Local Climate Influences on Precipitation, Cloud Water, and Dry Deposition to an Adirondack Subalpine Forest: Insights from Observations 1986–1996

Abstract

AbstractFew studies of total atmospheric deposition (dry deposition, cloud droplet capture, rainfall, and snowfall) of major elements (S, N, Ca, Mg, and K) have been conducted in high‐elevation forests. This paper presents the results of the first long‐term observations (1986–1996) of total atmospheric deposition (wet + dry + cloud water) to a subalpine forest in the northeastern USA. Total atmospheric deposition of N to a forest at 1050 m elevation on Whiteface Mountain, NY, averaged 17.2 kg ha−1 yr−1, with 6.5 kg ha−1 yr−1 deposited as NH4 and 10.8 kg ha−1 yr−1 as NO3. Total S deposition averaged 18.3 kg ha−1 yr−1. Orographic effects both enhanced rainfall and increased interannual variance of ion concentrations and wet deposition compared to nearby low‐elevation monitoring stations. Cloud droplet capture by the forest canopy varied substantially from year‐to‐year in response to changing meteorological conditions, contributing between 6 and 31% of total annual water inputs, which averaged 156.1 cm yr−1. Cloud water deposition was responsible for approximately 50%, and dry deposition approximately 10% of total annual N and S deposition. The signal from known decadal trends in atmospheric concentrations and fluxes of S in the northeastern USA was partially masked by high‐frequency (intra‐ and inter‐annual) variance associated with local climatic effects on precipitation and cloud water fluxes at this high‐elevation site. These observations suggest that atmospheric deposition rates to high‐elevation forests may be more responsive to climatic fluctuations and less responsive to recent and expected changes in atmospheric chemical burdens than in surrounding low‐elevation ecosystems.