BIOGEOCHEMICAL INTERACTIONS BETWEEN ACIDIC DEPOSITION AND A LOW-ELEVATION SPRUCE FIR STAND IN HOWLAND, MAINE

The biogeochemical interactions between acidic deposition and a forest ecosystem were investigated in a low-elevation spruce-fir stand in east-central Maine. A 0.2-ha plot was intensively instrumented for measurement of precipitation, throughfall, and soil solutions. Annual precipitation for 1989 had an average pH of 4.39 and an estimated 424, 191, and 231 mol.ha-1 deposition of H+, SO4(2-), and NO3-, respectively. Soil water flux was determined from precipitation and evaporation estimates. Ion flux data are presented for the 12-month period of 1989. Approximately 50% of inorganic strong acid acidity in precipitation plus unmeasured dry deposition was neutralized by the canopy for the measurement period reported. Soil and soil solution buffering were largely controlled by organic matter and mineral weathering. Mobilization of inorganic Al was minimal (< 3-mu-M) in both the Oa and Bs horizons. Ratios of Al/Ca2+ were well below values considered to cause inhibition of Ca2+ uptake. Annual deposition of SO4(2-) in throughfall (285 mol.ha-1) approximated output (291 mol.ha-1). Virtually 100% of wet-only NO3- input and 90% of wet-only NH4+ input were retained within the ecosystem.