The Legacy of 19th Century Iron Production in Central Pennsylvania: Soil Acidification and Trace-metal Mobilization Evidenced with Tree Rings

Abstract:

Soil acidification and metal loading from industrial emissions can limit forest growth and carbon sequestration of Eastern U.S. forests. Tree growth may be limited if the mobility of trace metals found within forest soils is increased to nearly toxic levels due to soil acidification. The iron production boom in central Pennsylvania, which lasted roughly from 1850-1910, would have altered soil compositions of surrounding forests due to large amounts of coal and biomass fuel pollution depositions. The regional collapse of the iron industry by 1910 allows a unique opportunity to observe recovery rates of the surrounding forests and their associated soils over the last century. The pollution history of iron production and rate of soil recovery at this site was determined using tree-ring width measurements and dendrochemical analysis. Six prominent tree species were analyzed for cation and trace metal concentrations retained in the woody structure. Current soil cation and trace-metal concentrations were compared to recent tree-ring chemical compositions. The persistence of soil acidification was determined by observing the changes in major cation concentrations retained in the woody structure over time. This altered soil pH would have mobilized certain trace metals either deposited by the iron production pollution or found naturally in the soil. The effects of soil acidification in the local region are evident in the changes in trace metal concentrations due to increased bioavailability and decreased soil pH. The combined analysis of trace metals and major soil cations yields a specific pollution history and evidence of forest recovery rates from the iron production emissions in central Pennsylvania.