Mangroves, wetlands, and seagrasses store vast amounts of "blue carbon." In fact, mangroves store more carbon per area than other tropical forests. Mangroves and wetlands do not only sequester carbon but also provide important protection from waves and storms to low-lying coastlines. Protection and investment in these coastal ecosystems has received a fair amount of attention this year during side events at COP21. Matthew Costa is a PhD student at the Scripps Institution of Oceanography who studies the natural history, biogeochemistry, and microbial ecology of organic sediments in Baja California Sur's mangrove forests for his PhD. He joins us today to explain the importance of mangroves for carbon sequestration and describes some of the realities of working in these ecosystems. Further biographical information is found at the end of the entry. For further exploration of mangrove carbon storage potential in the Gulf of California, check out dataMares from Dr. Octavio Aburto's research group at Scripps. A special thanks to Matthew for the article and to Dr. Aburto for use of images.
"Excruciatingly slow going through one quagmire after another, daily inundation with fluctuating pressures, and a thousand buzzing distractions that continually hinder progress—no, I’m not talking about an international policy summit, but rather an expedition into a mangrove forest. These coastal wetlands have long had the reputation of being putrid and impassible wastelands, and I guess that many would not be too excited about stepping into a smelly, mosquito-infested swamp. Yet, when I visit the mangroves of northwest Mexico to do my field research, I know that I am visiting places of special value. Mangrove forests are rich with biodiversity, support fisheries, protect coastlines, and filter run-off. What’s more, they hide buried treasure… organic carbon.
The key to wetlands’ rich stores of carbon lie in the fundamental chemistry of life. Plants use the energy of the sun to combine carbon dioxide, water, and nutrients to build organic matter. Carbohydrates, proteins, and all stuff of life is ultimately generated as a result of this “primary production.” This process of storing solar energy in the chemical bonds between carbon atoms, removed from the air as carbon dioxide and stored in the molecules of living things, takes on a special character in wetlands. Here, the building blocks are abundant: carbon dioxide is found in the air everywhere, water and sunlight abound, and nutrients, carried downstream by rivers or in by the tide, are quickly taken up by the plants. As a result, capture of carbon dioxide and production of organic matter proceed relatively unchecked, making wetlands among the most productive ecosystems in the world.
Still, production is only half of the story. The metabolism of plants, or of other organisms that eat them, releases that energy and converts the organic carbon back into carbon dioxide. This process, “respiration,” uses up oxygen quickly, but, in a wetland, the stagnant water prevents it from being replenished. As a result, wetland sediments are starved of oxygen, with sharp divisions between oxygen availability and absence. These oxygen boundaries actually help micro-organisms to recycle nutrients, which plants use to continue producing more organic matter. But, deeper down there is little oxygen or nutrients, just more and more accumulating organic matter. This material—dead leaves, shoots, and roots—is buried over the years by sediment and yet more organic matter, building carbon-rich deposits that can sometimes extend many meters down. This process of carbon burial in productive coastal ecosystems is one of the most important ways in which the Earth system removes carbon dioxide from the atmosphere over the long term. Don’t believe me that the power of wetlands to store carbon is important? What if I told you that the power of your car’s engine, the heat in your home, and even the electricity running this computer screen depend on it?
More than three hundred million years ago, the first woody plants evolved and spread across the land. Primary production vastly increased, and carbon removed from the atmosphere by this bonanza of growth was buried as organic matter accumulated in the first swamps. This period is known as the “Carboniferous,” because geological deposits from this time bear great amounts of carbon. In fact, so much carbon was sequestered by all of this excess photosynthesis that the composition of the atmosphere drastically changed, increasing oxygen and decreasing carbon dioxide in the air. Changes to global climate resulted, as temperatures dropped along with atmospheric carbon dioxide concentrations. Similarly, in nutrient-rich coastal seas, elevated primary production by phytoplankton (microscopic plant-like organisms) led huge quantities of organic matter to be buried on the sea floor. The sedimentary deposits formed by these ancient coastal ecosystems contain huge stores of energy and carbon, which since then have been transformed by time, pressure, and heat into the coal and petroleum of today.
