Seasonal variation of limnological parameters and phytoplankton dynamics in the high-altitude oligotrophic lakes of Tawang district, Arunachal Pradesh (India)

Seasonal variations of limnological parameters and phytoplankton dynamics in high-altitude oligotrophic lakes form a critical area of interest in assessing the implications and impact of climate change on fragile ecosystems and formulating effective conservation strategies. Thus, a study was conducted by sampling water from five High-Altitude Lakes (HALs) of Tawang district, Arunachal Pradesh between December 2019 and December 2021. The seasonal variations of seven physico-chemical parameters and phytoplankton's composition, distribution, and seasonal abundance were assessed. Further, the diversity, dominance, and evenness of phytoplankton were estimated and the relationship between limnological parameters and the phytoplankton species was established using Canonical Correspondence Analysis (CCA). The limnological parameters such as pH, dissolved oxygen, free carbon dioxide (FCO 2 ), alkalinity, hardness, conductivity, and total dissolved solids (TDS) show significant seasonal variations among the HALs. A total of 50 phytoplankton species belonging to 8 Class and 33 Family were recorded. The order of phytoplankton dominance was Bacillariophyceae > Cyanophyceae > Zygnematophyceae > Chlorophyceae > Chrysophyceae = Dinophyceae, Euglenophyceae = Klebsormidiophyceae. The most abundant species were Cymbella sp., Gomphonema sp., Fragilaria sp., Navicula sp., Nitzchia sp. (Bacillariophyceae), Volvox sp., Pediastrum sp., Microspora sp. (Chlorophyceae), Oscillatoria sp., Lyngbya sp., Calothrix sp., Chroococcus sp. (Cyanophyceae), Spirogyra sp., Mougeotia scalaris , Cosmarium sp., Closterium sp. (Zygnematophyceae). The abundance of phytoplankton species varied seasonally with most copious in winter. The distribution, abundance, and diversity of phytoplankton were largely influenced by pH, hardness, FCO 2 , conductivity, and TDS levels. So, the findings of the study could be helpful in exploring the potentialities of introducing cold-water fisheries in HALs to ensure food security under climate change scenarios.