Manipur: Rivers feeding Loktak Lake severely polluted by land use change, says study

Manish Chandra Mishra

A new study by Nagaland University has raised concerns over the health of Manipur’s Loktak lake, one of India’s most important freshwater ecosystems and the only floating national park in the world. The research confirms that land use changes in the catchment are directly deteriorating the water quality of rivers feeding the lake, threatening its biodiversity and the livelihoods of thousands who depend on it.

The study, led by Eliza Khwairakpam from the university’s Department of Environmental Science, analysed nine major rivers that drain into the lake. It found that agricultural runoff, expanding settlements and shifting (jhum) cultivation are the major factors influencing water pollution. The Nambul and Khuga rivers were identified as the most polluted, while the Iril and Thoubal rivers showed comparatively better water quality because of higher forest cover in their catchments.

The Nambul river recorded the poorest water quality, with dissolved oxygen levels as low as 0.02 milligrams per litre, which is far below the permissible dissolved oxygen limit of 4 milligrams per litre recommended for aquaculture by the Central Pollution Control Board. It also had a high biochemical oxygen demand (BOD) going up to 25 mg/L in the dry and 20 mg/L in the wet season, which indicates that a water body is highly polluted with organic matter. The study attributes this to heavy agricultural activity and settlement areas that together cover nearly 60 percent of the river’s catchment. Runoff carrying pesticides, fertilisers and domestic waste, including plastics from Imphal city, contributes heavily to this pollution.

In contrast, the Khuga river, though surrounded by 34 percent dense forest, also showed low water quality due to extensive jhum cultivation, which occupies about 42 percent of its catchment. The study observed that the traditional jhum cycle has reduced from around ten years to just one or two years, leading to soil erosion, nutrient loss and increased acidity in river water.

According to study author Khwairakpam, “Our study confirms that land use decisions across villages and forest landscapes upstream are directly impacting water quality downstream. This makes community-based land management and stricter control of agricultural runoff and waste discharge crucial for restoring Loktak lake.”

She further added, “Land management is not just an environmental concern but a livelihood protection strategy for the people of Manipur. Catchment-wide land regulation, sustainable agriculture practices and controlled jhum cycles will be vital for protecting India’s only floating national park and the endangered Sangai deer habitat within the lake.”

Loktak Lake covers about 287 square kilometres and supports hydropower, fisheries, transport and tourism. It is home to 132 species of plants and 428 species of animals, including the endangered Sangai deer found only in the Keibul Lamjao National Park within the lake. Despite its ecological importance, the lake has been listed under the Montreux Record, which identifies wetlands undergoing significant ecological changes.

This article originally appeared on Mongabay. Read the original article here.