The following is a summary of “Islands in the oil: Quantifying salt marsh shoreline erosion after the Deepwater Horizon oiling” written by R. Eugene Turner, Giovanna McClenachan and Andrew W. Tweel, published in the Marine Pollution Bulletin in September 2016 (Volume 110, Issue 1, 15 September 2016, Pages 316–323)
The 2010 Deepwater Horizon disaster was the worst oil spill event in U.S. history. Approximately 4.9 million barrels of Macondo oil were released into the Gulf of Mexico just 66km from the Louisiana coast. As clean up and restoration efforts began, it became clear that there was a severe lack of baseline data for the ecosystems and wildlife in the region. There has been a concerted effort over the past six years to monitor and record the short and long-term impacts of the spill in order to understand the extent to which oil affects an environment. Conveniently (from the scientific viewpoint), the marshes and islands of Louisiana were inconsistently oiled and provided a “potential natural laboratory” of control and experimental sites. Scientists could observe oiled and unoiled marshes that experienced the same natural tides, weather conditions, and human impacts over the same period of time. This type of experimental conditions are rare outside of a controlled laboratory situation.
Drs. Eugene Turner, Giovanna McClenachan and Andrew Tweel used this opportunity to monitor shoreline erosion – a key issue for Louisiana salt marshes. They had three primary questions: 1) How much faster did oiled shorelines retreat?, 2) How long do the effects of oiling last?, and 3) Is there recovery?. Using Google Earth satellite and aerial imagery and classifications from a multi-agency damage assessment organization (SCAT – Shoreline Cleanup Assessment Technique), 46 islands in Barataria and Terrebonne Bays were selected as study sites. Islands classified as heavily, moderately or lightly oiled were used as ‘oiled sites’ while those given the no oil designation were used as ‘unoiled sites’. Imagery stored publically on Google Earth provided images of the selected sites from 1989 to 2012 and enabled the scientists to measure the length and width of each island over time. Using these images, they were able to determine the erosion rate for the 20 years prior to the oil spill and establish a baseline to compare with the erosion rate following the spill.
After analyzing the data, the scientists determined that the rate of erosion at oiled islands for the first 12 months following the spill was 275% of the pre-spill erosion rate. That translates to an erosion rate nearly three times as fast as that seen before the spill and at unoiled sites. However, there was no detectable difference between the rates at oiled and unoiled sites after a year and a half. This suggests that there was some degree of recovery or stabilization over those 18 months. These results are consistent with those from other studies that tracked erosion rates after a shoreline was exposed to oil. Turner, McClenachan and Tweel stated that the resiliency and strength of the marsh sediment comes from the belowground biomass – the root system. Without the stability from the roots, sediment is easily washed away by the tides and regular wave action. This study demonstrated that the increased erosion rate caused by exposure to oil does slow over time but did not provide any evidence of recovery in affected marshes. Additionally, these scientists do not believe there can be a reversal to the damage without management intervention.
This is one of many studies examining Louisiana’s coastline and waterways. They are focused on a number of different issues pertaining to erosion, vegetation, food webs, soil, and microbial communities, but there are a few consistent messages emerging: a loss of habitat stability ripples through to all aspects of the community. Salt marshes and estuaries are vital nursery grounds for marine life that form the bedrock of Louisiana’s economy. The islands serve as resting spots and nesting grounds from local and migratory birds. In fact, 11 of the 30 Brown Pelican nesting sites along the Gulf are in Barataria and Terrebonne Bays. Without the islands and marshes, mainland Louisiana is at a higher risk for hurricane damage and sea level rise. They are essential habitats for the social and economic future of the state.
In order to collect data and answer scientific questions, scientists design and run experiments and conduct extensive fieldwork. These require planning, preparation, patience and a healthy dose of creativity. So what if you are trying to monitor the amount of land lost in a salt marsh over the course of a year? Does it require going out and physically measuring the marsh edge on a regular basis or could you capture the changes digitally? For the latter, you would need something reliable, tough and waterproof to stand up to the changing tides and the harsh weather conditions of a coastal salt marsh. CWC scientists Giovanna McClenachan and R. Eugene Turner, both of Louisiana State University’s Department of Oceanography and Coastal Science, tackled this challenge with every surfer, paddler and adventurer’s best friend – the GoPro®!
