Microbial indicator levels and environmental influences in the Chilika: A tropical coastal lagoon

Microbial pollution poses a significant threat to coastal ecosystems globally; therefore, periodic monitoring of pathogenic microbial communities is essential for determining the health of coastal water quality. The current study assesses microbial contamination levels in Chilika Lake, the largest lagoon in tropical Asia, and investigates how hydrological factors influence these communities. Subsurface water samples were collected from 31 locations and analyzed for indicator and pathogenic bacteria with physicochemical parameters, including water temperature (WT), salinity, total suspended matter (TSM), dissolved oxygen (DO), and nutrients such as nitrite (NO₂), nitrate (NO₃), ammonia (NH₄), phosphate (PO₄), silicate (SiO₄), and chlorophyll-a (Chl-a). The results indicated that high average levels of total coliforms, measuring 1.5 × 10⁴ cfu/ml, suggest potential contamination from sewage, likely associated with human activities in the southern region. Faecal coliform (FC) levels consistently remained below the safe limit of 100 cfu/100 ml, ensuring the water was safe for recreational activities and fishing. In the northern sector of the lake, river inflow reduced salinity, which enhanced Chl-a and dissolved oxygen levels due to increased photosynthetic activity. Pearson correlation analysis revealed significant relationships between total microbial populations and various environmental variables, including WT, DO, Chl-a, and nutrients such as NO₂ and NO₃. This study emphasizes the need for ecological measures to restore the lagoon and safeguard its ecosystem. It also underscores the importance of long-term monitoring for ecosystem health, enhancing tourism, fishing, and recreation decision-making.