Digging up and burning these fossil fuels has allowed us to harness a huge source of energy. You could say that our rapid growth and development as a species over the last couple hundred years has been powered by millions of years of sunlight, captured and buried by coastal ecosystems, and distilled into coal, oil, and other fossil fuels. We have learned how to reclaim the fire of an ancient star, but, as amazing as this alchemy is, it comes at a cost. Burning fossil fuels undoes the carbon sequestration accomplished by the ancient swamps and other productive ecosystems of the past. Increased carbon dioxide in the atmosphere increases its capacity for trapping the sun’s warmth, and we are already feeling the heat. Increasing temperatures, melting ice, rising sea levels, and decreasing ocean oxygen concentrations are just a few of the most direct effects. Climate change touches practically all of life on Earth, physiologically stressing organisms, shifting the geographic ranges of species, and in some cases destroying entire ecosystems (e.g., melting polar ice and flooded coastal environments). And, of course, it has serious implications for us. Millions of people live in low-lying cities vulnerable to sea level rise; record-breaking heat harms human health, water supply, and agriculture; and warmer oceans increase the frequency and intensity of deadly hurricanes and other weather events.
We need to act now to reduce carbon dioxide emissions, to slow down climate change, and to adapt to the changes that are already happening. This week in Paris the most important international climate summit in decades is taking place, with leaders and delegates from the world’s nations meeting to try to agree on how to tackle global climate change—a monumental task. Past efforts have been much like a slog through the swamp: slow and difficult, with numerous obstacles and distractions, and with only a murky view of the way ahead. It is my hope that, going forward, we will work together to pull us out of this morass before it’s too late, instead of sinking deeper into petty conflict and narrowly defined interests. With an elevated and global worldview, maybe we can attain the perspective to learn a different lesson from the wetlands. Mangrove swamps, seagrasses, marshes, and other coastal ecosystems are important sinks of atmospheric carbon dioxide. By sequestering carbon and storing it for long periods of time, they provide an irreplaceable service to humanity. Conserving these threatened ecosystems is one of the many steps we must take toward addressing our climate crisis. Already, half of the world’s mangroves have been destroyed by humans. We can’t afford to lose any more." - Matthew Costa
Matthew Costa studies mangrove forest ecosystems as a graduate student at Scripps Institution of Oceanography, at the University of California, San Diego. In 2011, he received his B.A. in Ecology and Evolutionary Biology from Princeton University, where he completed a bachelor’s thesis on mangrove species zonation in Bermuda, having conducted field research at the Bermuda Institute of Ocean Sciences. Matthew matriculated at U.C. San Diego in 2013 as a U.C. Regents Fellow in 2013 and in 2014 was awarded a National Science Foundation Graduate Research Fellowship. He is pursuing a Ph.D. in biological oceanography at Scripps Institution of Oceanography, the home of the Gulf of California Marine Program. His research with the G.C.M.P. focuses on the mangrove forests of Baja California Sur. Despite the physiological challenges faced by the mangrove trees in this arid environment at the northern limit of their range, these forests store large amounts of carbon in organic-rich sediments. Matthew leads the G.C.M.P.’s efforts to quantify these carbon stores and to understand the processes limiting their decomposition. Matthew and colleagues survey these forests by collecting sediment cores in the forests of the region and sampling them for chemical and metagenomics analysis. By measuring concentrations and isotopic ratios of carbon and key nutrients, microbial diversity and activity, and trace element records in these cores, they aim not only to map out the carbon stores of these forests, but to elucidate the processes that keep carbon locked away as organic matter in these sediments, rather than returning to the atmosphere as CO2. We will use this information to motivate strong protection of these forests based on the valuation of this ecosystem service, and to guide management with a scientific understanding of their carbon storage capacity. Google Scholar Profile.
Mangrove Carbon Sequestration in the Gulf of California (G.C.M.P)
Mangrove Ecosystem Services of Mangroves of the Galapagos: Fisheries and Carbon Storage (Charles Darwin Foundation and the G.C.M.P.)
Soil Nutrient Dynamics (Smithsonian Tropical Research Institute)