Digging up the truth about mangrove forests in the Gulf of California



Mangrove forests are packed with carbon, typically with more than 100 kilogram of carbon in just one square meter, more than in any other type of tropical forest (Donato et al., 2011). Even though the mangrove trees that we see do not compare in height and girth with those in upland tropical rainforests, they manage more than their share of carbon storage underground, in their vast root systems. The organic matter sequestered in the roots of these trees does not decompose quickly, and so thick layers of organic-rich peat are deposited over time, sometimes reaching several meters deep, spanning hundreds of years, and containing tons of carbon.

Thick layers of organic-rich peat are deposited over time in and around mangrove roots.
Thick layers of organic-rich peat are deposited over time in and around mangrove roots.

One goal in this project was to measure how much carbon is stored in the mangrove peat in the forests near the Bay of La Paz. In order to do this, we used a specialized sediment corer that let us reach down several meters and to take up sections of sediment. These cores show the history of organic matter deposition over time. Back in the lab, we are using elemental analysis to determine how much carbon is contained in the sediment layers that we discovered in the field. We are eager to know the amount of carbon stored in peat deep underneath the mangrove forests of the southern Gulf of California. Our work in this area took us to a remarkable diversity of forests, from tiny mangroves tucked beside a major port, to forests facing encroaching urban development, to large forests on nearly pristine uninhabited islands. The mangroves of this region are set apart by their very dry climate, severely limiting the amount of freshwater these plants receive each year. There are several questions which we seek to explore in these forests. Are larger forests are able to store more carbon per area? How do human impacts and proximity to coastal development influence carbon storage in mangroves? Are these desert mangroves able to produce and store large amounts of carbon despite the lack of freshwater? A second aspect of the mangrove forest that we are studying is the age and structure of the forest. To do this, we’ve taken samples at varying depths and used carbon 14 dating to determine their ages. Additionally, we’ve analyzed organic rich peat collected at different sites under a microscope to determine what species it originated from. These two techniques combined will allow us to better explain the life history of these mangrove forests.

Samples of mangrove peat are taken using a specialized sediment corer in order to measure how much carbon is stored.
Samples of mangrove peat are taken using a specialized sediment corer in order to measure how much carbon is stored.

Mangrove forests are highly valuable ecosystems, providing timber, supporting fisheries, and protecting coastlines from erosion. Our findings may add to the appreciation of the value of mangroves in this region, particularly if large amounts of carbon are found to be sequestered beneath these forests. As the problem of CO2 pollution grows in severity and global impact, it is of utmost importance that scientists discover, study, and protect the natural processes and places that keep carbon stored and out of the atmosphere.


Reference: Donato, D. C., et al. 2011. Nature Geoscience 4: 293-297.            








Authors Matthew Costa is a Graduate Student at Scripps Institution of Oceanography, UCSD.  He studies biological oceanography as he pursues graduate study in collaboration with the Gulf of California Marine Program.  His research interests include community ecology, biodiversity and functional diversity, and coastal ecosystem processes and services, particularly those of mangroves.  Prior to study at Scripps Institution of Oceanography, he performed undergraduate research on coral reproductive ecology and mangrove tree species zonation at the Bermuda Institute of Ocean Sciences while completing a Bachelor of Arts in Ecology and Evolutionary Biology degree at Princeton University.   Paula Ezcurra is a recent graduate from UCSB, where she obtained a B.S. in Aquatic Biology. While there, she aided in research on California kelp forest ecology through the Santa Barbara Channel LTER. Today, Paula continues to pursue her interest in coastal marine ecology and conservation as an intern in the Aburto Lab at SIO where she has focused her work in Mexican desert mangroves as part of her involvement in the Gulf of California Marine Program.

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