In light of the Deepwater Horizon oil spill in the Gulf of Mexico, the National Science Foundation (NSF) highlighted the Rapid Response Research (RAPID) mechanism (Dear Colleague Letter NSF 10-060) as quick-response research on natural or anthropogenic disasters and similar unanticipated events. In this RAPID project, the PIs will study the role of salt marsh plants and nitrogen inputs in the decomposition of simple vs. recalcitrant forms of carbon in association with the Deepwater Horizon oil-spill in the Gulf of Mexico. Recent studies have demonstrated that, contrary to expectations, nitrogen (N) inputs will not stimulate decomposition of recalcitrant carbon stored in salt marsh peat soil, and they may actually reduce it. However, the same is not true for sugars and other more simple forms of carbon. Given the potential input of a significant amount of complex hydrocarbons from the oil-spill into coastal salt marsh habitat in the Gulf, it will be important to be able to predict the effects of plants and of N inputs on rates of oil hydrocarbon decomposition and ecosystem function in these fragile habitats. Given the urgent situation facing Gulf area wetlands and the capacity to increase marsh exposure to nutrient-rich waters, results of this study could be critical for exploring oil spill mitigation options expeditiously. If nitrogen amendments to coastal wetlands increase the processing of crude oil, such management techniques may be implemented more rapidly and with greater precision. To disseminate findings among scientists and managers, the PIs will organize a workshop at the Society of Wetland Scientists (SWS) annual meeting, as well as make data available on the SWS website. Further, the PIs will involve undergraduate researchers and students in the greenhouse study at Villanova University through research funds and an existing Global Change Ecology course.
Following the Deepwater Horizon oil spill of May, 2010, a vast amount of oil was deposited in marshes around the Gulf of Mexico. Managing these lands in ways that accelerate removal of oil can limit the damaging effects of oil on marsh plants, wildlife and populations that depend on them. In the Mississippi Delta region, managers have the capacity to divert large flows of nutrient-rich river water or municipal waste over marshland, essentially fertilizing vast areas in these ecosystems. Several lines of evidence suggest that fertilizing marshes that are polluted with oil may accelerate the breakdown of that oil by microbes, but few studies have been done in a way that accounts for the important influence plants may have on the microbes in the soil that break down oil. The primary goal of our study was to determine how added nitrogen may influence the degradation of oil by soil microbes, particularly in the presence of plants that occur in Gulf marshes. As predicted, we found in a simplified lab incubation study that nitrogen additions stimulated microbial degradation of oil. We followed this finding with a more sophisticated experiment that that included the widespread marsh grasses Spartina alterniflora and Spartina patens at three levels of nitrogen addition. In this more realistic study, the effects of nitrogen fertilization on oil degradation depended on which plant was present. When the marsh grass S. alterniflora was present, nitrogen fertilization again stimulated oil breakdown. However, in the presence of a different marsh grass, S. patens, nitrogen fertilization surprisingly slowed oil breakdown, suggesting that fertilizing an oil-polluted marsh could actually exacerbate the effects of an oil spill. We attribute this surprising result to differences in how these plant species respond to nutrient addition and how that plant growth influences soil microbes. Marsh plants exert a great deal of control over the environment in which soil microbes live. Marsh plants leak oxygen to wetland soils from their roots, a process that stimulates microbial activity. Though most plants grow taller when fertilized, some plants produce fewer roots in response to fertilization because they no longer need as many roots to forage for nutrients. Wetland plants that have fewer roots will release less oxygen into the soil. Though fertilization may directly provide one limiting nutrient, nitrogen, it could ultimately deprive oil-consuming microbes of a more critical resource, oxygen. Based on our findings, managers should consider the identity of plants and type of marsh before fertilizing oil-polluted ecosystems as a remediation strategy. Moreover, beyond site-specific remediation, generally reducing nutrient loads that estuaries currently receive may benefit coastal marshes before they experience stressors like oil pollution, rising seas and storm surges.
