Effect of redox conditions on the release of dissolved organic matter and nutrients at the sediment-water interface and the role of microbes

Abstract

The dynamics of nutrients are closely related to microbial activities and substantially influenced by the redox conditions. This study conducted an incubation experiment on sediment under different redox conditions. Concentrations of dissolved organic carbon (DOC), nitrogen, and phosphorus were measured to investigate the release of nutrients from the sediment. An excitation-emission matrix and PARAFAC analysis were used to characterize dissolved organic matter (DOM). The structure of microbes and functional genes were analyzed via high-throughput sequencing and real-time polymerase chain reaction. Oxic conditions decreased the NH4+ and NO2− concentrations and reduced the increases in total nitrogen and DOC concentrations. Oxic conditions also exhibited a higher alpha diversity index and microbial community abundance. Regarding functional genes, the expression levels of nitrification genes (amoA) increased under all redox conditions, especially under oxic and original conditions, which explained the removal of ammonia nitrogen. Higher expression levels of nitrite-reducing genes (nirK and nirS) were found in oxic environments owing to the abundant NO3− supply. The expression of the anammox gene (hzo) is stimulated in anoxic environments, which contributes to the lack of oxygen and a higher concentration of NH4+.