Winter 2015 – GoMRI Researcher Interview with Dr. Irv Mendelssohn

(From Winter 2015 Newsletter) Dr. Irv Mendelssohn from Louisiana State University answered a few questions about his RFP-II project, Accelerating Recovery after the Deepwater Horizon Oil Spill: Response of the Plant-Microbial-Benthic Ecosystem to Mitigation Strategies Promoting Wetland Remediation and Resilience

1. Tell us a bit about your research. What are the goals of your project?

Coastal wetlands are well known for the variety of ecosystem services they provide to society, like storm protection, water quality enhancement, fisheries support, carbon sequestration and many others. Most, if not all, of these ecosystem services are dependent on a healthy vegetation community in association with functioning soil microbes and soil invertebrates. It is the goal of our research to understand the effects of the Deepwater Horizon oil spill on this integrated ecological system of vegetation, benthic microbes, and invertebrates, the extent of recovery thus far, and the remediation actions that might be taken to accelerate recovery where it is lagging. This goal is being addressed through a multi-investigator effort of Dr. Qianxin Lin and me investigating vegetative response and recovery, Dr. Aixin Hou assessing microbial responses, Dr. John Fleeger evaluating the algae and small invertebrates that live on and in the soil, and Dr. Don Deis, who studies the marsh snails and crabs that depend on the vegetation.

2. What is your background and how did you get involved with this kind of work?

My training is as a coastal plant ecologist attempting to understand the factors that control the health of coastal vegetation, particularly the ecological condition of coastal wetlands. I have carried out this research throughout the US and internationally during my scientific career of 40+ years. It was an oil spill that occurred in the marshes adjacent to Nairn, Louisiana on April 23, 1985, interestingly almost 20 years to the day of the Deepwater Horizon event that brought me into oil spill research. I assessed the initial impact of that spill on the affected saline marshes, and, through funding from the Louisiana Sea Grant Program with collaboration from colleagues Drs. Mark Hester and Jack Hill, formerly at LSU, we were able to identify controls on recovery. Subsequently, I was asked to assess impacts and response actions associated with oil spills in California, Texas, Canada, and a number of times again in Louisiana. During this period, Qianxin Lin joined my research group as a Ph.D. student investigating the differential response of marsh plant species to oiling. We later collaborated to establish an oil spill research program. We’ve worked together for almost 20 years on various oil spill projects, and have published more than 30 oil-spill related scientific publications. Thus, my interest in oil spill research started much before the Deepwater Horizon spill.

3. What are some of the methods you use to study the impacts of oiling on coastal wetlands? Have you faced any major challenges while carrying out your research?

Our research team uses a variety of methods from simple measurements of plant biomass to highly technical assessments of microbial composition and function with GeoChip microarray analyses and the quantification of oil-degrading genes with real-time quantitative polymerase chain reactions. Our major challenge has been the ever-decreasing extent of oiled shoreline marsh from which to sample due to shoreline erosion. Many of the oiled marshes have historically had high rates of shoreline erosion and, in addition, some shorelines may be seeing accelerated erosion due to oiling. As a result, our study sites are getting smaller and smaller, with less and less oiled shoreline.

4. What are some of the most significant or exciting findings so far in your work?

There have been a number of significant findings in our work so far, including: 1) While there were initially severe impacts to the vegetation-microbial-benthic ecosystem in heavily oiled marshes, recovery of vegetation, microbial communities, and invertebrates have generally been robust. For example, juvenile snails are recruiting and establishing in the heavily oiled sites indicating that population dynamics are starting to recover to that which is considered a healthy population. 2) Nonetheless, some individual species of plants and animals showed poor recovery along heavily oiled marsh shorelines, even though the general trend of recovery was the norm. 3) The oil-degrading microbial communities, which had faster recovery in moderately oiled sites than heavily oiled, were increasingly dominated by gram-positive (GP) PAH-degrading bacteria with time over a course of 30 months following the DWH spill; the microbial degradation of the petroleum residuals has come to its latter stage two and a half years after the spill. 4) Moderately oiled marshes showed few initial impacts or long-term effects on the plant, animal and microbial variables measured in our study. 5) Heavy oiling reduced the soil shear strength of surface soil with concurrent increases in surface erosion. 6) Certain petroleum hydrocarbons, such as naphthenic acids, were still present in sediments 48 months post-spill, which may pose an environmental concern.

5. What are the broader implications of your research and how might your findings inform the management of Gulf Coast wetland areas?

Our research supports the accepted paradigm that coastal wetlands are relatively resilient to oil spills. However, this should not be construed to mean that oil spills don’t have significant immediate (short-term) impacts to wetlands and the societal services they provide. Nor does this general resilience contradict observations of impacts to specific biota or functional processes.

From an oil spill response perspective, our research confirms the importance of preventing spilled oil from entering wetlands. However, once oil enters wetlands all cleanup activities should be benign with respect to the long-term health of the system, given that natural recovery to oiling can be high.

6. Can you tell us more about your research collaboration with fellow GoMRI researchers?

In collaboration with Amy McKenna, a GoMRI researcher, and her group at the National High Magnetic Field Laboratory, we have catalogued compositional changes of oil residuals in saltmarsh sediments in Barataria Bay over a course of four years post the oil spill by using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS).

6. If funding were not an issue, what would add to your project?

There are really an endless number of processes and biota that could be investigated relative to immediate response to oiling and recovery over time. Being able to incorporate aspects like fish ecology and biogeochemical nutrient cycling would have been very valuable. Also, our current microbial study is focused on DNA-based microbial community composition and structure. If we had more funding to support a postdoctoral researcher, we would also investigate dynamics of microbial community function in response to oil input, based on RNAs (i.e., transcriptomics). From a general perspective, this project would have greatly benefited from field experiments where different oiling scenarios and cleanup techniques could be evaluated under real world conditions. In lieu of this, large-scale greenhouse experiments that mimic the real world would be a valuable contribution.

[Back to the Winter 2015 Newsletter]