Estimating carbon stock and sequestration for supporting low carbon developments: The case of Pak Nam Prasae, Rayong province

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1 Estimating carbon stock and sequestration for supporting low carbon developments: The case of Pak Nam Prasae, Rayong province Monthira Yuttitham *, Nawinda Thongantang, Natchanok Pangsang, Ratiya Sasithorn, Satita Janthakhin, Sirijit Jongjityotin, Suchada Chanwan Faculty of Environment and Resource Studies, Mahidol University, Nakhon Pathom, 73170, Thailand Abstract: Mangroves could be key ecosystems in strategies addressing the mitigation of climate changes through carbon storage in biomass and soil. In Pak Nam Prasae, Klaeng District, Rayong Province, Eastern of Thailand, mangrove forest have been planted for restorations and to object to increased mangrove area. This study aimed to evaluate soil carbon storage, above-ground and below-ground biomass of mangroves forest which divided into traditional forest (Avicenia marina (Forsk.) Vierh., natural forest (Rhizophora mucronata Poia) and planted forest (Rhizophora mucronata Poia). To collect soil samples at 0-30 cm depth and analyzed soil physical, chemical properties and estimate soil carbon stock. In addition, determined differences the carbon storage in biomass. In study plot tree, height and diameter at breast height were measured. Allometric equations was applied to estimate the biomass of stems, branches, leaves and roots and estimated the carbon storage values in biomass by determined the carbon storage in form of above-ground and below-ground biomass from the analysis biomass values. The results from soil carbon was highest in natural forest followed by traditional forest and planted forest in ±20.63 ton C/ha, 43.78±15.87 ton C/ha and 25.81±4.31 ton C/ha, respectively. The study showed that the natural forest was the highest of biomass and carbon storage (9.93 ton/ha and 4.7 ton C/ha), followed by the traditional forest (6.89 ton/ha and 2.95 ton C/ha) and the planted forest (1.33 ton/ha and 0.63 ton C/ha). Keywords: Carbon stock; Carbon sequestration; Mangrove forest; Biomass; Pak Nam Prasae * Corresponding author. Tel.: (2201), Fax: address: monthira.yut@mahidol.edu, monthira.yut@mahidol.ac.th 1. Introduction In recent decades, the scientific community has issued several advances and alerts with regard to global climate change, its implications, and its origins. These changes have their origin associated with the increasing emissions of greenhouse gases (GHG) such as carbon dioxide, methane, and nitrogen oxides (IPCC, 2014). Forests play an important role in the carbon cycle and its regulation and potentially play important parts in carbon sequestration and stock. Mangrove forests have a tropical and subtropical distribution (Schaeffer-Novelli et al., 2000) and a great potential as atmospheric carbon sinks and sequestrations in terms of above-ground and below-ground biomass and soil carbon stock (Siikamaki et al., 2012). In 2000, Pak Nam Prasae, Klaeng district, Rayong Province, Eastern of Thailand, mangrove forest covered 1, rai or ha (6.25 rai = 1ha) (Department of Marine and Coastal Resources, 2013). The forest types covered by traditional forest and natural forest. Loses of area cause by deforestation by human activity; shrimp farm and change land to the community. It contribution and reduce large amount of mangrove forest. The government try to re-plant the mangrove forest again. The understanding of the contribution of mangroves for carbon stock is fundamental to further understand the role of these forests on a global scale, supporti ng low carbon developments. Thus, the objectives of this study to estimation of ecosystem carbon stock (soil carbon stock, and carbon store in above and below ground biomass) of mangrove forests across three different forest species (traditional forest (Avicenia marina (Forsk.) Vierh), natural forest (Rhizophora mucronata Poia) and planted forest (Rhizophora mucronata Poia). 2. Material and methods 2.1 Study site The study site is located in mangrove forest in Pak Nam Prasae, Klaeng district, Rayong Province, Eastern of Thailand (Fig. 1). The mangrove forest area under investigation covers 1,284 rai or ha (6.25 rai = 1 ha). Mangrove forest areas were covered 10,191 rai or 1, ha % of the 406

