Pollutants removal efficiency assessment of constructed subsurface flow wetlands in lakes with numerical models

•Models for pollutants removal efficiency assessment was put forward.•Constructed subsurface flow wetlands can remove over 60% COD and 49% TN in a lake.•The TP, with removal efficiency 34%, is relatively difficult to remove by wetlands.•Higher water temperature and water depth will increase the removal efficiency.•The bigger flow velocity is disadvantage to removal performance of wetlands. Ecological remediation with subsurface flow wetland is one of the most widely used methods for pollution abatement. Assessment on its implementation efficiency is necessary but difficult. To evaluate the pollutant removal effect of constructed subsurface flow wetlands, a wetland growth model coupling with a hydrodynamic water quality model has been put forward. The coupled model has been used to assess the impact of constructed subsurface flow wetlands on a polluted lake in Hubei Province, China. Four pieces of constructed subsurface flow wetlands composed of Reed and Smooth cordgrass with total area of 38.9 thousand square meters for pollutant removal have been designed for the lake. Results showed that reductions of chemical oxygen demand (COD), total phosphorus (TP) and total nitrogen (TN) were 246.38, 28.14 and 3.29 tons/year, respectively. Compared with the different pollutants, the removal efficiency of subsurface flow wetlands on TN (49%) is bigger than TP (34%), but less than COD (60%). Furthermore, the higher water temperature, smaller flow velocity and bigger water depth will improve the pollutants removal performance of subsurface flow wetlands.