Carbon, Nitrogen and Manganese in Shale Soil Profiles along a Climate Gradient

Open Access
Author:
Bingham, Nina Lynn
Area of Honors:
Geosciences
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Susan Louise Brantley, Thesis Supervisor
  • Maureen Feineman, Honors Advisor
  • Peter Daniel Wilf, Faculty Reader
  • Peter J Heaney, Faculty Reader
Keywords:
  • Climate change
  • soil organic matter
  • mathematical modeling
  • soil mixing
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, 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 have the largest effect on the element, j. Carbon and nitrogen are elements associated with organic matter and can attribute most of their deposition to the decay of plant litter on the surface. Manganese is often used in metal refineries and input into the atmosphere and eventually “rained out” onto the soil. We analyzed these three element’s concentrations in soils at samples sites which make up a climosequence down the east coast of the United States with 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 total concentration of C, N and Mn at each sample site with respect to the parent material for the soil and with account for soil strain. These values were compared against the mean annual temperature for each site. We saw a general increase in enrichment until ~11oC (after the Virginia site) and then a general decrease in enrichment until eventually every element studied was depleted at our end member in Puerto Rico. Pennsylvania has anomalously small concentrations of C and N compared to all other sample sites. We then fit our concentration profiles with a previously described diffusion based soil mixing model to determine what soil processes were acting on the soils in our transect. We discovered that soil mixing does not trend with mean annual temperature. We knew that the model greatly underestimated the input rates of C and N because of the model’s simplicity. The most realistic values for C and N input were determined for the Wales profile because Wales had high annual precipitation and low mean annual temperature which retards soil organic matter decomposition. Additionally, we realized that organic matter decomposition, which was not included in the model, plays an integral part in the more southern sample sites. This is especially true at the warmest sample site, Puerto Rico. There, the C and N inputs were large yet the profile was still depleted of C and N. The model did a good job at explaining accurately the transport and storage of Mn in the soil assuming Mn is relatively immobile. This means that the major process affecting the distribution of Mn in the soil is soil mixing. Also, Mn increases showed no trend with climate. A more complete (more processes incorporated) is necessary to better quantify soil processes associated with C and N storage and subsequently explain trends in SOM storage with temperature.