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Shan Jiang, Mark Kavanagh, Juan Severino Pino Ibánhez, Carlos Rocha. Denitrification-nitrification process in permeable coastal sediments: An investigation on the effect of salinity and nitrate availability using flow-through reactors[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-021-1811-5
 Citation: Shan Jiang, Mark Kavanagh, Juan Severino Pino Ibánhez, Carlos Rocha. Denitrification-nitrification process in permeable coastal sediments: An investigation on the effect of salinity and nitrate availability using flow-through reactors[J]. Acta Oceanologica Sinica.

# Denitrification-nitrification process in permeable coastal sediments: An investigation on the effect of salinity and nitrate availability using flow-through reactors

##### doi: 10.1007/s13131-021-1811-5
Funds:  The National Natural Science Foundation of China under contract Nos 41706081 and 41530960; the Scientific Research Foundation of SKLEC under contract No. 2017RCDW04; the Portuguese Foundation for Science and Technology (FCT), the EU (FEDER) and the Portuguese Government through project NITROLINKS—NITROgen loading into the Ria Formosa through Coastal Groundwater Discharge (CGD)-Pathways, turnover and LINKS between land and sea in the Coastal Zone under contract No. PTDC/MAR/70247/2006.
• Corresponding author: sjiang@sklec.ecnu.edu.cn
• Accepted Date: 2021-01-13
• Available Online: 2021-08-18
• Permeable coastal sediments act as a reactive node in the littoral zone, transforming nutrients via a wide range of biogeochemical reactions. Reaction rates are controlled by abiotic factors, e.g., salinity, temperature or solute concentration. Here, a series of incubation experiments, using flow-through reactors, were conducted to simulate the biogeochemical cycling of nitrate (${\rm {NO}}_3^-$) and phosphorus (P) in permeable sediments under different ${\rm {NO}}_3^-$ availability conditions (factor I) along a salinity gradient (admixture of river and seawater, factor II). In an oligotrophic scenario, i.e., unamended ${\rm {NO}}_3^-$ concentrations in both river and seawater, sediments acted as a permanent net source of ${\rm {NO}}_3^-$ to the water column. The peak production rate occurred at an intermediate salinity (20). Increasing ${\rm {NO}}_3^-$ availability in river water significantly enhanced net ${\rm {NO}}_3^-$ removal rates within the salinity range of 0 to 30, likely via the denitrification pathway based on the sediment microbiota composition. In this scenario, the most active removal was obtained at salinity of 10. When both river and seawater were spiked with ${\rm {NO}}_3^-$, the highest removal rate switched to the highest salinity (36). It suggests the salinity preference of the ${\rm {NO}}_3^-$ removal pathway by local denitrifiers (e.g., Bacillus and Paracoccus) and that ${\rm {NO}}_3^-$ removal in coastal sediments can be significantly constrained by the dilution related ${\rm {NO}}_3^-$ availability. Compared with the obtained variation for ${\rm {NO}}_3^-$ reactions, permeable sediments acted as a sink of soluble reactive P in all treatments, regardless of salinity and ${\rm {NO}}_3^-$ input concentrations, indicating a possibility of P-deficiency for coastal water from the intensive cycling in permeable sediments. Furthermore, the net production of dissolved organic carbon (DOC) in all treatments was positively correlated with the measured ${\rm {NO}}_3^-$ reaction rates, indicating that the DOC supply may not be the key factor for ${\rm {NO}}_3^-$ removal rates due to the consumption by intensive aerobic respiration. Considering the intensive production of recalcitrant carbon solutes, the active denitrification was assumed to be supported by sedimentary organic matter.

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沈阳化工大学材料科学与工程学院 沈阳 110142