4.1 Spatial Distributions and Seasonal Variations of Chromium
4.1.1 The inner Gulf of Thailand
The spatial heterogeneity distributions of Cr in the surface sediment were indicated entire the inner Gulf of Thailand (Figure 4.1a−c). In the southwest monsoon season (July 2017), the lowest Cr concentration was 11.72 mg/kg (GT26), where occurred at middle part of the inner Gulf of Thailand, while the
highest value of 80.16 mg/kg (CP13) was occurred at the mouth of the Chao Phraya River (Figure 4.1a). According to the distribution pattern, the relative high Cr concentrations were observed in the Chao Phraya, the Bangpakong and the Tha Chin River estuaries, subsequently decreasing concentrations were occurred from the river mouths to the lower part of the Gulf (Figure 4.1a). The average Cr in the surface sediment was 36.04±16.72 mg/kg, which was higher than the western part upper Gulf of Thailand [48], Phetchaburi province, Thailand [49]
but lower than those previously determined in the upper Gulf of Thailand by [51].
In addition, Cr concentration was significantly lower than those found in the northern Kaohsiung Harbor, Taiwan [101], the Pearl River estuary, China [102], the upstream Yangtze River, China [103], the Jiaozhou Bay, China [54], Masam Bay, Korea [104], Yellow River, China [105], Daya bay and adjacent shelf [55], and San Simon Bay, Spain [106]. Furthermore, Cr concentrations were higher than those reported Laizhou Bay, Chinaprotected area, China [107], the Yangtze River, China [52], Nyanza Gulf of Lake Victoria, East Africa [108], Halong bay, Vietnam [50], Gulf of Pozzuoli, Italy [53], Admiralty Bay, Antarctica [109], and Tuzla Aydinli Bay, Istanbul [56]. As the result, the average Cr concentration in southwest monsoon season which was relatively low to moderate concentration when compared to another coastal surface sediments (Table 4.2). Sediment quality guidelines are commonly used for the assessment of sediment quality in Thailand, and have been widely applied in environmental studies [110].
Compared with these criteria (42 mg/kg), the average concentration of Cr in the inner Gulf of Thailand was low.
In the northeast monsoon season (December 2017), the lowest Cr concentration was 5.61 mg/kg (GT28), where occurred at middle part of the inner Gulf of Thailand, while the highest value of 107.45 mg/kg (CP1) was occurred in the inner of the Chao Phraya River (Figure 4.1b). According to the distribution pattern, the relative high Cr concentrations were observed in the Chao Phraya, the Bangpakong and the Tha Chin River estuaries, subsequently decreasing concentrations were occurred from the river mouths to the eastern and western lower part of the Gulf (Figure 4.1b). The average Cr in the surface sediment was 38.14±22.19 mg/kg, which was higher than the western part upper Gulf of
Thailand [48], Phetchaburi province, Thailand [49] but lower than those previously determined in the upper Gulf of Thailand by [51]. In addition, Cr concentration was significantly lower than those found in the northern Kaohsiung Harbor, Taiwan [101], the Pearl River estuary, China [102], the upstream Yangtze River, China [103], the Jiaozhou Bay, China [54], Masam Bay, Korea [104], Yellow River, China [105], Daya bay and adjacent shelf [55], and San Simon Bay, Spain [106]. Furthermore, Cr concentrations were higher than those reported Laizhou Bay, China protected area, China [107], the Yangtze River, China [52], Nyanza Gulf of Lake Victoria, East Africa [108], Halong bay, Vietnam [50], Gulf of Pozzuoli, Italy [53], Admiralty Bay, Antarctica [109], and Tuzla Aydinli Bay, Istanbul [56]. As the result, the average Cr concentration in southwest monsoon season which was relatively low to moderate concentration when compared to another coastal surface sediments (Table 4.2). Sediment quality guidelines are commonly used for the assessment of sediment quality in Thailand, and have been widely applied in environmental studies [110].
Compared with these criteria (42 mg/kg), the average concentration of Cr in the inner Gulf of Thailand was low.
