Ephemeral Ponds

Ephemeral (often referred to as vernal or temporary) ponds are depressions which temporarily hold water on poorly drained soils. Vernal pools require sufficient catchment area for recharge; contours to hold water long enough to balance losses to infiltration or evaporation; and impervious soils to hold water. These are easily and frequently drained, often accidentally, when drainage is "improved", or water diverted due to minor alterations in soil elevations.

Ephemeral ponds are rarely mapped or protected and may contain a significant amount of water in the watershed. The abundance of ephemeral ponds in headwater areas buffer downstream peaks in water flow and ensure a steady supply of water long after rain falls. The loss of the water retention function of ephemeral ponds high in the watershed often necessitates downstream storm water control measures. It is much more effective to retain this upstream function than to try to restore wetland functions in downstream areas due to limited space and water volumes.

It is difficult to establish a food web in restored sites because of recent creation. Temporary ponds are used by woodland salamanders, and in open areas shallow puddles and even water filled tire ruts are used by toads. Toad tadpoles like warm water and prefer ponds in open locations rather than those in woodlands. The warmer the water, the faster the toad tadpoles develop. This is an adaptation to the short life that many spring ponds have. Many tadpoles are killed each year if there is not sufficient rain or runoff to keep the pond full of water for 30­45 days.

Ephemeral ponds in headwater areas buffer downstream peaks in flow and ensure a steady flow of water long after rain falls.