Greg Kareofelas

Biologist Carol Witham studies a vernal pool last year near the Jepson Prairie Preserve in Solano County. As this year's pools dry up for lack of rain, flowers are starting to appear.

Q&A: Biologist takes a look at Sacramento Valley's vernal pools

Published: Monday, Mar. 25, 2013 - 12:00 am | Page 1B
Last Modified: Monday, Mar. 25, 2013 - 7:00 am

Biologist Carol Witham, 56, is a specialist on vernal pools. These patches of land flood with water in the winter, bloom with flowers and aquatic wildlife in the spring and stay dry in the summer.

Witham also serves as president of the Sacramento Valley chapter of the California Native Plants Society. >

What are vernal pools?

Vernal pools are flooded with water in the winter, but completely dry in the summer. During winter, they are a breeding ground for aquatic invertebrates like fairy shrimp and tadpole shrimp. Frogs and salamanders also abound. Birds flock to the pools to eat the smaller animals. It's a very complicated food chain.

In the spring, beautiful flowers bloom from the vernal pools that are usually surrounded by grassland. The pools can be as small as a Jacuzzi, but can also be a few acres wide.

>How do vernal pools get formed?

They are formed because there is an impermeable layer in the soil called hardpan. That keeps the rainwater from being absorbed into the soil, creating a special environment for animals and plants to prosper.

>Where can we find vernal pools?

There are thousands of acres of them in Sacramento County alone. Vernal pools can be found in two main locations near Sacramento. The most classic place is Mather Field, along Eagles Nest Road, close to the Mather Golf Course. The second place is Rancho Seco Howard Ranch in Sacramento County.

Statewide, vernal pools exist throughout the Central Valley and in the coastal areas of San Diego.

>How long do these vernal pools last?

The pools exist year round, even if there is no water. The amount of water and how much of it, though, depends on the rainfall pattern. Many are almost dry now because of the lack of rain since January. With the water gone, some of them are starting to flower.

If we get a lot of rain now, it might just kill the flowers. It's a natural cycle that varies year to year.

>Are vernal pools a breeding ground for mosquitoes?

Undisturbed vernal pools in natural surroundings are not a breeding ground for mosquitoes. That is because there are other animals that will eat the mosquito larvae. However, disturbed vernal pools – close to a road or a house – that don't have as many organisms can in fact breed mosquitoes.

>What's the best time to visit a vernal pool?

Right now, during the spring when flowers bloom. But it really depends on the year. In the summer, the flowers are dry, just like the grassland.

For more information and to sign up for guided tours of vernal pools, visit: and

Call The Bee's Richard Chang, (916) 321-1018. Follow him on Twitter @RichardYChang.

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