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Variability and Vulnerability of Coastal ‘Blue Carbon’ Stocks: A Case Study from Southeast Australia

Version 2 2024-06-06, 12:04
Version 1 2017-05-11, 21:03
journal contribution
posted on 2024-06-06, 12:04 authored by CJ Ewers Lewis, Paul Carnell, J Sanderman, JA Baldock, Peter Macreadie
‘Blue carbon’ ecosystems—seagrasses, tidal marshes, and mangroves—serve as dense carbon sinks important for reducing atmospheric greenhouse gas concentrations, yet only recently have stock estimates emerged. We sampled 96 blue carbon ecosystems across the Victorian coastline (southeast Australia) to quantify total sediment stocks, variability across spatial scales, and estimate emissions associated with historical ecosystem loss. Mean sediment organic carbon (Corg) stock (±SE) to a depth of 30 cm was not significantly different between tidal marshes (87.1 ± 4.90 Mg Corg ha−1) and mangroves (65.6 ± 4.17 Mg Corg ha−1), but was significantly lower in seagrasses (24.3 ± 1.82 Mg Corg ha−1). Location (defined as an individual meadow, marsh, or forest) had a stronger relationship with Corg stock than catchment region, suggesting local-scale conditions drive variability of stocks more than regional-scale processes. We estimate over 2.90 million ± 199,000 Mg Corg in the top 30 cm of blue carbon sediments in Victoria (53% in tidal marshes, 36% in seagrasses, and 11% in mangroves) and sequestration rates of 22,700 ± 5510 Mg Corg year−1 (valued at over $AUD1 million ± 245,000 year−1 based on the average price of $AUD12.14 Mg CO2 eq−1 at Australian Emissions Reduction Fund auctions). We estimate ecosystem loss since European settlement may equate to emissions as high as 4.83 million ± 358,000 Mg CO2 equivalents (assuming 90% remineralization of stocks), 98% of which was associated with tidal marsh loss, and what would have been sequestering 9360 ± 2500 Mg Corg year−1. This study is among the first to present a comprehensive comparison of sediment stocks across and within coastal blue carbon ecosystems. We estimate substantial and valuable carbon stocks associated with these ecosystems that have suffered considerable losses in the past and need protection into the future to maintain their role as carbon sinks.

History

Journal

Ecosystems

Volume

21

Pagination

263-279

Location

New York, N.Y.

ISSN

1432-9840

eISSN

1435-0629

Language

English

Publication classification

C Journal article, C1 Refereed article in a scholarly journal

Copyright notice

2017, Springer Science + Business Media

Issue

2

Publisher

SPRINGER