Desert Vegetation Forty Years after an Oil Spill

Abstract

Deserts are the most frequent locations of terrestrial crude oil contaminations. Nevertheless, the long-term effects of petroleum hydrocarbons on desert ecosystems are still unknown, which makes risk assessment and decision making concerning remediation difficult. This study examined the long-term effects of petroleum hydrocarbons on perennial desert vegetation. The study site was a hyper-arid area in the south of Israel, which was contaminated by a crude oil spill in 1975. The contaminated area was compared to uncontaminated reference areas. The composition of perennial plants 40 yr after the oil spill was not significantly affected by the contamination. However, the size distribution of the two most dominant shrub species, Baker and (Moq.) Iljin., and the only tree species, Savi and (Forssk.) Hayne, were different from the reference. These differences can be explained by decreased recruitment. The estimated recruitment of in the last 40 yr post oil spill was 74% less than recruitment in the reference area. Low recruitment of may in the future lead to the loss of tree cover, which would change the entire ecosystem, as are keystone species on which a number of microorganisms, plants, and animals rely. Remediation of oil spills and preventative measures are recommended.

Seed Predation on Oil-Polluted and Unpolluted Vachellia (Acacia) Trees in a Hyper-Arid Desert Ecosystem

“…However, the overall predation rates on seeds of both Vachellia species and at both sites was very high (70.2 and 83.9% on fallen pods of V. tortilis and V. raddiana , respectively). Even if oil pollution may not have a major effect on seed predation, V. tortilis and V. raddiana seed germination [ 29 ] and recruitment [ 26 ] are both reduced on oil polluted soils. Oil pollution, in addition to seed predation, can therefore be considered a major threat to the survival of Vachellia trees.…”

“…We investigated two study sites affected by two oil spills in 1975 and 2014, respectively (hereafter “1975-site” and “2014-site”). During the first oil spill, around 10,000 m 3 of crude oil leaked into the reserve, and this was not followed by any remediation attempt [ 25 , 26 ]. The more recent oil spill deposited 5000 m 3 of oil; part of the contaminated soil was removed and the remaining was tilled in order to aerate the soil.…”

“…Half of the selected trees were, at the time of the spill, within 2 m of the trajectory of the oil flow (hereafter “polluted”), while the other half were at ≥10 m from the oil flow (hereafter “unpolluted”). Evidence of persistent negative effects of the oil on the bacterial and plant communities, even years after these major oil spills occurred, are provided by Girsowicz et al [ 28 ], Nothers et al [ 26 ], and Tran et al [ 29 ]. Differences in physical properties between oil-contaminated and noncontaminated soil are provided by Gordon et al [ 30 ].…”

“…Two major oil spills occurred in the Arava within the past 50 years. Oil from these spills has been shown to accumulate in the soil, negatively affecting Vachellia seedling survival and growth [ 25 ], and dramatically reducing the recruitment of young trees [ 26 ]. However, the interaction between oil pollution and biotic stresses such as seed predation on Vachellia trees has not yet been evaluated.…”

Rhizosphere Microbiome of Arid Land Medicinal Plants and Extra Cellular Enzymes Contribute to Their Abundance

“…The vegetation is either succulent (accumulating water) or non-succulent perennial hard plants. Both are true xerophytes and are well adapted to the low water conditions [1]. However, in such harsh climatic conditions, endemic micro-symbionts are of great importance for plant survival [2].…”