Soils strongly control water chemistry. Likewise, water chemically weathers soils. Our lab group is investigating the how soil geochemistry is shaped by topographic and hydrologic controls. In particular, accurate measurements of soil air CO2 concentrations (pCO2) are important for understanding carbonic acid reaction pathways for continental weathering, the global carbon (C) cycle, and climate change. While there have been many studies of soil pCO2, most sample or model simplified landscapes without accounting for complex topography. Dr. Hasenmueller's group has measured the depth distribution of soil pCO2 along variable topography where controls on soil pCO2 (e.g. soil depth, moisture, and temperature) vary from ridge tops down to the valley floor, among planar slopes and slopes with convergent flow (swales), and between north and south facing aspects.
Recent projects seek to answer:
1. How does soil pCO2 vary with topography?
2. What impact does variable soil pCO2 have on regolith weathering?
3. How does topography influence rooting depth and root respiration rates?
Jin, L., Ogrinc, N., Yesavage, T., Hasenmueller, E.A., Ma, L., Sullivan, P.L., Kaye, J.P., Duffy, C., Brantley, S.L., 2014. The CO2 consumption potential of gray shale weathering: insights from the evolution of carbon isotopes in the Susquehanna Shale Hills critical zone observatory, Geochimica et Cosmochimica Acta, 142, 260-280.
Monthly average soil pCO2 (μmol mol-1) contour plots as a function of soil depth (m) and time (month) for ridge tops, mid-slopes, and valley floors in the planar slope and swale depression at the Shale Hills Critical Zone Observatory. Darker colors represent higher CO2 concentrations. Geomorphologically comparable locations like the ridge tops and valley floors have similar pCO2 profiles. However, the mid-slopes differ by up to 6x for the same depth because of differences in total profile depth, soil moisture, and diffusivity.