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Hydrogeologic delineation of habitats for endangered species: the Comal Springs/River System

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 We delineate 18 distinct habitats for the endangered fountain darter in the Comal Springs/River system based upon a combination of vegetative, geologic, and hydrologic criteria. Comal Springs are the largest natural discharge from the Edwards aquifer of central Texas; they issue along faults which penetrate the confined portion of the aquifer. The springs are the head of the Comal River which is an important economic and recreational resource to the local community. The spring/river system is the home of the fountain darter, a federally listed endangered species. Previous studies of this system were on a large scale and lacked detail necessary for characterization. The fountain darter and other fauna in the Comal Springs/River system are threatened by the possibility of diminished flows and the concomitant habitat change. The 18 habitats are defined by the dominant species of vegetation, the substrate, and the flow conditions. Human alterations and spring discharge control the morphology of the river and the substrates. Stream velocities determined substrate conditions and, thus indirectly, the distribution of vegetation and habitats. In this system, hydrochemical parameters were uniform as were the soils adjacent to the stream; these factors were not important to the habitat delineation. The range of stream velocities necessary to maintain the habitats can be estimated with the Hjulstrom diagram. The darters were associated with a number of these habitats. We surmise that significant alteration of the system's habitats will occur if discharge conditions change.

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Received: 22 January 1996 · Accepted: 4 March 1996

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Crowe, J., Sharp Jr., J. Hydrogeologic delineation of habitats for endangered species: the Comal Springs/River System. Environmental Geology 30, 17–28 (1997). https://doi.org/10.1007/s002540050128

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  • Key words Edwards aquifer
  • Fountain darter
  • Habitat
  • Endangered species