This study turns to what is for many an everyday item – yogurt – as a critical zone observatory, a synergistic, place-based laboratory which aims to integrate heterogenous representations of planetary phenomena as they are registered at a common surface. Yogurt has an impressive cultural endurance largely derived from its prominence in various paradigms of health. The product has culturally endured in another sense: as a common cultural medium where humans and microbes have met for generations. This study begins with a profile of yogurt as most encounter it today to consider how normative notions of health interface with the temporal and spatial imaginaries entailed in commodity geographies. Commoditized yogurt is characterized by a low and limited microbial biodiversity compared to yogurts produced outside of the commodity context. Yogurt is therefore presented as a micro case study to consider modes by which we sense and valuate ecological phenomena beyond the perceptible surface, how such sens-abilities intersect models of health, and to what effect. To trace a history of yogurt along these contours, I introduce it as a particular kind of artefact: a global object. As an object of environmental history, I define a global object as a global commodity with a high potential to be re-localized, and therefore with a high potential to re-shape commodity geographies. However, this trajectory is contingent upon framing yogurt as a critical zone observatory – a site where global phenomena like human-microbial interaction may become familiar and intimate. Guided by new materialist theory, I weave together historical and ethnographic case studies from the following consortium: resident yogurt bacteria, artisanal yogurt producers and home fermenters, a mystical immunologist, and an 11th century linguistic scholar. Through these perspectives, I both sketch and apply a framework for de-centered, interspecies histories of cultural (re)production through an extended metaphor of biofilm: the coagulative bacterial structure giving yogurt its characteristic texture. In so doing I provide a re-articulation of “the probiotic” as an integrative case of human and more-than-human health. The study concludes by directing these implications towards a consideration of aesthetic engagement by displaying how fermentation practice may enliven matters of re-diversification and re-localization.

Dye tracer and time-lapse ground-penetrating radar (GPR) were used to image preferential flow paths in the shallow, unsaturated zone on hillslopes in two adjacent watersheds within the Susquehanna-Shale Hills Critical Zone Observatory (CZO). At each site we injected about 50 L of water mixed with brilliant blue dye (4 g/L) into a trench cut perpendicular to the slope (~1.0 m long by ~0.20 m wide by ~0.20 m deep) to create a line of infiltration. GPR (800 MHz antennae with constant offset) was used to monitor the movement of the dye tracer downslope on a 1.0 m x 2.0 m grid with a 0.05 m line spacing. The site was then excavated and the stained pathways photographed to document the dye movement. We saw a considerable difference in the pattern of shallow preferential flow between the two sites despite similar soil characteristics and slope position. Both sites showed dye penetrating down to saprolite (~0.40 m); however, lateral flow migration between the two sites was different. At the Missed Grouse field site, the lateral migration was ~0.55 m as an evenly dispersed plume, but at distance of 0.70 m a finger of dye was observed. At the Shale Hills field site, the total lateral flow was ~0.40 m, dye was barely visible until the excavation reached ~0.10 m, and there was more evidence of distinct fingering in the vertical direction. Based on laboratory and field experiments as well as processing of the radargrams, the following conclusions were drawn: 1) time-lapse GPR successfully delineated the extent of lateral flow, but the GPR resolution was insufficient to detect small fingers of dye; 2) there was not a distinct GPR reflection at the regolith-saprock boundary, but this interface could be estimated from the extent of signal attenuation; 3) the preliminary soil moisture conditions may explain differences in the extent of infiltration at the two sites; 4) rapid infiltration into the underlying saprock limited the extent of shallow lateral flow at both sites and can be seen using the mass balance calculation and the lateral extent of dye within the radargrams; and 5) variations in flow patterns were observed between sites with similar settings at Susquehanna-Shale Hills CZO. / Geology