典型盐碱地改良区农田排水沟水体与底泥界面氧通量研究

Experimental studies on the oxygen flux across the sediment-water interface in drainage ditches of saline water

农田排水沟水体与底泥中的氧含量决定了底泥中各种生源要素的最终归趋,对维持农田排水沟的水环境至关重要。本论文以陕西富平县卤泊滩盐碱地改良区农田排水沟水体与底泥为研究对象,从环境微界面角度出发,根据多年监测数据构建室内试验,采用高分辨率微环境固液剖面传感系统(丹麦Unisense微电极系统),探究了研究区农田排水沟水体与底泥界面氧通量变化规律。研究结果表明:底泥中的溶解氧随深度的增加逐渐减小,直至溶解氧浓度为零,到达厌氧层;溶解氧剖面浓度的实测值与Profile模型模拟值的相关系数均在0.995以上,表明该模型能客观地描述溶解氧在农田排水沟水体与底泥扩散边界层和底泥中的分布;农田排水沟上游不同监测点位的底泥含氧层厚度在3.5~6 mm之间,而下游监测点位的底泥含氧层厚度约为1.5 mm,差异显著;通过氧浓度线性分布、剖面拐点法得到氧气扩散边界厚度,上游监测点位的氧气扩散边界层厚度基本在1 mm,而下游监测点位的氧气扩散边界层厚度减少至0.2 mm。农田排水沟水体与底泥界面氧通量的测定,对于认识农田排水沟底泥的地球化学过程及水环境作用机理具有重要意义,可为农田排水沟水环境治理提供参考依据。

The micro-interface between the sediment of farmland drainage ditch and the water environment is an important place for oxygen transfer between the water phase and the sediment phase,which determines the fate of various solutes in the bottom sediment of drainage ditches.Accurate representation of the flux and diffusion boundary layer of the reactive components at the interface is very important for studying their environmental micro-interface behavior.In this paper,the water body and bottom sediment of farmland drainage ditches in a saline-alkali land improvement area of Fuping County,Shaanxi province is taken as the research object.Targeting the environmental micro-interface,an indoor experiment based on field monitoring data was conducted by using a high resolution microenvironment solid-liquid profile sensing system(unisense microelectrode system in Denmark).The variation of oxygen flux at the bottom of the drainage ditch was investigated.The results show that the dissolved oxygen in the bottom mud decreased gradually with the increase of depth until the dissolved oxygen concentration became zero and reached the anaerobic layer.The correlation coefficient between the measured concentration of dissolved oxygen profile and the simulated value of the Profile model was above 0.995,indicating that the model can reasonably well describe the distribution of dissolved oxygen in the boundary layer and bottom mud of the interface diffusion.The thickness of oxygen layer in different monitoring points in the upper reaches of the drainage ditch was between 3.5 and 6 mm,while the thickness of oxygen layer in the downstream monitoring point was about1.5 mm,significant differences were observed.The diffusion boundary thickness was obtained by the linear distribution of oxygen concentration and the profile inflection point method.The diffusion boundary layer of the upstream monitoring point position was about 1 mm,while the diffusion boundary layer of the downstream monitoring point position was 0.5 mm and 0.2 mm,respectively.The determination of oxygen flux at the micro-interface between water body and sediment in farmland drainage ditch is of great significance to know the geochemical processes and water environment mechanism of sediment in drainage ditch,which may provide reference for water environment management in farmland drainage ditch.