What aquatic insects reveal about the health of Assam’s Jatinga River

In the tranquil valleys of Assam’s Dima Hasao district, the Jatinga River flows undisturbed quietly through tribal lands and forested sanctuaries. To the naked eye, it looks clean and healthy. But deep beneath its surface, tiny creatures are quietly registering every change, every disturbance, every sign of stress it faces from human activity. These creatures — aquatic insects — are sounding an ecological alarm. 

Listening to the insects

A study titled “Aquatic insects as indicators of water quality: Seasonal distribution and biomonitoring insights from a hilly river in the Eastern Himalayan region, India” by Tanushree Chakravarty and Susmita Gupta focuses on the Jatinga River — a 71-km-long tributary of the Barak River that flows through the Indo-Burma biodiversity hotspot. The river supports thirteen tribal communities and runs along the Barail Wildlife Sanctuary, one of Assam’s ecologically rich protected areas.

Located within the Indo-Burma biodiversity hotspot, the Jatinga River is a vital tributary of the Barak River. Flowing over 71 kilometers through Dima Hasao and Cachar districts, it supports the lives of thirteen tribal communities and passes along the Barail Wildlife Sanctuary. According to the authors, this river represents a relatively pristine environment, yet it faces “low to moderate strain” from human activities such as sand and stone mining, agricultural runoff, and domestic waste discharge. The study, carried out from 2018 to 2019, was designed to capture these impacts across seasons and along different river stretches.

What insect diversity tells us about river health

Sampling was conducted at five sites, covering upstream (S1 and S2), midstream (S3), and downstream (S4 and S5) segments. Insects were collected at each site across seasons (pre-monsoon, monsoon, post-monsoon, and winter) using standard ecological methods like kick-net and all-out searches.

The research recorded 72 species of aquatic insects, belonging to 58 genera and 38 families across eight taxonomic groups. But beyond the variety, the presence or absence of certain insects helped scientists assess the river’s health using global biotic indices like BMWPTHAI, ASPTTHAI, SIGNAL2, EPT%, and HFBI.

According to the study, the upstream sites (S1 and S2) had consistently "good and clean water quality," with high scores in BMWPTHAI (78–105), ASPTTHAI (6.2–7.5), and SIGNAL2 (6.1–7). EPT% values — a key indicator of ecological health — ranged from 50.89% to 75.35% in these areas. These values refer to the presence of pollution-sensitive insect groups like Ephemeroptera, Plecoptera, and Trichoptera, often found in well-oxygenated, unpolluted water.

When the rains come, the river suffers

The study found that changes in seasons had a big impact on the insect life in the Jatinga River. During the monsoon, strong water flow disturbed the riverbed and washed away many sensitive insect species. “High monsoon flow rate resulted in the ‘doubtful quality’ of water in midstream and downstream sites,” the authors observed. In fact, some species that usually indicate good water quality disappeared entirely from sites like S3 and S4 during this time.

The researchers used a method called canonical correspondence analysis (CCA) to understand how different insects responded to environmental conditions. They found that insects in the upstream areas — such as Psephenoides subopacus, Epeorus aculeatus, and Rhithrogeniella tonkinensis — were found mostly in rocky areas with clean, oxygen-rich water. In contrast, downstream species like Micronecta sp. and Bezzia sp. were linked to more polluted conditions, including high levels of organic waste and free carbon dioxide.

Riverbed, chemistry, and community composition

“The structure of the riverbed is not just a passive feature — it actively governs insect distribution,” the report stresses. Sites with a dominance of fine sediments like silt and clay had much lower diversity. “Stable habitats such as boulders and pebbles offer micro-niches for scrapers and shredders,” the authors note, pointing to upstream sites that hosted species like Ptilomera assamensis and Hydropsyche sparna. “Environmental parameters like TDS and electrical conductivity exceeded permissible levels in some locations,” the report warned, citing standards set by the Bureau of Indian Standards (2012) and the WHO (2017).

Local pressure, global lessons

Anthropogenic pressure — especially in the form of unregulated sand mining, agriculture, and settlement waste — was a recurring theme in the study. “Such activities reduce substrate stability and increase sediment load,” the authors explained. This not only impacts insect communities but also reduces the river’s self-purifying capacity.

Why it matters

The decline of aquatic insects is not just a loss of biodiversity. These insects form the base of freshwater food chains — feeding fish, birds, and other wildlife. They also serve as early warning indicators, helping us detect and respond to ecological stress before it becomes irreversible.

Their decline or disappearance can affect fish populations, birdlife, and even humans who rely on the river for drinking water and irrigation. The authors conclude, “Aquatic insects are effective sentinels of river health. Their diversity, distribution, and abundance must be regularly monitored to ensure sustainable water resource management, especially in regions vulnerable to ecological stress.” In a time when India’s rivers are increasingly under pressure, this detailed and data-rich study stands out. As Chakravarty and Gupta’s study affirms, "listening to insects is not just ecological curiosity — it is a practical necessity for freshwater stewardship."

Citation:
Chakravarty, T., & Gupta, S. (2024). Aquatic insects as indicators of water quality: Seasonal distribution and biomonitoring insights from a hilly river in the Eastern Himalayan region, India. Cleaner Water, https://doi.org/10.1016/j.clwat.2024.100056