All About Vernal Pools Geology Here are some ways vernal pools form: * Ice age glaciers that create depressions * Streams and rivers that flood and create scour pockets in a floodplain * Streams that meander across a floodplain and create oxbows Soils Vernal pools have an impermeable soil layer that results in water ponding. Hydric soils may form if saturated for Upland * Groundwater that dissolves limestone bedrock under impermeable surface soil layers, creating sag ponds * Crescent-shaped wetlands that form on pingos All these low-lying areas fill with water, becoming vernal pools. long periods. Nutrient rich soils will layer over top of the impermeable soil. Wet Season Dry Season Surface Water Flow Surface Depression Subsurface Water Flow Vernal Pool (Forms in Surface Depression) Loam Soils Saturated Loam Soil Hardpan Layer Hardpan Layer Subsoils Subsoils Hydrology is the study of water and its movement on Earth and underground. Vernal pools receive most water from rain or snowmelt runoff and fill in the fall (autumnal), winter, or early spring (vernal). Some pools are close to the water table and have groundwater sources. Pools may also fill when nearby waterways overflow from heavy rains. Most pools dry up during summer. Hydrology Vegetation Grasses, rushes, and pondweeds provide egg-laying sites and cover from predators. Shrubs and trees provide shade that regulates water temperature. Leaves and woody debris also supports the food web. 48 Pennsylvania Angler & Boater * January/February 2021 www.fishandboat.comhttp://www.fishandboat.com