Abstract
The significance of aquatic lateral carbon (C) export in mangrove ecosystems highlights the extensive contribution of aquatic pathways to the net ecosystem carbon budget. However, few studies have investigated lateral fluxes of dissolved organic carbon (DOC) and inorganic carbon (DIC), partly due to methodological difficulty. Therefore, we evaluated area-based lateral C fluxes in a small mangrove estuary that only had one exit for water exchange to the coast. We sampled water from the mouth of the creek and integrated discharge and consecutive concentration of mangrove-derived C (ΔC). Then, we estimated the area-normalized C fluxes based on the inundated mangrove area. DIC and DOC concentrations at the river mouth increased during ebb tide during both summer and winter. We quantified the ΔC in the estuary using a two-component conservative mixing model of freshwater and seawater. DIC and DOC proportions of ΔC concentrations at the river mouth during ebb tide was between 34% and 56% in the winter and 26% and 42% in the summer, respectively. DIC and DOC fluxes from the estuary were estimated to be 1.36 g C m−2 d−1 and 0.20 g C m−2 d−1 in the winter and 3.35 g C m−2 d−1 and 0.86 g C m−2 d−1 in the summer, respectively. Based on our method, daily fluxes are mangrove area-based DIC and DOC lateral exports that can be directly incorporated into the mangrove carbon budget.
Highlights
Mangrove forests store a vast amount of “blue carbon”, which contributes to 10–15% of carbon burial in global coastal sediments, they occupy only 0.5% of the world’s coastal zone [1]and have been recognized as the most carbon-rich ecosystem in the world [2]
The range of the electric conductivity (EC) in the winter (Figure 2c, 1.69–5.0 S m−1 ) was more broad than in the summer (Figure 2d, 4.1–5.2 S m−1 ) because the tidal level remained high and seawater predominated at the river mouth all day in the summer, both days were close to the half-moon phase of the lunar cycle
The trend of dissolved inorganic carbon (DIC) (Figure 2e,f) and dissolved organic carbon (DOC) (Figure 2g,h) concentrations was opposite to the EC; the values were highest at ebb tide and decreased with increasing tidal levels with the lowest value at high tide
Summary
Mangrove forests store a vast amount of “blue carbon”, which contributes to 10–15% of carbon burial in global coastal sediments, they occupy only 0.5% of the world’s coastal zone [1]and have been recognized as the most carbon-rich ecosystem in the world [2]. Poungparn et al [6] suggested that high net primary productivity (NPP, 9.35 to 12.9 Mg C ha−1 year−1 ) and low Rh (from 1.72 to 2.63 Mg C ha−1 year−1 ) increased the NEP (up to 11.3 Mg C ha−1 year−1 ) of a secondary mangrove forest in eastern Thailand. These NEP values of mangrove forests are more than twofold greater than those of upland forests in East Asia [7]
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