Image source: https://aggietranscript.ucdavis.edu/the-relationship-between-genetic-diversity-and-disturbance-in-the-eelgrass-species-zostera-marina/
Blue carbon (Blue C) is the carbon stored in coastal ecosystems, such as mangroves, salt marshes and seagrass meadows. Correctly measuring the amount of carbon stored in these habitats is vital to avoid costly distortions in carbon markets and to efficiently manage conservation efforts. Recent research, however, points out significant problems in how carbon storage is often estimated.
A paper recently published by Dr. Alix Green, et al. in PLoS One describes the first published estimates of seagrass carbon storage in the UK. Based on thirteen seagrass meadows in the southwestern UK, the authors show that meadows of the species Zostera marina sequester much more carbon than previously thought. These findings suggest that the UK is currently missing out on lucrative carbon offsets and can be used to bolster the case for the ecological conservation of some of the study sites.
Previous estimates of Blue C in the UK depended upon data collected from sites across the globe, wherein 42% of all data points came from Australia and the Mediterranean and none from the UK.
The amount of carbon that Dr. Green’s group found stored in UK seagrass meadows represents both an economic boon and a conservation opportunity. At current prices of £24 per ton of carbon, the group estimates the UK’s Blue C stock at between £2.6 million and £5.3 million.
The monetary value of the sequestered carbon can benefit conservation efforts, for which arguments based upon species conservation often fail to sway opponents. As the authors note, conservationists and yachting enthusiasts in Studland Bay, one of the study sites, have quarrelled over the bay’s use for so long that “any efforts to approach a mutual solution are [now] met with animosity.”
Although Dr. Green’s findings point out the need for the UK to measure their own Blue C storage potential, independent of model estimates, their results also point to a more fundamental flaw in how Blue C storage is currently measured. The flux of carbon through a habitat, more than the amount found therein at a given point in time, provides a much more accurate and dynamic measure of an area’s true carbon storage potential. The problem is that current models rely too heavily on standing stock measurements.
“Hopefully,” writes Dr. Green, “future studies can investigate the flux of [carbon] and further add to the data pool, both locally and globally.”
Dr. Green’s findings resonate with those of Dr. Sofia Johannessen, of the Institute of Ocean Sciences in British Columbia, who has also published research demonstrating the shortcomings of an over-reliance on standing stock measurements.
“Standing stock is the wrong way to measure carbon storage potential. It’s the continuing burial flux, not the inventory, that matters for the drawdown of carbon dioxide. Sedimentation rates [the rate at which carbon is buried in seafloor sediment] can vary by orders of magnitude from one location to another. If carbon credits are awarded based on overblown estimates of carbon sequestration in seagrass meadows, and those credits are used to offset increased emissions somewhere else, the net effect could be an increase in carbon emissions to the atmosphere.”
How to best measure Blue C is a topic of fierce debate in the field. The financial incentives to getting it right should help to spur greater focus on the task.