Short-term assessment of diatom assemblages under high chemical oxygen demand and low silicon in a shipping zone of the Gulf of Khambhat, Gujarat, India
摘要
Offshore and onshore activities introduce significant amounts of organic carbon into coastal waters, elevating CO2 levels through microbial decomposition and contributing to ocean acidification. This process reduces the availability of dissolved silica, a key nutrient essential for diatom growth. As primary producers, diatoms link carbon and silica cycles and serve as sensitive bioindicators of aquatic health. A preliminary assessment of the coastal zones of the Cambay Basin identified two distinct areas: a highly economically active zone (Alang and Ghogha) with elevated chemical oxygen demand (COD) and variable Silicon (Si) levels, and another zone where COD remains within permissible limits with low Silicon (Khambhat). The influence of these differing environmental conditions on the structure of diatom assemblages was examined. Results revealed a shift towards opportunistic and pollution-tolerant diatom taxa, alongside a decline in more sensitive species, indicating ecological disturbance. Sentinel species like Entomoneis alata, Halamphora coffeaeformis, Chaetoceros gracilis, Iconella sp., and Surirella librile thrived under high COD, suggesting their potential as indicators of organic pollution. These findings underscore the value of diatom assemblages in monitoring the ecological impact of industrial and shipping activities and support the development of diatom-based indices for assessing coastal water quality.