Abstract
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 tonnes 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.
Highlights
Vegetated coastal ecosystems are highly productive ecosystems that play a critical role in the global carbon, water, and nutrient cycles (Sanders et al, 2014; Lovelock et al, 2017; Maher et al, 2018)
Over the past several decades, it is estimated that about one third of global mangroves, seagrass, and saltmarsh have been lost as a result of deforestation and habitat reclamation, coastal and urban development, nutrient enrichment, water quality degradation, and climate change (Alongi, 2002; Orth et al, 2006; Gedan et al, 2009; McLeod et al, 2011; Pendleton et al, 2012; Lovelock et al, 2015)
Global distribution of blue C systems is primarily governed by physical tolerances to climatic conditions such as temperature and rainfall, which limits and restricts mangrove and seagrass production toward temperate climates (Duarte et al, 2013), while saltmarsh are generally more adapted to cooler climates (Chmura et al, 2003)
Summary
Vegetated coastal ecosystems (i.e., seagrass beds, saltmarsh meadows, and mangrove forests) are highly productive ecosystems that play a critical role in the global carbon, water, and nutrient cycles (Sanders et al, 2014; Lovelock et al, 2017; Maher et al, 2018). Over the past several decades, it is estimated that about one third of global mangroves, seagrass, and saltmarsh have been lost as a result of deforestation and habitat reclamation, coastal and urban development, nutrient enrichment, water quality degradation, and climate change (Alongi, 2002; Orth et al, 2006; Gedan et al, 2009; McLeod et al, 2011; Pendleton et al, 2012; Lovelock et al, 2015) This decline in coastal blue C systems still continues today at rates estimated between ∼0.5–3% annually depending on ecosystem type (McLeod et al, 2011; Pendleton et al, 2012). These economic damages are associated with restoration efforts in wetlands with ecological benefits and undefined carbon offsets (Irving et al, 2011)
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