(a) (b)(c) Figure 4.9Spatial heterogeneity distributions of total organic matter (TOM) in the surface sediment and seasonal variations southwest monsoon season (a), the northeast monsoon season (b), and the dry season (c) entire the inner Gulf of Thail
4.2.2 Total organic carbon
The TOC Concentrations in surface sediment in southwest monsoon season were ranged from 2.79-43.17 mg C/g (Figure 4.10a) while the highest concentration of TOC was in the middle part of the inner Gulf of Thailand at station GT35 and the lowest concentration of TOC was in the mouth of the Mae Klong River at station MK9. The average TOC in surface sediment was 17.42±7.23 mg C/g. The results demonstrated that spatial distribution decreased from upstream to downstream for TOC.
The TOC Concentrations in surface sediment in northeast monsoon season were ranged from 3.44-30.22 mg C/g (Figure 4.10b) while the highest concentration of TOC was in the eastern part of the inner Gulf of Thailand at station GT19 and the lowest concentration of TOC was in the middle part of the inner Gulf of Thailand at station GT28. The average TOC in surface sediment was 15.08±6.33 mg C/g. The results demonstrated that spatial distribution decreased from upstream to downstream for TOC.
The TOC Concentrations in surface sediment in dry season were ranged from 2.76-35.50 mg C/g (Figure 4.10c) while the highest concentration of TOC was in the middle part of the inner Gulf of Thailand at station GT6 and the lowest concentration of TOC was in the inner part of the Thachin River at station TC2.
The average TOC in surface sediment was 13.72±7.25 mg C/g. The results demonstrated that spatial distribution decreased from upstream to downstream for TOC.
Total organic carbon (TOC) includes all organic carbon compounds present in sediments. The amount of organic matter that can be stored in sediments is influenced by a number of factors, such as types and sources of organic compounds sediment surface grain particle size and precipitation [115].
(a) (b)(c) Figure 4.10Spatial heterogeneity distributions of total organic carbon (TOC) in the surface sediment and seasonal variations in the southwest monsoon season (a), the northeast monsoon season (b), and the dry season (c) entire the inner Gulf of Thailand.
4.2.3 Total phosphorus (TP)
The TP concentrations in surface sediment in southwest monsoon season were ranged from 0.19-1.89 g/kg (Figure 4.11a) while the highest concentration of TP was in the inner part of the Chao Phaya River at station CP1 and the lowest concentration of TP was in the mouth of the Mae Klong River at station MK9.
The average TP in surface sediment was 0.57±0.30 g/kg. The results demonstrated that spatial distribution decreased from upstream to downstream for TP.
The TP concentrations in surface sediment in northeast monsoon season were ranged from 0.09-1.08 g/kg (Figure 4.11b) while the highest concentration of TP was in the inner part of the Bangpakong River at station BK1 and the lowest concentration of TP was in the middle part of the inner Gulf of Thailand at station GT28. The average TP in surface sediment was 0.46±0.21 g/kg. The results demonstrated that spatial distribution decreased from upstream to downstream for TP.
The TP concentrations in surface sediment in dry season were ranged from 0.15-1.14 g/kg (Figure 4.11c) while the highest concentration of TP was in the inner part of the Thachin River at station TC2 and the lowest concentration of TP was in the mouth of the Mae Klong River at station MK4. The average TP in surface sediment was 0.48±0.22 g/kg. The results demonstrated that spatial distribution decreased from upstream to downstream for TP.
Total phosphorus sources include both point and non−point sources. Excess phosphorus into the river, which are eventually migrates to marine ecosystems usually from industrial emissions, construction site urban areas, wastewater and agricultural runoff [116].
