Temporary pools

Where you find Temporary pools

About Temporary pools

Vernal pools, also called vernal ponds or ephemeral pools, are temporary pools of water that provide habitat for distinctive plants and animals. They are considered to be a distinctive type of wetland usually devoid of fish, and thus allow the safe development of natal amphibian and insect species unable to withstand competition or predation by fish. Certain tropical fish lineages (such as killifishes) have however adapted to this habitat specifically.

During most years, a vernal pool basin will experience inundation from local surface runoff, followed by desiccation from evapotranspiration. These conditions are commonly associated with Mediterranean climate. Most pools are dry for at least part of the year, and fill with the winter rains or snow melt. Some pools may remain at least partially filled with water over the course of a year or more, but all vernal pools dry up periodically. Some authorities restrict the definition of vernal pools to exclude seasonal wetlands with defined inlet and outlet channels. Such seasonal wetlands have larger drainage basins contributing higher concentrations of dissolved minerals, and increased probability of periodic scouring flows through the wetland. Low dissolved mineral concentrations of smaller vernal pool basins may be characterized as oligotrophic, and poorly buffered with rapid pH shifts due to carbon dioxide uptake during photosynthesis.

They are called vernal pools because they are often, but not necessarily, at their maximum depth in the spring ("vernal" meaning of, relating to, or occurring in the spring). There are many local names for such pools, depending upon the part of the world in which they are found. Vernal pools may form in forests, but they are more typically associated with grasslands. While many vernal pools are only a few meters in width, playas and prairie potholes are usually much larger, but are still otherwise similar in many respects, with high water in wet periods, followed by dry conditions. Some exclude desert playas from the definition of vernal pools because their larger closed drainage basins in areas with high evaporation rates produce higher concentrations of dissolved minerals, with salinity and alkalinity favoring different species. Playas may be inundated less frequently than vernal pools, and inundation typically coincides with colder weather unfavorable for plant growth.

Despite being dry at times, once filled, vernal pools teem with life. The most obvious inhabitants are various species of frogs and toads. Some salamanders also utilize vernal pools for reproduction, but the adults may visit the pool only briefly. Other notable inhabitants are Daphnia and fairy shrimp, the latter often used as an indicator species to decisively define a vernal pool. Other indicator species, at least in New England, are the wood frog, the spadefoot toad, and some species of mole salamanders. Certain plant species are also associated with vernal pools, although the particular species depend upon the ecological region. South African vernal pools, for example, have a different flora from Californian vernal pools. In some northern areas, tadpole shrimp are also common.

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