SEASONAL DYNAMICS OF TOTAL AND FAECAL COLIFORMS IN WASTEWATER-FED AQUACULTURE PONDS OF THE EAST KOLKATA WETLANDS, INDIA

Abstract

The East Kolkata Wetlands (EKW), India, represent an internationally important Ramsar wetland that naturally treats municipal wastewater while supporting productive sewage-fed aquaculture. The present study evaluated the seasonal and spatial distribution of Total Coliform (TC) and Faecal Coliform (FC) in four sewage-fed ponds Harhare Bheri, Sujit Mondal's Bheri, Bantala 2 No. Bheri, and Dakshin Gorumara Bheri during the pre-monsoon, monsoon, and post-monsoon seasons of 2025 using the Multiple Tube Fermentation technique following APHA regulations (2023). Both TC and FC exhibited pronounced seasonal and spatial variations, with maximum concentrations consistently recorded during the monsoon season and minimum values during the pre-monsoon period. Bantala 2 No. Bheri, receiving untreated dry-weather flow, showed the highest bacterial load, whereas Dakshin Gorumara Bheri recorded the lowest concentrations, reflecting significant differences in wastewater source, dilution, and hydraulic retention time. Statistical analysis confirmed significant differences among seasons and sampling stations for both TC (season: F = 17.11, p = 0.0033; station: F = 28.97, p = 0.0006) and FC (season: F = 8.57, p = 0.0174; station: F = 31.30, p = 0.0005). The findings demonstrate that wastewater characteristics and seasonal hydrological processes combine to regulate microbial dynamics in the EKW and highlight the need for continuous microbiological monitoring to ensure sustainable wastewater reuse, aquaculture productivity, and protection of public health.