Effect of carbaryl contamination on bioretention system nitrogen removal performance

Stormwater runoff is the main source of carbaryl in natural waters; bioretention cells can effectively retain and remove carbaryl from stormwater runoff. However, the accumulation of carbaryl in the bioretention cell impacts its stormwater purification ability, especially nitrogen removal performance. To investigate the mechanisms behind the influence of carbaryl in stormwater runoff on the nitrogen removal performance of bioretention cells, the purification of carbaryl in bioretention facilities was compared under four carbaryl concentrations (0, 0.5, 1.0, and 2.0 mg/L); the effects of carbaryl input on nitrogen removal and the microbial community structure inside the filler were analyzed. After entering the bioretention cell, carbaryl was mainly adsorbed within the filler at a depth of 10-30 cm, and the desorption-adsorption process continued during subsequent rainfall. Carbaryl input negatively affected the denitrification performance of the bioretention cell. The removal rate of nitrate nitrogen (NO₃^--N) decreased by 61.13-100.09%, and that of total nitrogen (TN) was reduced by 24.82-38.95%. Carbaryl accumulation reduced the abundance and diversity of microorganisms in the bioretention cell. The relative abundance of some denitrifying bacteria genera (Terrimonas, Bdellovibrio, Aquabacterium, Ohtaekwangia, Sphingomonas, and SWB02) also decreased, which was the main reason for the decrease in the nitrogen removal performance.