地下水埋深对农田排水沟氮磷去除效应的影响机制OACHSSCD

Farmland drainage ditches are often used to exclude surface water and irrigation tail water.While undertaking agricultural water withdrawal,they also show significant pollution interception potential.However,its pollution removal efficiency is not only affected by its own structural characteristics and internal microbial activities,but also closely related to the surrounding hydrological and environmental conditions.Clarifying the interaction mechanism between the hydrological environment and the sewage interception efficiency of farmland drainage ditches is the key to further optimize its pollution control function.Therefore,in this study,two drainage ditches with distinct groundwater depths'G-S(0.6-1.8 m)and G-D(4.8-5.9 m)'were selected for in-situ monitoring,index quantification,and path analysis to elucidate the influence of groundwater depth on nitrogen and phosphorus removal.Results showed that the flow reduction rates of G-S and G-D ranged from-38.18%-7.11%and 16.76%—57.99%,respectively.G-D showed strong retention and infiltration capacity,while G-S had weak or even negative flow reduction capacity.In terms of pollutant removal per 100 m,G-D achieved significantly higher removal rates for total nitrogen(TN:17.20%—58.35%)and total phosphorus(TP:-1.17%—57.83%)compared with G-S(TN:-3.59%—5.71%;TP:-6.56%—2.16%).This phenomenon was attributed to the difference in hydrological conditions caused by groundwater depth(path coefficient 0.99,P＜0.01).G-D maintained lower soil water content((20.94±4.59)%)and a larger hydraulic relative head difference(5.75 m),resulting in higher infiltration capacity(1.06 cm/h).In contrast,G-S had a low relative head difference(1.81m)and the soil was close to saturation(water content(30.74±8.32)%),leading to lower infiltration(0.38 cm/h).This study provides a scientific basis for designing farmland drainage ditches with enhanced capacity to intercept non-point source pollutants.