UTTAR PRADESH JOURNAL OF ZOOLOGY

Background: Lonar Lake, a unique meteorite impact crater lake in Maharashtra, India, is an extreme saline–alkaline ecosystem that supports diverse and specialized microbial and phytoplankton communities. Its phytoplankton diversity, including cyanobacteria, diatoms, and green algae, is strongly influenced by physico-chemical conditions and serves as a sensitive bioindicator of water quality, eutrophication, and ecological change.

Aim: Phytoplankton diversity is a crucial bioindicator of aquatic health. Hence, the present study was carried out to assess seasonal changes in phytoplankton diversity and water quality, particularly during the pre-monsoon and post-monsoon periods and to determine their influence on phytoplankton community structure in Lonar Carter Lake, thereby indicating the overall health of the corresponding aquatic ecosystem.

Study Design: Lonar Crater Lake, Buldhana, M.S. India.

Place and Duration of Study: The present study assessed phytoplankton diversity and water quality in Lonar Lake during the pre-monsoon and post-monsoon seasons, i.e., June 2024 and December 2024, respectively. The samples were collected from four different designated sampling stations in the early morning from the periphery of the Lonar Crater Lake.

Methodology: The standard methods of APHA (2017), Kodarkar (2006), and Trivedy and Goel (1984) were used for the analysis of phytoplankton and Water quality. From the surface to below the surface level, a V-shaped plankton net attached to a sampling bottle at the end was used to collect phytoplankton samples, and the bucket-rope too mechanism was used at certain sampling stations. The samples were stored in plastic bottles containing 4% formalin solution, kept in a cool, dark place. The phytoplankton samples were photographed under the microscope and were identified using standard taxonomic keys. 

Statistical Analysis was used to assessed Phytoplankton diversity using the Shannon–Wiener Diversity Index (H′), Pielou's Evenness Index (J′), Margalef’s’ (d) and Simpson's Dominance Index (D) to evaluate species diversity, evenness, and dominance within the phytoplankton community. One-Way Analysis of Variance (ANOVA) was performed to determine significant spatial and seasonal variations in phytoplankton diversity and abundance among sampling stations. Principal Component Analysis (PCA) was employed to identify the major physico-chemical variables influencing phytoplankton distribution and community structure.

Results: The phytoplankton species were assessed, belonging to three major classes comprising Bacillariophyceae, Cyanophyceae, and Chlorophyceae, across four sampling stations (S1, S2, S3, and S4) during June 2024 and December 2024. A total of 36 species were recorded, of which Cyanophyceae contributed the highest number (21 species), followed by 8 species of Bacillariophyceae and 7 species of Chlorophyceae. Among the recorded groups, Cyanophyceae was found to be the dominant class, represented by genera such as Spirulina, Arthrospira, Anabaena, Anabaenopsis, Microcystis, Oscillatoria, Raphidiopsis, and Pseudoanabaena. Bacillariophyceae (diatoms) formed the second major group, represented by species such as Navicula amphirhynchus, Navicula cryptocephalas, Navicula radiosa, Navicula sphaerophora, Pinnularia divergens and Pleurosigma sp. Similarly, Chlorophyceae (green algae) was represented by species such as Chlorella vulgaris, Oocystis sp., Pediastrum integrum, Tetraedron duospinum, Palmella mucosa, Kirchneriella obesa, and Quadrigula lacustris.

Based on the physico-chemical analysis, the lake exhibits elevated salinity, alkalinity, dissolved solids, chloride, phosphorus, COD, and BOD, along with critically low dissolved oxygen concentrations. These findings suggest continuous inputs of organic waste, nutrient-rich runoff, and dissolved salts. The overall water quality status indicated that the lake water was polluted and eutrophic, with significant organic and nutrient contamination. Although post-monsoon conditions show slight improvement due to dilution, the lake remains ecologically stressed and unsuitable for drinking or domestic use without extensive treatment.

Conclusion: The study confirmed that the phytoplankton community of Lonar Lake was a sensitive and reliable indicator of its ecological status. The shifts in species composition observed during pre-monsoon and post monsoon periods also reflects the underlying changes in nutrient load. Therefore, regulation of nutrient inputs, frequent monitoring of the primary producer along with detailed and regular scientific studies are essential steps towards restoring the sustainability of this unique ecological marvel.