Mangrove soil organic carbon stocks in the Madu Ganga Ramsar Site and Madampa Lake Sanctuary, Sri Lanka: A preliminary assessment

Estimating carbon stocks across various ecosystems is crucial for effective carbon crediting. Mangrove ecosystems are particularly noteworthy for their high carbon storage. However, variability in soil organic carbon stocks (SOCS) within mangrove ecosystems poses significant challenges to accurate carbon estimation. Various factors affect SOCS. These factors must be elucidated to accurately estimate the SOCS of mangroves. Thus, a study was conducted in the Madu Ganga RASAR Site (MGRS) and Madampa Lake Sanctuary (MLS) to determine the factors affecting its SOCS. Three community types, mixed-mangrove, Nypha, and Rhizophora-Bruguiera communities, were identified in MGRS and MLS mangroves. Three 15 × 15m² plots were randomly placed in each community type in each site. Plants with > 1cm dbh were identified and recorded. Soil samples were collected from four randomly selected points from each plot at 0-30, 30-60, and 60-90 cm depths. Organic carbon content, bulk density, pH, conductivity, salinity, and  TDS of soil were measured using standard methods. Ordination, ANOVA, ANCOVA, and correlation analysis were employed to analyze data. Ordination analysis revealed that selected plant communities have different plant compositions except for the mixed-mangrove community in MGRS, which overlaps with the Rhizophora - Bruguiera community. ANOVA reveals significantly high SOCS in the mixed-mangrove community (1117.5±86.0 Mgha-1) of MLS, while ANCOVA showed a significant relationship between SOCS and the plant community. Correlations of SOCS with TDS (r = 0.51) and with pH (r = 0.48) were also observed. The relationship between pH and SOCS was also revealed in the ANCOVA.  As plant community type and soil pH and TDS seem to correlate with the SOCS of mangroves, it was recommended to consider these factors in estimating the SOCS of mangrove ecosystems. A recommended protocol for the estimation of mangrove SOCS was developed. Soil carbon stocks at the Madu Ganga Ramsar site and Madampa Lake exceed those of other Sri Lankan mangroves and mangroves in South and Southeast Asia.