Abstract

Addition profiles show a net enrichment of an element, j, at the surface compared to the parent material. The excess concentration of the element is coming from an outside source where it is deposited on the surface and then subsequently incorporated into the soil profile through a variety of processes. The shape of these profiles can give clues to what processes are occurring in the soil and therefore have the largest effect on the element of interest (j). Carbon and nitrogen are elements associated with organic matter. Most of their deposition to soils can be attributed to the decay of plant litter on the surface. Manganese is often used in metal refineries and input into the atmosphere via emissions; it is eventually “rained out” onto the soil during precipitation events. We analyzed the elemental concentrations of C, N and Mn in soils along a climosequence that extends through the Appalachians of the United States and includes end members in Wales and Puerto Rico. C and N display addition profiles at every sample site. Mn only displays addition profiles in Pennsylvania and Virginia. We also determined the net added or lost mass of C, N and Mn at each sample site with respect to the soil parent material. These values were compared against the mean annual temperature for each site. We saw an increase in enrichment until ~11^oC (after the Virginia site) and then a decrease in enrichment until eventually every element studied was partially depleted at our end member in Puerto Rico. We then fit our concentration profiles with a previously described diffusion based soil mixing model to determine what soil  processes were acting on C, N and Mn concentrations in the soils along our transect.  We discovered that soil mixing does not trend with mean annual temperature, but higher precipitation sites had higher soil mixing rates. We also observed that the model provided a net input rate for C and N that includes an organic matter decomposition rate. We concluded that the latitude range which the soil decomposition rate overtakes the true C and N input rates occurs between VA and TN. This is the divide between increasing net mass of C, N and Mn in the soil and decreasing net mass. The model did a good job explaining accurately the transport and storage of Mn in the soil assuming Mn is relatively immobile. Mn additions showed no trend with climate. This is expected as Mn is associated with point source pollution. A more complete (more processes incorporated) model is necessary to better quantify the soil processes associated with C and N storage and subsequently explain trends in SOM storage with temperature.

Citation

Bingham, N (2013): C, N, and Mn in Shale Soil Profiles along a Climate Gradient . Bachelor of Science, Pennsylvania State University..