Mineral Soil and Solution Responses to Experimental N and S Enrichment at the Bear Brook Watershed in Maine (BBWM)

Abstract

Buried mineral soil-bags and natural solutions were studied as indicators of forest ecosystem response to elevated N and S inputs at the Bear Brook Watershed in Maine (BBWM). The BBWM is the site of a paired watershed manipulation experiment in a northern New England forested ecosystem. The study includes two small (~l0 ha each) catchments dominated by northern hardwood forests with red spruce in the upper elevations. Treatments consist of (NH4)3SO4 applied to the West Bear watershed six times per year, increasing N and S deposition 3x and 2x above ambient values, respectively. Buried mineral soil-bag changes over time reflected both the native soil environment and the treatments. Most of the treatment effects on mineral soils were evident as higher inorganic S found in the treated watershed soils. Adsorbed SO, in the buried mineral soil-bags increased by approximately 40% under softwood stands and 50% under hardwood stands over the study period. Hardwood soil solutions responded with significant increases in NO3 and SO, concentrations that resulted in accelerated cation leaching, primarily Ca and Al. Few differences that could be attributed to treatments were evident in soil solutions under softwoods. No treatment effects were evident in throughfall and stemflow chemistry.