Benthic Macroinvertebrates as a Biological Index of Water Quality in the Lower Thachin River

Guntharee Sripongpun


Thachin River is an important river in the central area of
Thailand. Pollution sources along the river cause its water quality
becomes worse, especially in the lower section. This study
collected water samples and benthic faunas for 1 year from June
1999 to May 2000 at 4 stations along the lower Thachin River.
Physical and chemical water quality parameters were analyzed every
month and the matrices, i.e. total species abundance, taxa richness,
percent dominant taxon, Shannon Weaver diversity index (H),
modified Hilsenhoff species - level biotic index (HBI), family biotic
index (FBI), biological monitoring working party (BMWP), and
average score per taxon (ASPT), were calculated. Generally,
water in the lower Thachin River during the study period was in
poor quality. Most of the values of DO, BOD and ammonia content
were higher than these values of surface water quality standard class
4. Benthic macroinvertebrate samples found in this area belonged
to 6 phyla (Annelida, Arthropoda, Mollusca, Nematoda,
Platyhelminthes, and Sipuncula), 11 classes, 29 orders, 50 families,
66 genera, 79 species and 4 unidentified species. The most
abundant species was oligochaete Ophidonais sp. According to
matrices’ results, water condition in the lower Thachin River was
impaired status every month during study period and at every
sampling station. H values of benthic faunas, as well as pH, DO,
and temperature values of water samples at the same stations or
nearby stations in this study were significantly different from those
of Sittilert’s study (1985). Benthic macroinvertebrates can be used
as a biological index of water quality in the lower Thachin River. Some relationships between matrices and water quality parameters
are significant, such as relationships between FBI values and these
water quality parameters (pH, salinity, COD content, and suspended
solid content). However, tolerant values of some benthic faunas are
not available as well as variability in natural habitat can affect taxa
richness. Nevertheless, these relationships can be improved by
taking sample at more stations and continual study for longer period
in order to obtain more informations about the related natural
variation in the study area. Furthermore, biomass measurement of
benthic macroinvertebrates and important parameters for their
distribution and abundance (such as the content of organic matter
and hydrogen sulfide in sediment) should be also analyzed in order
to get better results.

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