IMPACT OF LAND USE ON GROUNDWATER CHEMISTRY AND MICROBIAL COMMUNITIES IN GREAT BEND PRAIRIE AQUIFER

The High Plains aquifer is a vital source of irrigation and drinking water in the central US. Therefore, it is important to understand how changes in aquifer geochemistry and aquifer microbial communities affect the health of the aquifer. Our recent analysis of the Great Bend Prairie aquifer, a portion of the High Plains aquifer in south-central Kansas, indicates increasing levels of nitrate and total dissolved solids (TDS) in upper aquifer wells. Nitrate concentrations have increased above the recommended EPA limit of 10 mg/L as N for public sources of drinking water in seven out of twenty-four wells sampled. TDS increased by 78 mg/L on average in upper aquifer wells and decreased by 373 mg/L on average in lower aquifer wells. In addition, the sampled stable isotope ratios of nitrogen (¹⁵N/¹⁴N) and oxygen (¹⁸O/¹⁶O) fall primarily in the range associated with nitrification of ammonium-based fertilizers. Land use observed in the field site is primarily row crop agriculture. Collectively, these observations indicate that the increased levels of nitrate and TDS are most likely of anthropogenic source.

Currently, we know very little about the microbial communities inhabiting the High Plains aquifer. Our ongoing research considers the role of land use on aquifer microbial communities in the Great Bend Prairie aquifer. We hypothesize that land use significantly impacts the composition of the shallow aquifer microbial community and that the composition of the groundwater microbiome will be related to the composition of the soil microbiome. To test our hypotheses, we will analyze multiple samples of pasture and row crop soil microbiomes to compare with the composition and diversity of aquifer microbial communities. In addition, we will measure environmental parameters such as total nitrogen (TN), total organic carbon/dissolved organic carbon (TOC/DOC), and pH in the soil and aquifer at each site. After gathering data, we will perform a beta diversity test to compare the diversity of the microbial community species of each sample site to each other and to provided metadata (e.g. groundwater chemistry, soil chemistry, soil particle size distribution, spatial distance). We expect to find that land use, the soil microbiome, and the aquifer microbiome are intricately connected.