一种基于开放气室的土壤呼吸监测装置

A soil respiration monitoring equipment based on open chamber method

针对传统开放气室需要将气体取样至红外气体分析仪(IRGA)测量CO_(2)浓度的不便,设计了一种土壤呼吸监测装置,并提出了补偿气体CO_(2)浓度不稳定时的修正计算方法。通过计算流体力学仿真分析,将一种小巧、轻便、低成本的非色散红外传感器模块布置于气室内部的合适位置,替代IRGA。控制气体流量为3、4、5 L·min^(-1),根据仿真软件获得土壤呼吸速率为0.5、2、5、10μmol·m^(-2)·s^(-1)时气室内的CO_(2)体积分数场。以气室底面中心点为原点建立笛卡尔坐标系,结合传感器模块尺寸分析,发现对于所述气室,由点(-0.0465,0.0717,0.2090)(单位为m)为球心、直径0.05 m确定的球形区域内,测量CO_(2)浓度计算土壤呼吸速率的平均误差不超过15%。将布置传感器后的装置与LI-8100开路式土壤碳通量测量系统,以及自制的密闭气室进行实地对比测验,平均误差为10.8%,与仿真分析结果一致。

A soil respiration monitoring equipment was designed to overcome the inconvenience of conventional open chambers which required gas sampling in an infrared gas analyzer to measure CO_(2)concentration,and a correction calculation method was proposed for unstable CO_(2)concentration.A compact and lightweight low-cost non-dispersive infrared sensor module was installed in a suitable position inside the chamber as an alternative to the infrared gas analyzer through computational fluid dynamics simulation analysis.Under the controlled gas flow rate of 3,4,5 L·min^(-1),the CO_(2)concentration field inside the chamber at soil respiration rates of 0.5,2,5,10μmol·m^(-2)·s^(-1)was obtained according to the simulation software.The center point of the bottom surface of the chamber was used as the origin to establish Cartesian coordinate system.Combined with the analysis of sensor module dimensions,it was found that for the chamber described in this research,the average error in measuring CO_(2)volume fraction to calculate soil respiration rate did not exceed 15%in the spherical area determined by the point(-0.0465,0.0717,0.2090)(unit:m)as the center and the diameter of 0.05 m.After the deployment of sensors,the performance of the equipment was compared with the LI-8100 automated soil CO_(2)flux system and the self-made closed chamber in field,and the mean error was 10.8%,which was consistent with the results of the simulation analysis.