Modeling Soil Addition Profiles of Carbon, Nitrogen, Lead and Manganese Across a Climate Gradient.

Lead, manganese, carbon and nitrogen can all form what is known as a soil addition profile, where an element increases in concentration from the basal layer of soil to the surface. Lead and manganese (Pb and Mn), both toxic to humans in varied quantities, attribute most of their deposition to anthropogenic sources such as fossil fuel burning and metal refineries.  Carbon and nitrogen (C and N), however, owe at least part of their input to soils by natural cycles which include fixation by plants and microorganisms. It is prudent to quantify the processes which affect these elements because of their potential toxic effects on humans (Pb and Mn) and management of environmental resources in a warming climate (C and N). The purpose of this study was to analyze the concentrations of these elements in the soil as a function of depth in varying climates and model the processes controlling the observed concentration profiles. Soil samples were collected from five sites along a climate transect down the east coast of the US and two additional sites, Puerto Rico and Wales, and soil profile concentrations were measured. A mathematical model was created to reproduce the addition profiles specific to each element using a finite difference scheme in Matlab. The model incorporated an input source (wet/dry deposition) and several processes which occur in the soil, namely: erosion, mixing, and dissolution-precipitation. Results of this modeling effort will aid predictions of how C, N, Pb and Mn concentrations change with depth under various climatic conditions.