen paradigm can significantly affect the indicator that is 

 selected and is ultimately implemented in a monitoring program. One strategy is to work 

 through several paradigms, giving priority to those indicators that emerge repeatedly during 

 this exercise. 



Under EPA's Framework for Ecological Risk Assessment (EPA 1992), indicators must 

 provide information relevant to specific assessment questions, which are developed to 

 focus monitoring data on environmental management issues. The process of identifying 

 environmental values, developing assessment questions, and identifying potentially 

 responsive indicators is presented elsewhere (Posner 1 973, Bardwell 1 991 , Cowling 1 992, 

 Barber 1994, Thornton et al. 1994). Nonetheless, the importance of appropriate assess- 

 ment questions cannot be overstated; an indicator may provide accurate information that is 

 ultimately useless for making management decisions. In addition, development of 

 assessment questions can be controversial because of competing interests for 

 environmental resources. However important, it is not within the purview of this document 

 to focus on the development and utility of assessment questions. Rather, it is intended to 

 guide the technical evaluation of indicators within the presumed context of a pre-established 

 assessment question or known management application. 



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