Bio-monitoring: All you need is an eye

These biologists, who have specialised in the classification of organisms, can determine a river’s health with the unaided eye by simply studying the organisms present. There is little need, therefore, for bottling samples and rushing them to laboratories to place them in low-temperature incubators.

But if we talk about water quality, not all organisms are useful in determining that. Plankton gives an indication of quality at the topmost ecological layer of a water body only. Drawing inferences from fish is tricky since they keep moving. Therefore bio-monitoring programmes are conducted to track macro-invertebrates, organisms without a backbone, found in the lowest ecological zone in water. Such organisms are static and respond to changes in water quality. They are also visible to the unaided eye. Despite the inherent advantages of such techniques, a bio-monitoring protocol is not mandatory in India.

Better bio-monitoring

As per a July 25 study in Current Science, existing biotic indices do not take into account the abundance of the taxa. Researchers from University of Delhi detailed a novel methodology, called the macro-invertebrate water quality index (MWQI). The index draws inferences on river health from the fact that some species survive or even thrive in dirty waters while others are pollution intolerant. The authors argue MWQI is better than other invertebrate-based indices mostly based on the presence or absence of a particular taxon. The presence of a single individual of a taxon in a sample versus 100 individuals of the same taxon in another sample indicates different water quality. The only concern is when species have not been assigned a pollution sensitivity score. The index is indeed robust and influenced by the relative abundance of a species, said Akolkar. But it does not reflect the level of impairment in water quality for a particular use, such as drinking or bathing, she added.

Water as physical entity

The CPCB, a statutory body with the mandate to monitor water quality in India, was constituted under the Water Act, 1974. The agency has a penchant for incubators and lab coats; physicochemical indicators take precedence over bio-monitoring.

Following a five-year collaboration with Dutch and German scientists, CPCB created a databank in 1994 and classified species endemic to Indian rivers. Each of them was assigned a score indicating sensitivity to pollution. The situation is much the same at the Centre. Akolkar is the only official in CPCB’s biological laboratory who was part of the five-year protocol building exercise in the 1990s. Akolkar can even train someone in one hour to report on the quality of the Yamuna as it passes through Delhi.

Most rivers in the plains are no more than open sewers. Rivers of reasonably good quality or even recovering polluted rivers, biotic indices would be useful, he added. Biomonitoring sub-stratum collection may take one to two hours but can provide with an immediate impression of a waterbody. A grab sample for a physico-chemical parameter, for instance, is easy to collect. The biochemical oxygen demand test, a key indicator of organic pollution, takes five days to yield results. But despite criticism, there is a wealth of knowledge based on it. It is the only measure of readily biodegradable carbonaceous material, said Johnstone.

R C Trivedi, erstwhile deputy director of CPCB concurs. While biomonitoring is essential for a cumulative assessment, for restoration it is essential to understand the nature and magnitude of the toxicant, he said.

To have a reasonable assessment of river quality a full suit would be best, but it would be expensive and depend on the importance of the river. Both monitoring protocols are complementary, said Akolkar.