Ion leaching from a sugar maple forest in response to acidic deposition and nitrification

Year-to-year variation in acidic deposition within a mature sugar maple-dominated forest and in leaching of ions from the associated podzolic soil were examined at the Turkey Lakes Watershed between 1981 and 1986. Below-canopy inputs to the soil of SO42− and NO3− in throughfall averaged 640 and 295 eq. ha−1 yr−1; the corresponding ranges were 493–917 and 261–443 eq. ha−1 yr−1. The contribution of atmospheric deposition to SO42− NO3− and Ca2+ leaching decreased over the six years. During the study period, the mean annual volume-weighted NO3− concentration decreased in throughfall and forest-floor percolate and increased in the mineral-soil solution collected below the effective rooting zone. A substantial shift in the balance between SO42− and NO3−leaching from the mineral soil was observed; leaching of SO42−decreased and NO3− leaching increased with time. Leaching of Ca2+ and Mg2+ from the soil was increased as a result of excess NO3− production in the soil. The calculated output of NO3− from the soil, which averaged 1505 eq. ha−1 yr−1, considerably exceeded the atmospheric deposition of NO3−, whereas SO42− outputs were only moderately greater than inputs.