In situ determination and laboratory measurements of Cu fluxes in two dam sediments using DGT

Abstract
The technique of diffusion gradients in thin films (DGT) accumulates labile metals on a chelex resin after their diffusive transport through a hydrogel. DGT is capable to measure in-situ fluxes of metals in sediments, in response to the perturbation induced. Porewater concentration is lowered, but depending on the sediment, metal sorbed to particulate matter can either exchange with solution to maintain its concentration or not. We measured Cu fluxes in the sediments of two dams, in the field with an on-site DGT insertion technique and at the laboratory. Some experiments were also performed to measure directly fluxes in their porewaters after extraction. Results of experiments and calculations using the DIFS model allowed us to discriminate between both aquatic systems in their ability to sustain metal concentration in porewaters. The possibility of resupply was demonstrated for one sediment but particulate metal in the other sediment appeared tightly bound and not subject to release.