Vernal ponds comes from the Latin word vernalis meaning spring. They might also be called vernal pools, ephemeral ponds, ephemeral pools, temporary ponds, and seasonal wetlands. Vernal ponds are formed seasonally in shallow ground depressions from spring snowmelt, precipitation, and rising water tables. Vernal ponds provide a habitat for distinctive plants and animals because they experience cyclic periods of water inundation and drying, typically filling with water in the spring or fall and drying during the summer or in drought years.
Vernal ponds are small, isolated wetlands that have no permanent inlet or outlet and occur in forested settings. Vernal ponds can occur wherever the ground is concave and liquid water enters faster then it leaves. Some vernal ponds have an underlying impermeable clay layer (also known as a hardpan) that reduces water percolation. The impermeable layer prevents water from draining into lower soil layers, allowing vernal pools to become inundated for a very long period of time. This feature of vernal ponds means that the water is allowed to slowly evaporate instead of draining. This is a key factor in the development of vernal pool plant communities as it keeps the soil at the waters edge just wet enough for vernal plant communities to flourish while those closer to the center of the pool are more inundated, leading to zonation of plant communities as the water level recedes. This clay layer also allows pools to exist long enough to prevent upland species from developing, while existing for just enough time to prevent aquatic plant species from taking over.
Geological factors resulting in the formation of a Vernal Pond: Floodplains - when a stream overflows its banks entering the floodplain. Some of the overflow pockets do a good job of retaining water and become vernal pools. If this continues over the years it can lead to the creation of vernal pool habitats in the form of oxbow wetlands. Glaciers - glaciers created many isolated depressions through freezing, thawing and erosion that fill with rain water and snowmelt. This process is similar, in fact, to the way in which kettles are created. Sag Ponds - sag ponds form when surface water gathers in depressions formed by easily dissolved bedrock (such as limestone) underneath an impermeable soil layer. Eventually the soil sags and water gathers in the depression. Pingos – Pingos are formed by freezing and thawing processes on moist mountainous slopes. The upper layers of soil thaw first and slowly slide over the underlying frozen soil. The result is a landscape peppered with crescent-shaped wetlands. Human Activities - some vernal pools are created deliberately by people who wish to create wildlife habitat or to replace a seasonal wetland that was destroyed. Other pools are inadvertently created during any kind of surface disruption (mining, roadside ditches, agricultural fields, etc.) that creates shallow depressions that hold water long enough to support seasonal pool wildlife.
Generally drying up in late summer, these ponds are only temporary woodland reservoirs. They are slightly harder to identify during the summer and fall months; however, there are several clues to look for. Blackened, compressed leaf litter; gray soil; watermarks on surrounding tree trunks; and the presence of moisture-tolerant vegetation all suggest an area that collects water part of the year.
To distinguish vernal pools from briefly puddled upland depressions, true ponds, flowing waterbodies, and a variety of open wetland types, their definition can be further narrowed to sites that meet the following criteria:
• flooded long enough and frequently enough, and dried out long enough and frequently enough to harbor flora and/or fauna that have specialized adaptations or life cycles for coping with both inundation and water drawdown. Notably, permanent fish populations do not occur in vernal pools because they cannot survive prolonged drawdown.
• small enough and/or shaded enough they do not become established marshes, wet meadows, or wet prairies
• lack permanent surface water connection to other water bodies.
The character of any given vernal pool changes continually through time and is the result of a complex response to and interplay among climate, weather, hydrologic processes, water and soil chemistry, pool geometry, fire patterns, fauna, and vegetation. Because all of these factors tend to vary across the landscape, each vernal pool is assumed to be unique.
References used: https://extension.psu.edu/vernal-ponds-seasonal-habitats-for-wildlife https://mnfi.anr.msu.edu/abstracts/ecology/Vernal_Pool.pdf https://www.vernalpool.org/home
To log this cache please send your answers to the following questions:
1. What type of soil would you expect to find here? (sand, loam, clay, etc) Why?
2. Is there any water present?
Estimate the approximate surface area (length x width) of the vernal pond if water is present.
Describe the area if no water is present
3. How can you identify this as a vernal pond in the summer when there is no water?
4. How does snow effect the size of a vernal pond?
5. Which geological factor do you think resulted in the formation of this vernal pond?
(Optional) Post a picture of the vernal pond to help record its changes throughout the year. (face not required)