Characteristics of nutrients accumulation in the sediment of the surface-flow constructed wetlands of Mata Lake, China

As a nutrients reservoir of surface-flow constructed wetlands (SFCWs), the substrate plays an important role in water purification, and it is significant to investigate the accumulation and release characteristics of nutrients to maximize the efficiency of constructed wetlands (CWs) for wastewater purification. In this study, we analyzed the total nitrogen (TN), total phosphorus (TP) and organic matter (OM) in the bottom sediment and conducted static release experiments on column core samples in order to evaluate the accumulation characteristics of nutrients and the current status of the ecological water environment in the SFCWs, which has been in operation for 6 years. Results showed that: (1) The average concentration of TN, TP and OM were 2.30 ± 0.006 g/kg, 0.26 g/kg and 10.49 ± 0.04 g/kg, respectively. There were differences in the spatial distribution of nutrients based on ArcGIS spatial interpolation simulation analysis. (2) The organic index (Org-index) in the sediment was evaluated as lightly polluted and the TP was evaluated as clean, but the organic nitrogen (Org-N) index was evaluated as heavily polluted. (3) The release amount of nutrients in the static release experiment showed a general trend of ascending in about the first 10 days and then descending, and the maximum release rate was observed between 9 and 12 days.