On the natural variability of trace-metal content of particulate matter in a deep aquifer

A multilayer sampler (MLS) has been used in a deep phreatic aquifer to collect particulate matter transported by a natural gradient flow field. The trace-metal content (Fe, Mn, Cu, Zn, Ag) associated to the carbonate, organic and oxide fractions of the particulate matter has been characterized by Eulerian variability at a microscale level (< 1 m). The observed variability in metal content reflects the chemical heterogeneity of groundwater in contact with the particles, which is the result of the scale of variability of recharging water into the groundwater reservoir. These findings should be taken into consideration in the application of thermodynamic models for the understanding of natural systems.