Vernal pools, also called ephemeral pools, are temporary pools of water that support a unique ecosystem of plants and animals. They can vary in size from large puddles to small lakes and occur in a variety of habitats, such as forests, prairies, and even deserts. Vernal pools are usually filled with water by rainfall or snowmelt during the winter and spring and go dry during the hot dry weather of summer. In some drought years they may not fill at all, and during really wet years they may not go dry. The underlying soils of vernal pools are a fundamental part of the habitat and usually consist of a hardpan layer or bedrock, which causes retention of the water in the pools.
Vernal pools, because of periodic drying, do not support breeding populations of fish. For this reason many species of amphibians, Odonates (dragonflies and damselflies), and crustaceans have evolved to use vernal pools as part of their life-cycles. These species are referred to as obligate vernal pool species, because they will only breed in temporary pools of water where there are no fish to eat their eggs and young.
The hydroperiod is the length of time that surface water inundates the pools and determines which species will be present. Fewer species are able to exist in pools that dry up relatively rapidly as compared to pools that keep their water longer. Toad larvae mature about the fastest of all amphibians, and they can breed successfully in the smallest of puddles, requiring just a few days to mature. They usually breed in pools that are in open sunny areas so that the extra warmth will help their larvae grow faster.
In North America, many species of mole salamanders, frogs, and toads use vernal pools for breeding. Some lay their eggs in the fall, and some lay their eggs in late winter through spring. All are capable of maturing into adults in just a few weeks before the pools go dry. Numerous aquatic insects and other invertebrates live and breed in these ponds and provide food for the growing salamander larvae. Odonate larvae are ferocious predators which feed on the larvae of other insects. The larger larvae of the dragonflies will even take small tadpoles. Fairy shrimps and various types of microscopic crustaceans live and complete their whole life-cycles in vernal pools. Their eggs are capable of surviving the dry spells and hatch when the pools flood again. Various types of algae and annual plants grow here as well and provide food for tadpoles, crustaceans, and insect larvae.
“Earth’s cisterns will often be emptied, its pools become dry; but in Christ there is a living spring from which we may continually draw. However much we draw and give to others, an abundance will remain. There is no danger of exhausting the supply; for Christ is the inexhaustible well-spring of truth. He has been the fountain of living water ever since the fall of Adam. He says, ‘If any man thirst, let him come unto me and drink.’ And ‘whosoever drinketh of the water that I shall give him shall never thirst, but the water that I shall give him shall be in him a well of water springing up into everlasting life.’ ” The Signs of the Times, April 22, 1897.
“He who drinks of the living water becomes a fountain of life. The receiver becomes a giver. The grace of Christ in the soul is like a spring in the desert, welling up to refresh all, and making those who are ready to perish eager to drink of the water of life.” God’s Amazing Grace, 119.
David Arbour writes from his home in De Queen, Arkansas. He may be contacted by e-mail at: landmarks@stepstolife.org.