UC Santa Barbara

There is an urgent need to understand the effect of climate warming on the carbon dynamics of lakes and ponds in order to assess contributions to global carbon budgets. Currently, we are unable to predict how the exchange of carbon gases (i.e. CO2) across the air–water boundary and organic carbon storage in the sediments will be altered with realistic warming scenarios downscaled from climatic models. Given the prevalence of shallow systems and tight atmospheric coupling, we conducted a mesocosm experiment to test the impacts of warming on CO2 saturation in a shallow prairie pond. We outline and test three possible scenarios for the effect of warming on the CO2 saturation of ponds, resulting in either an increase, decrease or no net effect for CO2 saturation. We show that with approximately a two-degree (ºC) increase in average water temperature, the pCO2 of the warmed mesocosms was nine times greater than the ambient temperature mesocosms by the end of the 5-week experiment. Changes in water colour (a measure of dissolved organic carbon) in warmed systems indicate that decomposition of organic matter in the sediments and water column was the main contributor to the increase in pCO2 in the warmed mesocosms. Our results show that with warming, the release of CO2 from shallow ponds to the atmosphere will increase and carbon storage in the sediments will decrease, altering the current functioning of shallow prairie ponds and influencing the contribution of ponds to the global carbon cycle.