Phosphorus is often the limiting nutrient for algal growth in lakes and may limit productivity [117]. phosphorus sources in lakes include phosphorus in runoff from rock conditions and soil transport and agricultural water and sewage directly in the lakes and tributaries. Phosphorus may enter the water system as particles, or dissolved P may be associated with particles as they fall from the
water column. The amount of P in sediment can serve as a good predictor of the eutrophication probability of a water source [118]
(a) (b)(c) Figure 4.11Spatial heterogeneity distributions of total phosphorus (TP) in the surface sediment and seasonal variations in the sout monsoon season (a), the northeast monsoon season (b), and the dry season (c) entire the inner Gulf of Thailand.
4.2.4 Acid volatile sulfide (AVS)
The AVS concentrations in surface sediment in southwest monsoon season were ranged from 0.00-1.86 mg/g.dw (Figure 4.12a) while the highest concentration of AVS was in the mouth of the Thachin River at station TC14.
The average AVS in surface sediment was 0.27±0.48 mg/g.dw. The results demonstrated that spatial distribution decreased from upstream to downstream for AVS.
The AVS concentrations in surface sediment in northeast monsoon season were ranged from 0.00-2.21 mg/g.dw (Figure 4.12b) while the highest concentration of AVS was in the mouth of the Thachin River at station TC14.
The average AVS in surface sediment was 0.31±0.48 mg/g.dw. The results demonstrated that spatial distribution decreased from upstream to downstream for AVS.
The AVS concentrations in surface sediment in dry season were ranged from 0.15-1.14 mg/g.dw (Figure 4.12c) while the highest concentration of AVS was in the mouth of the Thachin River at station TC14. The average AVS in surface sediment was 0.06±0.15 mg/g.dw. The results demonstrated that spatial distribution decreased from upstream to downstream for AVS.
Distribution of AVS in sediments is very complex as a result of seasonal and spatial variations in the physical and chemical properties of pores water. The distribution of AVS concentration varies periodically and spatially, and the value of AVS increases with the depth of the sediment. At the surface sediment on the soil surface, its low values may be due to permeation of oxygen from surface water, which causes aerobic oxidation of sulfides and thus lower AVS levels [27].
(a) (b)(c) Figure 4.12Spatial heterogeneity distributions of acid volatile sulfide (AVS) in the surface sediment and seasonal variations southwest monsoon season (a), the northeast monsoon season (b), and the dry season (c) entire the inner Gulf of Thail
4.2.5 Water content
Percentages of water content in surface sediment in southwest monsoon season were ranged from 26.55-87.93% (Figure 4.13a) while the highest concentration of water content was in the inner of the Bangpakong River at station BK1 and the lowest concentration of water content was in the mouth the Mae Klong River at station MK3. The average water content in surface sediment was 53.22±16.89%. The results demonstrated that spatial distribution decreased from upstream to downstream for water content.
Percentages of water content in surface sediment in northeast monsoon season were ranged from 18.82-87.36% (Figure 4.13b) while the highest concentration of water content was in the mouth of the Tha Chin River at station TC8 and the lowest concentration of water content was in the eastern part of the inner Gulf of Thailand at station GT19. The average water content in surface sediment was 53.31±18.62%. The results demonstrated that spatial distribution decreased from upstream to downstream for water content.
Percentages of water content in surface sediment in dry season were ranged from 22.76-81.83% (Figure 4.13c) while the highest concentration of water content was in the eastern part of the inner Gulf of Thailand at station GT17 and the lowest concentration of water content was in the middle part of the inner Gulf of Thailand at station GT39. The average water content in surface sediment was 47.64±16.06%. The results demonstrated that spatial distribution decreased from upstream to downstream for water content.
Water content in sediment is the physical factor that indicates grain size and abundance of organic matter of sediment. Sediment that has low water content majorly consists of sand and has low organic matter [119].
(a) (b)(c) Figure 4.13Spatial heterogeneity distributions of water content (WC) in the surface sediment and seasonal variations in the southwe monsoon season(a), the northeast monsoon season (b), and the dry season(c) entirethe inner Gulf of Thail