Ly Hong Chuyen creator Shipin, Oleg V. Chairperson Annachhatre, Ajit P. Examination Committee Ebbers, Theo Examination committee Hul, Seingheng Examination committee International Fellowships Program Scholarship donor Ford Foundation, USA Scholarship donor Asian Institute of Technology Fellowship Scholarship donor text th Pathumthani Asian Institute of Technology 2013 monographic eng 75 leaves : ill. + 1 online resource The goal of this study is investigate the causes of filamentous algae bloom phenomenon which has occurred in the Mekong River in the Stung Treng Ramsar site Northern part of Cambodia for more than a decade during dry season. The study was conducted from September 2012 to April 2013. First of all, five filamentous algae species were identified by field survey and microscopic examination namely Cladophora sp, Rhizoclonium sp, Oedogonium sp, Spirogyra sp, and Microspora sp. The dominant species of filamentous algae are Cladophora sp (or Rhizoclonium sp), followed by Oedogonium sp, and the lowest rate of filamentous algae observed are Microspora sp and Spirogyra sp. Then, water quality in Mekong River which passes from Luang Prabang (laos) to Kratie (Cambodia) were detected with the purpose of finding out the explanations for filamentous algae boom phenomenon. The water parameters which were analyzed in this study are the concentrations of total phosphorus, total nitrogen, magnesium, and silicon. The results of data analyses pointed out the concentrations of total nitrogen and total phosphorus were always higher in rainy season due to cultivation during this period of time. As a result, the absence of agriculture activities in dry season could not be the main reason of algae blooms. Unlike total phosphorus and total nitrogen, the concentrations of magnesium and silicon in dry season were more elevated than rainy season because of construction activities (including dam construction, bank erosion, house construction, etc) in the period of dry season. However, the concentrations of magnesium and silicon were stable from 1995 to 2011. Moreover, by calculation the trophic status in study area, it was recognized that Stung Treng Ramsar site was mesotrophic that means the nutrient were moderate enrichment. Because of these reasons, the pollution from human does not play a role in the occurrence of filamentous algae in the Stung Treng Ramsar site. The abundant of filamentous algae were detected by some researches in some upstream tributaries of Mekong River such as Chiang Khong, Nan River (Thailand), Nam Tha, Luang Prabang, Vientiane (Laos). These kinds of algae are used as a main ingredient of food for human. The growth of filamentous algae was also observed in Northern Lake of Kratie where is around 200 km downstream from Stung Treng Ramsar site. The recognition of filamentous algae in different locations as well as the livelihood activities by fishing of residents among Mekong River is the factors to spread filamentous algae on the Mekong River. In conclusion, the role of non-point pollution in sustaining the blooms should not be underestimated. It is quite probable that the algae and their seasonal blooms are unlikely to disappear and are more likely to exacerbate ecological situation in the area. Therefore, finding the suitable measures to control and management the filamentous algae proliferation is needful. A thesis submitted in partial fulfillment of requirements for the degree of Master of Science in Environmental Engineering and Management Thesis (M.Sc.) - Asian Institute of Technology, 2013 Algal blooms Cambodia Algae Cambodia Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B02546 http://203.159.5.9/ait-thesis/detail.php?q=B02546 140612 20260818172404.0