Impacts of land management practices on blue carbon stocks and greenhouse gas fluxes in coastal ecosystems—A meta‐analysis

Abstract

Global recognition of climate change and its predicted consequences has created the need for practical management strategies for increasing the ability of natural ecosystems to capture and store atmospheric carbon. Mangrove forests, saltmarshes and seagrass meadows, referred to as blue carbon ecosystems (BCEs), are hotspots of atmospheric CO2 storage due to their capacity to sequester carbon at a far higher rate than terrestrial forests. Despite increased effort to understand the mechanisms underpinning blue carbon fluxes, there has been little synthesis of how management activities influence carbon stocks and greenhouse gas (GHG) fluxes in BCEs. Here, we present a global meta‐analysis of 111 studies that measured how carbon stocks and GHG fluxes in BCEs respond to various coastal management strategies. Research effort has focused mainly on restoration approaches, which resulted in significant increases in blue carbon after 4 years compared to degraded sites, and the potential to reach parity with natural sites after 7–17 years. Lesser studied management alternatives, such as sediment manipulation and altered hydrology, showed only increases in biomass and weaker responses for soil carbon stocks and sequestration. The response of GHG emissions to management was complex, with managed sites emitting less than natural reference sites but emitting more compared to degraded sites. Individual GHGs also differed in their responses to management. To date, blue carbon management studies are underrepresented in the southern hemisphere and are usually limited in duration (61% of studies <3 years duration). Our meta‐analysis describes the current state of blue carbon management from the available data and highlights recommendations for prioritizing conservation management, extending monitoring time frames of BCE carbon stocks, improving our understanding of GHG fluxes in open coastal systems and redistributing management and research effort into understudied, high‐risk areas.

Anthropogenic, Direct Pressures on Coastal Wetlands

“…Conservation of coastal wetlands can therefore contribute to the mitigation and adaptation to climate change (Neubauer and Verhoeven, 2019;Serrano et al, 2019). However, the Blue Carbon potential of coastal wetland restoration varies with inundation and rainfall (Negandhi et al, 2019) as well as management approaches (O'Connor et al, 2020). Degraded coastal wetlands could potentially be re-naturalized to promote an increase in carbon sequestration, as well as additional and valuable ecosystem services, such as denitrification and halophyte cultivation, for example Salicornia.…”

Estimating the Potential Blue Carbon Gains From Tidal Marsh Rehabilitation: A Case Study From South Eastern Australia

“…Historically, coastal ecosystems have been impacted and degraded by human intervention, mainly in the form of land acquisitions for agriculture, aquaculture, and coastal development (Wylie et al, 2016); eutrophication (Adam, 2002;Macreadie et al, 2017), and changes in sediment input resulting from the construction of dams, levees, and irrigation (Adam, 2002). Over 60% of coastal wetlands have been lost globally during the 20th century (Davidson, 2014).…”

“…Coastal wetlands may also face further stresses with keeping pace with sea level rise (SLR). Land elevation and the capacity to accrete sediment will be key factors when coping with this additional pressure (Adam, 2002). If the ability of coastal wetlands to accrete sediments exceeds the rate of SLR or if the surrounding environment allows for expansion inland (for example, the removal of any manmade barriers or infrastructure), these ecosystems may be able to survive or possibly increase in the future (Adam, 2002;Macreadie et al, 2017).…”

“…Land elevation and the capacity to accrete sediment will be key factors when coping with this additional pressure (Adam, 2002). If the ability of coastal wetlands to accrete sediments exceeds the rate of SLR or if the surrounding environment allows for expansion inland (for example, the removal of any manmade barriers or infrastructure), these ecosystems may be able to survive or possibly increase in the future (Adam, 2002;Macreadie et al, 2017). However, Macreadie et al (2017) found that Australian tidal marsh ecosystems, on average, accrete sediments at a rate of 2.09 ± 0.32 mm year −1 , considerably slower than the global rate of 6.73 ± 0.07 mm year −1 (Duarte et al, 2013).…”

Future carbon emissions from global mangrove forest loss

“…Improved management can reduce CO2 emissions from mangrove forest loss and enhance the sequestration potential of disturbed forests O'Connor et al, 2020), but management actions should be guided by predictions of future emissions, not just carbon storage. The effectiveness of management relies on understanding how much emissions can be avoided by specific actions, for instance, by reducing land conversion or by increasing restoration efforts.…”