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<p>This study investigates the environmental variability and phytoplankton bloom dynamics in Deepor Beel, a Ramsar wetland located in the northeast of India, in November (early post-monsoon) of 2024 and again in February (late post-monsoon) of 2025. Surface water temperatures across the six studied stations representing the Deepor Beel Ecological Time Series declined by ~ 2–3&#xa0;°C between the two sampling periods, accompanied by shifts in pH, dissolved oxygen, and nutrient concentrations. Total dissolved solids (TDS) and electrical conductivity (EC) increased notably in February 2025, indicating enhanced solute accumulation. Dissolved nitrate, <i>o</i>-phosphate, reactive silicate, and ammonium concentrations increased across all stations, while chlorophyll-a and carotenoid concentrations declined sharply, reflecting reduced phytoplankton biomass in February 2025. Phytoplankton communities exhibited a seasonal (early post-monsoon to late post-monsoon) shift from cyanobacterial (<i>Planktothrix</i> spp. dominated) assemblages in November 2024 to more taxonomically diverse communities in February 2025, including <i>Pediastrum</i> spp.<i>, Aulacoseira</i> spp.<i>,</i> and <i>Chlorella</i> spp. In November 2024, blooms were dominated by the cyanobacterium <i>Planktothrix</i> spp., comprising the majority of the phytoplankton community at stations DPB1, DPB2, and DPB5, with <i>Microcystis</i> spp. also contributing substantially at DPB5, DPB4, and DPB11. Both bloom-forming genera were tracked using bright-field microscopy and field emission scanning electron&#xa0;microscopy (FESEM). Molecular characterization using 16S rRNA and 18S rRNA metabarcoding data revealed station-specific bacterial heterogeneity, with&#xa0;dominance of Proteobacteria (Burkholderiaceae, Aeromonadaceae) and Bacteroidetes (Flavobacteriaceae). Eukaryotic communities were dominated by member of Fungi&#xa0;(Ascomycota and Basidiomycota), in addition to members belonging to Protists and other metazoan groups . Mantel tests revealed significant correlations between bloom-forming cyanobacteria and key environmental variables, highlighting distinct ecological drivers for <i>Planktothrix</i> and <i>Microcystis</i>. The analysis provided a robust, distance-based approach to link taxa with environmental gradients despite limited sample size. The findings from the study highlight the profound influence of seasonal environmental variability on microbial community structure and algal bloom dynamics, providing critical insights for management and conservation of tropical freshwater wetlands.</p>

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Nutrient-driven cyanobacterial blooms and microbial shifts in a lake-wetland system: a case study from a Ramsar-designated wetland of Northeast India

  • 期刊论文

  • 发表日期：

    2025年8月16日

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  • Rajkumari Nikita,
  • Anwesha Ghosh,
  • Raghu Chandrasekaran,
  • Nirupama Saini,
  • Punyasloke Bhadury

摘要

This study investigates the environmental variability and phytoplankton bloom dynamics in Deepor Beel, a Ramsar wetland located in the northeast of India, in November (early post-monsoon) of 2024 and again in February (late post-monsoon) of 2025. Surface water temperatures across the six studied stations representing the Deepor Beel Ecological Time Series declined by ~ 2–3 °C between the two sampling periods, accompanied by shifts in pH, dissolved oxygen, and nutrient concentrations. Total dissolved solids (TDS) and electrical conductivity (EC) increased notably in February 2025, indicating enhanced solute accumulation. Dissolved nitrate, o-phosphate, reactive silicate, and ammonium concentrations increased across all stations, while chlorophyll-a and carotenoid concentrations declined sharply, reflecting reduced phytoplankton biomass in February 2025. Phytoplankton communities exhibited a seasonal (early post-monsoon to late post-monsoon) shift from cyanobacterial (Planktothrix spp. dominated) assemblages in November 2024 to more taxonomically diverse communities in February 2025, including Pediastrum spp., Aulacoseira spp., and Chlorella spp. In November 2024, blooms were dominated by the cyanobacterium Planktothrix spp., comprising the majority of the phytoplankton community at stations DPB1, DPB2, and DPB5, with Microcystis spp. also contributing substantially at DPB5, DPB4, and DPB11. Both bloom-forming genera were tracked using bright-field microscopy and field emission scanning electron microscopy (FESEM). Molecular characterization using 16S rRNA and 18S rRNA metabarcoding data revealed station-specific bacterial heterogeneity, with dominance of Proteobacteria (Burkholderiaceae, Aeromonadaceae) and Bacteroidetes (Flavobacteriaceae). Eukaryotic communities were dominated by member of Fungi (Ascomycota and Basidiomycota), in addition to members belonging to Protists and other metazoan groups . Mantel tests revealed significant correlations between bloom-forming cyanobacteria and key environmental variables, highlighting distinct ecological drivers for Planktothrix and Microcystis. The analysis provided a robust, distance-based approach to link taxa with environmental gradients despite limited sample size. The findings from the study highlight the profound influence of seasonal environmental variability on microbial community structure and algal bloom dynamics, providing critical insights for management and conservation of tropical freshwater wetlands.