Seasonal growth dynamics and blue carbon storage of the intertidal seagrass Zostera noltei

The primary objective of this study was to assess the carbon assimilation potential of a bed of the intertidal seagrass, Zostera noltei, at Spurn Point on the East Yorkshire coastline at the mouth of the Humber Estuary. This population of seagrass, prior to this report, had not been subject to scientific investigation since 1936. Environmental factors that influenced the bed during the study period were thoroughly considered. Two field-based techniques were used to estimate the annual carbon assimilation. Short-term (< 1 h) gas-exchange enclosure experiments were conducted at sites with varying percentages of Zostera noltei cover. The findings yielded a peak photosynthetic carbon assimilation value of 58.8 mg C m-2 h-1. By combining the photosynthetic rate measurements with logger data recording incident irradiance measurements for the seagrass bed throughout the study period, hourly values were extrapolated to monthly and growing season estimates and converted to carbon drawdown. Additional MINI-PAM photosynthesis-irradiance analysis gave estimates of the
irradiances at which half the photosynthetic capacity was achieved. Dark respiration rates measured in the field were low and variable. For modelling net primary production, a respiratory loss of 10% of the maximum photosynthetic rate was set. An estimate was made of 57.5 gC m-2 over this period. The area of the Zostera noltei bed as of 2022, was estimated at 10,467.4 m2. Therefore, the bed size multiplied by our productivity factor per square meter estimated an overall productivity during the growth season for the bed to be 602 kg carbon fixed.

Aidan Jackson