Soil Organic Carbon Content in Different Wetlands of Chi River Basin

Abstract

Wetlands are considered as the most productive ecosystem on earth. However, the capacity to store soil carbon has a high degree of variability from place to place, and it depends on many factors. Wetland ecosystems have been studied in many regions, but little is known about the storage of soil organic carbon especially freshwater wetlands in Thailand. Thus, the aims of this study were; (1) to quantify soil organic carbon in wetlands of the Chi River Basin and (2) to study factors influencing the accumulation of organic carbon in wetlands soils.

Nine freshwater wetlands were selected as representatives of wetlands in the Chi River Basin. Three of hydrologic zones was set up in order to collect soil samples in each wetland: (1) intermittently flooded zone, (2) saturated zone, and (3) permanently flooded zone. Five sampling stations were randomly set up on each of hydrologic zone. Soil samples were collected at a depth of 0 – 50 cm and were divided into 5 cm increments to observe changes of soil organic carbon concentration in soil profiles. Core method was also used for collecting soil sample in order to determine soil bulk density. Coverage of vegetation was also investigated to assess dominated vegetation. The soil samples were dried at the room temperature and analyzed for soil organic carbon and soil parameters (soil pH and soil texture). Two-ways ANOVA was used for testing the effect of both hydrologic schemes and soil depths on the accumulation of soil organic carbon. One-way ANOVA was used to determine differences of soil organic carbon pools among soil depth, among hydrologic schemes, and among wetland sites.

The results revealed that wetlands in this study were dominated by herbaceous vegetation. Thus, these wetlands can be identified into freshwater marsh with mineral soils. Soil organic carbon concentration decreased with depth in soil profiles from all wetland sites, suggesting that wetland soils had sustained accumulation of soil organic carbon. Also, soil organic carbon was significantly higher in the upper soil depth. The soil organic carbon concentration (0 – 50 cm) differed significantly among hydrologic zones. Both intermittently flooded zone and saturated zone had higher soil organic carbon concentration while the permanently flooded zone was generally low in all wetlands. At a depth of 0 – 50 cm, Nonghan Kumphawapi had the highest soil organic concentration (36.69 g C kg−1). Nong Waeng Non-hunting Area had the lowest one (4.92 g C kg−1). The average of total soil organic carbon pool of all wetlands was 230±34.84 Mg C ha−1, ranging from 123 to 429 Mg C ha−1. Nonghan Kumphapi had the largest carbon pool while Bueng Kluea had the lowest one. Among hydrologic schemes of wetlands, the soil organic carbon pools were 77.38±11.63 Mg C ha−1 (38 – 142 Mg C ha−1) in the intermittently flooded zone, 85.14±13.53 Mg C ha−1 (38 – 152 Mg C ha−1) in the saturated zone, and 68.33±18.32 Mg C ha−1 (31 – 213 Mg C ha−1) in the permanently flooded zone. More than 50% of soil organic carbon pools of each wetland were generally stored in the upper 25 cm of the soil profiles.

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