This MRI RAPID award funds technical development of a novel analytic technique which separates sedimentary organic material based on its lability. RAPID proposal will increase sample throughput to allow Macondo wellhead blowout samples to be independently analyzed and will help elucidate organic material decomposition reaction kinetics for natural and Gulf-oil spill related geomorphological processes (land use, subsidence, sea level rise, sediment starvation). The ramped pyrolysis technique is based on the underlying hypothesis that older sedimentary organic material is more stable and thus breaks down at a higher temperature than younger sedimentary organic material - within the same sediment. Oil, being both old and potentially labile depending on degree of weathering, will challenge this hypothesis. Technical development funds will be used to better understand pyrolytic decomposition kinetics in sedimentary organic material containing oil pollutants. Funding will be used to build a parallel reactor, with some shared components, devoted to oil-spill related research and to perform chemical experimentation on pyrolysis residuals of interrupted decompositions. Solid state NMR will be used to determine pyrolysis residue chemical compositions during different stages in the reaction. Ultimately, radiocarbon analysis and X-ray near edge adsorption may be employed to differentiate the oil-derived material from natural organic matter. Freshly deposited oil, heavily weathered oil, and pristine coastal sediment will be measured from different sites and regions of the Gulf Coast, providing kinetics models from which coastal geomorphology can be investigated in terms of oil pollution during the next several years to decades. RAPID funding is sought to capitalize on the need to gain this information in a timely fashion while fresh oil is still washing ashore along the Gulf Coast and just beginning to weather and incorporate into sedimentary environments. This RAPID will support studies ranging from local coastal geomorphologic changes due to the oil spill to chronology of difficult-to-date sediment horizons in sediment sequences to riverine carbon cycling. Several undergraduate students will participate in fieldwork, sample preparation, and analyses. The P.I. has compiled a waiting list of undergraduates from different academic backgrounds that are eager for field and analytical experience. This project will advance knowledge of geomorphologic changes that may result from oil degradation of sediment-trapping marshes and mangroves. The project will enhance teaching at graduate and undergraduate levels. Current graduate students include 3 underrepresented minority students and two women. Results will be dovetailed into existing K-12 outreach programs and gain high visibility given the public concern over the Gulf oil spill. The PI . has established an excellent working relationship with the park manager at Grand Isle State Park and has routinely shared with the park data and observations from field surveys involving the oil spill. Environment-specific information will create a broader knowledge base whereby decisions concerning the cleanup and land-use change will be better understood.
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In response to the Deepwater Horizon oil platform explosion and subsequent uncontrolled release of oil from the Macondo well head (DWH), the Stable Isotope Laboratory, Tulane University (SILT U) sought and was rewarded funding to build a second ramped pyrolysis radiocarbon preparation unit. With anticipation of high demand for the instrumentation, it was deemed necessary to increase through-put of this instrumentation in order to avoid negatively affecting the other scientific aims of the ramped pyrolysis system. The most important aspect of this funding is the increase of analyses since the completion of the second ramped pyrolysis system at Tulane University. At the time the proposal was written, the throughput of the laboratory was about 2 samples per day (4 hour reaction time), maximum, with instrumental delays caused by episodic failures of different components. Implementation of a second system increased throughput and decreased down-time due to component failure, and it advanced the way we obtain data from the system allowing more efficient use of instrument time. We have run 10 times the amount of samples since the funding of this proposal; this has not only allowed publication of peer-reviewed articles on oil contamination, but also about other scientific questions that were not derailed by the increased demand on instrumentation from the DWH spill. Proof of Concept: How is ramped pyrolysis radiocarbon analysis beneficial to understanding the oil spill’s effects?: Our first aim with the new system was to test a suite of samples with known oil contamination to constrain changes in ramped pyrolysis reaction profiles and isotope content. The results of this experiment have been published in Environmental Research Letters (doi:10.1088/1748-9326/8/4/044038). Here, the SILT U group collaborated with researchers at Texas A&M University on a suite of samples collected from Barataria Bay, Louisiana. Using the measured content of polycyclic aromatic hydrocarbons (PAH’s) as a proxy for oil contamination, ramped pyrolysis was performed on two sets of samples having abundant or low levels of PAH’s. The results of ramped pyrolysis and isotope abundance measurements are shown in Figure 1. First, the shape of the reactions is much different. High-PAH samples have an abundance of pyrolysis products released at lower temperatures than low-PAH samples, much like raw Macondo crude oil treated in the same way. Low-PAH samples are more similar to uncontaminated Barataria Bay marsh sediment sampled before the occurrence of the oil spill. Second, the CO2 produced from combustions of the pyrolysis products has a lower radiocarbon abundance in the high-PAH samples than in the low-PAH samples. Because oil is radiocarbon-free (14C in oil has decayed to levels lower than our detection limit because the age of the oil is high relative to the half-life of 14C), these numbers reflect a mixture of approximately 90% oil and 10% ambient organic material that was present before the spill occurred. In low-PAH samples, there is still some evidence of oil contamination, however the isotope ratios are more similar to Barataria Bay sediments collected prior to the DWH spill. Ramped Pyrolysis Time Series: The main reason for building the second ramped pyrolysis reactor was to accommodate increased throughput of samples above and beyond the small sample set described in the proof-of-concept article. Facilitated by other funding to collect samples over a long period of time (EAR-1045845), the SILT U group has performed hundreds of measurements of oil-contaminated sediment samples from coastal Louisiana. The same trends observed in the proof-of-concept study persist. High levels of oil contamination are indicated by lower temperature pyrolysis products and lower levels of radiocarbon. In many samples, high levels of oil (>80% oil in the total organic carbon) are observed more than 800 days after the spill. The SILT U group has analyzed three different time series in three different sampling sites that were repeatedly visited after the DWH spill. Degradation patterns at the three locations are similar, but the rates of degradation of oil are controlled largely by energetics of the depositional environment with higher rates at the beach face (open Gulf of Mexico side) and lowest rates in Barataria Bay marsh. This work will be published as an open-source article as most publications from the SILT U group. Applicability of our Work: Isotopic characterization of the oil and its degradation components stored in the sediment is important to assess whether oil contamination is at the cause of environmental degradation. Arguably, nowhere can benefit more from this type of study than coastal Louisiana. The coastal wetlands here are sediment-starved, undergoing high rates of local sea level rise due to compaction, and threatened by higher rates of global sea level rise. They were already a stressed ecosystem before the DWH spill. Now we have an ample way to test whether geomorphic change in this environment is actually related to oil components in the environment or pre-existing processes.
