Nutrient removal characteristics of the bioretention cell under high concentration glyphosate stress

The pesticide glyphosate is widely used in agriculture and is frequently detected in the natural environment. However, the effect of glyphosate in stormwater runoff on the nutrient removal efficiency of bioretention cells remains unclear. Coal- and zeolite-modified bioretention cells were constructed in this study, and their ammonia‑nitrogen (NH₄⁺-N) removal efficiency was inhibited at the beginning of glyphosate stress. In the late stage of the stress test, the NH₄⁺-N removal efficiency gradually recovered to >90 %, the concentration of nitrate nitrogen (NO₃^--N) was stable at 10-15 mg/L, and the concentration of nitrite‑nitrogen (NO₂^--N) was stable at 0.05-1.81 mg/L. Glyphosate negatively impacted nitrogen removal performance. The total nitrogen (TN) concentration also increased, and its removal efficiency decreased to <10 %. Total phosphorus (TP) concentrations during the initial rainfall event were significantly correlated with glyphosate concentrations (p < 0.01), with effluent TP reaching a maximum of 121 mg/L. In the late stage of the stress test, the phosphorus removal capacity of the bioretention cell gradually recovered. The relative abundance of glyphosate-tolerant bacteria and dominant decomposition bacteria increased, while the abundance of some denitrifying functional bacteria decreased under stress, ultimately affecting the water purification effect of the bioretention cell. In summary, glyphosate stress reduced the nitrogen and phosphorus removal in the bioretention cell; the phosphorus removal capacity gradually recovered, but nitrogen removal remained inhibited.