Study links land use to water pollution in Manipur’s Loktak lake

GUWAHATI

A Nagaland University study has flagged an environmental worry for Manipur’s Loktak Lake, a freshwater ecosystem distinguished by its floating biomass called phumdi in the Meitei language.

The Keibul Lamjao National Park, home to the rare brow-antlered deer, is an integral part of the lake, whose nearest point is 40 km from Manipur’s capital, Imphal. Loktak is a designated Ramsar Site, recognised for its ecological significance, and requiring a high degree of sustainable management.

The findings of the study, undertaken by Eliza Khwairakpam of Nagaland University’s Department of Environmental Science, were published in the peer-reviewed International Journal of Environment and Pollution.

The study pointed out that changes in land use — agriculture, settlements, and shifting cultivation — have been deteriorating the water quality of rivers feeding the lake, threatening its biodiversity and the livelihoods of the local communities.

To understand the root cause of water pollution in the lake’s catchment area, the researcher conducted field samplings across nine major rivers that drain into Loktak. These rivers are Khuga, Western, Nambul, Imphal, Kongba, Iril, Thoubal, Heirok, and Sekmai.

Using detailed Land Use Land Cover maps provided by Manipur’s Forest Department, she compared different types of land activities, including agricultural areas, dense and degraded forests, settlements, jhum (shifting cultivation on hill slopes), and water bodies, against water quality indicators, including dissolved oxygen, biological oxygen demand, and temperature.

Stricter control needed

“Our study confirmed 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 run-off and waste discharge crucial to restoring the Loktak Lake,” Ms. Khwairakpam said.

The Nambul River was identified as the most polluted, with low oxygen levels and high organic contamination linked to 47% of the agricultural land, and 11% of the settlement areas in its sub-catchment. The Khuga River showed the second poorest water quality, despite having a higher forest cover.

The researcher attributed this to extensive jhum, which was recorded at 42% in the region.

In contrast, rivers including Iril and Thoubal, which flowed through greater forest-dominated landscapes, displayed better water quality, highlighting the protective role of natural vegetation.

“This study highlights the pressing environmental challenges arising from agricultural run-off, human settlements, and shifting cultivation, which are directly impacting the river water quality in the region,” Nagaland University’s Vice-Chancellor, Jagadish K. Patnaik, said.

Loktak Lake is home to 132 plant species and 428 animal species, and supports hydropower, fisheries, transport, and tourism. The lake features in the Montreux Record, a global warning list for wetlands undergoing serious ecological damage.

“Reduced fish populations, rising pollution levels, and increased sedimentation have now become growing concerns,” Ms. Khwairakpam said.

The study, conducted with field assistance from Manipur Pollution Control Board officials, was supported by the Indian Institute of Technology Delhi, along with Nagaland University.