Recently, Ping Xue, a doctor candidate majoring in Hydrogeology from School of Environmental Studies, published an article in the famous international periodical Journal of Hydrology (Chinese Academy of Sciences Q1, top journals). This research paper was entitled “Effect of bioclogging on the nitrate source and sink function of a hyporheic zone”, with Ping Xue, doctoral candidate of grade 2019, as the first author and Professor Jin Menggui, the research group instructor, as the corresponding author.
Nitrogen dynamic in a hyporheic zone (HZ) is mediated by microbes in the form of biofilms attached to sediment grains. Previous studies have neglected the influence of microbial effects on hyporheic nitrate function despite the fact that biofilm-induced clogging can significantly reduce sediment permeability and affect both residence time distribution and biochemical reaction rates. The Damköhler number of O2 is a dimensionless parameter used to evaluate the dominant role of hydrological transport and biogeochemical reaction on nitrogen cycling and it has been widely used to identify hyporheic function of net nitrate source-sink system. The classic Damköhler number of O2 is defined as the ratio between the timescale of water residence and the timescale of oxygen consumption. A dynamic microbial biomass has a considerable impact on Damköhler number of O2, not only does physical transport kinetic change due to the reduction of sediment hydraulic conductivity, but oxygen consumption rate is also dynamic because of the increased microbial concentrations within clogging layers. The classic Damköhler number (DaO2) with an average reaction timescale was not appropriate to determine hyporheic function for the context of biofilm growth induced streambed permeability and biogeochemical reaction rates changing with time. The authors proposed a new Damköhler number (DaO2∗) with a correction factor (the ratio between current bacteria and initial bacteria) to identify hyporheic function while accounting for the dynamic process of microbial growth. The results demonstrate that bioclogging is a significant process that should be understood and included for identifying hyporheic nitrate function and distinguishing the threshold transition times. The new Damköhler number of oxygen reflects the crucial role of microbial growth on physical transport kinetic and biogeochemical kinetic, and the criterion can be taken as a new indicator of the net nitrate system within streambeds with high nutrients loading.
The research is supported by National Natural Science Foundation of China, Natural Science Foundation of Hubei Province, the Fundamental Research Funds for the Central Universities, CUG and other projects.
Research information: Ping, X., Jin, M., Xian, Y., 2020. Effect of bioclogging on the nitrate source and sink function of a hyporheic zone. Journal of Hydrology, 590, 125425.
Paper link: https://doi.org/10.1016/j.jhydrol.2020.125425
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