Sequestration secrets of Northland’s coastline
Updated: Oct 10, 2021
Here in Northland we tend to take for granted the sizeable acreage of subtropical marine habitat such as mangroves, salt marshes and seagrass. But Dr Joe Russell, an Analytical Chemist from the UK, cast a fresh set of eyes on these Northland habitats pointing out just how valuable they are in helping us to sequester around 11% of the estimated 1,100,000-1,300,000 tonnes of carbon that Northlanders emit each year. In his research, Joe extrapolated that the ocean naturally sequesters around 24.92 tonnes per km2 or 25gms per m2. But what if we moved closer to shore and looked at what those coastal habitats may sequester.
The Blue Carbon Initiative gives a good summary of the importance of coastal habitats in carbon sequestration and their Scientific Working Group has developed the “Coastal Blue Carbon: methods for assessing carbon stocks and emissions factors in mangroves, tidal salt marshes, and seagrass meadows”. The National University of Singapore also published a study on how much carbon these types of coastal habitats sequester.
Using the data from these sources, Joe determined that the sequestration rates for the three types of Northland coastal habitats mentioned earlier, are significantly higher:
Saltmarshes 887g CO2 per m2 per year
Mangroves 615g CO2 per m2 per year
Seagrasses 304g CO2 per m2 per year
He then endeavoured to calculate the length of Northland’s coastline and determine the acreages of those particular habitats. NRC survey data for the east & north west coasts could be used but the majority of the west coast was estimated. The results are:
It is important to note that the 121,500 tonnes of CO2 estimated in the table above is not 'set in stone', It is Northlanders responsibility, as kaitiaki of these habitats, to ensure that there is no further degradation of these coastal habitats and that we actually nurture and restore these.
So, before you endorse that next ‘exciting coastal property development’ or proposed marina, or lobby for a relaxation in recreational fishing limits, think about the potential impact on our struggling efforts to sequester the ever increasing amount of carbon that we are producing.
Furthermore, unless you personally cultivated any of those habitats don’t expect to claim your share of that 121,500 tonnes as a means of wriggling out of (offsetting) your personal carbon emissions which we are all going need to work harder (every year we defer action makes it even harder) to reduce. That is something that we will be hearing more about following the release of the Climate Commission's draft report.
Download Dr Joe Russell's presentation (PDF)