Hyporheic descending flow inhibited microbial phosphate mineralization and sulfur oxidation, thus suppressing...

The phosphorus speciation in the hyporheic zone is crucial for the uptake and utilization of biological nutrients in the water and the protection of river ecological health. However, the mechanism of microbial-mediated phosphorus transformation under the complex hydrodynamic conditions of the hyporheic exchange is still unclear. In this paper, the effect and mechanism of hyporheic water exchange on the transformation of phosphorus speciation participated by microorganisms were discussed. The results showed that the hyporheic water exchange flux in the research section of the river was between 350.1 and 850.4 mm/d, mainly descending flow. In the high-intensity descending flow environment, the content of soluble reactive phosphorus in water was directly inhibited (r = -0.87, P < 0.05), and the expression of phosphorus mineralization gene phoD was significantly inhibited (r = -0.71, P < 0.01), which indirectly inhibited the transformation of the sediment phosphorus to soluble state. The sulfur oxidation process provided material and energy to promote the mineralization of organic phosphorus and the solubilization of inorganic phosphorus. The surface reduction environment caused by the descending flow inhibited the deep coupling process of phosphorus and sulfur cycle, and then inhibited the release of phosphorus in sediments. In this paper, the path of hyporheic exchange-gene expression-phosphorus speciation transformation was established and the phosphorus metabolism process under the influence of hyporheic water exchange was deeply analyzed, which provides a new theoretical perspective for revealing the hydrodynamic regulation mechanism of phosphorus cycle in the hyporheic zone.