Marsh plants mediate the influence of nitrogen fertilization on degradation of oil from the Deepwater Horizon spill

J Adam Langley,Thomas Shannon Iii,Reena U Palanivel,Samantha K Chapman,Helen K White

doi:10.1890/es14-00343.1

J Adam Langley, Thomas Shannon Iii + Show 3 more

Open Access

https://doi.org/10.1890/es14-00343.1

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Abstract

Coastal wetlands are commonly exposed to hydrocarbon pollutants derived from extraction disasters like the Deepwater Horizon oil spill. Naturally occurring microbes can degrade oil, but the rate of oil degradation depends heavily on the key chemical and biological factors. The goal of this study was to determine the influence of interactions between marsh plants and nitrogen (N) on the degradation of oil from the Deepwater Horizon oil spill. Oil disappearance was measured with gas chromatography (GC) focusing on the change in C18 n‐alkane‐to‐phytane ratio of oil, and instantaneous oil degradation rates were measured using an instantaneous carbon isotopic partitioning method. N addition often stimulates oil decomposition in soil slurries, but the effect of N in our mesocosms depended on plant species. N addition accelerated oil degradation in Spartina alterniflora mesocosms but slowed oil degradation in Spartina patens mesocosms. Across all plant and N treatments, oil degradation related to plant root growth. In many ecosystems including marshes, N addition has been shown to diminish root growth by reducing the need for nutrient foraging. Where N addition reduces root growth, N may ultimately exacerbate oxygen scarcity in marsh soils possibly negating or reversing the positive, direct effects that N has on oil degradation. Based on these findings, fertilization strategies that maximize marsh plant root growth will be the most effective at increasing the microbial degradation of oil and will have the greatest potential to mitigate the impacts of oil in marsh ecosystems.

Highlights

Following the Deepwater Horizon oil spill of 2010, oil was deposited on large stretches of marsh-dominated shorelines in the Gulf Coast region of the USA (Kokaly et al 2013)
Previous work has shown that application of N fertilizer may accelerate oil degradation on contaminated beaches (Atlas and Bartha 1972, Bragg et al 1994, Swannell et al 1999, Roling et al 2002, Snedden et al 2007; see preliminary study in Appendix), and inland soils (Westlake et al 1978); nutrient addition was found to have no effect on oil degradation in a field study in a Gulf Coast salt marsh (Tate et al 2012)
The primary goal of our study was to determine how added N influences the degradation of oil, in the presence of plants that occur in Gulf Coast marshes

Summary

Introduction

Following the Deepwater Horizon oil spill of 2010, oil was deposited on large stretches of marsh-dominated shorelines in the Gulf Coast region of the USA (Kokaly et al 2013). Previous work has shown that application of N fertilizer may accelerate oil degradation on contaminated beaches (Atlas and Bartha 1972, Bragg et al 1994, Swannell et al 1999, Roling et al 2002, Snedden et al 2007; see preliminary study in Appendix), and inland soils (Westlake et al 1978); nutrient addition was found to have no effect on oil degradation in a field study in a Gulf Coast salt marsh (Tate et al 2012) In this latter study, the authors suggested that instead of N, oxygen availability was the dominant factor limiting oil degradation. It is important to explore the role that these other interacting factors together may have on the degradation of oil

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