Assessing and mapping of carbon in biomass and soil of mangrove forest and competing land uses in the Philippines

Jose Castillo, Armando Apan, Maraseni Tek
2017
Mangrove forests provide many ecosystem goods and services, and are important carbon (C) sinks in the tropics. Yet, land use conversions in mangroves still continue, especially in Southeast Asia. Carbon stocks in biomass and soil as well as the soil emissions of greenhouse gases (GHG) are important parameters to quantify, monitor and map in mangrove area, and are vital inputs for assessing the Assessing the Carbon of mangrove forests and land uses that replaced mangroves iii Leaf Area Index
more » ... ) derived from Sentinel-2 was more accurate in predicting the overall aboveground biomass. However, the SAR-based model was more accurate in predicting the biomass in the usually deficient-to-low vegetation cover replacement land uses. These models had 0.82 to 0.83 correlation/agreement of observed and predicted value. Overall, Sentinel-1 SAR and Sentinel-2 multispectral imagery can provide satisfactory results in the retrieval and predictive mapping of aboveground biomass in mangrove area. In the third objective, the soil C stocks of the study land uses were quantified to estimate C losses in soil owing to conversion. I also evaluated the potential of GIS-based Ordinary Kriging for predictive mapping of the soil C stock distribution in the entire study site. On average, the soil C stock of mangrove forests was 851.9 MgC ha -1 while that of their non-forest competing land uses was less than half at 365.15 MgC ha -1 . Aquaculture, salt pond and cleared mangrove had comparable C stocks (453.6, 401, 413 MgC ha -1 , respectively) and coconut plantation had the least (42.2 MgC ha -1 ). Overall, C losses in soil owing to land use conversion in mangrove ranged from 398 to 809 MgC ha -1 (mean: 486.8 MgC ha -1 ) or a decline of 57% in soil C stock, on average. It was possible to map the site-scale spatial distribution of soil C stock and predict their values with 85% overall certainty using Ordinary Kriging approach. To achieve the fourth objective, the soil fluxes of CO 2 , CH 4 and N 2 O in the study land uses were investigated using static chamber method. I also evaluated the potential of GIS-based Ordinary Kriging for predictive mapping of the soil GHG fluxes in the entire study site. Results show that the emissions of CO 2 and CH 4 were higher in mangrove forests by 2.6 and 6.6 times, respectively, while N 2 O emissions were lower by 34 times compared to the average of non-forest land uses. CH 4 and N 2 O emissions accounted for 0.59% and 0.04% of the total emissions in mangrove forest as compared to 0.23% and 3.07% for non-forest land uses, respectively. Site-scale soil GHG flux distribution could be mapped with 75% to 83% accuracy using Ordinary Kriging. This study has shown that C losses in biomass and soil arising from mangrove conversion are substantial (63%; 571 MgC ha -1 ). Moreover, mangrove conversion heavily altered the soil-atmosphere fluxes of GHG, increasing the N 2 O fluxes by 34 times. The use of Sentinel imagery for biomass mapping, as well as the application of Ordinary Kriging for soil mapping of C stocks and GHG fluxes, offer good potentials for mangrove area monitoring. This study advances current knowledge on the C stocks and soil GHG fluxes in mangrove area and the C emissions owing to mangrove conversion. The mapping techniques presented here contribute to advancing the knowledge for mapping the biomass and soil attributes in mangrove ecosystem. Assessing the Carbon of mangrove forests and land uses that replaced mangroves iv
doi:10.26192/5c09b419f0cc2 fatcat:ni3ainbenzdorfcue3qai7uozm