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Exploring CO2(aq) limitation in temperate seagrass species: interspecific variability and biomass dependency
Citation:
Kaldy, J., E. Springer, C. Brown, AND T Chris Mochon Collura. Exploring CO2(aq) limitation in temperate seagrass species: interspecific variability and biomass dependency. International Seagrass Biology Workshop and World Seagrass Conference, Napoli, ITALY, June 17 - 21, 2024.
Impact/Purpose:
Marine plants such as seagrasses are major contributors to marine carbon sequestration through blue carbon stocks and have been proposed as a mitigation strategy for coastal acidification. Understanding the physiological constraints on seagrass carbon fixation and the impact that photosynthesis has on water column carbonate chemistry is imperative to predicting the remediation capacity for these plants. Further, this research informs ongoing modeling activities to better evaluate blue carbon potential as seagrass distribution changes in response to climate drivers such as warming temperatures. Previous SSWR research has shown that under nutrient enrichment associated with eutrophication seagrasses can be carbon limited resulting in plant death.
Description:
Seagrasses are often touted for their ability to remove CO2 from the water and sequester it in the sediments as “Blue Carbon”. Further, seagrasses have been hypothesized to be refugia for calcifying organisms that are sensitive to coastal acidification. However, seagrasses are also known to be carbon limited and that photosynthesis exacerbates diurnal variability in carbonate chemistry. We conducted a series of experiments to evaluate how whole plants of Zostera marina, Z. japonica, Phyllospadix torreyi and P. serrulatus change the carbonate chemistry of seawater during light saturated photosynthesis in closed 6 liter chambers. We evaluated how plant biomass (low, medium, high) influenced the carbonate chemistry over the course of 48 hours. Water column pH was measured hourly using iSAMI instruments plumbed directly into each chamber while total alkalinity (measured with Apollo auto titrator) was sampled at the beginning and end of each incubation. The rate of CO2 uptake was related to species biomass and all species were able to increase pH from about 7.9 to 9.5. There was a reduction in total alkalinity, especially in the high biomass treatments, likely because of a H+ pump associated with carbon uptake at the cellular level.