How fast do lakes breathe?

Investigating gas exchange between the water and air

Did you know that water bodies frequently exchange gases with the air?  It’s not quite breathing, but just like our lungs absorb oxygen and release carbon dioxide, ponds and lakes absorb and release gases such as oxygen, carbon dioxide, and methane.  The amount of gases that water bodies release is important for estimating greenhouse gas budgets at a global scale, and it also tells us a lot about the water body’s productivity and functioning.

A key question remains: how quickly does the water exchange gases with the air?

5.28_Westford Diffusion

Adding small amounts of propane to a pond allowed us to measure air-water gas exchange.

This is the question our research addressed (read the paper in Journal of Geophysical Research – Biogeosciences).  We set out to directly measure gas exchange rates in four small ponds in northeastern Connecticut.  In larger lakes, we can derive gas exchange rates from wind speed.  However, in smaller ponds that are sheltered from the wind, gas exchange rates are not well understood.  We found that gas exchange rates in small ponds were lower than in larger lakes.  But unexpectedly, we also found that gas exchange rates were extremely variable within and among ponds, and were hard to predict from environmental variables (e.g., wind speed, temperature, rainfall).


Gas exchange increases and becomes more variable with increasing lake size.

We decided to compare the variability we saw in small ponds to studies done in larger lakes.  We found that while gas exchange rates increased with lake size, so did variability.  This variability is not accounted for in global models of gas exchange, meaning our global estimates of carbon emissions from inland waters are more uncertain than we previously thought.  Moving forward, we need to (1) include uncertainty around gas exchange in global models and (2) measure gas exchange directly in ponds and lakes of all sizes, and especially in small and large systems that are currently understudied.


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