Gomez, Susana Karen
Pringle, David L.
University of Northern Colorado
Type of Resources
Place of Publication
University of Northern Colorado
Federal lands of the Arapaho and Roosevelt National Forests and Pawnee National Grassland (PNG) lie on the Niobrara play and bring high profits to the State of Colorado. Natural gas development, production, and associated processing activities; however, can be a substantial source of air pollution. Common fugitive emissions on typical PNG Oil and Natural Gas (O&NG) production sites include volatile organic chemicals (VOCs), such as benzene, toluene, ethylbenzene and the xylenes (BTEX). These VOCs can then deposit (wet or dry) onto or transfer (via soil or water) into surrounding vegetation. Minerals, including heavy metals, are also released during the production phase of O&NG development and can deposit near the emission source. There are also impacts beyond pollutants, including habitat loss, fragmentation and the alteration of vegetation communities due to O&NG construction and associated structures. The current study presents novel data related to (1) the ambient levels of common fugitive emissions on typical O&NG production sites (Chapter II) (2) the deposition of these emissions (BTEX) onto proximate flora (Chapter III) (3) the impact on mineral content in proximate flora (Chapter IV) and (4) reclamation success and shifts in plant community structure (Chapter V). In Chapter II, Volatile Organic Compounds (VOCs) were quantified in real-time and used to determine the spatial and temporal windows of exposure for proximate flora and fauna. We found that VOC concentrations generally increased during the 6 hr. day and were predominately the result of O&NG production and not vehicle exhaust. Thirteen of 24 VOCs had statistically significant differences in ambient levels between production groups, frequently above reference standards and thus at biologically relevant levels for shortgrass steppe flora and fauna. The most biologically relevant VOCs found at concentrations exceeding time weighted average permissible exposure limits (TWA PEL), were benzene and acrolein. Generalized Estimating Equations (GEEs) were used to measure the relative quality of statistical models predicting benzene concentrations on sites. For Chapters III-V sites were grouped according to status (PA or PR) and production date (spud date). Groups were as follows: PA = Plugged and abandoned in the 1980s, PR1 = Producing since 1980-1990, PR2 = Producing since 2000-2005, and PR3 = Producing since 2006-2013. We also measured the effects of Distance in all chapters with a maximum distance of 100 m from the wellhead. In Chapter II, Bouteloua gracilis (blue grama) and Bouteloua dactyloides (buffalo grass) leaves were collected and BTEX were quantified in plant tissue. Deposition and accumulation of BTEX onto proximate flora significantly decreased with production age (PA sites). Newer wells and sites with active pumpjacks had significant concentrations of benzene and toluene in vegetation. BTEX were present on every site except one plugged and abandoned site. The average concentration of toluene on all sites combined was 2.32 ppbv. The average concentration for benzene on all sites combined was 13.18 ppbv, but concentrations were as high as 176 ppbv. These concentrations are arguably biologically relevant as organisms within 100 m of O&NG production sites are likely breathing, and if grazing, consuming high levels of BTEX. In Chapter III, concentrations of minerals in Bouteloua leaves were quantified and their effects on foraging quality were determined. Of the macro minerals, K, P, and S were significantly higher in vegetation found at 25 m and 50 m than in those at 100 m. Calcium was highest in vegetation near PA sites, while P and K were highest in vegetation near PR1 and PR2 sites. Shoot concentrations of Cu, Br, Cr, Pb, Sr and Ba were higher further from the wellhead (100 m), indicating impact further than previously expected. There were still impacts near the wellhead, as Hg was significantly higher in vegetation at 25 m. Concentrations of Mn, Fe, and Ba were all highest in vegetation at PR3 sites, whilst Br was highest on PR1 sites and Sr was highest on PA sites. Concentrations of micro minerals in shoots were in the following order Fe > Cl > Pb > Br > Mn > Sr > Ba > Zn > Cu > Se > Ni > Hg > Cr. Concentrations of Se (5.67 ppm), S (0.33%), and K (1.21%) had the potential to exceed max tolerable concentrations for cattle (based on 2 kg daily mass intake). All other nutrient shoot concentrations were potentially appropriate for grazing cattle, depending on specific cattle and grazing characteristics. Toxic elements such as Br (54 ppm) and Sr (46 ppm) were present in shoot samples far below maximum tolerable levels, while concentrations of Hg (1.54 ppm) and Pb (83 ppm) were beyond daily maximum tolerable levels for cattle when considering a 2 kg DM diet. We also compared shoot nutrient levels to data collected by Fresquez et al. (1991) and concentrations of micro minerals were comparable to Bouteloua grown in sludge treated soils, indicating a substantial impact from O&NG production. This impact has had a lasting effect on soils and vegetation as seen with Pb levels on PA sites reclaimed over 30 years ago. In Chapter IV, we characterized proximate vegetation cover, diversity and functionality during well production and following abandonment. In general, PA 100 m sites were distinctly different from all PR sites. As expected, at 20 m and 50 m, sites had substantially more bare ground and introduced plant species than at 100 m and PR3 sites had the highest percentage of bare ground. There were 16.5% introduced plant species on all plots combined and 2% of plant species sampled were invasive. Satisfactory reclamation was achieved at 50 m on PR1 and PR2 sites as vegetation was at 80% total cover when compared to 100 m. Our PA sites were the highest in plant diversity indices and PR3 were the lowest. With the high cover scores and diversity indices on PA sites it seems recovery over time is possible. We did not find high plant functional redundancy on our O&NG sites; instead, we found high plant species diversity and high functional diversity on PA sites. These disturbed plant communities with greater spatial heterogeneity than blue grama-dominated sites are shifting in community structure. We found that novel intensities of O&NG disturbances along with other synergistic disturbances promoted species and functional shifts in vegetation. The PNG has had an exponential increase in O&NG drilling and extraction in the last decade and results indicate production has caused a novel and biologically relevant impact on native flora and fauna.
Pawnee National Grassland (Colo.)
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