38 Figure 9 Soil pH in three hydrological zones in Bueng Lahan, (A) the intermittently flooded zone, (B) the saturated zone and (C) the permanently flooded zone. 79 Figure 18 The distribution of soil organic carbon (SOC, Mean±S.E.) over a depth of 0 − 50 cm in the soil profile of three hydrological zones of Bueng Lahan; A = the periodically flooded zone, B = the saturated zone and C = the permanently flooded zone. 83 Figure 22 The distribution of soil organic carbon (SOC, Mean±S.E.) over a depth of 0 − 50 cm in the soil profile of three hydrological zones of Nong Han Kumphawapi; A.
84 Figure 23 Distribution of soil organic carbon (SOC, Mean±S.E.) along 0−50 cm in the soil profile of the three hydrological zones of Huai Suea Ten; A =. 86 Figure 25 Distribution of soil organic carbon (SOC, Mean±S.E.) at 0 − 50 cm depth in the soil profile of the three hydrological zones of Bueng Kluea; A = intermittently flooded area, B = saturated area and C = permanently flooded area.
INTRODUCTION
- Backgrounds
- Objectives of the study
- Scope of the study
- Expected results and application
- Hypothesis of the study
- Conceptual framework of the study
Remains of organic materials are accumulated under an anaerobic condition as organic matter, which is combined with mineral fractions to form soil organic carbon (Mitsch and Gosselink 2015). In Thailand, the function of wetlands as sinks of soil organic carbon is less understood and rarely studied. To highlight the function and services of wetland in the Chi River Basin as a national carbon sink, the study of soil organic carbon on wetland soils is urgently needed.
To study the relationship between soil organic carbon and the factors influencing the accumulation of organic carbon in wetland soils. The research was mainly focused on the accumulation of organic carbon in wetland soils at a depth of 0 – 50 centimeters.
REVIEW LITERATURES
Definitions of wetlands
Characteristics of wetlands
Global carbon reservoirs
Roles of wetlands in the global carbon cycle
Wetland ecosystems in Thailand
As a result, soil carbon stocks have been estimated in many ecosystems in Thailand, especially in protected areas. In the northern region, the complex mountainous topography creates many important rivers (Ping, Wang, Yom and Nan). There are 10 important wetland areas in the Chi River Basin – 3 areas of international importance and 7 areas of national importance (Table 10).
For example, 80% of the income in the community around Sop Mun-Chi comes from the wetland. In addition, many important wetlands in the Chi River basin are important for fish production and inland fisheries of local people.
METHODOLOGY
- Study sites
- Sample collection
- Soil sampling and soil preparation
- Analysis of soil samples
- Calculation of soil organic carbon
- Statistical analysis
However, soil samples were also passed through a 0.5 mm sieve for soil organic carbon analysis. Soil organic carbon concentration (g C kg−1) of each soil depth interval was calculated from equation 1 (Bernal and Mitsch 2008). Soil carbon stock (C-stock) was calculated by multiplying soil carbon concentration (SOC) by soil density (B.D.) and soil depth interval (depth) as shown in equation 2 (Batjes 2014). g C kg‒1) = Concentration of soil organic carbon in each of the soil layers.
Two-way analysis of variance (ANOVA) was used to determine differences in soil organic carbon concentration, with soil depth and three hydrologic conditions as the main fixed factors. Independent sample t-test was used to find the difference between soil organic carbon stocks between the upper soil (0 – 25 cm) and the lower soil (25 – 50 cm).
RESULTS AND DISCUSSIONS
Results
- Soil textures and particle size distributions
- Soil bulk densities
- Vegetation coverages
- Soil reaction (soil pH)
- Profiles of soil organic carbon
- Soil organic carbon in different wetlands
- Soil organic carbon pools
However, the total number of species in the periodically flooded zone was higher than that in the saturated zone (Table 8). The soil pH of the intermittently flooded zone ranged from 6.5 to 7.9 (slightly acidic – moderately acidic). Similarly, soil pH in the permanently flooded zone ranged from 6.4 to 7.9 (slightly acidic and moderately alkaline).
The soil pH varied from 5.0 to 6.7 (very strongly acid - neutral) in the intermittently flooded zone. In the intermittent flooding zone, the soil pH varied from 4.5 to 5.2 (very strongly acid - strongly acid). The soil pH in the intermittently flooded zone varied from 4.6 to 4.8, and the pH in the saturated zone varied between 4.5 and 4.8.
In the intermittently flooded zone, soil pH varied between soil depths, ranging from 4.6 to 4.9 (very strongly acid). The soil organic carbon concentration did not differ significantly between the saturated zone and permanently flooded zone and g C kg−1 respectively). However, the occasionally flooded zone had a marked decrease with depth in soil organic carbon concentration.
At Nonghan Kumphawapa, the concentration of soil organic carbon in the intermittently flooded zone and the permanently flooded zone decreased with soil depth, while the saturated zone fluctuated throughout the soil profile (Figure 22). However, soil organic carbon concentration was not significantly different between the saturated site and the permanently flooded site. The profile obtained from the intermittently flooded area and the saturated area had more soil organic carbon than the profile of the permanently flooded area.
