Role of Naga Nullah tributary as a major polluter of Loktak: a Ramsar site from Manipur, India with 3 decades in the Montreux records of the wetland’s convention

For 3 decades, Loktak—a Ramsar site from the northeastern region of India (Manipur) in the Indo Burma hotspot has been in the Montreux list of Ramsar convention. Among the major threats to the wetland, the 36 tributaries play a significant role in the pollution of the Ramsar site. Therefore, the research was undertaken as a part of the ongoing continuous process to assess the characteristics of the major polluting tributaries of the wetland. The present paper reports the pioneer study conducted at Naga Nullah, one of the most polluted tributary during 2019–2021. During the study, water parameters showed low pH (5.95 ± 0.09), high electrical conductivity (1620 ± 0.55 µS cm⁻¹), high turbidity (26.01 ± 2.13 NTU), high total dissolved solids (700 ± 1.83 mg L⁻¹), poor dissolved oxygen content (0.32 ± 0.01 mg L⁻¹), high nitrate and phosphate concentrations (51.73 ± 0.02 and 0.94 ± 0.03 mg L⁻¹), respectively. The Water Quality Index (WQI) and irrigation water quality parameters calculated showed that the river water is unsuitable for both drinking and irrigational usage. Ultimately, the river empties into Nambul river and makes the river the main polluting tributary of Loktak. The Nambul river showed decreased pH (6.97 ± 0.44–6.28 ± 0.09) and dissolved oxygen (1.62 ± 0.01–0.32 ± 0.01 mg L⁻¹), increased electrical conductivity (1000 ± 1.28–1640 ± 2.16 µS cm⁻¹), turbidity (43.0 ± 1.06–69.4 ± 1.96 NTU) and total dissolved solids (334 ± 0.78–710 ± 2.97 mg L⁻¹) after Naga Nullah discharges its heavily polluted water collected from the Imphal Urban region.