In the dry season (May 2018), the spatial heterogeneity distribution of Cr concentrations in the surface sediment of the inner Gulf of Thailand was ranged from 8.63−119.47 mg/kg (Figure 4.1c). Surprisingly, both the lowest and highest Cr concentrations were occurred at TC13 and TC15, which located in the mouth of the Tha Chin River (Figure 4.1c). According to the distribution pattern, the relative high Cr concentrations were occurred at the Bangpakong, the Chao Phraya and Tha Chin River estuaries and trend to decrease to the lower part of the Gulf (Figure 4.1c). The average Cr concentration in the surface sediment was 37.67±19.29 mg/kg, which was higher than the western part upper Gulf of Thailand [48], Phetchaburi province, Thailand [49] but lower than those previously determined in the upper Gulf of Thailand by [51]. In addition, Cr concentration was significantly lower than those found in the northern Kaohsiung Harbor, Taiwan [101], the Pearl River estuary, China [102], the upstream Yangtze River, China [103], the Jiaozhou Bay, China [54], Masam Bay, Korea [104], Yellow River, China [105], Daya bay and adjacent shelf [55], and San
Simon Bay, Spain [106]. Furthermore, Cr concentrations were higher than those reported Laizhou Bay, China protected area, China [107], the Yangtze River, China [52], Nyanza Gulf of Lake Victoria, East Africa [108], Halong bay, Vietnam [50], Gulf of Pozzuoli, Italy [53], Admiralty Bay, Antarctica [109], and Tuzla Aydinli Bay, Istanbul [56]. As the result, the average Cr concentration in southwest monsoon season which was relatively low to moderate concentration when compared to another coastal surface sediments (Table 4.2). Sediment quality guidelines are commonly used for the assessment of sediment quality in Thailand, and have been widely applied in environmental studies [110].
Compared with these criteria (42 mg/kg), the average concentration of Cr in the inner Gulf of Thailand was low.
The mean concentrations of Cr in the surface sediment of the inner Gulf of Thailand in the southwest monsoon season (36.04 mg/kg) compared to the northeast monsoon season (38.14 mg/kg) and dry season (37.67 mg/kg) (Figure 4.2). The mean difference of Cr in the surface sediment between the seasonal variation did not vary significantly (p>0.05). The mean concentration of Cr in the surface sediments of the inner Gulf of Thailand changes similarly in three seasons. In other words, the average concentration of Cr in surface sediments in southwest monsoon and dry season is lower than that in northeast monsoon season. The amounts of Cr concentration in surface sediment varied seasonally as follows: northeast monsoon season > dry season > southwest monsoon season.
The reason for the change was that there was more rainfall in the southwest monsoon season, causing tides in the inner Gulf of Thailand. Due to increased flow turbulence, some of the sediment and Cr in the sediment are displaced and washed away from the riverbed. As northeast monsoon season and the dry season begin increased temperature and evaporation and the termination of the precipitation period led to an increase in the concentration of Cr in the water and ultimately precipitate as Cr transfer from water to the sediment [111]. Industrial activities are one of the major sources of heavy metal contamination of the environment, especially in developing countries. Floods also lead to the distribution of toxic into the environment, about the floods of Thailand in 2011
due to some industrial estates affected. Raising concerns about heavy metals from
industrial wastewater contamination [112].
(a) (b)(c) Figure 4.1 Spatial heterogeneity distributions of chromiumconcentration in thesurface sediment and seasonal variations southwest monsoon season (a), the northeast monsoon season (b), and the dry season (c) entire the inner Gulf of Thailand.
Figure 4.2 A comparison of the chromium concentration in surface sediments of the inner Gulf of Thailand between southwest monsoon season, northeast monsoon season and dry season. The box shows the 25th and the 75th percentiles, and the whiskers represent the smallest and the largest concentration. (alphabet indicated significant difference at p<0.05 using the DMRT analysis).
Table 4.2 Comparison of Cr concentration of surface sediments in the inner Gulf of Thailand with other regions.
Locations Cr (mg/kg) References
The upper Gulf of Thailand 138.9 [51]
Northern Kaohsiung Harbor, Taiwan 113.5 [101]
Pearl river estuary, China 106 [102]
The upstream Yangtze River, China 101.43 [103]
Jiaozhou Bay catchment, China 69.30 [54]
Masam Bay, Korea 67.1 [104]
Yellow River, China 62.4 [105]
Daya Bay and adjacent shelf 59.03 [55]
San Simon Bay, Spain 42.46 [106]
The inner Gulf of Thailand
southwest monsoon season 36.04±16.72
This study northeast monsoon season 38.14±22.19
dry season 37.67±19.29
Liazhou River protected area, China 35.06 [107]
Yangtze River estuary, China 34.64 [52]
Nyanza Gulf, of Lake Victoria (East Africa) 33.85 [108]
Ha Long Bay, Vietnam 27.00 [50]
Western past the upper Gulf of Thailand 23.84 [48]
Gulf of Pozzuoli (GoP), Italy 14.00 [53]
Phetchaburi province, Thailand 10.45 [49]
Admiralty Bay, Antarctica 8.10 [109]
Tuzla Aydinli Bay, Istanbul (Turkey) 1.66 [56]