Reconstructing Pittsburgh's Pollution History with Dendrochemistry: an Analysis of Trace Metal Concentrations in a Schenley Park Red Oak Tree

The city of Pittsburgh, Pennsylvania has a rich history of industrial activity, particularly steel manufacturing. This, combined with other urban waste, leaves a legacy of environmental pollution across the landscape. This study compares trace metal concentration data from a Pittsburgh tree to local and national industrial production records and local climatic data. Trace metal concentrations (lead, copper, cadmium, zinc, and nickel) in the annual growth rings of a red oak tree (Quercus rubra) from Schenley Park in Pittsburgh were measured. This metal record was used to explore the consequences of pollution over the 126 year life of this tree (1881-2006). Trace metals and wet deposition sulfate concentrations are related (r2 range of 0.0631 and 0.3458) as are national steel production and regional wet deposition sulfate concentrations (r2 = 0.7670). However, these relationships break down in the 1990s as trace metal concentrations in the tree rings continue to increase and pollution inputs decrease. One potential explanation is the increasing dominance of vehicular traffic in urban systems. Nitrate emissions from vehicles could increase soil acidity and metal bioavailability, facilitating metal uptake by plants. This suggests that Pittsburgh pollution legacy issues should be a continued concern as increased trace metal availability will impact both urban ecosystems and human populations