Content area
Full text
Abstract
The fluorescence properties of dissolved organic matter (DOM) in ground water in the Permian limestone of northeast England is determined from six monitoring boreholes, a private water supply well and from a natural resurgence in a flooded collapse doline in the environs of Darlington, County Durham, northeast England. Measurements of both protein and "fulvic-like" fluorescence was undertaken from January to December 1999. The wavelengths of fulvic-like fluorescence excitation and emission and of protein fluorescence emission were all determined to be sensitive fingerprints of organic matter fluxes through the ground water, with water within the till and within both gypsum and limestone strata deep inside the Magnesian Limestone being differentiated by these parameters. Previous research has suggested that proteins in waters are "young" in age, hence our seasonal variations suggest that we are sampling recently formed DOM. The rapid response of all deep borehole samples suggests relatively rapid ground water flow, probably through karstic cave systems developed in the gypsum and solution widened features in the dolomitic limestone. Our results suggest that use of both protein and fulvic-like fluorescence wavelength variations provides a DOM signature that can be used as a natural tracer.
Introduction
Dissolved organic matter (DOM) is a ubiquitous constituent of natural water, derived from the decay of plant and animal matter from within the catchment. In most river systems, most DOM is thought to be soil derived, with typical concentrations in the British Isles ranging from 1 to 15 mg/L (Tipping et al. 1997). Of the biodegradable fraction, research has suggested that this predominantly comprises humic substances, with smaller amounts of carbohydrates and amino acids; with most carbohydrates and amino acids being humic bound (Volk et al. 1997). Between 40% and 60% of DOM is fluorescent (Senesi 1993); this fluorescent material principally comprises protein and organic acids. The presence of fluorescent DOM in river and ground water systems has long been recognized. It may generate problems when artificial fluorescent dyes are used to trace water within, for example, cave systems (Smart et al. 1976). Figure 1 presents fluorescence excitation-emission matrices (EEMs) of typical ground water and riverine organic matter. DOM fluoresces with the same wavelengths as photine (340 to 350 nm excitation, 430 to 450 nm emission; Smart and Laidlaw...