Using Epiphytic Lichens to Monitor Nitrogen Deposition Near Natural Gas Drilling Operations in the Wind River Range, WY, USA
2013
McMurray, Jill A. | Roberts, Dave W. | Fenn, Mark E. | Geiser, Linda H. | Jovan, Sarah
Rapid expansion of natural gas drilling in Sublette County, WY (1999-present), has raised concerns about the potential ecological effects of enhanced atmospheric nitrogen (N) deposition to the Wind River Range (WRR) including the Class I Bridger Wilderness. We sampled annual throughfall (TF) N deposition and lichen thalli N concentrations under forest canopies in four different drainages of the WRR. Measurements of TF N deposition and N concentrations in lichen thalli were highest at plots closest to drilling operations (<30 km). N concentrations in lichens decreased exponentially with distance from drilling activity. Highest TF N deposition, 4.1 kg ha -1 year-1, coincided with clear evidence of damage to lichen thalli. This deposition value is above estimated preindustrial deposition conditions (0.9 kg N ha-1 year-1) and regional critical loads (a deposition value below which ecosystem harm is prevented) of N deposition for sensitive ecosystem components. N concentrations in Usnea lapponica were strongly correlated (r = 0.96) with TF N deposition, demonstrating that elemental analysis of lichen material can be used to estimate TF N deposition. N concentrations below 1.35 % in U. lapponica and 1.12 % in Letharia vulpina were associated with estimated background conditions of 0.9 kg N ha-1 year-1. Additional lichen sampling in the Bridger Wilderness is recommended to further quantify and monitor spatial patterns of N deposition and to define areas of elevated N deposition. © 2013 Springer Science+Business Media Dordrecht (outside the USA).
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