Zelalem Bedaso, Ph.D.
The global population has increased exponentially causing several challenges surrounding sustainability, including greater food production needs. To meet these demands and boost agricultural productivity, more efficient practices and fertilizers are used. Synthetic fertilizers and other nutrient sources have resulted in water quality degradation and pollution. Much of the Great Miami River Watershed’s streams and aquifers in southwestern Ohio are affected by nitrate contaminants originating from anthropogenic sources including synthetic and organic fertilizer used for agriculture, human wastes (domestic, industrial, and municipal wastes), and urbanization. High nitrate concentrations cause ecological disturbances across all trophic levels. Nitrate levels greater than 10 mg/L also pose a danger to human health, if the contaminant reaches drinking water sources. Water quality monitoring stations report nitrate concentrations in surface and groundwater, but a nitrate contaminant source has not been identified.
Here we used isotope ratios of nitrogen (δ15N) and oxygen (δ18O) and boron (δ11 B ) in nitrates to identify sources for surface and groundwater. We sampled soil and water from different sites within the Great Miami River catchment. Agricultural sampling sites for water and soil included a city of Dayton owned inorganic farm field, a farm field in Shelby County, and manure from local cows, chickens, and pigs. Soil and water samples from natural sites included forest and grassland landscapes in both Englewood and Germantown Metropark, a forest plot adjacent to Shelby County farm fields, and Estel Wenrick Wetland. Outfall samples were collected from official City of Dayton outfalls in Downtown Dayton and the Lily Creek outfall zone. Wastewater treatment effluent water samples were collected from the Engelwood and Miamisburg wastewater treatment plants. For the Summer 2017 field work season, a total of 3 manure, 32 soil samples, and 35 water samples were collected. These samples were analyzed by the University of Utah using an AgNO3 – precipitation method. Boron samples were analyzed at Page | 3 Stony Brook University using negative ion thermal ionization mass spectrometry. Fall 2018 surface water sampling was primarily done along the Great Miami, Mad, and Stillwater River. Addition samples were taken at City of Dayton outfalls and Miami Conservancy District groundwater monitoring wells. A total of 40 water samples were collected during this field season and they were analyzed at the University of California- Davis Stable Isotope Facility using a bacterial dentification assay method.
Using the stable isotope of nitrogen and oxygen we established the unique isotopic composition of different contaminant sources such as agriculture, septic systems, and animal waste. The additional analysis of boron helped to distinguish anthropogenic sources of nitrate from natural sources so that there is greater comprehension of how human activity is affecting water resources within a catchment. Our results show a distinct low δ15N for commercial synthetic fertilizers (0.4±4‰) and high δ15N for animal and human waste (13.0±1.3‰). In general, the δ15N from river samples collected during the low river flow lies within a range of human and animal waste, whereas δ15N values of groundwater suggest that the nitrates might have been derived from soil organic matter or synthetic fertilizers. Additional GIS analysis was used to assess nitrate concentration levels within the watershed and a major contamination area, where nitrate levels exceeded 5 mg/L, was identified at the confluence of the 3 rivers and it spans the region downstream, heading southeast. This research provides a regional baseline for nitrate contaminant source tracing and helps to better inform state and local water quality and nutrient management planning based on these findings.
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Buzeta, Rachel Kristine, "Nitrate Contaminant Tracing in Surface and Groundwater in the Great Miami River Watershed: Environmental Isotope Approach" (2019). Honors Theses. 206.