Spatial variation in bacterial community and dissolved organic matter composition in groundwater near a eutrophic lake

The aim of this study was to reveal the variation in dissolved organic matter (DOM) components, bacterial community composition, and their co-relationships during groundwater migration. A well-studied shallow eutrophic lake, Lake Taihu, was selected to explore the DOM components and bacterial communities during groundwater replenishment from the lake using three-dimensional fluorescence-parallel factor analysis and high-throughput sequencing, respectively. Six fluorescent components of DOM were identified, including four humic-like components (C1: λ= 330 / 400 nm, C2: λ= 260 , 350 / 450 nm, C3: λ= 270 , 380 / 480 nm, and C6: λ= 220 / 410 nm) and two protein-like components (C4: λ= 230 , 280 / 320 nm, C5: λ= 230 , 290 / 340 nm). With increasing distance to Lake Taihu, the fluorescence intensity of C1, C3, C4, and C5 decreased within 15 km away from lake shore and then tended to be stable. Thirty-three phyla of bacteria were identified in the aquifer, including Proteobacteria (61.9% of total bacteria), Bacteroidetes (15.0%), Planctomycetes (4.8%), Verrucomicrobia (3.4%), and Actinobacteria (3.3%). The relative abundance of Proteobacteria was significantly positively correlated with the fluorescence intensity of C1–C3, while the relative abundance of Actinobacteria showed the opposite relationship with the fluorescence intensity of C1–C3. The relative abundances of Novosphingobium and Limnohabitans were positively correlated with the fluorescence intensity of C4–C6. Our work suggests that the influence of groundwater replenishment from a eutrophic lake on DOM in the surrounding aquifer may extend to within 15 km from the lake shore. A large amount of DOM inputs (especially humic acid-like components) can induce variation in groundwater bacterial community composition and thus affects the groundwater biogeochemistry.