Soil temperature regime in mixed prairie rangeland after pipeline construction and operation

Pipeline construction and operation affect the soil thermal regime of the disturbed area by: (1) alteration of soil texture, bulk density, and water content and thus alteration of soil thermal properties, and (2) heat from the compressed fluid flowing through the pipe. Soil tem peratures over pipelines may also be influenced by sparse vegetative cover as a result of pipeline construction if revegetation is not successful, in which case near-surface temperatures would be af fected; or by heat from the pipeline, in which case subsurface soil temperatures would be affected. These effects could alter plant growth in the vicinity of the pipeline. A study was conducted in Solonetzic mixed prairie rangeland of southern Alberta to evaluate soil temperature responses to pipeline construction and operation. Specific objectives were to quantify these responses and assess their vertical and lateral extent on adjacent natural gas pipelines, installed in 1957 and 1981, with diameters of 0.86 and 1.07 m, respectively. Soil temperatures were monitored throughout the year to a depth of 1.10m directly over the two pipelines, adjacent to the 1981 trench at distances of 3.0 (pipelay area) and 10.0 m (work area) and in the adjacentundisturbednative prairie. Pipeline construction and opera tion in Solonetzic mixed prairie rangeland caused greater maxima in, and more pronouncedfluctuations of, near-surface soil temperature comparedto the undisturbed prairie. Soil temperatures at depths up to 0.80 m above the 1981 pipe, and to at least 3 m laterally from it, increased during the winter months, while temperatures during the summer were cooler in the 1981 trench. The 0°C isotherm was much shallower over winter in the 1981 trench than in all other monitoring locations. Differences in the thermal regime between the 1981 and 1957pipelines could not be attributed to any single cause due to a complicated interaction of factors anddifferent reclamation practices used following installationof the two pipelines.Construction traffic altered the thermal regime of the work area. Mid-summer near-sur facetemperatures werehigh at all locations, less affectedby pipeline construction and operation and likely limiting to plant growth.