| Microbial activity development in soil materials placed over processed oil shale is vital to plant litter decomposition, cycling of nutrients, and soil organic matter accumulation and maintenance. Samples collected in the summers of 1979, 1980, and 1981 from revegetated soil 30-, 61-, and 91-cm deep overlying spent oil shale in the Piceance Basin of northwestern Colorado were assayed for dehydrogenase activity with glucose and without glucose, for phosphatase activity, and for acetylene reduction activity. Initial ammonium and nitrite nitrogen oxidation rates and potential denitrification rates were determined in 1981.; Zymogenous dehydrogenase activity, phosphatase activity, nitrogenase activity, potential denitrification rates, and direct microscopic counts were lower in surface soil 30 cm deep, and were frequently lower in surface soil 61 cm deep over processed shale than in a surface-disturbed control area soil. Apparently, microbial activities are stressed in these more shallow replaced soils. Soil 61 cm deep over a coarse-rock capillary barrier separating the soil from the spent shale, frequently had improved biochemical activity. Initial ammonium and nitrite nitrogen oxidation rates were lower in all replaced soils than in the disturbed control soil.; Soil core samples taken in 1981 were assayed for dehydrogenase and phosphatase activities, viable bacteria, and viable fungal propagules. In general, microbial activity decreased quickly below the surface. Zymogenous dehydrogenase and phosphatase activity and numbers of viable fungal propagules tended to decrease more rapidly in the disturbed control soil than in the replaced soils. At depths greater than 45 cm, microbial activities were similar in buried spent shale and surface-disturbed control soil.; Salinity (electrical conductivity) analysis of soil core samples indicated that the potential existed for upward movement of salts from the spent shale into the adjacent overlying soil and that some potentially toxic elements (B, Mo) have been translocated into the soil from the shale. However, surface soil salinity had decreased since 1977.; Microbial and biochemical activities in soil overlying spent oil shale are sensitive to soil depth and other management variables. Further study of microbial activities and factors affecting their establishment and succession in soil over processed oil shale is needed. |
