Trends in Water Chemistry in a Maple Forest on a Steep Slope

Abstract

Year-to-year variation in SO42-,NO3-, Ca2+, K+, and Mg2+concentrations in forest floor and mineral soil percolatefrom a forested, podzolic soil at the Turkey Lakes Watershedon the Precambrian Shield was assessed for monotonic trendsbetween 1986 and 1995. Our objective was to examine howrapidly ion concentrations in soil percolate equilibratedafter stabilization of SO42- concentrations inprecipitation. Significant negative trends were detected inmonthly Ca2+, and Mg2+ concentrations in forestfloor and SO42-, Ca2+, and Mg2+ inmineral soil percolate during the 10-year-period. Thedecline in Ca2+ and Mg2+ was greater than annualdecreases in SO42- and NO3- in forestfloor percolate and proportional to the reduction inSO42- in mineral soil percolate. Response ofmineral soil percolate to a 15 μmolc L-1SO42- decrease in wet-only precipitation between1985 and 1986 was a gradual decline in SO42-concentration through 1995. The five-year meanSO42- concentration in bulk precipitation, forestfloor percolate, and mineral soil percolate decreased 8, 9and 18 μmolc L-1 from 1986–90 to 1991–95.Microbial (mineralization of organic S) and sorption(release from and/or retention in the pool of insolubleSO42-) processes in the soil were logicalexplanations for the observed changes in SO42- inmineral soil percolate.