Spatiotemporal dynamics of cyanobacterial blooms in the middle and lower reaches of the Xin River (Jiangxi, China) and their driving factors.

This study analyzed phytoplankton monitoring data (2019-2023) from the middle-lower reaches of the Xin River to clarify cyanobacterial spatiotemporal distributions and their environmental drivers. Sixty-six phytoplankton genera across seven phyla were detected, with Chlorophyta being the dominant phylum, followed sequentially by Bacillariophyta and cyanobacteria. The inter-annual variation of phytoplankton biomass ranged from 2.42 to 11.46 mg/L, while the cyanobacteria biomass varied from 0 to 2.63 mg/L, accounting for 7.54% of the total phytoplankton biomass. The dominant cyanobacteria species included Microcystis, Planktothrix, and members of Phormidioideae, with the dominant species showing some heterogeneity across different regions. For the study area, the average River Trophic Status Index (RSI) was recorded as 54.89, indicating seasonal water quality variations: favorable during the dry season; slightly polluted in most river sections during the rising period; moderately polluted in most sections during the wet period; and generally slightly polluted during the rece ssion period. Statistical analyses (Pearson correlation and redundancy analysis (RDA)) revealed that cyanobacteria and their dominant species had significant correlations (p < 0.05) with environmental factors including total phosphorus (TP), orthophosphate (PO4 3--P), dissolved total nitrogen (DTN), chemical oxygen demand (CODMn), Secchi Depth (SD), were the primary environmental factors driving the spatiotemporal distribution of cyanobacteria. This study provides for the first time an earlier seasonal emergence of cyanobacteria in lake entrance areas, addresses the domestic gap concerning inadequate attention to small and medium-sized rivers (e.g., the Xin River) relative to large lakes such as Taihu Lake and Chaohu Lake and holds crucial reference value for early warning systems aimed at preventing cyanobacterial encroachment into Poyang Lake.