Dr. Diana Karwan, Assistant Professor of Forest Hydrology, University of Minnesota, will present "Short Term Fallout Radionuclides Reveal Sediment Mixing and Transport in the Critical Zone" from 3:30pm – 5:00pm in 401 Steidle Building.  

Abstract:

Short-term radionuclides, such as Beryllium-7, Lead-210, and Cesium-137 (⁷Be, ¹³⁷Cs, ²¹⁰Pb) provide numerous insights into critical zone mixing processes. In addition to 1-dimendional soil inventories quantifying net erosion and deposition, these isotopes can be used to quantify perturbations on event to decadal time scales as well as the links between terrestrial and aquatic portions of the critical zone.  In this seminar, I will discuss short term fallout radionuclide profiles collected in the Shale Hills CZO and explore their use for examining sediment profiles, disturbance, and erosion rates over the past half-century.  
To date, ¹³⁷Cs and ²¹⁰Pb have been used to locate and date areas of mixing and sediment mobilization within the Critical Zone at the Susquehanna Shale Hills CZO.  Based on total ¹³⁷Cs fallout estimates, SSH CZO received 4000 – 6000 Bq/m^{2 137}Cs during widespread atomic weapons testing in the 1950s and early 1960s.  The total inventory in a mid-slope planar profile, when adjusted for decay since peak fallout in 1963, confirms this activity.  However, swale transects in a similar slope position have a lower inventory, indicating net erosion since atomic weapons testing circa 1963.  ¹³⁷Cs also indicates soil mixing and erosion in mounds associated with older upturned trees, for which the bole is no longer completely intact. With a total inventory of 850 Bq/m² and consistent vertical pattern of low concentration through the entirety of the mound, ¹³⁷Cs profile implies the tree throw occurred after 1963, the peak of regional ¹³⁷Cs fallout.  These results narrow the time estimate of disturbance provided by other chemical makers (e.g. manganese markers of industrialization).

For our off-campus collaborators, you may join the meeting via Zoom meetings:  https://psu.zoom.us/j/149561187