Seasonal dynamics exert a dominant influence on limnological processes in Himalayan lakes, yet integrated assessments coupling physicochemical variability with phytoplankton community structure remain scarce for mid-altitude systems. This study investigated seasonal and spatial patterns in water quality and phytoplankton dynamics in Lake Bhimtal through monthly sampling at six stations over one complete annual cycle. Permutational multivariate analysis of variance (PERMANOVA) revealed a highly significant temporal effect on overall water quality (F = 15.70, p = 0.001), whereas no significant spatial differentiation was detected among stations (F = 0.94, p = 0.533), reflecting seasonal forcing as the principal driver of physicochemical variability. Water temperature ranged from 10.6 °C (January) to 26.1 °C (July) and was negatively correlated with total phytoplankton abundance, which peaked during winter and early spring (February 1356.67 ± 99.25 cells L⁻1; March 1103.33 ± 95.14 cells L⁻1) and reached its annual minimum during the monsoon (August 270.00 ± 65.06 cells L⁻1).A total of 21 phytoplankton taxa belonging to four algal classes were recorded. Bacillariophyceae dominated throughout the study period, contributing 44–48% of total phytoplankton density, followed by Chlorophyceae (22–25%), Zygnematophyceae (15–18%), and Cyanophyceae (12–15%). PERMANOVA confirmed significant effects of both month (F = 5.341, p < 0.001) and station (F = 2.954, p < 0.001) on community composition, though temporal variation consistently explained a greater proportion of community-level variance. Bray–Curtis dissimilarity among seasons ranged from 0.704 to 0.835, with the greatest turnover occurring between monsoon and pre-monsoon assemblages (0.835). SIMPER analysis identified Ankistrodesmus, Diatoma, and Nitzschia as the primary contributors to inter-seasonal dissimilarity. BIO-ENV analysis identified total dissolved solids (TDS; ρ = 0.2703) as the strongest single predictor of phytoplankton community structure, with marginally higher associations when combined with ammonium (ρ = 0.2667) or water temperature and TDS together (ρ = 0.2659). Canonical correspondence analysis (CCA) further revealed that winter and early spring assemblages were associated with elevated nutrient concentrations (nitrate, phosphate, TDS, and dissolved oxygen), while monsoon assemblages were aligned with higher water temperature and reduced nutrient influence. Seasonality, mediated through temperature-driven mixing, monsoonal hydrology, and nutrient redistribution, emerged as the principal regulator of physicochemical conditions and phytoplankton dynamics in Lake Bhimtal, while spatial heterogeneity among stations played a secondary role, underscoring the importance of season-centred monitoring and management of mid-altitude Himalayan lake ecosystems.

Patterns and drivers of physicochemical and phytoplankton variability in a Himalayan lake ecosystem

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发表日期：

2026年5月26日

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Suresh Chandra,
Ananya Khatei,
Bhawna Gehlot,
M. Junaid Sidiq,
Raja Aadil Hussain Bhat,
Parvaiz Ahmad Ganie

摘要

Seasonal dynamics exert a dominant influence on limnological processes in Himalayan lakes, yet integrated assessments coupling physicochemical variability with phytoplankton community structure remain scarce for mid-altitude systems. This study investigated seasonal and spatial patterns in water quality and phytoplankton dynamics in Lake Bhimtal through monthly sampling at six stations over one complete annual cycle. Permutational multivariate analysis of variance (PERMANOVA) revealed a highly significant temporal effect on overall water quality (F = 15.70, p = 0.001), whereas no significant spatial differentiation was detected among stations (F = 0.94, p = 0.533), reflecting seasonal forcing as the principal driver of physicochemical variability. Water temperature ranged from 10.6 °C (January) to 26.1 °C (July) and was negatively correlated with total phytoplankton abundance, which peaked during winter and early spring (February 1356.67 ± 99.25 cells L⁻¹; March 1103.33 ± 95.14 cells L⁻¹) and reached its annual minimum during the monsoon (August 270.00 ± 65.06 cells L⁻¹).A total of 21 phytoplankton taxa belonging to four algal classes were recorded. Bacillariophyceae dominated throughout the study period, contributing 44–48% of total phytoplankton density, followed by Chlorophyceae (22–25%), Zygnematophyceae (15–18%), and Cyanophyceae (12–15%). PERMANOVA confirmed significant effects of both month (F = 5.341, p < 0.001) and station (F = 2.954, p < 0.001) on community composition, though temporal variation consistently explained a greater proportion of community-level variance. Bray–Curtis dissimilarity among seasons ranged from 0.704 to 0.835, with the greatest turnover occurring between monsoon and pre-monsoon assemblages (0.835). SIMPER analysis identified Ankistrodesmus, Diatoma, and Nitzschia as the primary contributors to inter-seasonal dissimilarity. BIO-ENV analysis identified total dissolved solids (TDS; ρ = 0.2703) as the strongest single predictor of phytoplankton community structure, with marginally higher associations when combined with ammonium (ρ = 0.2667) or water temperature and TDS together (ρ = 0.2659). Canonical correspondence analysis (CCA) further revealed that winter and early spring assemblages were associated with elevated nutrient concentrations (nitrate, phosphate, TDS, and dissolved oxygen), while monsoon assemblages were aligned with higher water temperature and reduced nutrient influence. Seasonality, mediated through temperature-driven mixing, monsoonal hydrology, and nutrient redistribution, emerged as the principal regulator of physicochemical conditions and phytoplankton dynamics in Lake Bhimtal, while spatial heterogeneity among stations played a secondary role, underscoring the importance of season-centred monitoring and management of mid-altitude Himalayan lake ecosystems.