Process Controls of the Live Root Zone and Carbon Sequestration Capacity of the Sundarbans Mangrove Forest, Bangladesh

Abstract

<jats:p>The conservation of coastal wetland ecosystems, like mangrove forests and salt marshes, represents a critical strategy for mitigating atmospheric emissions and climate change in the 21st century. Yet the existence of these environments is threatened by human-induced disturbances, namely deforestation and accelerated sea-level rise. Coastal systems maintain surface elevation in response to sea-level rise through a combination of physical and biological processes both above and below the ground surface. The quantification and relative contribution of belowground process controls (e.g., seasonal water content, organic matter decomposition) on surface elevation change is largely unexplored but crucial for informing coastal ecosystem sustainability. To address this knowledge deficit, we integrated measurements of surface elevation change of the live root zone (0.5 to 1 m depth) with geotechnical data from co-located sediment cores in the Sundarbans mangrove forest (SMF) of southwest Bangladesh. Core data reveal that the primary belowground controls on surface elevation change include seasonal fluctuations in pore-water content and the relative abundance of fine-grained sediments capable of volumetric expansion and contraction, supporting an elevation gain of ~2.42 ± 0.26 cm yr−1. In contrast to many mangrove environments, the soils of the SMF contain little organic matter and are dominantly composed (&gt;90%) of inorganic clastic sediments. The mineral-rich soil texture likely leads to less compaction-induced subsidence as compared to organic-rich substrates and facilitates surface equilibrium in response to sea level rise. Despite a relatively high soil bulk density, soil carbon (C) density of the SMF is very low owing to the dearth of preserved organic content. However, rates of C accumulation are balanced out by locally high accretion rates, rendering the SMF a greater sink of terrestrial C than the worldwide mangrove average. The findings of this study demonstrate that C accumulation in the SMF, and possibly other alluvial mangrove forests, is highly dependent on the continued delivery of sediment to the mangrove platform and associated settings.</jats:p>

Stok Karbon Organik Sedimen di Kawasan Ekosistem Mangrove Pesisir Kabupaten Kolaka Sulawesi Tenggara

“…Kisaran nilai SBD ini lebih rendah dibandingkan SBD yang diperoleh oleh beberapa penelitian lain. Bomer et al (2020) memperoleh SBD berkisar antara 0,6 sampai dengan 1,0 g cm -3 , Chen et al (2020) memperoleh SBD berkisar antara 1,46-1,96 g cm -3 dengan kedalaman sedimen 50 cm. Selain itu, Hasidu et al (2021b) memperoleh nilai SBD berkisar antara 1,2387±0,2469 g cm -3 sampai 1,4919±0,2948 g cm -3 di kawasan mangrove bekas lahan tambak (hasil suksesi mangrove secara alami).…”

“…Nilai SBD ini dapat mempengaruhi SOC yang ada di dalam suatu kawasan. Sementara itu, kadar C-organik yang diperoleh (Tabel 1) hampir sama dengan yang diperoleh oleh Rahman et al (2021) yang memperoleh persentase kadar karbon sedimen berkisar antara 0,3 sampai dengan 4,4%, namun cenderung lebih kecil dari yang diperoleh oleh Bomer et al (2020) yang berkisar antara 3,7% sampai dengan 6,5%.…”