by Jean Cutler Prior
Hanging Bog State Preserve, Linn County.In the field of ecology, the base upon which an organism lives is called its substrate. Geology is about substrates, and includes earth materials that support plant and animal communities. These two fields are literally knit together by their common ground.
Examples include Pikes Peak where bedrock substrates provide exquisite microhabitats (see cover) as well as expansive rock-bound blufflands. In other substrate settings, Iowa’s Water Monitoring Program counts on tiny creatures that cling to the bottom of rocks in streambeds to tip off investigators about stream health and water quality. The permeability of rock and soil substrates affects the groundwater contribution to a stream’s baseflow and to cool water essential for some aquatic life. Dinosaur fossils bring the dimension of time to life’s substrates, providing insight into the ecology of prehistoric environments. In the photo at left, a gravel substrate hosts a shoot of heat-generating skunk cabbage as it emerges through the last icy coatings of winter. Throughout Iowa, the base upon which all life exists – our geological substrates and deeper geological infrastructure – consists of silty glacial clays, wind-blown silt and sand, river gravel and sand, as well as limestone, dolomite, sandstone, and shale bedrock. These underlying foundations affect our state’s agricultural productivity. Their engineering characteristics affect building construction, and their value as mineral and aggregate resources affects our economy. Their porosity affects both how well we contain waste buried in the ground, and at the same time how well we protect the quality of our drinking water supplies – the quality of Iowa’s human ecology.
photo by Clay Smith
Adapted from Iowa Geology 2001, No. 26, Iowa Department of Natural Resources