The word 'Vernal' is derived from the Latin word Vernalis for “Spring”.
This is the Vernal Pond in the Tenhave Woods Nature Center. It is an example of a unique ecosystem that is an important component of the Earth. The specialized plants and animals that inhabit this "micro-ecosystem" have evolved to survive only in these pools. They wouldn't exist if it wasn't for the geology which created the soil necessary for a vernal pond to form. These important wetlands are some of the most vulnerable because they are small, isolated, and often dry, making them almost unrecognizable. Vernal ponds are easily recognized in the early Spring when they are filled with water. In the Summer, they are more difficult to recognize as they are generally (but not always) dry. The best indicators during the Summer months are: blackened and compressed leaf litter, buttressed tree trunks and water marked tree trunks.
The ponds are essentially geologic depressions that are flooded during winter and spring. They fill with the melt water of winter snow and spring rain. The water collects in these depressions because the vernal pond lies either on an underlying soil layer called claypan or hardpan. The general characteristic of claypan is being a distinct soil layer that is largely impervious to water. Claypan is a dense, compact, slowly permeable layer in the subsoil having a much higher clay content than the overlying soil. Claypan is usually hard when dry, and plastic and sticky when wet. It limits or slows the downward movement of water through the soil. This is what helps keep the water in the pond.
Throughout the Winter and Spring months, this vernal pond will collect enough water to fill up. Although the water may not get too deep, it will be enough to serve its purpose. During the wet season, Insects, Crustaceans, and Plants take advantage of the abundant moisture for reproduction. Creatures that inhabit the pools are perpetuated with the production of cysts and/or eggs, and plants produce seeds that become buried in the muddy pond bottom. The mud protects the cysts, eggs, and seeds from predators and the dry, hot Summer months. The plants and animals that inhabit in this environment have evolved to thrive under conditions that vary from extremely wet to completely dry. In the late summer, the amphibians have dug deep into soil and have gone dormant to wait for the next wet season. During this time the pond is full of resting cysts, eggs and seeds that will survive through the summer until the onset of the rains begin the new cycle.
The nature of the soil is instrumental in determining whether vernal ponds will develop. The soil here is a type of Loam soil which is composed of sand, silt and clay. Loam soil is one that combines all three of these types of particles in relatively equal amounts. Loams are gritty, moist and retain water easily. They also generally contain more nutrients, minerals and humus than other soils.
The next layer is Claypan which is mostly composed of clay minerals (phyllosilicate minerals), minerals which impart plasticity and harden when dried, and variable amounts of water trapped in the mineral structure by polar attraction. Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks (usually silicate-bearing) by low concentrations of carbonic acid and other diluted solvents. In addition to the weathering process, some clay minerals are formed by hydrothermal activity. Clay deposits may be formed in place as residual deposits, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Because the subsoils and claypan are impervious to water, rainwater will stand in depressions in the soil and cannot seep down into the ground. Instead, the water evaporates slowly.
Vernal Ponds change in volume and size in response to varying weather patterns. The size can range from a few square feet to several acres. A pond which is too small and/or shallow may dry too quickly for species which rely on them to complete their lifecycles while one that is too large and/or deep may never dry completely. Climatic changes associated with the seasons cause dramatic changes in the appearance of vernal ponds. During a single season, ponds may fill and dry several times. In years of drought, some ponds may not fill at all.
Note that Tenhave Woods Nature Center hours are Dawn to 8 PM daily. Please do not enter this area during the closed hours. Logs that are done during the closed hours will be deleted.
The requirements to log this cache must be completed as follows. Please do not post your answers to your log. E-mail us with your answer to get credit for this cache. To log this Earthcache, you must complete these tasks:
1) Post a photo of your GPS, your Team with the pond in the background.
2) Estimate the area of the vernal pond by multiplying the length times the width. Then send an email to me through my profile with the estimate of the area of the pond.
3) Vernal Ponds are a type of wetland. Other than being home to unique species of plants and animals, name an important function of wetlands.
4) Tell us whether you believe the soil in the pond is fragile or resilient.
PLEASE NOTE: I will not be sending follow up requests for answers. If you do not complete the requirements,your log will be deleted. In order to claim this Earth Cache, you must follow through with the requirements, not just visit the site.
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