2 total area in the Rayong province and 1,534,584 rai or 245, ha or 0.84 % of mangrove area in the whole area mangrove area of Thailand in 2014 (Department of Marine and Coastal Resources, 2017). The soil, above and below ground biomass were samples. The forests types were divided into traditional forest (Avicenia marina (Forsk.) Vierh including 3 plots), natural forest (Rhizophora mucronata Poia including 3 plots), and planted forest (Rhizophora mucronata Poia including 3 plots). Fig. 1 Location of the study site mangrove forest in PakNam Prasae, Klaeng district, Rayong Province, Eastern of Thailand (modified from Sanit Aksornkaew, 2002) 2.2 Soil carbon stock Soil C content was measured from soil sample at depth 0-30 cm. the sample were collected from three different mangrove forest types as mention above. The calculations of soil carbon stock in the mangrove forest at was given by the formula in Eq. (1) as follow; Soil C stock (g C/m 2 ) is equal bulk density (g soil/m 3 ) multiplying by soil C content (g C/g soil). In addition, the soil physical properties was measured; bulk density by core method (Blacke and Hartage, 1986) and soil texture by hydrometer (USDA, 1996). Soil chemical properties was measured; soil reaction, organic matter by Walkey and Black Method (Walkley and Black, 1947), available phosphorus (P) by Bray II (Bray and Kurtz, 1945), available potassium (K) by Atomic absorption Spectrophotometer, Cation Exchange Capacity (CEC.) and Base Saturation percentage (%BS). Finally, the soil fertility was estimated by using the standard method and fertility rate by National Soil Survey Center, 1996 (USDA, 1996). 2.3 Estimation of above-ground and below-ground biomass This study were estimated above-ground and below-ground biomass of the three types of forest species (traditional forest, natural forest and planted forest age around 3 years in 2016). Sample plot; DBH measurement, species and land cover were measures and recorded. The diameter at breast height (DBH) was measured and the allometric equations uses from different plant species. The allometric equations for Rhizophora spp. using Eq. (2); WS is (D 2 H) 0.945, WB is (D 2 H) , WL is (D 2 H) , WT is WS + WB + WL. The other plant species using Eq. (3); WS is (D 2 H) , WB is (D 2 H) , WL is (D 2 H) , WT is WS + WB + WL. Where; WS 407

3 is above ground biomass in truck (kg), WB is above ground biomass in branch( kg), WL is above ground biomass in leaf ( kg), D is diameter at breast height (cm), H is tree height ( m) (Komiyama et al, ) These equations were originally proposed for the region where this study site is located. Thereby, it was thought most appropriate to use them for the biomass calculation in this study. Thus, carbon storage was calculated from all biomass multiplying by carbon fraction (CF) (Department of Marine and Coastal Resources, 2008). The average of carbon ratio in percentage of dry weight Rhizophora equal (Faculty of Forestry, Kasetsart University, 2011( and other species equal (IPCC, 2006). The dry weight of root ratio and tree of Rhizophora equal (Faculty of Forestry, Kasetsart University, 2011( and other species equal (IPCC, 2006). 3. Results According to soil and biomass survey and analysis in this study in Pak Nam Prasae, Rayong Province in Eastern Thailand was investigated. The details were as follows. 3.1 Soil carbon stock The natural forest is highest fertility (11.80±1.47) followed by planted forest (9.53±0.52) and traditional forest (9.33±1.48). In addition, the result show that overall soil fertility are in the range of medium fertility (Table 1). Soil carbon is also highest in natural forest (12.22±2.06 kg C/m 2, 19.55±3.30 ton C/rai and ±20.63 ton C/ha), followed by traditional forest (4.39±1.59 kg/m 2, 7.02±2.54 ton C/rai and 43.78±15.87 ton C/ha) and planted forest (2.58±0.43 kg/m 2, 4.13±0.69 ton C/rai and 25.81±4.31 ton C/ha), respectively (Table 1). The comparison between soil carbon in each plot and forest types and species. It was found that there are deference between forest types in term of soil carbon stock at (p<0.05). Table 1 Soil parameters and soil organic carbon stock in difference forest species Parameters Natural forest (Rhizophora mucronata Poia) Traditional forest (Avicenia marina Planted forest (Rhizophora mucronata Poia) OM (%) 3.27± ± ±0.25 B.S. (%) 27.45±89.6 ± ±0.00 CEC (cmol/kg) 0.65± ± ±0.15 P (mg/kg) 6.52±24.81 ± ±4.25 K (mg/kg) ± ± ±80.74 Fertility 11.80± ± ±0.52 Fertility rate Medium Medium Medium TOC (%) 5.52± ± ±0.14 Bulk Density 0.78± ± ± ph 0.30± ± ±0.60 Sand (%) 1.52± ± ±1.85 Silt (%) 11.91± ± ±1.24 Clay (%) 5.32± ± ±0.84 Soil Texture Loamy Sand Sand Sand SOC (kg C/m 2 ) 12.22± ± ±0.43 SOC 3.30± ± ±4. 13 SOC 20.63± ± ± N Note: 1 ha = 6.25 rai 408

