, Volume 48, Issue 1-2, pp 251-261

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

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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 SO4 2− 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 SO4 2− 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 SO4 2− and NO3 leaching from the mineral soil was observed; leaching of SO4 2−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 SO4 2− outputs were only moderately greater than inputs.