21 - Geospatial assessment of water quality of a dying tropical river and its environmental implications

Abstract

The deltaic tropical rivers are very complex from the perspectives of hydromorphological, and ecological systems due to multiple anthropogenic threats like channel modifications, hydrological alternation, and point and nonpoint sources of pollution. Therefore, the present study has been an attempt to investigate the condition of river water quality and ecological stress of the Jalangi river based on remotely sensed data and specific indices—floating algae index (FAI, Normalized difference turbidity index (NDTI), Normalized Water Index (NDWI), and Green Chlorophyll index (CIg) accompanied with proper validation through comparing the water quality of the sampled water. The results reveal that the upper reach exhibited the highest average CIg value (0.73), whereas the lower value (0.22) was found downstream of the upper reach. With a range of 0.027 in the 7th reach, downstream to Krishnagar, to −0.08 in the 4th reach, the average normalized difference turbidity index (NDTI) was measured as being −0.074. The strong correlation between CIg and NDTI (R2=0.6541) suggests that chlorophyll concentration has a significant effect on turbidity. The significant reduction in river discharge due to seasonal disconnection from the Padma river induces the pollution of the Jalangi river. Besides the critical environmental flow, the release of industrial wastewater, urban run-off, and household waste all contribute significantly to the rise in river turbidity.