Bixby State Preserve

The Algific Talus Slopes at Bixby State Preserve Bixby State Preserve is located 3 mi. north of Edgewood, Iowa in Clayton Co. The majority of the preserve is a valley carved by Bear Creek in dolomite and limestone of the Niagara Escarpment. The diatoms posted in this file were collected during May, 1988 and May 1989 from various substrates that included mosses, soils, liverworts, and rock scrapings. All substrates were contained within what are known as "Algific Talus Slopes". These north to northeast facing slopes are globally unique habitats found only in N.E. Iowa, N.W. Illinois, and S.W. Wisconsin, the majority located in Iowa. Their uniqueness comes from the cold (1-2 degrees C.) moist air that seeps either directly from exposed limestone fissures or through soil overlying fissures. A network of fissures and cracks articulates with subterranean dissolution caves above the slopes. The plateau above the valley is strewn with sinkholes characteristic of karst topography. The sinkholes are connected to the caves by a network of fissures and cracks. During the winter and early spring relatively warm light air flows up and out the sinkholes. This draws cold moist air in through the talus slopes, condensing and freezing moisture on the cave walls. The result is a substantial ice build on the cave walls. During late spring and through the summer air flow reverses because the cave air is colder and heavier than the air overlying the plateau. The warm flowing plateau air melts and evaporates the cave ice which vents through the talus slopes. The cold moist air provides a favorable and consistent microclimate for the growth of an unusual flora of aerophillic to semi-aerophillic diatoms.

A schematic x-sec of an algific talus slope

If you'd like more information about these habitats you can contact either Dave Johnson ( or Dr. Paul Whitson Dept. of Biology, University of Northern Iowa, Cedar Falls, IA 50614 1-319-273-6034.

Taxa in this archive

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