Substantial overnight reaeration by convective cooling discovered in pond ecosystems

Trends in freshwater dissolved oxygen (DO) reflect whole-ecosystem properties and influence organismal survival and behavior. Here we show that small ponds have unique oxygen dynamics that differ from larger lakes. We discovered that ponds undersaturated in DO experienced substantial increases in oxygen concentration overnight. Nighttime increases in DO occurred on 45% of the nights sampled and resulted in DO saturation increasing 12-fold (22% saturation) on average. Oxygen spikes were likely to occur when ponds became at least 1.8°C warmer than the air and later in the season when oxygen levels were low (