4 3.2 Biomass The above-ground biomass was presented in Table 2. The biomass was highest in natural forest and followed by traditional forest and planted forest. Above-ground biomass and below-ground was presented in natural forest (6.71±3.38 ton/ha and 3.22±1.62), traditional forest (5.42±1.96 ton/ha and 1.47±0.53 ton/ha) and planted forest (0.90±0.09 ton/ha and 0.43±0.04 ton/ha). The lowest in showed in planted forest area because the average age of this site is 3 years. It have a high potential to improve carbon store in this forest type because this is a young plant (Table 2). Table 2 Above-ground, below-ground biomass and carbon store in biomass Forest types Natural forest (Rhizophora mucronata Poia Traditional forest (Avicenia marina (Forsk.) Vierh. Planted forest (Rhizophora mucronata Poia) Above-ground biomass Below-ground biomass Total Biomass C in biomass 6.71± ± ± ± ± ± ± ± ±0.26 Root biomass C in root 3.22± ± ± ± ± ± ± ± ±0.13 Biomass C store Discussion The results showed that soil carbon stock in mangrove forest in In Pak Nam Prasae, Klaeng District, Rayong Province, and Eastern of Thailand was higher than soil carbon in upland soil in general. When compared the results from this studied with other mangrove forest soil area in Thailand. The results from this studied is in the range of soil carbon stock from others mangrove forest in Thailand. Previous reported the above-ground biomass is ton C/rai and below-ground biomass 6.21 ton C/rai and the total is ton C/rai (Department of Marine and Coastal Resources. 2017). This studied were higher than that reported except the young forest in term of planted forest by average age 3 years. In addition, young mangrove forest in this study showed the average lowest carbon store not only in above and below ground but also in soil carbon stock. This is can explain that the young generation of forest can store more carbon in the future when there are growing to the big plant (Abby et al., 2014). 5. Conclusion In this study we present the results of carbon sequestration potential by stock of carbon in soil and above-ground and below-ground biomass. The low carbon developments was investigated. The total average soil carbon stock was ±20.63 ton C/ha, 43.78±15.87 ton C/ha and 25.81±4.31 ton C/ha in natural forest, traditional forest and planted forest, respectively. The total average biomass was 4.7, 2.95, 0.63 ton C/ha in natural forest, traditional forest and planted forest, respectively. Thus, the results demonstrate that with mangrove area, additional benefits in terms of soil carbon stock and aboveground and below-ground carbon store in biomass. According to the findings for environmental benefits, mangrove forest may help highlight the potential to carbon sequestration and help to low carbon developments. Acknowledgement This research was supported by Faculty of Environment and Resource Studies, Mahidol University. The authors gratefully acknowledge the contribution to Department of Marine and Coastal Resources, Ministry of Natural Resources and Environment, Thailand for access to research sites and data support. 409

5 References Abby, L. and Luzhen, C Soil carbon stocks and accumulation in young mangrove forests. Soil Biology & Biochemistry, 75, Blake, G.R. and K.H. Hartge Bulk Density. In: A. Klute, editor. Methods of Soil Analysis. Part 1-Physical and Mineralogical Methods Second Edition. Madison WI: American Society of Agronomy; 1986 plant-nutrient-instructions.html. Bray II, R.H. and Kurtz, L.T Determination of total organic and available forms of phosphorus in soils. Soil Sci., 59, Department of Marine and Coastal Resources Manual for calculate loses of mangrove forest deforestation, Bangkok. Department of Marine and Coastal Resources Province mangrove forest [Online]. Available at: [Accesses 15 January 2016]. Department of Marine and Coastal Resources Central database system and data standard for marine and coastal resources [Online]. Available at: [Accessed on 13 October 2018]. IPCC IPCC Guidelines for NATIONAL Greenhouse Gas Inventories Volume 1 5. IPCC Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri RK and Meyer LA (eds)]. IPCC, Geneva, Switzerland, 151. Sanit Aksornkaew Population and Coastal Resources. [Online]. Available at: [Accessed on 13 October 2018]. Schaeffer-Novelli, Y., Cintron-Molero, G., Soares, M.L.G. and De-Rosa, T Brazilian mangroves. Aquat Ecosys Health and Manag, 3, Siikamaki, J., Sanchirico, J.N. and Jardine, S.L Global economic potential for reducing carbon dioxide emissions from mangrove loss. P Natl Acad Sci USA, 109(36), DOI: doi/ /pnas USDA, Soil Survey Laboratory Method Manual. Soil Survey Investigations Report No.42 Version p. Walkley, A. and Black, I.A Chromic acid titration method for determination of soil organic matter, Soil Sci. Amer. Proc.,