Tracing Groundwater-Surface Water Processes in a Chalk Catchment Using Fluorescence Properties of Dissolved Organic Matter

Abstract

Understanding the nutrient movement within catchments is important for effective environmental management of river and wetland ecosystems. The fluorescence properties of groundwater and surface water (including a waste-water outlet) samples were examined in a Chalk catchment to investigate the use of dissolved organic matter (DOM) as a natural tracer of groundwater-surface water interactions and to 'fingerprint' sources of DOM within the groundwater and surface water system. Fluorescence centres were observed in fulvic acidlike and aromatic protein-like regions of the emission-excitation matrix in both groundwater and surface water samples. A decrease in the fluorescence intensities of the fulvic acid-like material was observed with depth (down to 25m) in the Chalk interfluve and adjacent to the river highlighting the role of the soil zone as an important source of DOM. Groundwater from gravels adjacent to the river show a signature that is a mixture of both members, i.e. deep groundwater and the surface water. Samples from sand deposits adjacent to the river show less of a river signature (i.e., less connectivity) than the gravel aquifers. There appears to be little evidence to suggest that there is a significant source of DOM in the shallow groundwater system (from animal waste sources) emanating from a cattle barn adjacent to the river, and that the sewage outlet is the main source of DOM within the river system down stream. These findings corroborate the conceptual model of groundwater movement and demonstrate the potential of intrinsic fluorescence as a natural tracer for investigating groundwater-surface water interactions