Using Epiphytic Lichens to Monitor Nitrogen Deposition Near Natural Gas Drilling Operations in the Wind River Range, WY, USA

Abstract

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.