Mekong River Commission

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Fisheries Research and Development in the Mekong Region
Volume 14, No.3, December 2008

Assessing water quality

A new technical paper assesses the water quality of the Mekong, its tributaries and the Delta.

Water quality is one of the key factors affecting the environmental health of the Mekong River system. In 1985, the Interim Mekong Committee established the Water Quality Monitoring Network (WQMN) to provide an ongoing record of the water quality of the river, its major tributaries and the Mekong Delta. Ninety stations were sampled during 2005. Of these, 55 are designated 'primary stations' as they have basin wide, or transboundary, significance. The remaining 35 are designated 'secondary stations'. Twenty-three of the primary stations are located on the mainstream, (17 on the Mekong, and 6 on the Bassac), 23 on tributaries, and 9 on the delta.

MRC Technical Paper No. 19, An assessment of water quality in the Lower Mekong Basin, documents data recorded from 1985 to 2005 or, in some cases, the sub-set of data recorded from 2000 to 2005. Three main categories of water-quality indexes (WQI) are used for the protection of aquatic life, human impact and agricultural use. Each category is subdivided into classes according to the number of chemical parameters (DO, pH, etc.) that meet guideline thresholds. The classes are high, good, moderate and poor quality for aquatic life; not impacted, slightly impacted, impacted and severely impacted for human impact; and no restrictions, some restrictions, and severe restrictions for agricultural use. In the mainstream and tributaries, the WQI for aquatic life is mostly high quality. However, in the delta only one station is classed as high quality and two others are good quality. Of the remainder, four are moderate quality and one is poor quality. Signs of significant human impact on water quality are observed at stations in the uppermost part of the LMB and downstream of Phnom Penh. The lower index values at the downstream stations reflect higher population densities, particularly in the highly-populated and intensively-farmed delta. At all but one of delta stations, the index for human impact is classed as severely impacted. In the mainstream and tributaries, the index for agricultural use is consistently at the level of no restrictions. However, at some stations on the Cau Mau peninsula of the delta, the index for agricultural use is classed as severe restrictions.

The paper evaluates three major sources of pollution: urban areas, industrial wastewater and agriculture. While there is no strong evidence for transboundary pollution within the basin, it finds there is some evidence for transboundary transmission of pollutants from the Upper Mekong Basin into the LMB. The paper also finds no sign of any significant basin-wide trends for any parameter. With the continuing development of both agriculture (increased use of fertilisers) and urbanisation, there is reason to expect changes in water quality in some tributaries. It is possible that reforestation of areas in the Khorat Plateau will lead to water-quality improvement. The paper identifies salinity, acidification and eutrophication as the three principal water quality issues in the lower basin.

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Text based on excerpts from the summary



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