Partitioning of lead in pristine and runoff-impacted waters from acidic wetlands in the New Jersey Pinelands

Abstract

We have examined the roles of dissolved organic carbon (DOC) and pH in determining patterns of Pb fractionation in surface water from Sphagnum-dominated peatlands in undisturbed and urbanized watersheds of the Pinelands of New Jersey. In undisturbed wetlands, the water is highly acidic (pH 3.5) and has high concentrations of DOC; wetlands receiving urban runoff are less acidic and have lower concentrations of DOC. The effects of PH were separated from the effects of DOC by experimentally raising the pH of water from the undisturbed site to 6.0. A separation procedure was compiled from the literature to separate the soluble Pb fraction into labile (exchangeable on ion-exchange resin) and non-labile fractions, and the latter fraction was further separated into photo-oxidation-sensitive and insensitive fractions. In low pH, high DOC waters, 95% of added PbCl2 remained soluble, and 56 to 80% of this Pb was labile (varying with contact time with the resin). In high-pH swamp waters, a smaller fraction (64 to 71%) remained soluble; the distribution of the soluble Pb among non-labile forms varied with the source of the water. Pb fractionation in runoff was quite different from that in runoff-impacted swamp water at the same pH, and may reflect differences in DOC and/or higher levels of Fe in the runoff.