Scientists have been studying coastal marsh erosion (or land loss) in Louisiana and along the Gulf Coast for years because salt marshes are vital to local fisheries and tourism. Erosion of the marsh edges can occur naturally due to tidal and wave action but there is also evidence that human related activities and disturbances are causing the rate of erosion to increase in some locations. McClenachan and Turner are specifically interested in how exposure to oil (like from the 2010 spill) effects the rate of erosion. They chose a study site in Bay Batiste in Plaquemines Parish, Louisiana to try out their GoPro camera setup and were able to capture photos at two-hour intervals during four to six-week periods from August 2014 to September 2015!
McClenachan and Turner attached two GoPro cameras to a PVC pole that was initially 1.5m from the marsh edge and aimed at a target pole. Additional poles were placed to the left and right of the study site to serve as reference markers in the pictures. The cameras, designed to function in any number of conditions, took photos throughout each day capturing the changing tides, passing storms and the gradual decrease in soil around the marsh grass roots. Using these images, the scientists saw that more sediment was lost during times when the roots of the marsh grass were dead. This happens naturally each year but can also occur when the marsh is exposed to oil and other pollutants. The marsh grass dies or their root systems are damaged and they can no longer serve as a stabilizer for the sediment. Moreover, since studies are showing that remnants of oil can remain in the sediment for years, scientists are worried about the long term impacts of the spill on the stability of marshland.
We don’t have all of McClenachan and Turner’s data, as they haven’t published this study yet, but it seems safe to make some general conclusions: 1) land loss is happening, 2) healthy grass and root systems help stabilize marsh sediment, 3) exposure to oil appears to increase the rate of land loss in marshes, and 4) there is a lot more research that needs to be done.
**McClenachan and Turner put together a time-lapse video to show the dramatic changes to this segment of marsh during the study period. Watch carefully and you will notice the additional poles added to mark the new marsh edge as sediment erodes away.**
Science is a unique profession because your career is based almost solely on your name. As a student you have to read many scientific papers and it is easy to forget that the author of that paper is still a person. These researchers have ambitions, passions, families, and people who have helped them along the way. The Coastal Waters Consortium has many researchers at all levels and we wanted to feature some of them to show off not just their work, but their personalities as well.
Dr. Gregory Olson is a Research Associate II in the Response and Chemical Assessment Lab under Dr. Ed Overton. Currently Dr. Olson is working on sediment analysis for trace crude oil components as well as biomarker analysis and fingerprinting for specific crude oils.
Dr. Olson reports, “One of the more surprising things I have seen is the resiliency of sequestered oil in coastal marshes. Some of the samples we analyze show signs of delayed weathering. This has impacted my work with utilizing oil fingerprinting techniques to get a better idea of what kind of oil we are seeing in these samples.”
His work for Dr. Overton has not only helped understand the oil Dr. Overton’s lab is studying, but clarify some things for other researchers within the CWC. As scientists it can be difficult to explain to family members and friends what they do for a living. Often the people close to them have a vague understanding of they day to day life at work. Dr. Olson’s family believes he makes “environmental tea” and then runs it on the CSI (TV show) machine looking for pollutants. According to Dr. Olson this explanation “is not too far from the truth!”
Every job has its highlights and for Dr. Olson “field sampling is my favorite part of the job. I love being out on the water all day, cannot beat fresh air and sunshine!”. It is this part of the job for many field scientists. The part that gets them through the days when they have to process samples inside. Dr. Olson agrees saying “my least favorite part of the job is sample analysis, strictly speaking. It is fun when discovering something new or interesting but over time the process can get mundane. Integrating the same 75 odd compounds per sample for batches of 30, 50, or 100 samples can get tiresome.” All scientists agree that even though proces
sing samples can get tedious it is always exciting to realize that you have found something interesting.
Science is often a fine balance of planning and adapting to situations. This means that field science has a level of unpredictability that leads to some pretty interesting stories. For Dr. Olson recalls a time when “…I was out with another research assistant going to collect samples. It wasn’t until after we put the boat in the water that we realized we forgot to replace the drain plug! We scrambled to get it in place as our boat was taking on water. Luckily we were able to do so rather quickly and the boat was no worse for wear.”
It is always important for us to appreciate all of our hardworking scientists at the Coastal Waters Consortium! Dr. Gregory Olson is only one example of the great people that we have working on the questions of oil in the Gulf of Mexico.