Seagrass Organic Carbon Stocks Show Minimal Variation Over Short Time Scales in a Heterogeneous Subtropical Seascape
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Blue carbon initiatives require accurate monitoring of carbon stocks. We examined sources of variability in seagrass organic carbon (Corg) stocks, contrasting spatial with short temporal scales. Seagrass morphology and sediment Corg stocks were measured from biomass and shallow sediment cores collected in Moreton Bay, Australia. Samples were collected between 2012 and 2013, from a total of 77 sites that spanned a gradient of water turbidity. Environmental measures of water quality between 2000 and 2013 revealed strong seasonal fluctuations from summer to winter, yet seagrass biomass exhibited no temporal variation. There was no temporal variability in Corg stocks, other than below ground biomass stocks were slightly higher in June 2013. Seagrass locations were grouped into riverine, coastal, and seagrass loss locations and short temporal variability of Corg stocks was analysed within these categories to provide clearer insights into temporal patterns. Above ground Corg stocks were similar between coastal and riverine meadows. Below ground Corg stocks were highest in coastal meadows, followed by riverine meadows. Sediment Corg stocks within riverine meadows were much higher than at coastal meadows and areas of seagrass loss, with no difference in sediment Corg stocks between these last two categories. Riverine seagrass meadows, of higher turbidity, had greater total Corg stocks than meadows in offshore areas irrespective of time. We suggest that Corg stock assessment should prioritise sampling over spatial gradients, but repeated monitoring over short time scales is less likely to be warranted if environmental conditions remain stable.
KeywordsBlue carbon Carbon sequestration Carbon stocks Carbon sinks
The Environmental Health and Monitoring Program (EHMP, Government of Queensland) provided water quality data. The authors thank J. Gudiño, M. Lyons, E. Kovacs, R. Babcock, and S. Phinn for help in the field, and Moreton Bay Research Station. N. Adi, S. Ortiz, G. Minatel, and R. de Albuquerque helped with seagrass sample processing. Thanks to the Marine Spatial Ecology Laboratory at the University of Queensland for continued feedback, in particular to C. Brown and E. Aurellado.
This work was supported by a Post-Graduate Scholarship and research funding from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), an International Postgraduate Research Scholarship, and a University of Queensland Centennial Scholarship to JSV. Funding was provided by a Collaborative Research Grant Integrating Remote Sensing and Autonomous Underwater Vehicle Collected Field Data from CSIRO to CR. MIS was supported in part by an ARC SuperScience Fellowship from the Australian Research Council. The study was also supported by an ARC Laureate Fellowship to PJM and the Coastal Carbon Biogeochemistry Cluster at CSIRO.
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