UC San Diego

The global climate crisis has drawn attention to the carbon sequestration and storage ecosystem services performed by mangrove forests. In this dissertation, I investigate belowground carbon stocks in mangrove ecosystems and describe patterns of carbon distribution with depth belowground, across variable coastal landscapes, and from the equator to the northern limit of mangroves on the west coast of North America. The results of my research support the thesis that mangrove forest belowground carbon stocks possess significant spatial variation driven mainly by variation in the sediment column depth and that this variation are predicted by different paleoecological, geomorphological, or climatic factors on the local, landscape, and regional scales. Chapter 1 discusses mangrove distributions, adaptations, ecology, and ecosystem services; describes the state of scientific knowledge on mangrove blue carbon; and introduces three investigations into mangrove carbon stocks which I performed as my doctoral research. Chapter 2 describes a coring study of the sediments of four mangrove sites in Baja California Sur, Mexico. I demonstrate the accumulation of peat only below the zone of root growth and find carbon density does not decline with depth and age even in 5,000-year-old peat deposits, though there is a loss of nitrogen and a shift in microbial diversity and δ15N indicating microbial nitrogen turnover. In chapter 3, I document over an order of magnitude of variation in carbon stocks along the coasts of the Galapagos. I test the roles of coastal geology and wave exposure in driving this variation and find that carbon stock variance is greater among lava sites than sites with soil. In chapter 4, I gather data from cores collected at 80 sites from the Galapagos, the Pacific and Caribbean coasts of Panama, and the Baja Peninsula to compare mangrove sediment carbon density and depth regionally. Carbon density is relatively invariable and does not increase with annual rainfall, while highly variable sediment depth increases with relative sea-level rise rate, and the relationship between sediment depth and coastal slope becomes less positive with increasing relative sea-level rise. Chapter 5 discusses the implications of these results for the study and management of mangrove ecosystems.