Environmental effects of oil and gas lease sites in a grassland ecosystem.

The northern Great Plains of Saskatchewan is one of the most significantly modified landscapes in Canada. While the majority of anthropogenic disturbances to Saskatchewan's grasslands are the result of agricultural practices, development of petroleum and natural gas (PNG) resources is of increasing concern for grassland conservation. Although PNG developments require formal assessment and regulatory approval, follow-up and monitoring of the effects of PNG development on grasslands is not common practice. Consequently, the effects of PNG activity on grasslands and the spatial and temporal extent of such impacts are largely unknown. This paper examines the spatial and temporal extent of PNG development infrastructure from 1955 to 2006 in a grassland ecosystem in southwest Saskatchewan. The effects of PNG development on grassland ecology were assessed from measurements of ground cover characteristics, soil properties, and plant community composition at 31 sites in the study area. PNG lease sites were found to have low cover of herbaceous plants, club moss (Lycopodiaceae), litter, and shallow organic (Ah) horizons. Lease sites were also characterized by low diversity of desirable grassland plants and low range health values compared to off-lease reference sites. These impacts were amplified at active and highly productive lease sites. Impacts of PNG development persisted for more than 50 years following well site construction, and extended outward 20 m-25 m beyond the direct physical footprint of PNG well infrastructure. These results have significant implications with regard to the current state of monitoring and follow-up of PNG development, and the cumulative effective of PNG activity on grassland ecosystems over space and time.