Biological monitoring of rivers in Thailand: use and adaptation of the BMWP score

The performance of the BMWP biotic score, which is based on macroinvertebrates, in accurately classifying 23 sites on the River Ping system in northern Thailand, was assessed through comparison with physical and chemical data. Sites were located on the main River Ping, a highly polluted tributary (Kha Canal), a relatively unpolluted tributary (River Taeng) and an upland stream tributary system (River Klang). Data were collected between December 1990 and September 1993. The purpose of the research was to determine whether the BMWP score, originally developed in the U. K., could be employed successfully in Thailand and potentially also in other subtropical and tropical developing countries. Biological monitoring techniques such as the BMWP score are low-tech, rapid means of assessing water quality, and involve significantly lower financial costs than chemical monitoring techniques. The BMWP score was capable of distinguishing between sites that were heavily impacted by organic pollution and relatively unpolluted sites, and showed some potential to identify lower levels of pollution. The overall performance was considered to be similar to that recorded in the U. K. It was noted during the study that several of the taxa used in the BMWP score were absent in Thailand and that other taxa were present that would potentially be useful indicators. The BMWP score was therefore modified by removing 15 taxa not present in Thailand and adding 11 replacement taxa. Also, in the modified score, 6 sets of families were combined due to taxonomic difficulties and 7 odonatan families were allocated lower scores. The modified procedure, named the BMWPTHAI score, did not significantly alter the way in which sites were classified, but was easier to use. There is strong potential for application of the BMWPTHAI score in Thailand and other developing countries, although some further testing is first recommended.