Abstract:
Mangroves in Sri Lanka serve as critical blue carbon sinks, yet their sediment
carbon storage remains understudied, limiting their incorporation into national
climate change mitigation strategies. This study presents the first quantitative
assessment of soil organic carbon (SOC) stocks in the mangrove ecosystem of
Koggala Lagoon, located in the southern province of Sri Lanka. Soil samples
were collected from ten sites using cylindrical corers at depths of 0–15 cm and
15–30 cm. Samples were processed using standard procedures including ovendrying,
the Loss on Ignition (LOI) method for organic matter determination, and
conversion to SOC stocks expressed in Mg C ha-1. Results revealed substantial
spatial variability in SOC stocks across the lagoon, ranging from 14.74 to 66.93
Mg/ha in the topsoil layer. High-performing sites (Site 02: 66.93 Mg/ha; Site
07: 59.16 Mg/ha) demonstrated carbon storage potential more than 4.5 times
greater than low-performing sites (Site 03: 14.74 Mg/ha). Unexpectedly, several
sites exhibited atypical vertical carbon distribution patterns, with Site 10 showing
higher subsoil carbon content (72.55 Mg/ha) than topsoil (47.19 Mg/ha), suggesting
complex sediment dynamics potentially influenced by deep-rooted vegetation
or historical land use. These findings have critical implications for blue carbon
accounting and conservation strategy. The heterogeneous distribution of SOC
stocks indicates that national carbon inventories and credit schemes must avoid
generalized assumptions to prevent overestimation. The study confirms Koggala
Lagoon mangroves as significant carbon reservoirs and emphasizes the necessity
of their conservation as natural climate solutions. This baseline data provides essential
evidence for incorporating mangrove ecosystems into Sri Lanka’s climate
change mitigation frameworks and highlights their underappreciated role in global
carbon sequestration efforts.
