Spatial heterogeneity of nitrogen-enriched sediment microbial communities and their environmental drivers in shallow eutrophic Honghu Lake, China

Understanding the spatial heterogeneity of sediment microbial communities and their potential environmental drivers is crucial for effectively managing eutrophication in the shallow Honghu Lake. Overall, the entire lake was classified as moderately eutrophic (mean TLIΣ = 64.17) with nitrogen-enriched in sediment (Severe Pollution, mean S TN = 4.87). Regionally, sediment microbial communities and some environmental factors exhibited spatial heterogeneity. Specifically, sedimentary manganese (S Mn) in the North Lake District (NLD) was 74.65% and 95.44% higher than in West (WLD) and East (ELD) Lake Districts; conversely, sediment total nitrogen (S-TN) in the NLD was 45.66% and 41.98% lower than that in WLD and ELD; the NLD recorded the lowest trophic state, characterized by the highest Secchi depth (SD), the lowest chemical oxygen demand (COD Mn ), relatively higher water total nitrogen (W-TN) and phosphorus (W-TP), and the lowest chlorophyll a (Chl.a). Sediment microbial diversity followed the trend: NLD > WLD > ELD, with NLD communities being structurally distinct from the similar WLD/ELD groups. Redundancy analysis (RDA) and Mantel tests identified S Mn, SD and S-TN as the primary drivers shaping these spatial variations, with S Mn and SD positively correlated to the NLD communities and S-TN positively correlated to the WLD/ELD communities. Functional microorganisms also exhibited spatial heterogeneity with NLD group was enriched with C/N-cycling taxa whereas WLD/ELD groups were enriched in C/S-cycling taxa. These findings elucidate the divergent roles of heavy metals and nutrients in shaping microbial niches, providing valuable insights into the biogeochemical cycling and ecological health of shallow lakes.