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Intro > Classification > Depressions > Sinkhole
Sinkhole
Wetland Class: Depressions
Wetland SubClass: Isolated Depression
Introduction: Sinkhole
Landscape Setting and Hydrology
Sinkholes usually form where subsurface dissolution of limestone causes subsidence, or where surface rock is dissolved into a subterranean void. Where the bottom of the basin is closed, or it is sealed by sediment, sinkholes collect rainwater and runoff, and may maintain standing water for extended periods, or permanently. They typically have deep accumulations of highly organic sediments. Sinkhole wetlands are classified here as depressions, because they are usually shallow and relatively small, even though some sinkholes may have characteristics more typical of lakes, particularly where they have been modified to serve as farm ponds. Vegetation
Sinkholes can support various wetland communities. Deep sinkholes have open water with a perimeter wetland of emergent and floating-leaved plants. Shallow sinks, which commonly dry out in late summer, may support shrub-dominated wetlands; very shallow sinks may be forested with typical floodplain tree species. Many sinkholes have been deepened or otherwise modified to serve as farm ponds or as wildlife water sources in forested areas. Remaining examples in good condition suggest that forested sinks may have been similar to mountaintop depressions in supporting disjoint populations of bottomland species. Isolated populations of plant species typical of coastal plain habitats have been found in sinkholes in the Missouri Ozarks, and it is likely that some Arkansas sinks may similarly harbor threatened or endangered species. The species listed below were observed in a single forested sink in good condition, and a disturbed sink with a somewhat intact emergent zone. Characteristic Plants
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| Gleditsia triacanthos | honey locust | | Quercus palustris | pin oak | |
| Acorus calamus | sweetflag | | Carex spp. | sedge | | Eleocharis spp. | spikerush | | Ludwigia spp. | primrose willow | | Polygonum spp. | smartweed | | Ranunculus spp. | buttercup | | Smilax bona-nox | greenbrier |
Distribution
Sinkholes occur where limestone is at or near the surface. They are largely restricted to terraces and rolling uplands in the Ozarks, north of the Buffalo River. They can be observed in pastures throughout the region, though these are usually not in good condition. Forested sinks on public land can be can be found within the Ozark National Forest.
Other Isolated Depression Community TypesMountaintop Depression
Sand Pond
Unconnected Alluvial Depression
Valley Train Pond
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