Factors Determining Seagrass Blue Carbon Across Bioregions and Geomorphologies

Abstract

Seagrass meadows rank among the most significant organic carbon (Corg) sinks on earth. We examined the variability in seagrass soil Corg stocks and composition across Australia and identified the main drivers of variability, applying a spatially hierarchical approach that incorporates bioregions and geomorphic settings. Top 30 cm soil Corg stocks were similar across bioregions and geomorphic settings (min‐max: 20–26 Mg Corg ha−1), but meadows formed by large species (i.e., Amphibolis spp. and Posidonia spp.) showed higher stocks (24–29 Mg Corg ha−1) than those formed by smaller species (e.g., Halodule, Halophila, Ruppia, Zostera, Cymodocea, and Syringodium; 12–21 Mg Corg ha−1). In temperate coastal meadows dominated by large species, soil Corg stocks mainly derived from seagrass Corg (72 ± 2%), while allochthonous Corg dominated soil Corg stocks in meadows formed by small species in temperate and tropical estuarine meadows (64 ± 5%). In temperate coastal meadows, soil Corg stocks were enhanced by low hydrodynamic exposure associated with high mud and seagrass Corg contents. In temperate estuarine meadows, soil Corg stocks were enhanced by high contributions of seagrass Corg, low to moderate solar radiation, and low human pressure. In tropical estuarine meadows formed by small species, large soil Corg stocks were mainly associated with low hydrodynamic energy, low rainfall, and high solar radiation. These results showcase that bioregion and geomorphic setting are not necessarily good predictors of soil Corg stocks and that site‐specific estimates based on local environmental factors are needed for Blue Carbon projects and greenhouse gases accounting purposes.

Substantial seagrass blue carbon pools in the southwestern Baltic Sea are spatially heterogeneous, mostly autochthonous, and include relics of terrestrial peatlands

“…Regional heterogeneity observed here was comparable to previous regional evaluations of blue carbon in Z. marina meadows (e.g. Röhr et al 2016;Prentice et al 2019), but local heterogeneity was much greater, with previous measurements reporting <10 times more Corg content in vegetated vs unvegetated sediments (Table 5), or similar carbon content between these sublocations (Prentice et al 2019(Prentice et al , 2020Mazarrasa et al 2021;Krause et al 2022). Overall, average Corg stocks in the German Baltic Sea fit within the global range reported for those of Z. marina (318 + 10 to 26,523 + 667 g C/m 2 ), but more closely resembled Z. marina Corg stocks in the Mediterranean Sea (8,793 + 2,248 g C/m 2 ), Funen area of Denmark, and Skagerrak coast of Sweden, than Corg stocks in other parts of the Baltic Sea (Table 5).…”

“…tropical vs. temperate environments), regionally, and even locally (within a seagrass meadow) (e.g. Kennedy et al 2010, Röhr et al 2018, Prentice et al 2020, Mazarrasa et al 2021). Consequently, it is difficult to apply ecological economic approaches to provide accurate economic valuations and determine seagrass habitat contributions to the national remaining CO 2 budget without introducing a large degree of uncertainty.…”

“…seawater depth, Lavery et al 2013, Serrano et al 2014, Mazarrasa et al 2017a; decreased water motion, Prentice et al 2019; lower wave height and exposure, Samper-Villarreal et al 2016), (2) anthropogenic inputs (Macreadie et al 2012, Mazarrasa et al 2017a,b, Ricart et al 2020), (3) seagrass properties (e.g. species composition, Serrano et al 2014, 2019; increased seagrass complexity, Jankowska et al 2016, Samper-Villarreal et al 2016, Mazarrasa et al 2018, 2021), and (4) sediment characteristics (e.g. Dahl et al 2016, Röhr et al 2016, Gullström et al 2018, Miyajima et al 2017).…”

Seagrass biomass and sediment carbon in conserved and disturbed seascape

“…Sampling at deeper depths was constrained by the extensive reef flat and hard limestone deposits in the study site. Hence, we standardized the sampling depth to 30 cm (similar to the standardization by Mazarrasa et al, 2021). Sediment samples were subdivided every 5 cm ( n = 6 per core), placed into airtight bags, then preserved at 4°C until laboratory analysis was performed.…”

Organic carbon storage in sediments of seagrass habitats in the lagoons of Lakshadweep Archipelago, west coast of India

“…It is predicted that the CO 2 levels would exceed 1000 ppm and the average pH of the oceans could fall by 0.5 units (equivalent to a threefold increase in the concentration of hydrogen ions) by the year 2100 if global emissions of CO 2 continue to rise on current trends (The Royal Society, 2005). Seagrass meadows rank among the most significant organic carbon (C org ) sinks on earth (Mazarrasa et al, 2021;Serrano et al, 2018;. The carbon storage potential of seagrass meadows from Indian waters is known from the Gulf of Mannar and Palk Bay , Chilika and Pulicat Lakes (Kaladharan et al, 2021a) along the east coast and from Kadalundi Estuary (Kaladharan et al, 2021b) along the west coast.…”