Environmental impact studies of the Navajo and Kaiparowits Power Plants. Annual report No. 4, 1 Jun 1974--31 May 1975

During the fourth year of study, field investigations were concentrated at 8 study sites in the vicinity of Page, Arizona. The central purpose of this study was twofold: (1) to determine what effects effluent from power plant operation would have on the ecosystems; and, (2) to determine whether those effects would be ecologically significant. A monitoring program was initiated to determine natural patterns of change. Plant abundance was greatest in the spring when soil moisture levels were also highest. Much variability probably resulted from variations in microclimate. Changes in the dynamics of small mammal populations were clearer and were possibly strongly influenced by green vegetation growth and preceding rainfall amounts. A procedure for determining the best combination of factors for revegetation success is being developed. Annual primary production in the desert grassland has been determined. The behavior of desert soils under exposure to simulated effluent is discussed. The response of Lake Powell diatoms to in situ exposure to mercury was evaluated and compared to laboratory experiments reported earlier. (GRA)