The periodically flooded zone showed higher SOC concentrations in many wetlands (Bueng Lahan, Nong Waeng Non-Hunting Area, Huai Suea Ten, Nonghan Kumphawapi, Nong Pla Khun,). However, the storage soil organic carbon in the permanently flooded zone was also found in Nonghan Kumphawapi.
Discussions
- Characteristics of studied wetlands
- Distribution of soil organic carbon in freshwater wetlands
- Comparison of soil organic carbon
In this study, the accumulation of soil organic matter had the same trend in the soil profile of all wetlands. For another reason, it is probably undecomposed organic matter and plant remains that lead to a high content of soil organic carbon at these depths. This may have suggested that very little soil organic carbon is stored in the soils (Bernal and Mitsch 2008).
In the studied wetland, soil organic carbon was either high in the intermittently flooded or saturated zone. The productivity of the plants is generally associated with soil organic carbon in freshwater wetlands (Brinson et al. 1981). They suggested that more carbon accumulation in the open water was a result of the effect of permanent anaerobic condition providing a slow decomposition of soil organic carbon in this area.
Thus, based on field observations, it can be concluded that lower soil organic carbon in submerged areas may be the result of lower plant productivity (Bauer and Black 1994). As a result, sediments are trapped in this area and provide a greater accumulation of organic carbon in the soil. A study of soil texture showed that marshes, where soil organic carbon was high, tended to accumulate fine sediments such as clay and silt.
The soils in these wetlands always have a dark color (Supp.. Table 9), indicating that they contained a lot of soil organic matter in the soil profiles. When wetlands were compared with other ecosystems in Thailand in this study, the wetlands stored higher soil organic carbon than forest ecosystems. Soil organic carbon storage in studied wetlands was greater than that of agricultural land uses.
CONCLUSIONS
Conclusions
Therefore, the amount of soil organic carbon in wetlands depended on the hydrological zone of the wetland. Freshwater wetlands in the Chi River basin had different sizes of soil organic carbon (SOC) pools. Nonghan Kumphawapi had the largest set of SOC, while Bueng Kluea had the smallest set of SOC.
Both internationally important wetlands (Nonghan Kumphawapi and Bueng Lahan) showed high carbon storage capacity. However, many of the nationally important wetlands also had a larger SOC pool such as Nong Sam Muen, Huai Suea Ten and Sop Mun-Chi. When the SOC pools of these wetlands were compared with other ecosystems in Thailand, especially forest ecosystems, these wetlands showed greater carbon storage than some forest ecosystems and agricultural land uses.
Furthermore, the carbon storage capacity of these wetlands was shown to be as great as the storage of freshwater wetlands in other regions. This suggested that these wetlands provided the regulation service as a carbon sink in the Chi River Basin. Therefore, the Chi River Basin wetland should be highlighted as an important carbon sink at a broader scale, such as watershed scale, national scale, or regional scale.
The implication of the study
Therefore, these important wetlands should be singled out as one of the nation's important ecosystems, which can offset greenhouse gases from the atmosphere. The difference of the hydrological zone in the wetland zone resulted in the different accumulation of soil carbon content, which was high in both the intermittently flooded zone and the saturated zone. More than half of the carbon pools are stored in the upper soil depth, suggesting that if the soil structure of these areas is disturbed by agricultural activities, soil organic carbon will be easily oxidized and emitted into atmosphere.
Moreover, the top 25 cm is the general depth for plowing in agricultural activities, which was extensive in most areas of wetlands in the Chi River Basin. Adame MF, Kauffman JB, Medina I, Gamboa JN, Torres O, Caamal JP, Reza M, Herrera-Silveira JA (2013) Carbon stocks of tropical coastal wetlands within the karst landscape of the Mexican Caribbean. Bauer A, Black AL (1994) Quantifying the effect of soil organic matter content on soil productivity.
Cowardin L, Carter V, Golet F, LaRoe E (1979) Classification of wetlands and deep-water habitats of the United States, 2nd edn. Howe AJ, Rodríguez JF, Saco PM (2009) Surface development and carbon sequestration in disturbed and undisturbed wetlands in the Hunter Estuary, southeastern Australia. IPCC (2013) Climate change 2013: the physical science basis: Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.
Jobbágy EG, Jackson RB (2000) The vertical distribution of soil organic carbon and its relationship to climate and vegetation. Mcleod E, Chmura GL, Bouillon S, Salm R, Björk M, Duarte CM, Lovelock CE, Schlesinger WH, Silliman BR (2011) A blueprint for blue carbon: towards a better understanding of the role of vegetated coastal habitats in it. Ricker MC, Lockaby BG (2015) Soil organic carbon stocks in a large eutrophic floodplain forest of the southeastern Atlantic Coastal Plain, USA.
Villa JA, Mitsch WJ (2015) Carbon sequestration in diverse wetland plant communities in the Big Cypress Swamp region of southwest Florida. Walalite T, Dekker SC, Schot PP, Wassen MJ (2018) Unraveling the ecological functioning of the Songkhram Monsoon River floodplain in Thailand by integrating soil, water and vegetation data.
