Mangrove sinkholes (cenotes) of the Yucatan Peninsula, a global hotspot of carbon sequestration

Abstract

Mangroves are among the most carbon-dense ecosystems on the planet. The capacity of mangroves to store and accumulate carbon has been assessed and reported at regional, national and global scales. However, small-scale sampling is still revealing 'hot spots' of carbon accumulation. This study reports one of these hotspots, with one of the largest-recorded carbon stocks in mangroves associated with sinkholes (cenotes) in the Yucatan Peninsula, Mexico. We assessed soil organic carbon (SOC) stocks, sequestration rates and carbon origin of deep peat soils (1 to 6 m). We found massive amounts of SOC up to 2792 Mg C ha^-1, the highest value reported in the literature so far. This SOC is primarily derived from highly preserved mangrove roots and has changed little since its deposition, which started over 3220 years ago (±30 BP). Most cenotes are owned by Mayan communities and are threatened by increased tourism and the resulting extraction and pollution of groundwater. These hot spots of carbon sequestration, albeit small in area, require adequate protection and could provide valuable financial opportunities through carbon-offsetting mechanisms and other payments for ecosystem services.

Keywords: Caribbean; Yucatan; carbon credits; karst; soil organic carbon; wetlands.

Figure 1.

(a,b) Sampling sites within the east coast of the Yucatan Peninsula, near Tulum, Mexico; (c) the sinkholes are surrounded by dense mangrove forests, (d) the peat underneath the mangroves can be 6 m deep (Casa Cenote, pictures MF Adame).

Figure 2.

Mangrove peat accumulation in cenotes (a) during the early to mid-Holocene (11.7–8.2 thousand years BP) when sea level was low but rising at rates beyond the capacity to increase elevation in situ, (b) during the mid to late-Holocene (8.2–4.2 thousand years BP) when rates of sea-level rise decelerated and mangrove initiated vertical accretion through root production at similar rates to sea-level rise and (c) at present day when deep mangrove peats have developed, and vertical growth corresponds to sea-level rise.