Comparative Evaluation of Trophic State Index of the Gharni Reservoir, Udgir, Dist: Latur Using Selected TSI Models

Abstract

Availability of good-quality water is a growing global concern and access to safe freshwater is increasingly recognized as a universal human right. Water resources in Maharashtra are unevenly distributed spatially and temporally, and specifically the Marathwada region lies in a rain-shadow zone and frequently experience water scarcity, making effective water resources management essential
for addressing deficits in rainfall-dependent areas. In this study, the trophic status of the Gharni Reservoir, Maharashtra, India, was assessed using different Trophic State Index (TSI) models. Surface water samples were collected from August 2019 to January 2021, and key parameters—Secchi Disk Depth (SDD), chlorophyll-a (Chl-a), and total phosphorus (TP)—were analyzed using the TSI models proposed by Carlson (1977), Cheng and Lei (2001), and Markad, Landge, Nayak, Inamdar, and Mishra (2019). The Carlson (1977) model underestimated the trophic status of the Gharni Reservoir, yielding TSI values in the range of 50-60. In contrast, Cheng and Lei’s (2001) model overestimated the trophic state, with TSI(SDD) values exceeding 100, indicating its unsuitability for this reservoir. The model developed by Markad et al. (2019) provided the most reliable assessment, showing peak performance, with TSI values ranging between 70 and 80. Overall, the Gharni Reservoir exhibits mesotrophic to hypereutrophic conditions on a seasonal basis. While increased productivity can enhance fish yield, excessive nutrient enrichment poses a risk to the long-term ecological balance of the reservoir.