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<br />ASPECTS OF PRECIPITATION ENHANCEMENT <br /> <br />25 <br /> <br />more general discussion of ecological effects of weather modification <br />(Cooper and Jolly 1969), and a comprehensive assessment of potential <br />impacts of artificial ice-nucleating agents (Klein 1978). <br />Aside from the Sierra Ecology Project (SEP), the bulk of the research on <br />environmental effects was completed by Ithe early 1980s. The focused <br />investigations addressed concerns such as the direct effects of added <br />snow on large and small mammals and indirect effects through change <br />in type and abundance of food supply, possible physical and biological <br />changes in aquatic systems, and impacts on vegetation. Thereby, the <br />sensitivities of various ecosystems were estimated (e.g., Table 2.3). Some <br />of the specific studies and results from the ecology projects are reviewed <br />in the 1983 edition of these "Guidelines" (Committee on Weather Modi- <br />fication of the Irrigation and Drainage Division 1983). <br />The essence of the results is that changes that might be expected in the <br />environmental factors (i) were most often subtle, nil, or indiscernible in <br />relation to other natural influences (e.g., effects of fire or insects on forest <br />vegetation); (ii) would be of the same type and magnitude as would <br />result from a sustained increase of a corresponding percent in natural <br />precipitation (e.g., as a gradual change in herb species composition might <br />occur in a wetter climate); (iii) might be beneficial as often as not and <br />depending on point of view (e.g., as when fish habitat increases with lake <br />level); and (iv) would have net outcomes that strongly affect ecosystem <br />management practices (e.g., as when increased weed growth and grass- <br />land productivity occur together). During the 1970s, the most common <br /> <br />TABLE 2.3 Sensitivity Matrix for Selected Environmental Issues <br />(USDI 1977b) <br /> <br /> Environmental Setting <br />Environmental Issue" Alpine Forest Rangeland Agricultural <br />Erosion <br />Surface erosion 1 1 2 <br />Mass wasting 2 1 2 <br />Avalanches 2 2 <br />Microclimate <br />Snow duration 2 2 <br />Soil moisture 1 1 1 1 <br />Water yield 2 2 1 2 <br />Water quality <br />Physical 1 1 2 <br />Chemical 1 1 2 <br />Channel processes 1 1 1 2 <br />Sediment yield 2 1 2 <br />Vegetational productivity 2 2 <br />Nutrient loss 2 2 <br /> <br />"Presumed environmental responses to prolonged predpitation augmentation of 20%.1: <br />detectable but insignificant; 2: readily detectable, sometimes important. <br />