Effects of tillage on lead shot distribution in wetland sediments

At Sacramento National Wildlife Refuge, California, we examined 2 types of deep tillage (disking and plowing) as possible management options for reduc ing lead pellet densities in wetlands. In addition, we examined the vegetat ion changes that resulted from tilling. Both disking and plowing moved lead pellets below the zone of availability for dabbling ducks (>10 cm). Howeve r, plowing moved a higher percentage of pellets into the 15-20-cm layer of sediment (P = 0.02). Similarly, plowing was more effective (P = 0.04) than disking or controls in redistributing pellets below the deeper zone of avai lability (>20 cm) for tundra swans (Cygnus columbianus). Maximum height of vegetation increased (P < 0.001) on tilled plots during the first and secon d year after treatment. Tillage initially reduced percent cover (P = 0.03) and density (P < 0.001) of swamp timothy (Crypsis schoenoides), but resulte d in increased swamp timothy cover and stem density by the second year post treatment. Percent cover by California loosestrife (Lythrum hyssopifolium) showed the opposite trend, with an initial increase (P < 0.001), followed b y a decrease to levels similar to control plots in the second year. In cert ain managed wetlands, disking and plowing can be effective management tools for redistributing residual lead shot deeper into wetland sediments and po tentially reducing waterbird mortality due to lead poisoning.