Our project is based on the hypothesis that measurable geophysical signatures are associated with anaerobic iron sulfide precipitation in wetland soils. If correct, the possibility exists to improve understanding of this important microbial process by using state-of-the-art geophysical technologies to non-invasively image the evolution of such processes in situ. In order to investigate our hypothesis we have constructed a two-dimensional experimental tank that facilitates electrical measurements with a high spatial sampling density. The dimensions of the tank are 2.0 m x 1.0 m x 0.15 m and it has been instrumented with 119 electrode ports for measuring three geophysical properties (1) electrical conductivity; (2) induced polarization; (3) self potential. We have designed a study based around a successful column experiment that we completed in collaboration with scientists at University of California-Berkeley. We have selected a known sulfate reducing bacteria, D. vulgaris, which can tolerate slightly oxic conditions as we expect to have in our tank (being too large to enclose in an anaerobic chamber). We intend to fill the experimental tank with well sorted, relatively coarse sand and saturate it with a synthetic groundwater that includes nutrients required to stimulate microbial growth as well as dissolved iron and sulfate. In order to investigate the sensitivity of geophysical measurements to biomineralization, D. vulgaris will be injected at three locations of the tank but with differing amounts of nutrients to promote growth. We will monitor the electrical geophysical properties as the iron sulfide precipitation progresses. We anticipate that the unique advantages of geophysical datasets (non-invasive, spatially continuous) will permit an improved understanding of the processes of iron sulfide precipitation in soils. Applications of the technology to wetlands environments are expected.
Experimental tank for two-dimensional metal-sulfide precipitation experiments
showing connections of 119 electrodes during calibration measurements on water