High arsenic levels in sediments, Jianghan Plain, central China: Vertical distribution and characteristics of arsenic species, dissolved organic matter, and microbial community

Elevated arsenic (As) levels in groundwater pose a risk to the local population that relies on this resource for their living needs. Here we analyzed samples collected from a sediment core recovered from Jianghan Plain, China, a region experiencing high As concentrations in groundwater. We evaluated the vertical distribution of As forms, fluorescent dissolved organic matter (DOM), microbial assemblages, and a suite of anions and cations. Our aim was to elucidate the As species in the local groundwater and their migration and transformation in the aquifer. As(III), Fe, Mn, TOC, SO42−, and NO3− were negatively correlated with depth, whereas As(V) and As(Total) did not show any correlation with depth, nor was As correlated with the amount and characteristics of DOM. High concentrations of As inhibited the metabolic activity of bacteria and thereby limited the production of fluorescent DOM. Sulfate-reducing bacteria transformed free-sulfate radicals to S2− and promoted the dissolution and fixation of arsenic. We identified three main forms of arsenic that varied with depth: FeOOH (absorption), COO (absorption), and FeAsS. Microbial communities also varied with depth, and Novosphingobium and Brevibacillus showed high relative abundances in the sediment profile. TOC and DOM were strongly depleted in strongly As-enriched depths. [Display omitted] •Negatively linear correlation was found between most chemicals and sediment depth.•Three main forms of arsenic with varied abundance at different depths were present.•Abundant Novosphingobium and Brevibacillus were identified at the depths enriched with As.•Depleted TOC and DOM were found at the depths enriched with As.•Metabolism of microbes with organic matter enhanced arsenic release from sediment.