ASSESSMENT OF TROPHIC STATUS OF SARDAR SAROVAR RESERVOIR, GUJARAT: AN APPLICATION OF CARLSON'S TROPHIC STATE INDEX

Abstract

Fluctuations in hydrological conditions and external nutrient loading play a critical role in regulating the trophic status of the Sardar Sarovar Reservoir, thereby influencing its overall ecological health as evaluated using Carlson's Trophic State Index (CTSI). In this study, CTSI was used to assess the changes in the trophic state of the Sardar Sarovar reservoir throughout a year (June 2018 to January 2019). The variation in trophic status of the Sardar Sarovar reservoir can be attributed to the "trophic burst" phenomenon, when the reservoir attained its full reservoir length (from 121.89 m to 138.68 m), submerging the adjacent vast area. The submerged area enhanced the available nutrients within the reservoir. Trophic state indicators such as Secchi disc transparency, total phosphorus, and chlorophyll-a were considered, as CTSI integrates physical, chemical, and biological components to evaluate reservoir trophic status. The investigation showed that the Sardar Sarovar reservoir could be classified as an "eutrophic" water body in accordance with the comprehensive trophic state index. The shift of mesotrophic reservoirs toward eutrophic nature can be attributed to the accumulation of nutrients in the submerged catchment area, which is reflected in the values of trophic state indicators. The seasonal inflow of water also contributed to the variation in the trophic state of the studied reservoir, highlighting the combined influence of hydrological dynamics and nutrient enrichment on the progressive eutrophication of the Sardar Sarovar reservoir. Overall, these findings suggest that while the reservoir is currently eutrophic due to a trophic burst, scientific management of nutrient loading offers significant potential for sustainable fisheries and ecological stability.