Rain-induced soil denitrification in a highly acidic, hardwood forest watershed in the Catskill Mountains of New York, U.S.A

The effects of delivered rain, temperature, and clear-cutting on denitrification were investigated in acidified, well-drained upland forest soils in the Catskill Mountains of New York, U.S.A. Repacked soil methods were used to investigate aspects of denitrification including limiting nutrients, soil horizon comparisons, and the roles of oxygen and moisture. The soils exhibited symptoms of nitrate saturation and denitrification rates decreased with the addition of nitrate. Denitrification was limited to shallow organic-horizon soils, and water amendments and labile carbon amendments enhanced denitrification. Aerobic intact cores with acetylene inhibition (AI) were used to measure base and water-amended denitrification rates. Intact core denitrification rates were nonnormally distributed with many low or undetectable rates and a few high rates (0 to 0.18 μMol N₂O h−1 core −1). Rain was required for denitrification to occur in these well-drained soils, otherwise, rates were insignificant. Cores amended with deionized water (DI) or collected after rain accounted for most of the positive and high denitrification rates. Unamended cores collected after dry periods showed little or no denitrification. Because core rates showed large differences at soil moisture extremes (dry and saturated) and dependency on incubation temperatures, attempts were made to clarify the relationships among denitrification, delivered rain (up to 2.54 cm), and temperature (6 to 28°C). DI volume and temperature were exponentially-related to denitrification rates and their effects were additive; the highest denitrification rates were at higher temperatures with larger DI amendments. The largest DI amendment (2.54 cm) elicited responses in most soils; smaller amendments (0.25 and 0.50 cm) resulted in smaller responses with greater variability and only negligible effects in very dry soils. Using continuous monitoring data for temperature and rain, and experimentally-derived rain parameters in simplistic budget calculations resulted in increased denitrification estimates at all sites relative to budgets that did not, and showed that denitrification was significant through episodic events rather than through consistent emission. Rainfall drove denitrification in these acidified, well-drained soils during the growing season, especially during the summer.