Ecological disturbance in the anthropocene: legacy effects of orphaned oil wells on metabolic phenotype of free-living rodents and vegetative community

Abstract

While catastrophic large marine oil spills often receive considerable media attention, highly localized and smaller-scale inland spills occur from defunct oil and natural gas wells. Oklahoma has over 15,965 documented orphaned, unplugged oil wells (UOWs) and the environmental impacts of these are not fully understood. As piping from UOWs corrode over time, petroleum escapes via open well bores, fractures in well casings, valves, connectors, and cracks in old wellheads. These escaping compounds contaminate soil and groundwater, presenting direct hazards to plant and animal species. Polycyclic aromatic hydrocarbons (PAHs) are a class of hazardous compounds found in crude oil and can persist in the environment for decades. Specifically, 16 PAHs are listed by the United States Environment Protection Agency (US EPA) as priority contaminants of concern. Currently, the effects of UOWs on plant and animal communities are not well understood. Using two study locations in Cushing, Oklahoma, we assessed the effects of UOWs on (1) site-specific habitat quality and (2) resident deer mice (genus Peromyscus) physiology. To assess habitat quality, we conducted site-specific vii vegetative surveys and Floristic Quality Assessment (FQA) was used to measure site disturbance. At the same sites, we measured free-living deer mice resting metabolic rates and hematological indices. In accordance with substantial data showing PAH exposure causes mammalian hematological damage, altered immune function, and metabolic rate shifts, we hypothesized legacy PAH contamination will lead to physiological differences in free-living Peromyscus individuals collected near UOWs. Results from this study showed decreased metabolic rates and hematological changes in deer mice collected near UOWs. We found differences in FQA values between sites, indicating disturbance in vegetative communities near UOWs. This study expands understanding of the environmental impacts of UOWs. These FQAs provide landowners and Oklahoma Energy Resource Board (OERB) with information regarding the area following remediation for some UOW sites and prior to remediation of others. In addition to this research, further FQAs conducted across the state, as well as a comprehensive species list for Oklahoma, will springboard what is known about vegetative disturbance associated with UOWs. Additionally, Peromyscus health data from this study can be used for biomonitoring and across-site comparisons. Finally, future studies can monitor deer mice population trends at the sites for the present study to characterize temporal shifts associated with UOW remediation. All this information can be used to assess the success of UOW habitat remediation and restoration projects.