Hi Siyue

There are currently 3 main methods to measure aquatic GHG fluxes -

1. measurement of water-side gas partial pressures using an air water equilibrator and a gas analyzer  and modelling fluxes based on an empirical model of transfer velocity (normally based on windspeed, current etc) and the difference in partial pressures between air and water

2. Floating chamber/helmet measurements - the flux is directly measured in a chamber floating on the water surface

3. Micrometeorology methods (e.g. Eddy covariance, gradient flux etc) - the flux is measured directly above the water surface.

All 3 methods have there advantages and disadvantages for example Method 1 requires an empirical model of transfer velocity to be used, which may or may not be applicable to the system being studies. Method 2 may induce artificial turbulence and therefore increase flux rates and Method 3 requires a relatively large "footprint" to be measured i.e. it requires a large area of water (10's to 100's of meters) and therefore may not be suitable for small lakes, streams rivers and estuaries.

We have been using cavity ring down spectrometers (CRDS) coupled to air water equilibrators successfully for measuring CO2, CH4 and N2O partial pressure in water, and one advantage is that we can get the carbon and nitrogen stable isotope ratios (using the particular instruments we have) which give us information about the source and sinks of these GHG.

Attached are some of the papers our group has produced on aquatic GHG fluxes and methodology that you might find useful.

In terms of future directions - i personally think that improvement of micrometeorology methods will be the way forward. Particularly with the improvement of laser based instrumentation (CRDS TDL etc), the ability to directly measure not only bulk fluxes of GHG but also the isotope ratio of these fluxes will provide significant insight into aquatic GHG sources and sinks.

Article Methane and carbon dioxide dynamics in a subtropical estuary...

Article Novel Use of Cavity Ring-down Spectroscopy to Investigate Aq...

Article Carbon dioxide and methane emissions from an artificially dr...

Article Estuarine canal estate waters: Hotspots of CO2 outgassing dr...

Article Coupling Automated Radon and Carbon Dioxide Measurements in ...

Article Carbon dioxide dynamics driven by groundwater discharge in a...

Article Drivers of pCO2 variability in two contrasting coral reef la...

Thanks for your excellent publications,  Maher. At present, I have used the emperical modeling to quantify the GHG from lakes and reservoirs at large scale. while I am thinking I should get some advanced in-site methods for accurate determination. I know LGR is a good one to du this research though I have not used. I have read some papers of yours and Santos's. I will try to contact you and meet you later.