Carbon, Water & Energy
Carbon is the molecular building block of life, carbon balances in the atmosphere and earth can also change life. Increasingly, carbon emissions and sinks have become important in the context of anthropogenic climate change [CO2] emissions from anthropogenic activities (e.g. burning of fossil fuels) have increased. [CO2] accumulation in the atmosphere, acting as a greenhouse gas, is now accepted to be responsible for anthropogenic global warming].
Water is necessary for life on earth and establishing a better understanding of its dynamics will help to secure a better life for South Africa. Energy is the force that drives the rate of change of interconnected processes between carbon and water. To integrate carbon, water and energy dynamics, SAEON and UKZN (headed by Prof. Colin Everson) has established a complex instrument array in catchment VI at Cathedral Peak.
Carbon dioxide fluxes are being measured by SAEON using an Eddy Covariance system. The water budget and dynamics of the catchment is being balanced by rain gauges, stream flow, soil moisture spatial and temporal movement, and evapotranspiration. Energy/heat dynamics are being measured by Colin’s the Large Aperture Scintillometer and SAEONs Eddy Covariance system.
Eddy Covariance measurements
Air moves in horizontal and vertical fluxes or eddy’s, such as the eddy’s carrying water vapour seen over a hot mug of coffee. If one is able to quantify eddy movement over the mug of coffee, and the amount of water vapour in the air parcels in the eddies, through calculations one would know exactly how much water is in flux and leaving the mug of coffee. Simply put, this is exactly what eddy covariance measures do in principal.
The two main components of an eddy covariance tower are an ultrasonic anemometer and infrared gas analyser. The ultrasonic anemometer outputs are used to calculate eddy fluxes and the infrared gas analyser outputs to quantify important atmospheric gases. The covariance of the eddy flux and gas quantification then allows the determination of exchange rates of atmospheric gases. Important gases analysed by this method are water vapour, carbon dioxide and methane. Heat of the eddy parcels is also calculated allowing the calculation of heat flux as well.
Large Aperture Scintillometer
The Large Aperture Scintillometer (LAS), similar to the Eddy Covariance tower measures heat flux. The advantage of the LAS system is that it measures the heat flux over larger areas (several kilometers) compared to the Eddy Covariance system, which just measures at a single point. The particular type of heat flux the LAS system measures is sensible heat flux, i.e. the conductive heat flux from the earth’s surface to the atmosphere.
The LAS system measures sensible heat flux by transmitting and receiving optical radiation between two fixed points. Interference in the transmissions between the two fixed points is caused by variations in temperature, humidity and pressure fluxes. These types of fluxes or eddy’s are sometimes visible to the human eye. An example of this is when distortions are visible over a hot surface, e.g. a tar road on a warm day. These distortions are also known as scintillations. Scintillations are caused by differences in the temperature and humidity (to a lesser extent pressure) and vary greatly in size. A LAS has two main components, a receiver and a transmitter. The receiver calculates the amount of scattering/interference that has occurred over the known distance from the LAS transmitter. Mathematically, the interference is related to the temperature and humidity to calculate the sensible heat flux.
Cosmic Ray Probe (funded and driven by Prof Colin Everson from UKZN)
The cosmic ray probe is a state of the art instrument that measures soil moisture within the soil profile over an area of ~30ha from a single point. This new technology has only been used at three sites in South Africa. This work is being driven and funded by Prof Colin Everson who has an 18 year history of working in the catchments. Unlike other methods of measuring soil moisture, such as Time Domain Reflectrometry or Neutron probes, the Cosmic Ray Probe method is non-invasive.
The earth’s atmosphere is continually bombarded by high energy radiation (incorrectly named cosmic rays), that collide with particles in the earth’s atmosphere. These collisions result in the production of secondary cosmic rays that are composed of high energy protons and atomic nuclei. The cosmic rays are mostly scattered and absorbed upon reaching the soil. A proportion of the cosmic rays escape back in to the air depending on the soil moisture. In drier soils, fewer cosmic rays (particularly fast neutrons) escape and conversely, in wetter soils a greater proportion of fat neutrons are absorbed. The cosmic ray probe estimates soil moisture water content by calculating the proportion of escaped fast neutrons and the incoming fast neutrons.
