THE ASSOCIATION OF FINE-PARTICLE MINERALOGY AND FOLSOMIA CANDIDA OCCURRENCE IN A COASTAL LAKE MICHIGAN AQUIFER

Folsomia candida (Fc) is a common soil arthropod of the order Collembola. Fc usually occurs in leaf litter or shallow soils, and has been established as a standard test organism for evaluating ecotoxicity of soils. An ongoing research project was started when Fc was discovered in a shallow (2.5 to 5.7 m below grade) lake-plain aquifer located along the southwestern coast of Michigan. Because Fc occurrence and abundance varies between locations, the research team has attempted to find correlations with ground-water and aquifer physiochemical parameters. Fc feeds on fungi attached to leaf litter or soil (specifically silt and clay-sized) particles. Fc in groundwater occurs at depths where no leaf litter occurs, but the generally sand-rich soils of the study area do contain silt and clay-rich portions at, or slightly above (within ~25 cm) the water table, meaning a food substrate exists for the insects.

This poster reports on attempts to associate the presence of Fc in groundwater with the mineralogy of the very-fine silt and clay-sized sediment at the water-table interface. Two sample types were collected for analysis. One type was soil boring samples collected from the water table depth at different surface locations in the study area. The second type was the suspended particles present in water samples collected from wells. Both types were dry sieved, separated, re-suspended, and flocculated into three distinct size fractions: 35-5 µm, 5-2 µm, and < 2 µm. Fractions from each sampling location were analyzed by X-Ray diffraction and an ICDD library matching program. Results indicate that very-fine silt and clay particles at the water table are primarily 7 minerals: quartz, dolomite, calcite, kaolinite, chlorite, with possible goethite and hydrated iron phosphate (Fe₅(PO₄)₄(OH)₃^.2H₂O). Preliminary analysis indicates that on the scale of the study area (~ 1 km²), the occurrence of Fc can be divided into 2 broad mineralogical associations: (1) Fc is generally not associated with chlorite, dolomite or calcite, goethite, and hydrated iron phosphate; and, (2) Abundant Fc tends to be associated with quartz-dominated sediments that lack a carbonate phase. All samples contain kaolinite. Further research is in progress to determine if a significant relationship exists between Fc occurrence in groundwater and aquifer fine-particle mineralogy.