USING GENETIC CHARACTERIZATION OF A GROUNDWATER ARTHROPOD AS A POTENTIAL METHOD TO IDENTIFY CROSS-GRADIENT MIGRATION PATHWAYS IN AQUIFERS

Folsomia candida (Fc) is a soil arthropod that usually occurs in leaf litter or shallow soils, is found in all parts of the world and has been established as a standard test organism for evaluating ecotoxicity of soils. This presentation reports on recent work from an ongoing investigation of Fc occurrence in a shallow (2.5 to 5.7 m. below grade) lake-plain aquifer along the southwestern coast of Michigan, USA. Fc occurrence in groundwater is uncommon to rare, or at least has been under-reported in the literature. In general, ground water arthropods have been overlooked as effective bioindicators in aquifers. This presentation reports on a project to investigate the use of Fc as a bioindicator of pore-scale to mesoscale processes within an aquifer. Specifically, the investigators propose that an understanding of Fc mobility in the aquifer may yield important insight on previously unrecognized subsurface spatial relationships. Because Fc mobility in groundwater is a function of longitudinal and cross-gradient flow pathways, the research addresses whether Fc observed in spatially-separated ground water wells are genetically isolated or connected populations.

DNA was extracted from individual Fc collected from different wells. ISSR (Inter-Simple Sequence Repeat) markers were used to examine gene flow between Fc populations. ISSRs are highly sensitive genetic markers capable of detecting even single nucleotide polymorphisms in clonally reproducing species over short geographic distances. Preliminary data indicate that the Fc populations in some wells are genetically dissimilar, indicating limited transportation pathways exist in the aquifer or at the water table-vadose zone interface, over a distance of 200 meters. Genetic connection is evident between populations in some wells, separated by distances ranging from 100 to 300 meters. These observations are somewhat related to groundwater flow direction. Further work will determine if DNA fingerprinting of groundwater arthropods can be used to reveal unrecognized longitudinal and cross-gradient migration corridors in aquifers.