Under what conditions could eelgrass measurably drawdown carbon? Relating carbon drawdown to pCO2, irradiance, and leaf area index of Zostera marina
Seagrass meadows, common to coastal habitats, have been identified as potential short-term refugia for calcifying organisms from ocean acidification (OA). In nearshore, soft-sediment habitats of the Salish Sea, eelgrass (Zostera marina L.) is the dominant seagrass species, and several studies have f...
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| Format: | Text |
| Language: | English |
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Western CEDAR
2019
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| Online Access: | https://cedar.wwu.edu/wwuet/904 https://cedar.wwu.edu/cgi/viewcontent.cgi?article=1933&context=wwuet |
| Summary: | Seagrass meadows, common to coastal habitats, have been identified as potential short-term refugia for calcifying organisms from ocean acidification (OA). In nearshore, soft-sediment habitats of the Salish Sea, eelgrass (Zostera marina L.) is the dominant seagrass species, and several studies have found that eelgrass is effective at taking up inorganic carbon and may be carbon-limited, potentially increasing uptake potential in the future. However, irradiance levels vary throughout a day and can therefore influence rates of carbon uptake and release through the relative rates of photosynthesis and respiration. Eelgrass meadows vary in terms of meadow size, shoot density and morphology, and water residence time which could affect rates of carbon uptake of eelgrass meadows and their influence on localized water chemistry. We conducted a series of mesocosm experiments manipulating pCO2, irradiance, and leaf area index (LAI) to assess how these factors interact and contribute to OA variability in the nearshore environment. Our findings demonstrate that increased pCO2 may release the eelgrass from carbon limitation and increase carbon uptake rates. The effect of increased pCO2 on eelgrass carbon uptake was only evident at high irradiance, and high LAI. While greater shoot density increased overall carbon uptake, this effect may diminish as self-shading and/or carbon limitation brought on by photosynthetic carbon uptake emerge at high density. Therefore, eelgrass meadows could potentially measurably drawdown carbon but only when eelgrass with sufficiently high LAI is exposed to saturating irradiance conditions with relatively long water residence times and/or with shallow water depth. We identified rates of carbon uptake and rates of pH increase as a function of LAI. This information will help natural resource managers understand variability of OA due to the photosynthetic activity of eelgrass in meadows throughout the Salish Sea. |
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