Eresay Alcantar-Velasquez

Education: Bachelor of Science in Geology (May 2023)

McNair Project: Tracing a Microbial Flow through Aquifer, Soil, and Stream

Mentor: Matthew Kirk, Ph.D.

Microorganisms drive chemical reactions that influence water quality, soil health, and greenhouse gas fluxes. To better understand these impacts, numerous studies have examined microbial communities in soils, aquifers, and streams. However, few studies have examined the extent to which these communities are connected within a single system, research that could potentially shed new light on community assembly. In this study, we examined microbial communities in soil, well sediment, and stream sediment within a native grassland catchment at Konza Prairie Biological Station. Streamflow is predominantly contributed by oxic groundwater discharge from shallow aquifers, leading us to hypothesize that stream microbial communities would have a greater similarity to those in the aquifers than to those in watershed soils. To test this hypothesis, we analyzed microbial communities in our samples using MiSeq amplicon sequencing. We sequenced ITS to analyze fungi and 16S rRNA genes to analyze bacteria and archaea. Alpha diversity calculations show that the microbial communities were most diverse in the stream sediment samples, potentially reflecting the dynamic nature of streams and the variety of surficial and subsurface inputs they receive. Well sediment samples had the lowest fungal diversity but, for bacteria and archaea, were insignificantly different from those in soils in terms of observed features. Beta diversity calculations show distinct groupings between communities in the soil and stream sediment samples, but their relationship with well sediment communities varied. In terms of bacteria and archaea, well sediment communities had the greatest overlap with those in stream sediment samples, consistent with our hypothesis, but for fungi, the well sediment communities had the greatest overlap with soil communities. High relative abundances of Glomeraceae, an obligate plant associate, in well sediment samples suggest that at least some of the aquifer fungi are transported by groundwater recharge from overlying soils, potentially contributing to overlap in fungal communities between the wells and soils. These results show that links between microbial communities along hydrologic flow paths do not have clear directionality and depend on the identity of the populations being examined.