Pond Biogeochemistry

During my Ph.D., I found that the ecology of small ponds is largely shaped by the system’s very unique biogeochemistry.  Specifically, small ponds receive large quantities of terrestrial leaves each autumn from litter fall.  These leaves are broken down in the ponds, a process that consumes oxygen, produces carbon dioxide and methane, and creates a very distinctive environment for the organisms that call small ponds home.

Carbon Cycling

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Drawing by Chai Rin Kim, Yale Daily News

Inland freshwaters tend to be net sources of carbon to the atmosphere, meaning that the system breaks down more carbon (through respiration) than it produces (through photosynthesis). I found that small, forested ponds (<1,000 m2) are among the most supersaturated water bodies on Earth for both carbon dioxide (CO2) and methane (CH4). As such, these understudied ponds play a disproportionately large role in greenhouse gas production relative to their size.  I published these findings in Biogoechemistry.

I also conducted a meta-analysis to look at  CO2 and CH4 fluxes from 427 lakes and ponds world-wide, and evaluate the importance of very small ponds(<1,000 m2) to global carbon emissions.  I found that while small ponds only comprise 9% of lakes and ponds by area, they account for about 15% of CO2 and 41% of CH4emissions.  These ponds are small but mighty in their ecological significance!  This work is published in Nature Geoscience.

Oxygen Dynamics

Small ponds are very low oxygen environments, yet are productive and support a wide array of invertebrate and amphibian consumers. I studied oxygen dynamics in small, forested ponds and discovered an important phenomenon: small ponds receive substantial overnight influxes of oxygen from the atmosphere. As ponds cool overnight, turbulence is generated at the air-water interface, which increases oxygen invasion into the pond. These bursts of oxygen may help support pond organisms in otherwise low oxygen habitats.  Check out our paper in Geophysical Research Letters.

Gas Exchange Rates

I mentored a Yale undergraduate on her senior honor’s thesis, which looked at gas exchange rates in small ponds.  Gas exchange rates govern how quickly gas is transferred between the air and the water, and therefore mediates how much carbon (CO2 and CH4) is emitted from ponds.  We conducted whole-pond experiments where we added low levels of propane to four small ponds, and then measured propane loss over time, which we used to estimate gas exchange rates. This work is published in JGR – Biogeosciences.

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Measuring gas exchange rates in small ponds using a propane gas tracer.

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