SCG-NSoil profile CO2 gradient monitoring system

Soil respiration is the main carbon source for terrestrial ecosystems. According to reports, the average annual soil respiration of 18 forest types in the European Flux Project EUROFLOX accounts for 49% of their total primary productivity（Janssens et al., 2001）Law et al. (2001) found that soil respiration accounts for about three-quarters of the entire ecosystem respiration. The subtle changes in soil carbon pool will have a significant impact on atmospheric CO2 concentration, so studying soil carbon dynamics and CO2 emissions has become an urgent and important topic for predicting changes in atmospheric CO2 concentration. There have been many studies on soil surface CO2 flux (total soil respiration), but this is clearly not enough to explain the process of soil CO2 production. The study of soil profile CO2 vertical gradient has become an increasingly hot topic in soil respiration and even ecosystem carbon cycling research. Continuous monitoring of CO2 production at different levels (depths) of soil is crucial for understanding soil CO2 dynamics, as it can elucidate the changing characteristics of CO2 flux from soil to atmosphere with seasons, light, temperature, humidity, and soil properties. In addition, soil vertical gradient CO2 monitoring can be compared with widely used vorticity related monitoring to quantitatively study and analyze carbon exchange in ecosystems. In recent years, a series of creative technological methods have been studied abroad, and the SCG-3 soil profile CO2 gradient monitoring system is an integrated in-situ CO2 continuous monitoring system developed based on the above research.

according toFick's first law,In the case of steady-state diffusion, the flow rate of diffusion material per unit cross-sectional area perpendicular to the diffusion direction per unit time is called diffusion fluxJThe concentration gradient at the cross-section is directly proportional to the concentration gradient. Soil profile CO2 flux（μmol CO2 m⁻²s⁻¹）According to this law, the specific calculation formula is:

J= -D(dC/dx)

of whichDThe diffusion coefficient of CO2 in soil (unit: m)²/s， C is the concentration of CO2 at a depth of x (in meters), which is related to soil temperature, soil volume moisture content, and soil porosity,dC/dxFor concentration gradient, the "-" sign indicates that the diffusion direction is the opposite direction of the concentration gradient, that is, diffusion from high concentration areas to low concentration areas.

SCGThe soil profile CO2 gradient monitoring system consists of CO2 sensors, O2 sensors (optional), soil temperature sensors, soil moisture sensors, soil surface respiration chambers (optional), data collectors, and ground meteorological stations with different burial depths in the soil profile. The soil surface respiration chambers are divided into transparent and non transparent types, with the transparent chamber used to measure soil respiration and net respiration of plant photosynthesis.

Characteristics of the system:

l Non disturbance in-situ continuous measurement of soil profile CO2, moisture, and temperature (standard configuration is 3 layers) can be used to obtain soil CO2 flux (soil respiration) through Fick's first law, thereby achieving high temporal resolution in-situ monitoring of soil respiration

l VaisalaMeteorological sensors automatically measure and record air temperature and humidity, air pressure, rainfall, wind speed and direction, etc

l Soil porosity measurement can be conducted to determine the CO2 diffusion coefficient, while soil permeability measurement can be used to determine the relationship between soil permeability and soil moisture and gas flux

l TRIME-PICO32Soil moisture intelligent sensor, accurately measuring soil moisture and temperature

l Optional single channel or multi-channel fluorescent fiber optic soil profile oxygen in-situ monitoring module

l Optional wrapped plant stem flow monitoring module or THB stem flow monitoring module can be used to monitor the dynamic relationship between stem flow and in-situ CO2

l ACETransparent or non transparent soil respiration chamber method (optional) for measuring surface soil respiration, which can be used to supplement, calibrate, or compare soil profile CO2 gradient measurement data

l Wireless data transmission allows for online browsing and downloading of data at any time

l Optional micro root window root system dynamic monitoring system

l Battery powered or solar powered

Main technical indicators:

