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Stable aggregate dynamics and carbon storage in acidified forest soils: Influence of atmospheric deposition and conifer conversion at the Fernow Experimental Forest J. E. Kemner Understanding anthropogenic changes to forested ecosystems is crucial to appropriately manage forests for overall ecosystem health, soil quality, water quality, and carbon (C) sequestration potential. This research explored the effects of ecosystem change caused by increased atmospheric nitrogen (N) deposition and stand conversion from mixed-species hardwood to monoculture Norway spruce. Research activities for this thesis occurred in three experimental watersheds at the USDA Forest Service Fernow Experimental Forest (FEF), West Virginia, USA. I measured soil aggregation and organic matter (OM) content in a paired watershed study to investigate the influence of forest fertilization in Watershed 3 at FEF, a native hardwood forest that was clear-cut concluding in 1969 and has received 35 kg nitrogen (N) as (NH4)2SO4 fertilizer per year since 1989. Results were compared to those from Watershed 7 at FEF, a natural hardwood regrowth following clear cut harvest concluding in 1969, which is considered an appropriate reference for this study. Furthermore, I compared the results from Watershed 7 to nearly adjacent Watershed 6, which was converted to a monoculture of Norway spruce (Picea abies) following clearcut harvest, and planting in 1973. Both watersheds were maintained barren via herbicide from 1967 to 1969. In Watersheds 6 and 7, I also quantified select ecosystem pools of C and N, including vegetation biomass, forest floor, and mineral soil to create an ecosystem budget for C and N. Long-term atmospheric deposition and stream export of nitrate (NO3-N) were also quantified. Soil from both the fertilized watershed and the spruce watershed demonstrated dispersion of macro-aggregates and greater weight in the <53 μm soil aggregate size class – unassociated clay particles or free microaggregates relative to the reference watershed, which was associated with lower soil pH. Soil from the reference watershed has greater aggregate weight in the macro-aggregate size classes (between 250 2000 μm), and in the B-horizon, greater organic matter (OM) content in macroaggregates. Soil from the fertilized watershed exhibits greater intra-aggregate OM beneath arbuscular mycorrhizal-associated (AM) tree species with labile litter, while soil in the reference watershed contains more intra-aggregate OM beneath ectomycorrhizal-associated (ECM) tree species. The spruce watershed conversion has significantly impacted N cycling, as system atmospheric inputs of NO3-N are equal, yet streamflow exports from Watershed 6 are negligible, and spruce soil inorganic N content is more than 5 times lower relative to that of the reference watershed. In the A-horizon soil in the spruce watershed, microbially-active C is significantly lower, measured as permanganate oxidizable carbon (POXC). As many parts of the world have been exposed to long-term atmospheric deposition of N and sulfur (S)-based compounds and been converted to coniferous planted forests, further study to determine how these systems will respond to our changing global climate is necessary.

Stable aggregate dynamics and carbon storage in acidified forest soils: Influence of atmospheric deposition and conifer conversion at the Fernow Experimental Forest