Drivers and modelling of blue carbon stock variability in sediments of southeastern Australia

Abstract

Abstract. Tidal marshes, mangrove forests, and seagrass meadows are important global carbon (C) sinks, commonly referred to as coastal “blue carbon”. However, these ecosystems are rapidly declining with little understanding of what drives the magnitude and variability of C associated with them, making strategic and effective management of blue C stocks challenging. In this study, our aims were threefold: (1) identify ecological, geomorphological, and anthropogenic variables associated with 30 cm deep sediment C stock variability in blue C ecosystems in southeastern Australia, (2) create a predictive model of 30 cm deep sediment blue C stocks in southeastern Australia, and (3) map regional 30 cm deep sediment blue C stock magnitude and variability. We had the unique opportunity to use a high-spatial-density C stock dataset of sediments to 30 cm deep from 96 blue C ecosystems across the state of Victoria, Australia, integrated with spatially explicit environmental data to reach these aims. We used an information theoretic approach to create, average, validate, and select the best averaged general linear mixed effects model for predicting C stocks across the state. Ecological drivers (i.e. ecosystem type or ecological vegetation class) best explained variability in C stocks, relative to geomorphological and anthropogenic drivers. Of the geomorphological variables, distance to coast, distance to freshwater, and slope best explained C stock variability. Anthropogenic variables were of least importance. Our model explained 46 % of the variability in 30 cm deep sediment C stocks, and we estimated over 2.31 million Mg C stored in the top 30 cm of sediments in coastal blue C ecosystems in Victoria, 88 % of which was contained within four major coastal areas due to the extent of blue C ecosystems (∼87 % of total blue C ecosystem area). Regionally, these data can inform conservation management, paired with assessment of other ecosystem services, by enabling identification of hotspots for protection and key locations for restoration efforts. We recommend these methods be tested for applicability to other regions of the globe for identifying drivers of sediment C stock variability and producing predictive C stock models at scales relevant for resource management.

Factors Determining Seagrass Blue Carbon Across Bioregions and Geomorphologies

“…However, previous seagrass Blue Carbon studies have explored the variability and drivers of soil Corg stocks within constrained spatial scales (e.g. meadow scale, coastal geomorphic settings or bioregion) independently (Lavery et al 2013;Miyajima et al 2015;Oreska et al 2017;Serrano et al 2019;Ewers Lewis et al 2020;Ricart et al 2020).…”

“…However, previous seagrass Blue Carbon studies have explored MAZARRASA ET AL. (Large, Small, and Unvegetated), Geomorphic Setting (Coastal and Estuarine), and Bioregion (Temperate Southern Ocean and Tropical Indo-Pacific) the variability and drivers of soil C org stocks within constrained spatial scales (e.g., meadow scale, coastal geomorphic settings or bioregion) independently (Ewers Lewis et al, 2020;Lavery et al, 2013;Miyajima et al, 2015;Oreska et al, 2017;Ricart et al, 2020;Serrano et al, 2019).…”

Comment on bg-2021-27

“…Knowing the relative contributions of locally produced (autochthonous) and imported (allochthonous) carbon also elucidates the underlying mechanisms by which blue carbon habitats store and accumulate carbon. Overlying vegetation can significantly impact sediment carbon stocks; however, it is rarely the dominant source of carbon buried within blue carbon habitats (Kennedy et al, 2010;Lewis et al, 2020;Mazarrasa et al, 2015;Prentice et al, 2019). In many cases, contributions from terrestrial habitats, macroalgae, and suspended particulate organic material contribute as much or more to carbon buried in blue carbon sediments than do autochthonous sources (Drexler et al 2020;Kennedy et al, 2010;Leorri et al, 2018;Ricart et al, 2020).…”

Quantifying blue carbon and nitrogen stocks in surface soils of temperate coastal wetlands

“…The accumulation and storage of carbon (SOC and IC) in blue carbon habitats is inherently linked to the characteristics of their environmental setting (Bouillon et al 2008;Lovelock et al 2014;Lavery et al 2019;Ewers Lewis et al 2020;Owers et al 2020). For example, the temperature, precipitation patterns, geomorphology and hydrodynamics of an environment influence the structure and colonisation of the coastal vegetation, and the deposition of organic matter (Owers et al 2016b;Ewers Lewis et al 2020). As such, variability of SOC stocks in blue carbon environments is primarily considered to be a function of the in-situ vegetation given their significant contribution of carbon inputs to the soil (Saintilan et al 2013).…”

“…As such, variability of SOC stocks in blue carbon environments is primarily considered to be a function of the in-situ vegetation given their significant contribution of carbon inputs to the soil (Saintilan et al 2013). The type of aboveground vegetation may therefore provide an indication of below-ground soil carbon stocks resulting from autochthonous carbon additions (primary productivity) and allochthonous carbon capture (sediment accumulation) (Bouillon et al 2003;Lamb et al 2006;Ewers Lewis et al 2020). This highlights the importance of understanding soil carbon dynamics under different types of vegetation to gain better understanding of SOC storage in the blue carbon system.…”