component activities, but it may possess unique characteristics as well. Road 

 building is an example of a typical activity class which is a composite of 

 many individual activities, such as vegetation removal, grading, filling, 

 digging, and others. 



Activity description and categorization may be achieved using data from 

 two basic sources: (1) field observations of actual construction performances 

 and (2) detailed step-by-step descriptions of how construction-operation- 

 maintenance processes occur. It should be remembered that regardless of the 

 hierarchical level of development being considered, the ecological alterations 

 are caused only by individual activities even though changes may be frequently 

 attributed to an activity class. 



Primary Ecological Alterations 



As a conceptual interface between activities in ecosystems and ecosystem 

 changes, primary ecological alterations (PEA's) show the first, most direct, 

 ecological responses to activities and thereby define the points of access to 

 the ecosystems impact analysis. A list of primary ecological alterations is 

 presented in Figure 6-1. The categories were drawn from several sources, 

 including Leopold et al. (1971), Sorensen (1971), Dee et al. (1972), Moore 

 et al. (1973), Dickert and Domery (1974), and Rice Center for Community Design 

 and Research (1974, 1976). Primary ecological alterations are presented in 

 five sequential categories: direct biotic effects, transfer of materials, 

 changes in properties, energetic changes, and changes in water movement. Each 

 category is prefaced by a question which specifies the condition by which any 

 PEA in that category can be identified. 



The PEA categories are arranged sequentially, from the top to the bottom 

 of the list. This arrangement avoids correlated responses between natural 

 processes and the resulting effects or movements of materials, phenomena which 

 should be detected with the ESD model. For example, increased rate of water 

 flow causes erosion of sediment; yet increased rate of flow is the primary 

 alteration - erosion of sediment is a subsequent response. Therefore, in 

 reading down the list, sediment removal would be identified as a primary 

 alteration only if it is indeed a direct and immediate alteration (e.g., of 

 topsoil removal). 



PEA's are determined either (1) as a result of direct field observations 

 or (2) through deductive processes resulting from careful review of accurate 

 project descriptions. A definitive set of PEA's may vary for a given activ- 

 ity, depending upon the ecosystem type; for example, the set of PEA's generated 

 as a result of vegetation removal in the coastal uplands differs from the set 

 of PEA's resulting from vegetation removal in the brackish marsh. Finally, 

 certain activity types have a larger number of primary ecological alterations 

 than have others, as would be expected. 



144 



