Does Regional Development Influence Sedimentary Blue Carbon Stocks? A Case Study From Three Australian Estuaries

Mitigating climate change through the reduction of atmospheric CO2 levels is of interest,
particularly through maintaining and re-establishing natural ecosystems that act as
carbon sinks, such as coastal vegetated habitats or “blue carbon” systems. Here
we compare sedimentary blue carbon (C) stocks from 37 sediment cores collected
in pristine (n = 13), agricultural (n = 11), and urban (n = 13) estuaries within the
same geomorphological region, located on the eastern coast of Australia. The mean
estimated C stocks for each carbon system (seagrass, mangrove, and saltmarshes)
were 402 78, 830 109, and 723 100 Mg C ha􀀀1, respectively, conservatively
estimated up to 3 m depths. Analysis of variance revealed no significant difference
between C stocks per area (C ha􀀀1) considering each habitat type and between specific
estuaries. However, the total estuarine C stocks were found to be greater with increasing
levels of conservation, based on larger areas of blue carbon vegetation. The potential
loss of C to the atmosphere from these small regional estuaries are 500,574 118,635
tons of CO2 equivalent (CO2e), based on specific assumptions. The implication of these
results are that there are large C stocks in small regional estuaries which supports the
protection of blue C systems in developing coastal areas and highlights the uncertainties
of the CO2 emissions from potential blue C habitat degradation.