Physicochemical Parameters and Phytoplankton Composition in a Semi-Arid Indian Reservoir: Kotpally, Telangana

Abstract

The present study provides a comprehensive limnological assessment and phytoplankton composition analysis of the Kotpally Reservoir, situated in Vikarabad District, Telangana, over a one-year period from October 2024 to September 2025. The objective was to examine the seasonal variations in physicochemical parameters, characterize phytoplankton diversity and abundance, and evaluate the trophic status of the reservoir. Monthly water samples were collected from five fixed stations representing the inlet, mid-lake, outlet, and near-shore zones. Standard methods (APHA, 2017) were used to determine physicochemical parameters including temperature, pH, dissolved oxygen (DO), biological oxygen demand (BOD), nitrate, phosphate, and other key indicators. Phytoplankton samples were identified and enumerated using the Sedgwick-Rafter method and taxonomic keys (Prescott, 1978). The results revealed distinct seasonal trends in water quality. Temperature ranged between 20°C and 34°C, while pH remained slightly alkaline (7.1–8.6). DO levels were highest during winter and lowest during the pre-monsoon period, whereas nitrate and phosphate concentrations peaked during monsoon months due to nutrient inflow from runoff. A total of 45 phytoplankton taxa were recorded, distributed across five major classes: Chlorophyceae, Bacillariophyceae, Cyanophyceae, Euglenophyceae, and Dinophyceae. Chlorophyceae dominated the assemblage, particularly during pre-monsoon, while diatoms (Bacillariophyceae) were prevalent in cooler months. Diversity indices indicated moderate to high diversity, with Shannon–Wiener values ranging from 1.8 to 2.9.

Introduction

Limnology, the study of inland waters, integrates physical, chemical, and biological analyses to understand lake, reservoir, and river functioning. Phytoplankton are central to these studies as they form the base of aquatic food webs and respond quickly to changes in nutrients, light, temperature, and hydrodynamics, making them effective bioindicators of ecological condition and trophic status. Quantitative metrics like chlorophyll-a, species richness, and diversity indices, combined with physicochemical data, provide insights into reservoir productivity, eutrophication risk, and impacts on fisheries and human use.

In semi-arid regions of peninsular India, reservoirs and irrigation tanks are vital for irrigation, fisheries, groundwater recharge, and ecosystem services. Seasonal climate variations, especially the monsoon-driven shifts in water quantity and quality, necessitate regular limnological monitoring. Regional studies across Andhra Pradesh, Karnataka, and Maharashtra highlight seasonal phytoplankton dynamics influenced by nutrient pulses, emphasizing the need for multi-season sampling and integrated physicochemical and biological assessments for effective reservoir management.

Kotpally Reservoir in Vikarabad district, Telangana, is a small-to-medium irrigation reservoir supporting fisheries, livestock, and recreation. Despite its importance, systematic limnological and phytoplankton data are limited. This study conducted monthly sampling over one year (October 2024 – September 2025) to assess seasonal physicochemical parameters, phytoplankton composition and abundance, and the reservoir’s trophic and ecological status.

Sampling was carried out at five stations representing inlet, mid-lake, outlet, and near-shore zones. Physicochemical parameters (temperature, pH, dissolved oxygen, nutrients, and others) were measured using standard APHA methods. Phytoplankton were collected via net hauls and integrated water samples, identified to genus/species level, quantified, and analyzed using diversity indices (Shannon–Wiener, Pielou’s evenness, Margalef’s richness). The study provides a comprehensive, seasonally resolved understanding of Kotpally Reservoir’s ecological condition to inform local management and conservation.

Conclusion

One year of limnological monitoring of Kotpally Reservoir (Oct. 2024-Sep. 2025) documented well-defined seasonal changes in water quality processes that largely reflect seasonal changes in monsoon hydrology and resultant dry season warming. Peak temperature, turbidity, and nutrient concentration occurred during monsoon runoff and dissolved oxygen and clearer conditions 7 occurred in cooler months. There were 45 taxa of phytoplankton (5 major groups of Chlorophyceae, Bacillariophyceae, Cyanophyceae, Euglenophyceae and Dinophyceae). Chlorophytes prevailed when the monsoon conditions were warm and low-flow, diatoms flourished in cold/post monsoon months, and at periods of cyanobacterial aggregates in near-shore areas of high nutrient concentration. Diversity indices climaxed after the monsoon after which there was a high richness and evenness. Trophic metrics suggest a system that periodically shifts between mesotrophy and localised eutrophy: mean productivity is such as to allow for fisheries and may typically be nutrient limited; however, hypoxia risk and near shore cyanobacterial blooms indicate periods of nutrient enrichment risk and thus localised eutrophy. Ecologically, such processes increase the hypoxia potential after the bloom senescence, cyanotoxin exposure, and adverse effects on fish health and uses by human activities. Our proposed priority actions to ensure sustainable management are as follows de-emphasize catchment nutrient inputs (riparian buffers, optimal use of fertilizer, livestock management), enhance local sanitation/wastewater treatment, periodically desilt to remove nutrient-rich sediments, and reflect on directed aeration/destratification in problem areas. Implement a regular surveillance program (Monthly physicochemical sample, chlorophyll-a, phytoplankton counts and toxin screenings) and an early-warning mechanism of cyanobacterial boom, and stakeholder interpersonal interaction with local farmers and fisheries. To ensure the ecological and socio-economic functioning of the reservoir, the long-term monitoring of the system, sediment nutrient flux scientific research, chlorophyll-a time series to calculate Carlson TSI, molecular taxonomic research, and comprehensive watershed-wide management planning should be introduced into the future work.

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Copyright

Copyright © 2025 Dr. Koppula Sampath, Dr. David Wilson, Dr. K Y Karuna. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.