Carbon stockpiles abound in mangrove sinkholes

A deep divebeneathmangrove sinkholes has found the highestsinglecarbonstocksever reported, further highlighting the importance of mangroves as carbonsequesters.

Dr Fernanda Adame from Griffith University’s Australian Rivers Instituteled the research, published in Biology Letters, in which she and the team sampled mangrove peat soil from three sinkhole sites acrossYucatanPeninsulain the south of Mexico.

The sinkholes, or cenotes, aredeep pockets of mangrove that can be found inland, in freshwater or along the coastlineand the sites studied by Dr Adame and the teamwere found in water 5-10m deep with carbon layers thatranged from 1-6m.

Dr Adame assessed the soil organic carbon (SOC) stocks, sequestration rate and carbon originof the three sites, and found SOCstocks of up to 2792 Mg Cha-1, the highest value reported in literature so far.

“To put it into perspective, a tropical forest has about 400 tons of carbon per hectares;the mangroves in these cenoteshad 2700tons,” Dr Adame said.

“The extraordinary amount of carbon in these mangroves is due to their high productivity, but also to the unique sea-level history of the region. Mangroves accumulate carbon when sea level rises slowly.

“We found mangrove roots that were highly preserved since their deposition, which we found to be around 3000 years ago.”

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 samplingsuch as this studyis still revealing ‘hot spots’ of carbon accumulation.

Dr Fernanda Adame.

Dr Adame said thecarbon stored in the cenotesoilsshould be apriority for conservation, as disturbing it wouldcause massive emissions.

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,” she said.

“Yucatan is threatened by poorly planned tourist developments, which have resulted in mangrove deforestation, groundwater over-extraction, and pollution of the aquifer due to poor sewage management.

“Our hope is that his data will provide information to create carbon projects that will benefit the Mayan communities of the region whoown thesecenotes.

The research ‘Mangrove sinkholes (cenotes) of the Yucatan Peninsula, a global hotspot of carbon sequestration has been published’ inBiology Letters.