ISSN 1905-7873 Â© 2012 - Maejo International Journal of Science ...

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28Maejo Maejo Int. J. Int. Sci. J. Technol. Sci. Technol. 2012, 2012, 6(01), 6(01), 28-46 28-46 Full Paper Maejo International Journal of Science and Technology ISSN 1905-7873 Available online at www.mijst.mju.ac.th Benthic diatoms of Mekong River and its tributaries in northern and north-eastern Thailand and their application to water quality monitoring Sutthawan Suphan 1,* , Yuwadee Peerapornpisal 1 and Graham J. C. Underwood 2 1 Department of Biology, Faculty of Science, Chiang Mai University, 50200, Thailand 2 Department of Biological Sciences, University of Essex, Colchester, Essex, United Kingdom CO4 3SQ * Corresponding author, e-mail: suttawan@hotmail.com Received: 7 February 2011 / Accepted: 6 May 2011 / Published: 26 January 2012 Abstract: Biomonitoring of benthic diatoms was performed to assess the water quality of Mekong River and its tributaries in northern and north-eastern Thailand. Fourteen sampling sites along the river and its tributaries were investigated. Two hundred and fifty-two species in 53 genera of diatoms were recorded. Each sampling site had distinct water chemistry and other physical variables. Cluster analysis identified 11 groups at 80% similarity. The relationship between diatom community composition and water quality variables was determined by statistical techniques. A number of diatom species were found to be useful as indicators of some physico-chemical properties of water. Keywords: benthic diatoms, water quality, biomonitoring, Mekong River _______________________________________________________________________________________ INTRODUCTION One of the most important natural resources for human life is water resource. Human use including household, industrial, agricultural and recreational activities affects water quality. There is an urgent need to develop a more sustainable practice for the management and efficient use of water resources as well as the need to protect the ecosystems where these resources are located. Therefore, it is important to monitor the quality of our limited water supplies. Presently, there are several methods to monitor water quality. One of the methods that is successfully used for monitoring aquatic environments around the world is biological assessment of water quality. It is considered an essential part in the assessment of the ecological quality of running waters apart from
Maejo Int. J. Sci. Technol. 2012, 6(01), 28-46 29 the data obtained from other sources such as hydrology, eco-morphology, physico-chemical water analysis and eco-toxicological analysis [1]. In rivers and streams, benthic diatoms, the most common and diverse primary producers [2], are regarded as bioindicators due to their sensitivity and strong response to many physical, chemical and biological changes [3]. Diatoms are successfully used for monitoring aquatic environments around the world, especially in Europe, USA and Japan [4-5]. In Thailand, Mekong River flows through Chiang Rai province in the north. As it continues along its path in Laos, it once again flows back into Loei, Nong Khai, Nakhon Panom, Mukdaharn, Amnaj Charoen and Ubon Ratchadhani provinces in the north-east of Thailand. There are many smaller rivers which are tributaries that may affect the Mekong River. Thus, the water quality in the Mekong River and its tributaries should be monitored continuously. There have been few studies of diatoms in the Mekong River in the past [6-8]. In this study, the diversity and distribution of benthic diatoms in the Mekong River and its tributaries in northern and north-eastern Thailand was investigated. In addition the relationship between diatoms species and some water physico-chemical properties was studied. The basic ecological data that could be applied to develop sustainable water resources were also obtained. Furthermore, the study should provide more information on diatoms in the South-east Asian region where very few reports on benthic diatoms were documented. MATERIALS AND METHODS Study Area Fourteen sampling sites along the Mekong River and its tributaries in northern and northeastern Thailand were selected based on the distance and environmental impact. Nine sites were located along Mekong River and five sites along its tributaries. The detail of each sampling site is shown in Figure 1. Diatom samples and physico-chemical water quality were determined 3 times per year in each season during July 2005 – April 2007. Benthic Diatom Collection and Identification Ten replicates of benthic diatoms were collected at each sampling site. Diatoms were taken from stone surfaces using a toothbrush and a 10-cm 2 plastic sheet. The samples were put in plastic boxes and fixed with Lugol’s solution on site. Diatom samples were then taken to the laboratory and cleaned by concentrated acid digestion method [9]. Briefly, each sample was centrifuged at 3,500 rpm for 15 minutes. The diatom cells were placed in an 18-cm core tube, added with concentrated nitric acid, heated in a boiler (70-80 o C) for 30-45 minutes, and rinsed 4-5 times with deionised water. Each cleaned diatom sample was mounted on a microscope slide with Naphrax ® , a mountant with a high refractive index [9-10]. Up to 300 diatom valves were counted and identified with an Olympus CH30 microscope at ×1000 magnification. Taxonomy and nomenclature was determined according to the relevant references [8, 11-17].
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