A laboratory experimental research into the bioturbation effects of Sinonovacula constricta on the content of nitrogen forms in columnar sediments

The bioturbation effects of Sinonovacula constricta on the transformation of different forms of nitrogen in sediments were studied based on a laboratory experiment in this study. Two treatment groups and a control group were set up according to different biological densities (99 ind./m², 249 ind./m²), and a 20-day laboratory experiment was carried out in the condition of water temperature 23 ℃, salinity 26 psu, and pH8. The columnar sediments were stratified and cut from top to bottom, and the changes of different forms of nitrogen content in the sediment were analyzed. Results showed that the content of total nitrogen (TN) in the sediment increased after the bioturbation of S. constricta. The content of non-transferable total nitrogen (NTN) increased by 30.94%, and the content of transferable total nitrogen (TTN) decreased by 20.57%. The content of organic-sulphide form (OSF-N) was the highest among the four forms, accounting for 9.31% of TN, which was the main form of TTN. The content of carbonate form (CF-N) was the lowest and only 2.77% of TN. The ion exchange form (IEF-N) and the iron manganese oxide form (IMOF-N) accounted for 3.39% and 3.06% of TN, respectively. Above all, the bioturbation of S. constricta promoted the conversion of OSF-N to other forms, as well as the conversion of transferable total nitrogen to non-transferable total nitrogen.