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Different CO2exchange pathways were monitored for a year in short- and tall-formSpartina alternifloragrasses in a southeastern USA salt marsh at North Inlet, South Carolina. The tall form of grass growing close to a creek under favorable conditions reached a higher standing biomass than the short form of grass growing in the interior marsh. However, the photosynthetic parameters of both forms of grass were equivalent. The tall canopy had greater net canopy production, 973 versus 571 g C m−2year−1, canopy growth, 700 versus 131 g C m−2year−1, and canopy respiration, 792 versus 225 g C m−2year−1, but lower sediment respiration, 251 versus 392 g C m−2year−1. In a single growing season, tall-canopy biomass increased to intercept all the available solar radiation, which limits gross photosynthesis. Total respiration increased during the growing season in proportion to live biomass to a level that limited net production. Theoretically, the difference between net canopy production and canopy growth is carbon allocated to belowground growth and respiration. However, the computation of belowground production by this method was unrealistically low. This is important because carbon sequestration is proportional to belowground production and accounts for most of the vertical elevation gain of the marsh surface. Based on the allometry of standing live biomass, alternative estimates of belowground production were 927 and 193 g C m−2year−1in creekbank and interior marshes, which would yield gains in surface elevation of 0.2 and 0.04 cm/year, respectively.
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Large global variations in the carbon dioxide removal potential of seaweed farming due to biophysical constraints
Abstract Estimates suggest that over 4 gigatons per year of carbon dioxide (Gt-CO2year−1) be removed from the atmosphere by 2050 to meet international climate goals. One strategy for carbon dioxide removal is seaweed farming; however its global potential remains highly uncertain. Here, we apply a dynamic seaweed growth model that includes growth-limiting mechanisms, such as nitrate supply, to estimate the global potential yield of four types of seaweed. We estimate that harvesting 1 Gt year−1of seaweed carbon would require farming over 1 million km2of the most productive exclusive economic zones, located in the equatorial Pacific; the cultivation area would need to be tripled to attain an additional 1 Gt year−1of harvested carbon, indicating dramatic reductions in carbon harvest efficiency beyond the most productive waters. Improving the accuracy of annual harvest yield estimates requires better understanding of biophysical constraints such as seaweed loss rates (e.g., infestation, disease, grazing, wave erosion).
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- Award ID(s):
- 2022927
- PAR ID:
- 10422679
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Communications Earth & Environment
- Volume:
- 4
- Issue:
- 1
- ISSN:
- 2662-4435
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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