MICRO- AND NANO-SCALE WEATHERING OF BASALT IN INCIPIENT SOILS

Soil microorganisms are critical drivers of rock weathering, biogeochemical cycling of elements, and soil formation. Understanding the interplay between the microbial community and their physical-chemical environment can shed light on transformation of soils as landscapes respond to changing precipitation and temperature regimes. The Landscape Evolution Observatory (LEO) at Biosphere 2 provides an opportunity to monitor incipient soil formation in zero-order basins filled with ground basalt that mimic a loamy sand soil texture under controlled environmental conditions. Basalt weathering is one of the most important contributors in controlling atmospheric carbon dioxide concentrations in geologic time. Three replicated slopes, currently lacking vegetation, are instrumented with a dense network of sensors and samplers that are capable of capturing water, carbon, and energy dynamics at a high spatiotemporal resolution to establish landscape evolution patterns. The goals of our study were a) to investigate the surfaces of the basalt grains for micro- and nano-scale weathering patterns, b) to quantify mineral transformation at high resolution, and c) compare microbial diversity and abundance patterns to micro- and nano-scale weathering patterns. We utilized a combination of scanning electron microscopy, focused ion beam techniques, transmission electron microscopy, various spectroscopic techniques and synchrotron based quantitative x-ray diffraction to reach our goals. Preliminary results show organo-mineral layer formation on surfaces of the basalt grains, which can slow the weathering rates. We expect to see elemental depletion zones to about 30-50 nm depth into the minerals and an increase in the proportion of amorphous materials in the samples. The results gained from this study can help us further understand the interactions between microorganisms and minerals during incipient soil formation prior to plant colonization of the landscapes.