The fate and effects of lead (Pb) at active and abandoned shooting ranges in a boreal forest ecosystem
Year: 2015
Type: dissertation
Abstract: Despite the known toxicity of lead (Pb) and the ban on waterfowl hunting, Pb pellets are still used at shotgun shooting ranges around the world. After firing a shotgun, pellets spread across wide areas, ending up in nearby ecosystems, which typically are forests in Finland. Still, little is known about the effects of Pb in these ecosystems and hardly anything about changes in ecosystem structure and function after range abandonment. Thus, ecosystem-level research was conducted in a shotgun shooting range area to evaluate the fate and effects of Pb in a boreal forest ecosystem and the possible recovery of the system after range abandonment. Bioaccumulation, the leaching and vertical distribution of Pb in the soil, soil nutrients and their leaching as well as structure and activity of decomposer community were studied at two contaminated sites (active [NC] and abandoned [OC] shooting ranges) and a control site, each locating in the same pine forest stand. Furthermore, tree growth, nutritional status and litter production were measured. Total Pb pellet burdens at the contaminated sites were similar, reaching up to 4 kg m-2, and shooting activity had lasted for 20 years at both sites, but occurred 20 years earlier at OC. Total Pb concentrations at the shooting ranges were extremely high, and Pb accumulated in the biota. The vertical distribution of Pb in the organic soil horizon differed between the shooting range sites, with total Pb concentrations at NC being higher in the upper F layer than in the lower H layer, but vice versa at OC. Soil fungi and all studied faunal groups (enchytraeid worms, microarthropods and nematodes) except protozoans were affected negatively by Pb. Lead decreased phosphate (PO43-) and increased nitrate (NO3-) concentrations. pH was also increased by Pb, which can further affect the biota directly or indirectly by changing Pb availability and toxicity. In the entire organic soil horizon, the negative effects of Pb were less pronounced at OC than at NC. In addition, pine needle litter decomposed faster at OC than at NC, and tree (Pinus sylvestris) radial growth was suppressed at NC after shooting activity started and increased at OC after shooting activity ceased. However, in the H layer the effects were stronger at OC, enchytraeid worms being completely absent. Furthermore, leaching of Pb through the organic soil horizon was twice as high at OC as at NC. A decrease in total Pb concentrations and toxicity in the topmost soil layer and enhanced litter decomposition rate at the abandoned shooting range indicate an on-going recovery process. In boreal forest soils that are characterized by low decomposition rates and little soil mixing due to the scarcity of earthworms, a less contaminated soil layer is gradually formed when shooting activities cease. This topmost soil layer can provide habitat for the decomposer biota and promote the recovery of soil functions. However, at the same time the dissolution of Pb from pellets deeper in the soil increases toxicity of the humus and the leaching of Pb, increasing risks to the ecosystem and groundwater quality. These findings suggest that communities and functions in Pb-contaminated boreal forest ecosystems depend on contamination history. However, despite Pb-induced changes in the decomposer communities, only slight changes in ecosystem processes were detected. This indicates high resistance of boreal forest ecosystems to this type of stress.
Source: Työväentutkimus Vuosikirja
Author: Salla Selonen
Language: English
Topic: Heavy metals in environment
Subfield: Pollution
Field: Environmental Science
Domain: Physical Sciences
SDG: Life on land
Open Access status: green
OpenAlex ID: W2210313196