Kody Barone of the University of Texas Marine Science Institute is trying to determine how much carbon has been lost as a result of a mangrove die-off along the Texas coast. Above: Dead mangroves and new mangrove saplings are seen with a patch of 6-foot-tall live mangroves (background) on Mustang Island on Feb 20. Photo by Kody Barone
Wetland ecosystems, in particular mangroves, serve an important role in slowing down climate change. They do this by capturing greenhouse gasses from the atmosphere via photosynthesis and storing these gasses underground in the form of organic carbon (coined “blue carbon”).
Since their introduction to the Texas coast over a century ago, dwarf black mangroves have been performing this carbon sequestration processes, providing Texas a natural pathway to mitigating the pollution released by burning fossil fuels.
Worldwide, these ecosystems have been declining due to natural and anthropogenic disturbances such as hurricanes and in some regions even logging. One such local example occurred in February of 2021 when winter storm Uri hit Texas, resulting in the death of more than 2,000 hectares of the mangroves along our coast. This drastic die-off event brings up the possibility for not only the release of the carbon they have been storing over the last 100 years, but a decline in the amount of carbon our local wetlands are able to deposit.
Freeze-dried soil samples are ready to be sieved and homogenized with a mortar and pestle for use in various lab analyses. Photo by Kody Barone
Exactly how much carbon is being lost from these ecosystems? How fast is the carbon leaving? Is the carbon remaining in the soil heavily degraded? My work at UTMSI is trying to find those answers. However, before I could begin to answer these questions, I first had to find a location in Port Aransas that harbored mature mangroves that survived winter storm Uri. This proved to be difficult, but in June of 2023, after weeks of searching, I found several patches of 6-feet-tall, bright green, healthy mangroves in the Port Aransas Nature Preserve at Charlie’s Pasture, close in proximity to the Mustang Beach Airport. I have since found several other patches of “old growth” mangroves near the lighthouse on Harbor Island and on the backside of Mud Island.
After the mangroves were located, I collected multiple soil samples with the help of research scientist Kaijun Lu and undergraduates Nathalie Scott, Kadee Loyd and Sofia McKelvey. Playing with mud over the course of four days brought us a total of 355 samples that would be used for various lab analyses which tell me the amount of carbon and nitrogen, quality of carbon, what types of plants produced the carbon and nitrogen and sizes of the grains of sediment in the soil.
Nathalie Scott, an undergraduate at UTMSI, holds up a sediment core after extracting it from under a mangrove tree on Mud Island. Photo by Kody Barone
From recent lab experiments I estimate a total of 569 tons of carbon have been lost if 2,000 hectares of mangroves died from the freeze. This is the equivalent of carbon dioxide burned from 250,000 gallons of gasoline or the average energy needed to supply 272 homes for one year! It is also important to keep in mind that this loss of carbon will continue to grow as the carbon sequestered by these mangroves has ceased until they are able to reestablish a mature and healthy population.
Where did this carbon go exactly? Multiple pathways of carbon loss may be possible including the release of carbon back to the atmosphere in the form of carbon dioxide or methane due to microbes and the erosional processes of carbon attached to sediment grains being washed away as dead mangrove roots lose their ability to hold onto sediment.
Kody Barone is a University of Texas Marine Science Master’s student whose specialty is soil organic carbon biogeochemistry.
While this loss of carbon is devastating news, the mangrove population has been steadily recovering. However, so is the rate of winter storms Texas is experiencing. Although carbon storage in our local wetlands can recover from Uri, if mangroves cannot keep up with an increase in intense freeze events we may begin to see a decline in these natural combaters of climate change.
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