فهرست مطالب p. wichittrakarn

Landslide disasters in Thailand between 1970 and 2011 revealed a notable pattern: they primarily originated on mountain slopes, distinguished by a deeper soil profile. This soil profile comprised clay loam and sandy loam textures and was situated over aged geological formations of granite and shale rocks. The affected areas included the southern and northern provinces of Thailand.This study investigated the consequences of landslide hazards on stream water and sediment quality in two watersheds: the Mae Phul–Mae Prong watershed in Uttaradit province, the northern part of Thailand, and the Klong Kram watershed in Surat Thani province, the southern part of Thailand. These watersheds had experienced recurrent landslides, primarily on mountain slopes characterized by deep clayey and sandy loam soils over old granite and shale rock types as well as old granite limestone. During wet and dry periods in April and November 2015, 108 samples were collected from 18 stations (9 stations in the Klong Kram watershed and 9 stations in the Mae Phul–Mae Prong watershed). These samples included upland soil, stream water, and sediments. For upland soils, 1 kilogram samples were collected through auger and V-shaped pit techniques using a stainless-steel spade, with composite sampling conducted at 0–30 centimeters across all 18 stations. Stream water was collected in one part using a 1-L polyethylene bottle at 30 centimeter from the stream layer, while other samples were compositely collected in sterilized glass bottles to determine coliforms. Soil and sediment samples were compositely collected from the bottom using a stainless-steel spade. All samples were stored at 4 degrees Celsius and transported to a laboratory for analysis. The insight gained from these collection efforts elucidated the dynamics of landslide impacts at the spatial scale for the two watersheds. Most water samples met Thai surface water quality standard for various parameters; however, microbial contamination of the water samples attributed to community activities along stream banks was detected. Notably, arsenic was consistently detected in upland soil, stream water, and sediment samples. For Uttaradit, the average arsenic concentrations were 0.22 ± 0.09 milligram per kilogram, 0.01 ± 0.14 milligram per liter, and 9.74 ± 4.42 milligram per kilogram in upland soil, water, and sediment samples, respectively. For Surat Thani, arsenic concentrations were 87.63 ± 208.83 milligram per kilogram, 0.01 ± 0.01 milligram per liter, and 19.44 ± 36.38 milligram per kilogram in upland soil, water, and sediment samples, respectively, particularly near landslide scars where the arsenic concentrations were significantly higher in sediments and upland soils compared with stream water, highlighting the role of landslides near streams. These data suggest that sediment transport from upland soil in the landslide scar into stream water affects water quality, particularly in terms of arsenic concentration near the landslide scar, often surpassing natural standards. The study concluded that stream water was directly affected by landslides as these watersheds were unsuitable for consumption due to arsenic and microbial contaminations. This conclusion emphasizes the critical need to incorporate landslide hazard considerations into watershed management practices to safeguard downstream communities and preserve water resources.

The bacterial community plays a crucial role in the nitrogen cycle. Oxidation ponds act as a natural treatment system for wastewater and are designed to promote the growth and activity of certain bacterial species that remove contaminants from the water. The nitrogen cycle in these ponds involves the conversion of nitrogen compounds through biological processes by bacteria. The presence or absence of certain bacterial species can greatly influence the efficiency of the nitrogen cycle in these ponds. This research investigates the relationship between bacteria and nitrogen dynamics, the key components of wastewater treatment, in oxidation ponds. This work aims to identify the bacterial community composition in oxidation ponds, investigate the role of bacteria in the transformation and removal of nitrogen compounds from wastewater in oxidation ponds, and evaluate the impact of environmental factors on the microbial communities and nitrogen dynamics in oxidation ponds. This study was carried out in the oxidation wastewater treatment at the King’s Royally Initiated Laem Phak Bia Environmental Research and Development or LERD Project, in Phetchaburi, Thailand. Wastewater samples were collected from the 1st–5th oxidation ponds at a depth of 30 centimeter from the water surface and analyzed for various quality parameters including temperature, dissolved oxygen, potential of hydrogen, biochemical oxygen demand, nitrates, ammonia, and total kjeldahl nitrogen. Next-generation sequencing by Illumina Miseq was used to examine the 16S ribosomal ribonucleic acid of bacteria in the collected samples. Correlation test was used for statistical analysis. The temperature, potential of hydrogen (1st to 5th ponds), and dissolved oxygen (2nd to 5th ponds) in the oxidation ponds were within the standard value. Fifteen bacterial phyla were identified in the five oxidation ponds, with phylum Proteobacteria accounting for the highest population comprising 47.56% of the total bacterial population. Genera Novosphingobium (phylum Proteobacteria), Ammonia-11 (phylum Verrucomicrobiota), and Vicinamibacteraceae (phylum Acidobacteriota) have the strongest relationships with ammonia, nitrate, and total kjeldahl nitrogen (R2 = 0.9710, 0.986, 0.8124). The bacterial population is a crucial factor in nitrogen nutrient and water quality. Novosphingobium is involved in the removal of ammoniafrom wastewater, Verrucomicrobiota act as denitrifiers, and Vicinamibacteraceae increases the total kjeldahl nitrogen levels.