Based on research in streambed materials underlying rivers, distinct zones of hydrogeologic, geochemical, and ecological activities have been defined (Rouch, 1988). The ecotonal assemblage of animals in the interstitial space is a function of the hydraulic conductivity of the sediment and the dissolved oxygen concentration of the interstitial water. In cave streams, interstitial pores exist within the streambed deposits, yet few researchers have investigated the possibility that aquatic troglodytic species might reside in these interstitial spaces. Information is lacking regarding the habitat preferences of aquatic troglodytic species. It is generally assumed such species prefer open-water conditions, pools and riffles (Barr, 1968; Brown and Willis, 1984). Scientists conducting in-cave organism counts have assumed that the number of individuals found during visual stream inspections is equal to the number of organisms present. Schubert (1993) have shown that southern cavefish prefer to reside within the interstitial pore spaces of streambeds (gravel-sized substrate with interstitial spaces that the fish can enter) and not in the water column proper. If the preferred habitat is in interstitial spaces of the streambed, then the number of organisms that are counted during visual inspections may markedly underestimate the true number of organisms present. Residing in the interstitial spaces would appear to provide shelter from predation, and access to food, as many of the aquatic troglodytic species forage. This exploratory project asks: 1. What is the hydrogeologic setting of the various habitats? The hydrogeologic setting will be characterized by determining the hydraulic conductivity, porosity, and grain size distribution of the streambed material and the hydraulic gradient along the stream reach. 2. What is the geochemistry of the water in interstitial pore space? The geochemical setting will be characterized by determining the concentrations of dissolved oxygen and bicarbonate and by determining the temperature, pH, and Eh of the interstitial water as a function of depth. 3. What is the exchange rate between the flowing water and the interstitial water? The exchange rate between the flowing water and the interstitial water will be determined by analyzing the fluctuations in the temperature of the flowing water and the interstitial water at one site. Understanding where the aquatic troglodytic species reside, and the geochemical and hydrogeological regimes of those locations, will aid scientists who need to enumerate populations, determine habitat requirements, and conserve the biota. The ability to quantify and model sub-channel geochemical and hydrological processes is critical to improving our understanding of the habitat requirements of aquatic troglodytic species. This exploratory proposal solicits funding for research that will describe the geochemical and hydrological habitat of three karst streams, which are the habitats for four aquatic troglodytic species. This research represents a new line of inquiry for the Principal Investigator and a first step in determining the geochemical and hydrodynamic environment of aquatic troglodytic species. This exploratory research project is the first effort to link the geochemical and hydrodynamic conditions to the habitat requirements of aquatic troglodytic species.
