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Mangrove forests significantly contribute to energy flow, nutrient and carbon cycling in the coastal ocean, being a sink for atmospheric CO2. Mangroves forests are highly productive and store high amount of carbon both in their soils and in their biomass. During leaf litter decomposition, nutrients and carbon can be recycled or exported to adjacent...
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Context 1
... the depletions at the end of the experiment ranged between 0.2 and 0.7 ‰. Conversely in the Avicennia stand during the rainy season, we observed δ 13 depletion during the entire experiment, with the final value being 2.7 ‰ more negative than the original value (Fig. 4.8). ...
Context 2
... terrestrial ecosystems, C isotopic fractionation occurs during OM decomposition due to physical, chemical, and biological processes and depends on several parameters, including litter quality, environmental conditions, and microbial biomass ( Connin et al., 2001;Feng, 2002). The mean δ 13 C values of the original yellow leaves were -28.2 ± 0.53 ‰ and -29.1 ± 0.52 ‰ for the Avicenia alba and Rhizophora apiculata leaves, respectively (Fig 4.8 a, b). These values were consistent with those measured in previous studies ( Bouillon et al., 2003;Marchand et al., 2005). ...
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The land for mangrove forest rehabilitation in Setapuk Besar Village, North Singkawang District is quite alarming due to abrasion and seawater intrusion. Leaf litter decomposition of Rhizophora spp. produce essential nutrients that function as a source of food and support the life of mangrove plants. The purpose of this study was to calculate the r...
Citations
... In 2000, Can Gio mangrove forest was recognized by UNESCO as the first Mangrove Biosphere Reserve in Vietnam. In this region, replanted mangrove forests are dominated by Rhizophora apiculata Blume, they cover 23,508 ha over a total mangrove area of 49,180 ha (Vinh, 2018). This region is affected by irregular semi-diurnal tides, and the tidal amplitude ranges from 2 m at mean tide to 4 m during spring tides (Tri et al., 2000). ...
... The highest fluxes were measured when the temperatures were maximum just at the beginning of the rainy season. This period corresponds to the lowest productivity of the ecosystem most probably because the lack of water during the dry season induced a stress on mangrove trees (Vinh, 2018). We suggest that the very high temperature and the first rains at the beginning of the rainy season increased ecosystem respiration. ...
... Yepez et al. (2007) showed that CO 2 release from respiration during the first summer rains can be more than 45% of the carbon fixed by plants during the growing season. Conversely the lower fluxes, either from the soil or from the trunk, were measured during the middle of the rainy season, which corresponds to the fruiting period and the highest litterfall (Vinh, 2018). Huxman et al. (2004) suggested that following a rainfall pulse, a period of net ecosystem accumulation of CO 2 should occur, because of increasing rates of ecosystem photosynthesis through plant acclimation and/or leaf growth, concomitantly to a decrease of ecosystem respiration. ...
Despite being organic-rich, mangrove soils are usually characterized by low rates of CO2 emissions due to waterlogged conditions, mangroves being thus considered as valuable blue carbon sinks. However, these emissions are highly variable, notably depending on climatic parameters. Can Gio mangrove is a tropical one, being the largest in Vietnam, having being replanted after the war in the late 70’s. The main objectives of this study were to quantify the seasonal variability of CO2 emissions at different interfaces (soil-air, water-air, and trunk-air) within a mature Rhizophora stand, and to assess the influence of these emissions on the vertical CO2 concentration profiles in the canopy. CO2 emissions from the soil in the dark were the highest of the different interfaces studied, and were among the highest measured for a mangrove soil, with a mean yearly value reaching more than 270 mmol CO2 m-2 d-1. We suggest that the very high temperatures characterizing Southern Vietnam all year round were responsible for these elevated CO2 emissions. In addition to temperature, the first rainfall pulse of the monsoon resulted in the highest CO2 fluxes both from the soil, reaching up to 500 mmol CO2 m-2 d-1, and from the trunks, reaching almost 230 mmol CO2 m-2 d-1. Because rainfall pulses are usually followed by a period of increasing rates of ecosystem photosynthesis, and a decrease of ecosystem respiration, we measured lower CO2 fluxes during the middle of the wet season. Additionally, it is possible that, during the rainy season, part of the CO2 produced within the soil was exported trough pore-water seepage, which was enhanced because of the higher level of the river. Concerning CO2 emissions at high tide within the Rhizophora stand, the seasonal trend followed the one of precipitation. During the rainy season, estuarine waters are enriched in organic matter and CO2 due to increased runoff in watersheds, and consequently CO2 fluxes from the water column were the highest. However, these emissions were much lower than those from the soil at low tide or from the trunks. Eventually, CO2 concentrations profiles in the canopy varied with the season, the tide, and the night-day alternation. Elevated CO2 concentrations at the root level may imply that prop roots can produce high amount of CO2 but also that they may trap gas emitted from the soil or the water column, possibly acting as physical barriers to air movement. Further studies using eddy-covariance technique should be developed to confirm the hypothesis suggested in this preliminary study.
Keywords
Mangrove forestCarbon dioxideBlue carbonMonsoonVietnam
