Report on the 2015 biomonitoring survey of the lower mekong river and selected tributaries

This report describes the biomonitoring survey conducted in 2015 in the Lower Mekong Basin, which contributes to the evaluation of the overall ecological health of the river. The objectives of the report are to: (i) describe the biological indicator groups sampled during 2015; (ii) use this information to derive biological indicators for the sites examined in 2015; and (iii) use biometric indicators to evaluate these sites.

A total of 41 sites – the same 41 sites assessed for the EHM 2011-13 surveys – were assessed, ranging from rocky rapids, sandy-alluvial areas of tributaries and the mainstream, Tonle Sap Lake and adjacent rivers, including estuaries of the delta areas. The 2015 EHM was conducted based mainly on an agreed and standardized methodology. Three biological metrics of the aquatic ecological health were calculated for each of four groups of organisms, including benthic diatoms, zooplankton, littoral macroinvertebrates and benthic macroinvertebrates. The biological metrics were: average abundance, average richness, and Average Tolerance Score per Taxon (ATSPT). Signs of a healthy ecosystem can be defined through high abundance, high average richness, and low ATSPT (signifying scarcity of pollutionsensitive species) of species. 

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