Abstract
Mangroves can capture and store organic carbon and their protection and therefore their restoration is a component of climate change mitigation. However, there are few empirical measurements of long-term carbon storage in mangroves or of how storage varies across environmental gradients. The context dependency of this process combined with geographically limited field sampling has made it difficult to generalize regional and global rates of mangrove carbon sequestration. This has in turn hampered the inclusion of sequestration by mangroves in carbon cycle models and in carbon offset markets. The purpose of this study was to estimate the relative carbon capture and storage potential in natural and restored mangrove forests. We measured depth profiles of soil organic carbon content in 72 cores collected from six sites (three natural, two restored, and one afforested) surrounding Muisne, Ecuador. Samples up to 1 m deep were analyzed for organic matter content using loss-on-ignition and values were converted to organic carbon content using an accepted ratio of 1.72 (g/g). Results suggest that average soil carbon storage is 0.055 ± 0.002 g cm−3 (11.3 ± 0.8% carbon content by dry mass, mean ± 1 SE) up to 1 m deep in natural sites, and 0.058 ± 0.002 g cm−3 (8.0 ± 0.3%) in restored sites. These estimates are concordant with published global averages. Evidence of equivalent carbon stocks in restored and afforested mangrove patches emphasizes the carbon sink potential for reestablished mangrove systems. We found no relationship between sediment carbon storage and aboveground biomass, forest structure, or within-patch location. Our results demonstrate the long-term carbon storage potential of natural mangroves, high effectiveness of mangrove restoration and afforestation, a lack of predictability in carbon storage strictly based on aboveground parameters, and the need to establish standardized protocol for quantifying mangrove sediment carbon stocks.
Highlights
The concentration of atmospheric CO2 has increased by forty-percent since the beginning of the industrial revolution and continues to increase concentrations by 2 ppm annually (Dedysh, Derakshani & Liesack, 2001; Le Quere et al, 2012)
Similar Aboveground biomass (AGB) and tree density in afforested and natural sites suggests that 20 years is sufficient for a mangrove forest in this region to reach maturity; lower AGB and higher tree density at the restored sites suggests that the mangrove forest is still maturing 10 years after restoration
Carbon standing stocks Carbon concentration (g C cm−3) did not vary significantly between natural or restored mangroves, suggesting that carbon standing stock in ten year old restored mangroves with significantly less aboveground growth is approximately equivalent to stock in natural mangroves that are likely at least 40–50 years old (Alongi, 2002)
Summary
The concentration of atmospheric CO2 has increased by forty-percent since the beginning of the industrial revolution and continues to increase concentrations by 2 ppm annually (Dedysh, Derakshani & Liesack, 2001; Le Quere et al, 2012). Identifying effective, efficient, and politically acceptable approaches to reduce the atmospheric concentration of CO2 is one of society’s most pressing goals. Reducing atmospheric CO2 via carbon sequestration—transferring carbon to a safe biological or geological reservoir—is one such solution. Terrestrial vegetation plays a key role in the global carbon cycle as both a sink and a source of anthropogenic CO2: total forest carbon uptake is 2.3 ± 0.4 Pg C yr−1 (Pan et al, 2011), whereas the loss of vegetation via land use change adds 1.1 ± 0.7 Pg C yr−1. While terrestrial forests as a whole are a net sink, tropical land use change emits 1.3 ± 0.7 Pg C yr−1 (Pan et al, 2011). Conservation of existing vegetation is critical for preventing further carbon emissions as well as for preserving carbon sequestration potential
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