VARIATION IN THE ISOTOPIC COMPOSITION OF SPRING WATER

The ecology of cave organisms is poorly known. However, schlerochronolgy can be used to extract basic information, such as lifespan. This method relates the stable isotopic composition of growth bands of carbonate-secreted hard parts of the cave taxa (i.e. snail shells, cavefish, otoliths and cave crayfish statocysts) to the isotopic composition of the spring water in which the taxa are living. The variations observed in the spring water (seasonal, storm-related, etc.) are recorded sequentially in the biologically secreted carbonates. To determine the isotopic variation of spring water, water samples at Maramec Spring in southern Missouri, home to the endangered southern cave fish, are being collected. Initially, water samples were collected hourly over a 24-hour period and the carbon isotopic composition of the dissolved inorganic carbon was analyzed. The standard deviation of the 24 samples was 0.3 o/oo, with an average error on individual samples of 0.3 o/oo, indicating no variation in isotopic composition at this time scale. This was not surprising, given the long residence of the water in this karstic system (approximately 3 weeks). In addition, water samples are also being collected daily, along with daily physical and chemical information of the spring water (pH, depth, turbidity, temperature, conductivity, and dissolved oxygen concentration). Limited data have shown a daily range, over a month period, in isotopic composition of about 7 o/oo, from -8 o/oo to -15 o/oo. These isotopic data will be related to the chemical and physical data collected. Water samples will also be collected over a storm event to determine the isotopic variation of this type of hydrologic disturbance.