The influence of forests on pedochemical cycling of base cations, sulfur, and atmospherically-derived lead

Forests are an important component of the soil system and influence a variety of biogeochemical processes. Unfortunately, much remains to be understood with regards to forest effects on pedochemistry because variability in other soil forming factors naturally influence forest composition. I use field sites and experiments that constrain other soil forming factors to isolate forest type effects on the behavior and distribution of base cations, S and Pb in soils, providing new insight with regards to these pedochemical systems and their possible alteration due to biogeochemical change.;I examine base cation depletion and chemical weathering under conifer plantations and northern hardwood forests. In surface soils, conifer forests aggressively deplete soils in nutrient cations relative to deciduous forests, but at depth, deciduous soils are more depleted. I attribute surface trends in soil depletion profiles to the more aggressive weathering agents produced by conifers associated with decomposition/fine root exudation, but at depth northern hardwood deep root networks and high nutrient demands produce a more depleted soil.;Sulfur speciation in organic rich surface horizons (OSH) indicates that during decomposition of soil organic matter (SOM), S species distribution and behavior is dynamic. In conifer soils, organic sulfide and sulfoxide are relatively reactive phases of S, while sulfonate and organic sulfide are relatively inert. Conversely, S reactivity is not tied to speciation in deciduous soils. This difference could be tied to rapid C and S mineralization of high quality deciduous litter that is independent of speciation. This work also examines the behavior of previously unknown but important components of the soil S cycle in intermediate S species.;The behavior of anthropogenic Pb in OSH is related to speciation and forest type. Gasoline-derived Pb inventories in OSH are higher in conifer soils relative to deciduous soils. This is due to the higher scavenging capability of conifer canopies and slower decomposition of conifer SOM. Pb speciation during decomposition is dynamic, with increased association of Pb with pedogenic Fe/Mn mineral phases during decomposition. This suggests that geochemical parameters governing mineral stability will increasingly influence the behavior of Pb in OSH over time.