Abstract
Oil pipelines are vulnerable at river crossings since floods can expose and rupture pipes, releasing oil that floats and coats floodplain vegetation. This study investigated the consequences of oil coatings on leaves of cottonwoods (riparian poplars), the predominant trees in floodplain woodlands around the Northern Hemisphere. The study compared conventional crude oil (CO) versus diluted bitumen (dilbit, DB), heavy oil originating from the Alberta oil sands; with petroleum jelly (PJ) as a reference. The treatments increased leaf surface temperatures (Tleaf) in narrowleaf and plains cottonwoods (Populus angustifolia, P. deltoides) and balsam poplars (P. balsamifera) (Control = 21.8°C, PJ = 23.7°C; CO = 26.2°C; DB = 28.1°C; Tair = 25°C). The leaf warming followed stomatal occlusion from the foliar coating, which would reduce transpiration and evaporative cooling, combined with increased solar warming with the darker oils. Tleaf varied across the three cottonwood species, with cooler, narrow, narrowleaf cottonwood leaves; intermediate plains cottonwood leaves; and warmer, darker, balsam poplar leaves (average Tleaf: narrowleaf = 23.8°C, plains = 24.3°C, and balsam = 26.7°C), with similar warming in each species following the different treatments. Across species and treatments, Tleaf was tightly correlated with foliar condition, which assessed turgor versus wilting of leaf blades and petioles, along with leaf necrosis and senescence (r2 = 0.980, narrowleaf; 0.998, plains; 0.852, balsam). This tight association indicates validity of both Tleaf and foliar condition as diagnostic measures. Crude oil and dilbit had similar foliar impacts, and for both, leaf abscission occurred within 2 to 3 weeks. Consequently, following an oil spill, remediation should commence quickly but extending vegetation removal beyond a few weeks would have limited benefit since the contaminated leaves would have abscised.
Highlights
Pipelines provide efficient means of transporting crude oils across North America and worldwide [1]
For the post-hoc comparisons between treatments, the crude oil (CO) and dilbit (DB) treated leaves were significantly different than the control (C) or petroleum jelly (PJ) treated leaves (p
Prior studies have demonstrated the blockage of transpiration with petroleum jelly (PJ) [26,33,40], and our study indicates a similar response to foliar coatings of crude oil (CO) or dilbit (DB)
Summary
Pipelines provide efficient means of transporting crude oils across North America and worldwide [1]. Pipelines are vulnerable at river crossings and the risk increases during flood events when swift flows erode the channel bed and banks and flex and rupture the exposed pipe [2,3]. When pipelines rupture during flood events, the released oil floats on top of the flood waters that flow over the floodplain [4]. These zones are commonly colonized by riparian vegetation which filter out some of the floating oil, coating the stems and leaves, as well as the banks (Fig 1). For the clean-up and remediation, some of the most intensive and expensive efforts involve the removal of oil-contaminated riparian vegetation but the nature and timing of the responses to oiling by the cottonwoods or other riparian plants are poorly understood, as are the environmental consequences from the vegetation removal
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