PEAT BOGS AND OIL SPILLS: SILICATE WEATHERING RESEARCH IN THE SIEGEL LAB

By 1984 Don Siegel was establishing his research program at Syracuse University with several MS students working in physical hydrogeology. Don’s PhD research however was on silicate weathering chemistry at the watershed scale and he was looking for a student to work in aqueous geochemistry. I started working that year with Don as an MS student and then continued on for a PhD in geochemical kinetics.

We started working together on the USGS Bemidji research site, an oil contaminated sand and gravel aquifer in Minnesota near the town of Bemidji, along with many other scientists from the USGS. Preliminary water analyses identified a plume of inorganic solutes coincident with the oil plume suggesting that aquifer minerals were weathering associated with the oil degradation. At first we used SEM methods to examine sand grains, and we found that both feldspar and carbonates in the contaminated zone were pitted compared to the background zone. But we found that quartz also displayed characteristic triangular pitting indicating chemical weathering, even in a water that was greatly supersaturated with respect to quartz.

This simple finding led us in a variety of exciting directions. Continued investigations of the aqueous and mineral chemistry at Bemidji showed that the silicate weathering was occurring in the anoxic region of the plume in the region of greatest DOC concentration, not the region of most acidic pH. Further laboratory investigations established that silicate weathering accelerated in the presence of some organic acids but not others, and quartz solubility increased. We extended this work in collaboration with others with a field investigation of silicate grains in peat from the Red Lake peat bogs (another of Don’s scientific passions) and found a similar relationship between organic acid concentration, anoxia, high silica concentration, and etch-pitted silicates.

Over the next 3 decades I continued researching silicate weathering at Bemidji and other locations, and with the help of many fantastic graduate students we established that attached microorganisms were most likely responsible for the silicate weathering via the production of organic chelators and perturbed pH at the mineral surface. Throughout this time however I relied on Don as a geochemical sounding-board and good friend to help hone our ideas.