Coastal carbon storage in degraded, natural, and restored mangrove ecosystems of Guyana

Abstract

Mangroves are among the most carbon-rich forests in the tropics due to their capacity to sequester and store carbon within their ecosystems. However, the combination of natural and human-induced phenomena causes changes in these ecosystems which can affect the flow of carbon within them. In the wet and dry seasons, we examined and compared the carbon content stored in aboveground biomass, standing litter, and soil in natural, degraded, and restored mangrove ecosystems located along the Guyana coastline. During a one-year period, a point-centred quartered method was used for tree sampling, while a randomised block design was used for standing litter and soil sampling. Our study revealed that the natural ecosystems exhibited higher carbon pool levels (29.58–35.14 Mg ha⁻¹), followed by the degraded ecosystems (30.49–32.27 Mg ha⁻¹), and then the restored ecosystems (22.81–27.63 Mg ha⁻¹). Significant differences were documented only in carbon found in aboveground biomass between ecosystem states, particularly within the natural ecosystems, due to the presence of mature trees with larger diameters at breast height. While seasonal fluctuations exist between the various carbon pools, particularly within the degraded ecosystems, our findings yielded insignificant differences between seasonality for all three carbon pools. However, linear mixed-effect models revealed that seasonality may influence the soil and standing litter carbon concentrations to an extent. Positive correlations in the restored ecosystems suggest that the larger carbon stocks in aboveground biomass may be associated with carbon stocks in soil and standing litter, unlike the negative correlations seen in the natural and degraded ecosystems. Our study provides some evidence that the overall carbon storage capacity of mangroves is influenced by the current state of their ecosystem, that is, ecosystems characterised by minimum disturbances may possess a greater capacity for carbon storage in comparison to ecosystems that are currently experiencing or have recovered from disturbances.