Role of dominant macrophytes to treat Nambul river, the main polluter of Loktak - a dying Ramsar site in the Indo Burma hot spot (Manipur, India)

Abstract

As a part of the monitoring process of the main polluting tributary of Loktak, the paper analyzed the water characteristics of the main polluted stretch of Nambul river i.e. Imphal Urban region. The results showed low pH (6.23 ± 0.32), high electrical conductivity (1373 ± 50.33 µSm^-1), high turbidity (25.40 ± 0.90 NTU), poor dissolved oxygen content (0.53 ± 0.24 mgL^-1), high nitrate, and phosphate concentrations (9.27 ± 0.40 and 2.05 ± 0.10 mgL^-1, respectively). The Water Quality Index values indicate that Nambul river is unfit for drinking. Moreover, the Sodium Percentage, Sodium Adsorption Ratio, and Kelly's Ratio revealed the unsuitable nature of the river for irrigation. Therefore, in order to clean the river water, lab scale microcosm experimentation was carried out to highlight the potential of the dominant macrophytes viz. Eichhornia crassipes (Mart) Solms and Pistia stratiotes (L.) as phytofilters. The results showed increased pH (7.6 ± 0.11 and 7.5 ± 0.1), higher dissolved oxygen content (5.87 ± 0.30 and 3.28 ± 0.30 mgL^-1), less turbidity (0.60 ± 0.25 and 0.40 ± 0.15 NTU) and reduced nitrate and phosphate concentrations (0.37 ± 0.03 and 0.52 ± 0.01 mgL^-1, and 0.534 ± 0.025 and 0.346 ± 0.01 mgL^-1, respectively).Novelty statementThe present study showed the deteriorating water quality of Nambul river, the main polluting source of Loktak - a Ramsar site in the Montreux records.Water Quality Index calculated was above the unsuitable level for drinking at all the sampling locations in the Imphal Urban region.Sodium percentage, sodium adsorption ratio and Kelly's ratio were above the desired limit, making the river water unfit for irrigation.Further, the microcosm experimentation showed that the dominant macrophytes viz. Eichhornia crassipes (Mart) Solms and Pistia stratiotes (L.) can control the pollution level of Nambul.

Keywords: Eichhornia crassipes (Mart) Solms; Loktak lake; Nambul river; Water Quality Index (WQI); physico-chemical characteristics; wetlands.