Seasonal variability in organic substances in surface and cave waters at Marengo Cave, Indiana

Water samples from forest soils and a shallow cave underlying them were col lected for the hydrological year 1996-1997. The soil waters did not display much seasonal variability in concentrations of organic substances in them but the cave waters yielded distinct highest levels in the spring and autum n seasons. The important controls on the amount of organic substances reach ing the cave are the seasonal fluctuation in volume of the percolation wate rs and the soil's ability to provide organic material for these waters. Flu orescence studies of the organic compounds isolated from these waters revea led shorter peak excitation and emission wavelengths for the cave waters th an for the soil waters, a result of both differences in concentration and p robably also of significant change in the proportional organic assemblages in the waters. Precipitation appears to affect the fluorescence in both wat ers, with the dry autumn producing the highest yields. Molecular size fract ionation revealed how the larger hydrophobic compounds are preferentially r emoved from the water before it reaches the cave, with the consequence that the smaller hydrophilic compounds become the dominant fluorophore there. C opyright (C) 2000 John Wiley & Sons, Ltd.