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Rain allows vernal pools to spring to life

MERCED NATIONAL WILDLIFE REFUGE — The endangered California tiger salamander, tadpole shrimp and vernal pool fairy shrimp were without a home last year in the Snobird unit of the Merced National Wildlife Refuge.

Dry conditions did not allow their sensitive habitat of vernal pools to fill with the rainwater they needed.This year, however, the rain did come.

The invertebrates that depend on this special type of wetland were again able to swim, breed and complete their life cycles. Bright yellow and purple wildflowers sprang up in halo-shaped rings around the pools.

But now that March has turned dry, pools are evaporating at a quick rate. These conditions made the wildflowers — goldfields, tidy tips and lupin — flourish early. But unless more rain is to come this spring, they will disappear along with the water bugs that live within the pools.At least, until the next good water year comes.

Vernal pools are naturally occurring wetlands made by a depression in the landscape with a hard pan clay bottom, said Jack Sparks, outdoor recreation planner for the wildlife refuge.

They fill by rainwater in fall, winter and early spring and dry up only when the water evaporates. “Vernal pools are completely controlled by nature — that defines them,” he said.

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