title: Does soil water saturation mobilize metals from riparian soils to adjacent surface water? A field monitoring study in a metal contaminated region.
abstract: In the Noorderkempen (NW Belgium), a large area (about 280 km(2)) is contaminated with cadmium (Cd) and zinc (Zn) due to historical pollution by the Zn smelters. Direct aquatic emissions of metals have diminished over time, however the surface water metal concentration largely exceeds quality standards, mainly during winter periods. Monitoring data were analyzed to reveal whether these fluctuations are related to seasonal redox reactions in associated contaminated riparian soils that drain into the rivers. A field survey was set up with soil pore-water and groundwater monitored for three years in transects of soil monitoring points perpendicular to rivers at contaminated and non-contaminated sites. Site averaged surface water concentrations of a 15 year dataset exceeded local quality standards 4 to 200-fold. Winter averaged metal concentrations significantly exceeded the corresponding summer values 1.3-1.8 (Zn) and 1.5-2.4 fold (Cd). Zinc and Cd concentrations in water were positively related to Fe and Mn but not to Ca, K or Na suggesting that redox reactions and not dilution processes are involved. In ground- and pore-water of the associated riparian soils, the concentrations of Zn fluctuate by the same order of magnitude as in surface water but were generally smaller than in the corresponding contaminated rivers. In addition, correlations of dissolved Zn with Fe and Mn were lacking. This analysis suggests that redox reactions in streams, and not in riparian soils, explain the seasonal trends of Zn and Cd in surface water. Hence, river sediments and not riparian soils may be the cause of the winter peaks of Zn and Cd in these rivers.
authors.affiliation: Division of Soil and Water Management, K.U.Leuven, Kasteelpark Arenberg 20 - box 2459, 3001 Heverlee, Belgium. lvlaer@sckcen.be
authors.forename: Liesbeth
authors.initials: L
authors.lastname: Van Laer
authors.forename: Erik
authors.initials: E
authors.lastname: Smolders
mesh_terms: D001530:Belgium; D002104:Cadmium / Q000032:analysis; D004784:Environmental Monitoring; D060587:Groundwater / Q000032:analysis; D008670:Metals / Q000032:analysis*; D010084:Oxidation-Reduction; D045483:Rivers / Q000737:chemistry; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*; D014867:Water / Q000032:analysis*; D014873:Water Pollutants / Q000032:analysis*; D015032:Zinc / Q000032:analysis
chemical_list: D008670:Metals; D012987:Soil; D012989:Soil Pollutants; D014873:Water Pollutants; D002104:Cadmium; D014867:Water; D015032:Zinc