Exploring present and future carbon dynamics in connected mangrove forests and seagrass beds: How important is it?
Biochemistry
Soil Sciences
Final Report Abstract
Carbon sequestration is one of the most important ecosystem services provided by mangrove forests and seagrass beds that support climate change mitigation. Mangrove forests and seagrass beds are important ecosystems that sequester significantly greater amounts of carbon in their sediments. Ecosystems that exchange energy, organisms and materials are considered connected. This project focuses on connectivity as the specific exchange of particulate organic matter (POM). Although mangrove forests and seagrass beds usually occur adjacent to each other they are frequently evaluated independently without taking into account how connectivity between these coastal vegetated ecosystems can influence ecosystem services such as carbon accumulation. Therefore, a comparison of connected and isolated ecosystems will help to understand the effect of connectivity on carbon accumulation. Five global sites in Singapore, Adelaide, Zanzibar, Florida and Bonaire, were chosen to evaluate the influence of connectivity. The general hypothesis was that mangrove forests and seagrass beds that are connected with each other would have greater quantities of carbon in the sediment, compared to those that are isolated from each other. Sampling for sediment carbon content analysis was conducted across all sites, furthermore, other aspects such as connectivity with other ecosystems (i.e. salt marsh, macroalgal beds), community characteristics, nutrient concentrations and geomorphic settings were tested and compared separately in each place. Results of this dissertation showed in Singapore and Zanzibar that no significant differences between mangrove forests connected with seagrass beds and isolated mangrove forests. Sediment carbon accumulation only increased in connected mangrove forests in Australia. Contrary to the general hypothesis, isolated seagrass beds had up to double the sediment carbon content compared with connected beds. Results in Singapore and Australia showed that mangrove forests are crucial donors of organic carbon (OC) (10-70%) to adjacent ecosystems such as seagrass beds and mud flats. In Zanzibar, community species composition associated with prop roots in mangrove forests and large-leaved seagrass plants were correlated with higher sediment carbon content. Whilst in Florida higher sediment OC levels were found in areas with higher shoot density and coverage. The area of tidal channels as well as the area covered by mangrove forest were positively correlated with sediment OC content in mangrove forests in Zanzibar. Anthropogenic induced changes such as changing freshwater fluxes and reduction of mangrove forest area in Singapore as well as reduction of area of healthy mangrove trees in Bonaire affected carbon accumulation not only in the forests but also in adjacent seagrass beds. Factors such as mangrove forest cover area, community composition and state of mangrove communities influenced both the sediment carbon accumulation in forests and exported POM which could affect the amount of carbon accumulated in the adjacent ecosystems. Including inorganic carbon content in blue carbon studies concerning seagrass beds is critical, since this was an important component of their sediment carbon content. Geomorphic settings such as presence of low energy rivers can also enhance sediment carbon accumulation in connected ecosystems. Besides connectivity other factors at the seascape level such us geomorphic settings or anthropogenic induced changes in the seascape settings could influence the connectivity and the sediment carbon content. Results of this dissertation in connectivity between different coastal vegetated ecosystems as well as terrestrial ecosystems highlight the importance of the conservation of all interconnected ecosystems for carbon accumulation ecosystem services.
Publications
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2020. Impacts of wetland dieback on carbon dynamics: A comparison between intact and degraded mangroves. Science of the Total Environment
Senger F, Saavedra Hortua DA, Moosdorf N, Engel S, Gillis LG
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2020. Sources of Particulate Organic Matter across Mangrove Forests and Adjacent Ecosystems in Different Geomorphic Settings. Wetlands
Saavedra Hortua DA, Friess DA, Zimmer M, Gillis LG
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2020. Stronger together: Do coral reefs enhance seagrass beds “blue carbon” potential? Frontiers in Marine Science
Guerra-Vargas L, Gillis LG, Mancera-Pineda JE
