Cowichan Estuary Blue Carbon Project
CERCA initiated the Cowichan Estuary Blue Carbon Project in cooperation with the University of Victoria in 2017. The framework conditions were just right as it turned out. Tristan Douglas who grew up at the shore of the Cowichan Estuary was at the time searching for a suitable research project for his graduate studies at UVIC. Although his scientific interest actually focused on micro-biology he soon got excited about our proposed blue carbon project. After completion of his comprehensive fieldwork he now has entered the final phase of the project and has produced the following report for our website. On behalf of CERCA I would like to take this opportunity to express our sincere Thanks to Tristan for having undertaken such a challenging assignment and wish him all the best for the elaboration and his upcoming thesis defense.
Dr.Goetz Schuerholz, CERCA Chair
Cowichan Carbon Sequestration: CERCA Report, November 2019
Tristan Douglas
Carbon sequestration is the process whereby atmospheric carbon dioxide (CO2) is captured by plants and photosynthetic microorganisms for long-term storage in soils and sediments. This natural process slows the atmospheric and marine accumulation of greenhouse gases and is therefore of great interest as a means of mitigating global climate change. In recent years, coastal ecosystems have received much interest in their potential as highly efficient carbon sinks via blue carbon - the carbon that is sequestered in coastal ocean ecosystems. Since marine sediments are largely anoxic, the carbon that is sequestered there does not undergo degradation, is not converted back into CO2, and can remain buried for millennia.
One of the main concerns regarding blue carbon is therate of loss of important vegetated marine ecosystems is much higher than anyother ecosystem on the planet, even compared to rainforests. Current estimatessuggest a loss of 2-7% per year, which is not only lost carbon sequestration,but also lost habitat that is important for managing climate, coastalprotection, and ecological health. Currently, industrial activity in CowichanBay remains a threat to its ecological function and potential role in carbonsequestration. Dredging, tugboat activity, and the daily grounding of log boomsin the bay are suspected to degrade eelgrass beds and microbial biofilms, whichmay inhibit the carbon sequestration capability of the estuary and impact itsecology.
In 2017, CERCA, in partnership with the University of Victoria, initiated a project aimed at assessing the carbon sequestration potential of the Cowichan Estuary. This was partially modeled after a 2016 Comox Valley Project Watershed Society study in which they tested a standard carbon sequestration protocol and found that the K’ómoks Estuary has an estimated carbon storage capacity of 42.5 tons per year. While the K’ómoks Estuary is 70% covered in eelgrass, the Cowichan Estuary is largely comprised of open mudflats. With this in mind, the Cowichan study was primarily aimed at quantifying carbon sequestration in the mudflat, to see whether photosynthetic microbial growth on the surface of the mudflat could facilitate carbon sequestration comparable to that of eelgrass, as it had been reported to in several studies globally.
In the summer of 2017, a total of 18 sediment cores were taken from the Cowichan Estuary mudflat, salt marsh, eelgrass bed, as well as the intertidal areas that the log booms affect. Three sediment cores from the mudflat were chosen for carbon sequestration analysis, a process that first requires establishing a rate at which sediment is being deposited from the water column. It was not possible to determine a sedimentation rate for the three mudflat cores, because there was no measurable accumulation of sediment. The specific results from the sedimentation analysis suggest that the Cowichan Estuary mudflat could be an erosional environment, rather than a depositional one.
It is possible that the hydrodynamic conditions in the adjacent salt marsh and eelgrass in Cowichan Estuary facilitate more sediment deposition than the mudflats and can be used to establish a carbon sequestration rate for those habitats. Because sediment cores were taken from the salt marsh and eelgrass, the sedimentation and organic carbon in those cores can be compared to the mudflat cores. Currently, the focus of this study has shifted its focus to the contribution of seagrass and salt marshes to carbon storage in the sediment in the Cowichan Estuary. Sedimentation rate analysis for two sediment cores is in progress. Understanding where deposited organic material in an estuary comes from is also important, and sources of organic material in all the cores are being assessed and compared by habitat type using the CERCA Cowichan Estuary habitat map that was completed in 2017.
Furthermore, microbial diversity is an important metric for overall ecological health, carbon sequestration potential, nutrient cycling, and is valuable information for many future lines of inquiry regarding ecosystem function. Microbial diversity in the Cowichan Estuary using is now being evaluated with next-generation genetic sequencing. While analyzing this data, emphasis will be placed on comparing microbial diversity in salt marsh and eelgrass sediments with adjacent sediments with no vegetation cover.