The fate of lead from duck shooting and road runoff in three western Australian wetlands

Abstract

This investigation examined whether lead shot from duck shooting was acting as a source of lead in an alkaline wetland ecosystem typical of popular duck-shooting areas in Western Australia. A polluted urban wetland and a pristine wetland were also studied for comparison. Lake Wannamal receives an estimated 82 kg of lead shot per year from duck shooting and no lead from any other known source. Lake Monger was estimated to receive 138 kg of lead per year from road runoff, leachate from a sanitary landfill site, and lead from aerosols. Thomsons Lake has no known source of lead from human activities.

Lead concentrations in sediments did not differ significantly (P < 0.05) between Lake Wannamal and Thomsons Lake and apparently represent natural background levels. Lake Monger sediments were contaminated (mean: 192 ± 82 µg Pb g^-1 dry weight); the main source appeared to be runoff from a nearby freeway.

Lead concentrations in Baumea articulata Blake, Typha orientalis Presl and Schoenoplectus validus Love were generally low; concentrations in the roots were higher than those in the leaves, suggesting that lead is poorly translocated. Lead concentrations in submerged macrophytes and in sediments were similar, which may be attributable to periphyton on the plants binding lead in seston resuspended by water turbulence.

The cyanobacterium Microcystis sp. accumulated lead to low concentrations, believed to be from soluble lead in the water column. Macroinvertebrates accumulated lead to low concentrations, but no evidence was found of biomagnification. Lead concentrations were only slightly higher in macroinvertebrates in Lake Monger than in macroinvertebrates in the other lakes, indicating that lead uptake was poor even in a contaminated lake.