Inland waters are an important part of the global carbon cycle. Because many inland waters are located on low-lying parts of the landscape, they can receive high loads of terrestrial carbon (think leaf litter, sediments, dissolved carbon), which gets broken down by microbes in the water. This breakdown of carbon results in the respiration of carbon dioxide (CO2) and when no oxygen is present, can produce methane (CH4). When CO2 and/or CH4 concentrations in the water exceed atmospheric concentrations, they diffuse out of the water and into the air, meaning that inland waters can emit greenhouse gases to the atmosphere.
In a study published last week in Nature Geoscience, Meredith Holgerson (visiting student in the Strecker Lab) and co-author Dr. Peter Raymond report that small ponds (< 1,000 m2) play an important role in inland water carbon cycling. These small ponds have previously been excluded from global carbon budgets because the ponds are difficult to map and were often assumed to play a small role in greenhouse gas emissions. Yet, this new study estimates that small ponds only account for about 9% of lakes and ponds by area, yet contribute 15% of CO2 and 41% of CH4 emissions. To put it simply, small ponds play a disproportionately large role in carbon emissions from inland waters.
This study is an important step in understanding stocks and flows of carbon on a global scale. For instance, because most of the CO2 and CH4 released from small ponds is likely derived from terrestrial carbon sources, we could currently overestimate how much carbon terrestrial forests store. It will be important for future studies to (1) better map the global extent of small ponds on the landscape, and (2) integrate carbon emissions from small ponds into global carbon models.