Fluorescence wavelength and intensity variations of cave waters

The fluorescence properties of groundwaters percolating into four cave syst ems have been monitored over the period 1997-1998. Fluorescence was excited between 220 and 400 nm and the emission measured from 300 to 500 nm using a fluorescence spectrophotometer. Three fluorescence centres were observed; one at the excitation-emission pair of 290-340:395-430 nm, (humic-like, pr obably fulvic acid), one at 265-280:300-370 nm (protein like) and a less de fined region of high fluorescence at 230-280:310-420 nm (humic and/or prote in like). The most consistent fluorescence intensity was observed in the ex citation-emission pair of 290-340:395-430 nm, attributed to a fulvic acid s ource. Subtle differences (+/- 5%) in the fluorescence excitation and emiss ion wavelength of this fluorescence peak in the groundwater were observed b etween the four sites, and the fluorescence intensity varied considerably ( x 60) between the four sites. Both the wavelength and the intensity variati ons in fluorescence are caused by the differences in the vegetation cover, soil type and humification. Data from the most intensely monitored site (Br own's Folly Mine, England; 9 sample stations, 10-20 days frequency sampling ) revealed no spatial variability in the 290-340:395-430 nm (fulvic acid) f luorescence; in contrast time-series analysis suggests that the seasonal va riations do occur, with a decrease in the emission wavelength correlating w ith the first (autumn) peak in fluorescence intensity, and a decrease in th e excitation wavelength correlating with a second (winter) fluorescence int ensity peak. Results demonstrate the potential of utilising fluorescence wa velength variations in sourcing karst groundwaters, and as a possible palae oenvironmental proxy of the overlying soil conditions if trapped within the cave speleothems. (C) 1999 Elsevier Science B.V. All rights reserved.