1. Soil moisture measurement:

a.TRIME-PICO32Intelligent sensor, TDR measurement technology, measurement range 0-100% volumetric moisture content, accuracy±1%, with a repeatability of ± 0.2%, measuring a volume of 250ml (optional PICO64, measuring a volume of 1250ml, can accurately reflect the moisture content of soil containing gravel);

b.Soil temperature measurement range: -20℃～50℃Measurement accuracy: ± 0.2℃

c.Waterproof rating IP68

2. Soil CO2 measurement: Non dispersive single beam dual wavelength infrared technology (NDIR), measurement range 0-5000ppm, 0-7000ppm, 0-10000ppm, 0-20000ppm optional, accuracy ± 1.5%, response time 30 minutes;

3. The standard configuration includes monitoring of CO2, soil moisture, and soil temperature in a 3-layer (SCG-3) soil profile

4. Single channel or multi-channel soil profile oxygen measurement module (optional), fluorescent fiber optic O2 measurement technology, high stability, zero oxygen consumption, response time of 5 seconds, measurement range of 0-50%, accuracy better than 0.4%

5. Standard 16 channel data collector (optional 32 channels to monitor CO2 concentration, soil moisture, and soil temperature above 3 layers):

a.It can store 220000 sets of timestamp data with a resolution of 16 bits,± 20 mV up to ± 2.5 V 8Range input, accuracy 0.03%;

b.The measurement interval can be adjusted from 3 seconds to 4 hours, with an average data interval of 3 seconds to 4 hours;

c.Voltage 6.5-15VDC, standby power consumption 150 μ A, measured power consumption 15mA, weight 140g;

d.Lithium battery backup, 3V, can be used for more than 5 years;

e.Operating temperature -20-60 ° C;

f.Professional data download and analysis software, capable of data download, online observation, statistical analysis (such as hourly average, daily average, total, minimum value, maximum value, data correlation analysis), chart display, and system settings;

6. Soil porosity measurement: pressure chamber volume of 1000ml, pressure range of -1 to 3bar, pressure resolution of 1mbar

7. In situ measurement of surface soil permeability: measurement range 0.003-3cm/s, measurement pressure 1-3hPa, water potential measurement range 0-800hPa, soil volume moisture content 0-70%

8. Package type stem flow monitoring module: SHB heating technology, used to monitor stem fluid flow of 5-20mm

9. Trunk flow monitoring module: THB heating technology, internal heating of tree trunks, used for monitoring trunk flow of over 10cm

10. Monitoring soil surface CO using respiration chamber method₂Flux (optional): The standard configuration is the ACE soil respiration monitor,There are two modes to choose from: closed and open, with transparent or non transparent breathing chambers available for each mode,measuring rangedo40.0 mmols m^-3（0-896ppm）,Resolution of 1ppm，Equipped with an automatic zero calibration device

11. Meteorological Monitoring: Vaisala Meteorological Sensor, Temperature Monitoring Range -52℃～60℃, accuracy ± 0.3 ℃; The atmospheric pressure monitoring range is 600-1100hPa, with an accuracy of ± 0.5hPa; The relative moderate monitoring range of air is 0-100%, with an accuracy of ± 3%; Rainfall output resolution of 0.01mm, accuracy of 5%

12. Wireless data transmission, browsing and downloading data through software terminals, and performing statistical analysis on the data

13. Root ecological observation (optional): composed of micro root canals, micro root canal microscopes, and analysis software. The standard micro root canal diameter is 44mm (inner diameter 42mm), with high transparency, toughness, and rain resistance. The length of the micro root canal endoscope is 17 inches, 22 inches, 28 inches, and 37 inches to choose from. The micro root canal imaging unit is a 1/4 "color CCD with 768 x 494 pixels and a signal-to-noise ratio of 48DB. A handheld high-resolution imaging unit and a 1/3" color CCD can be optionally equipped, with a resolution of up to 1600 x 1200 pixels; Communication and image capture through USB and computer, easy to operate

The above figure shows the changes in CO2 flux R (top) and CO2 concentration (bottom) at different soil profile depths (5cm, 12.5cm, 35cm) in summer and autumn. The rainfall situation is shown on the right vertical axis (taken from Z. Nagy et al., 2011). The research shows that the eddy method underestimates the CO2 flux (especially when the flux is low), and the grassland in arid areas often has a reverse CO2 flux from atmosphere to soil after rainstorm.

Origin: Europe