Balancing Carbon, Water and Energy budgets: Catchment VI, the holistic approach
Carbon is the molecular building block of life, carbon balances in the atmosphere and earth can also change life. Increasingly, carbon emissions and sinks have become important in the context of anthropogenic climate change [CO2 emissions from anthropogenic activities (e.g. burning of fossil fuels) have increased. CO2 accumulation in the atmosphere, acting as a greenhouse gas, is now accepted to be responsible for anthropogenic global warming].
Water is necessary for life on earth and establishing a better understanding of its dynamics will help to secure a better life for South Africa. Energy is the force that drives the rate of change of interconnected processes between carbon and water. To integrate carbon, water and energy dynamics, SAEON and UKZN (headed by Prof. Colin Everson) has established a complex instrument array in catchment VI at Cathedral Peak.
Carbon dioxide fluxes are being measured by SAEON using an Eddy Covariance system. The water budget and dynamics of the catchment is being balanced by rain gauges, stream flow, soil moisture spatial and temporal movement, and evapotranspiration. Energy/heat dynamics are being measured by Colin’s the Large Aperture Scintillometer and SAEONs Eddy Covariance system.
Photo above: Prof Colin Everson (right) explaining to scientists the functioning and significance of the Eddy Covariance system in catchment VI at Cathedral Peak.
Eddy Covariance measurements
Air moves in horizontal and vertical fluxes or eddy’s, such as the eddy’s carrying water vapour seen over a hot mug of coffee. If one is able to quantify eddy movement over the mug of coffee, and the amount of water vapour in the air parcels in the eddies, through calculations one would know exactly how much water is in flux and leaving the mug of coffee. Simply put, this is exactly what eddy covariance measures do in principal.
The two main components of an eddy covariance tower are an ultrasonic anemometer and infrared gas analyser. The ultrasonic anemometer outputs are used to calculate eddy fluxes and the infrared gas analyser outputs to quantify important atmospheric gases. The covariance of the eddy flux and gas quantification then allows the determination of exchange rates of atmospheric gases. Important gases analysed by this method are water vapour, carbon dioxide and methane. Heat of the eddy parcels is also calculated allowing the calculation of heat flux as well.
Large Aperture Scintillometer
The Large Aperture Scintillometer (LAS), similar to the Eddy Covariance tower measures heat flux. The advantage of the LAS system is that it measures the heat flux over larger areas (several kilometers) compared to the Eddy Covariance system, which just measures at a single point. The particular type of heat flux the LAS system measures is sensible heat flux, i.e. the conductive heat flux from the earth’s surface to the atmosphere.
The LAS system measures sensible heat flux by transmitting and receiving optical radiation between two fixed points. Interference in the transmissions between the two fixed points is caused by variations in temperature, humidity and pressure fluxes. These types of fluxes or eddy’s are sometimes visible to the human eye. An example of this is when distortions are visible over a hot surface, e.g. a tar road on a warm day. These distortions are also known as scintillations. Scintillations are caused by differences in the temperature and humidity (to a lesser extent pressure) and vary greatly in size. A LAS has two main components, a receiver and a transmitter. The receiver calculates the amount of scattering/interference that has occurred over the known distance from the LAS transmitter. Mathematically, the interference is related to the temperature and humidity to calculate the sensible heat flux.
Cosmic Ray Probe (funded and driven by Prof Colin Everson from UKZN)
The cosmic ray probe is a state of the art instrument that measures soil moisture within the soil profile over an area of ~30ha from a single point. This new technology has only been used at three sites in South Africa. This work is being driven and funded by Prof Colin Everson who has an 18 year history of working in the catchments. Unlike other methods of measuring soil moisture, such as Time Domain Reflectrometry or Neutron probes, the Cosmic Ray Probe method is non-invasive.
The earth’s atmosphere is continually bombarded by high energy radiation (incorrectly named cosmic rays), that collide with particles in the earth’s atmosphere. These collisions result in the production of secondary cosmic rays that are composed of high energy protons and atomic nuclei. The cosmic rays are mostly scattered and absorbed upon reaching the soil. A proportion of the cosmic rays escape back in to the air depending on the soil moisture. In drier soils, fewer cosmic rays (particularly fast neutrons) escape and conversely, in wetter soils a greater proportion of fat neutrons are absorbed. The cosmic ray probe estimates soil moisture water content by calculating the proportion of escaped fast neutrons and the incoming fast neutrons.
