Factors regulating carbon sinks in mangrove ecosystems

Abstract

Mangroves are recognized as one of the richest carbon storage systems. However, the factors regulating carbon sinks in mangrove ecosystems are still unclear, particularly in the subtropical mangroves. The biomass, production, litterfall, detrital export and decomposition of the dominant mangrove vegetation in subtropical (Kandelia obovata) and tropical (Avicennia marina) Taiwan were quantified from October 2011 to July 2014 to construct the carbon budgets. Despite the different tree species, a principal component analysis revealed the site or environmental conditions had a greater influence than the tree species on the carbon processes. For both species, the net production (NP) rates ranged from 10.86 to 27.64 Mg C ha year and were higher than the global average rate due to the high tree density. While most of the litterfall remained on the ground, a high percentage (72%-91%) of the ground litter decomposed within 1 year and fluxed out of the mangroves. However, human activities might cause a carbon flux into the mangroves and a lower NP rate. The rates of the organic carbon export and soil heterotrophic respiration were greater than the global mean values and those at other locations. Only a small percentage (3%-12%) of the NP was stored in the sediment. The carbon burial rates were much lower than the global average rate due to their faster decomposition, indicating that decomposition played a critical role in determining the burial rate in the sediment. The summation of the organic and inorganic carbon fluxes and soil heterotrophic respiration well exceeded the amount of litter decomposition, indicating an additional source of organic carbon that was unaccounted for by decomposition in the sediment. Sediment-stable isotope analyses further suggest that the trapping of organic matter from upstream rivers or adjacent waters contributed more to the mangrove carbon sinks than the actual production of the mangrove trees.

Improved estimates on global carbon stock and carbon pools in tidal wetlands

“…Sediments account for the largest proportion (60.4%) of ecosystem carbon stock. Mangrove sediments are not carbon saturated and can accrete considerable mineral and organic carbon input from marine and/or riverine sources over millennia 38,39 , and the anoxic saline conditions reduces organic matter and root decomposition, which also contribute to sediment carbon storage and surface elevation increase 24,40 through biogenic accretion 41 . We only extrapolate data on sediment carbon stock in the top metre of sediment but mangrove soils can be much deeper (>3 m in many estuarine settings) 42 .…”

Methane Emissions from Subtropical and Tropical Mangrove Ecosystems in Taiwan

“…The sample with the tin plate was placed in an oven at 60 • C until a constant dry weight was attained (W 2 ). The water content and bulk density were calculated by Equations (2) and (3), respectively [17].…”

“…Then, the subsample was placed in an oven at 450 • C for 4 h and weighed as W 3 as the ash-dried weight. The organic matter content was obtained by Equation (4) [17].…”

“…However, other factors regulating greenhouse gas emissions from mangroves have seldom been discussed. Previous studies established the carbon budgets in mangrove ecosystems [16,17]. Nonetheless, neglecting the emissions of greenhouse gas in the carbon budgets could possibly overestimate the carbon storage capacity.…”

Spatiotemporal Evolution and Features of Net Carbon Sink of Farmland Vegetation in Chongqing, China

“…Foreign scholars have paid more attention to carbon pools of forest [10][11][12] than carbon sources/sinks in agricultural or farmland system. But the latter is arousing a growing interest in the academic circle.…”