Nitrogen Isotopes as Indicators of Nitrate Sources in Minnesota Sand‐Plain Aquifers

Abstract

Nitrate concentrations in excess of national drinking‐water standards (10 mg/1 as N) are present in certain sand‐plain aquifers in central Minnesota. To investigate nitrate sources in the aquifers, nitrogen‐isotope values of nitrate (δ15NNO3No3) were measured in shallow ground water from 51 wells in five land‐use settings. The land‐use settings and corresponding average nitrate concentrations (as N) and δ15NNO3 values are: livestock feedlots, 12.7 mg/1, 21.3%0; cultivated‐irrigated fields, 13 mg/1, 7.4%0; residential areas with septic systems, 8.3 mg/1, 6.0%0; cultivated‐nonirrigated fields, 15.5 mg/1, 3.4%0; and natural, undeveloped areas, 3.8 mg/1, 3.1%0. Values of δ15NNO3 less than 2%0 suggest that nitrogen from commercial inorganic fertilizers exists in ground water beneath all settings except the feedlots. Values of δ15NNO3 greater than 10%0 suggest that nitrogen from animal waste is present in ground water beneath certain feedlots, cultivated‐irrigated fields that are fertilized with manure, and residential areas with septic systems. Values of δ15NNO3 between 22 and 43%0 in ground water beneath the feedlots probably result from denitrification. Values of δ15NNO3 increase with depth in many locations in the sand‐plain aquifers. These increases may be caused by progressive denitrification with depth or by changes with depth in the proportions of nitrate from different sources. Similarly, variations of δ15NNO3 values from 1986 to 1987 in certain locations may be due to temporal variations in the amounts of denitrification or to changes in the proportions of nitrate from different sources. Ambiguities in the interpretation of changes in δ15NNO3 values could be eliminated by increasing the spatial and temporal frequency of sampling.

Historical reconstruction of wastewater and land use impacts to groundwater used for public drinking water:Exposure assessment using chemical data and GIS

“…The ability to differentiate nitrate measured at a well among contamination sources, including septic or fertilizer inputs, would improve (1) our understanding of the relations between the appearance of this chemical at impacted wells and surrounding land use, (2) the ability of land use indicators to reveal likely sources of contamination, and (3) provide insight into the types of cocontaminants that might be present. For nitrate, use of techniques such as nitrogen-isotope analysis has allowed such differentiation (Komor et al, 1993).…”

Nitrate (NO2+NO3–N) in ground water of the Upper Snake River basin, Idaho and western Wyoming, 1991–95

“…The slightly lower value may be the result of the addition of nitrogen from commercial inorganic fertilizer. The 515 N values in the A&B study area were much lower than the +10 permil value suggested by Coplen (1993, p. 239) and Komor and Anderson (1993) for 5 15 N from animal waste, which helps to confirm that domestic septic systems and cattle manure provide minimal nitrogen in that area.…”

“…Both investigators suggested that 515 N values for animal wastes are greater than +10. Kreitler (1975) determined that natural soil 515 N values in areas not affected by anthropogenic NO2+NO 3 -N sources are from +2 to +8 permil; Komor and Anderson (1993) Kreitler (1975). The median 515 N value in the A&B study area was +3.6 permil.…”

“…Values of 815 N are determined specifically for nitrogen within the NO 2+ NO 3 -N molecule; they can serve as an indicator of the source of that NO 2 +NO 3 -N. Coplen (1993, p. 239 (Helsel and Hirsch, 1992)] ganic fertilizer are less than +3.5 permil; Komor and Anderson (1993) suggested that 515 N values for commercial inorganic fertilizer are less than 2. Both investigators suggested that 515 N values for animal wastes are greater than +10.…”

Hydro-geochemical Nature and Nitrates Contamination Charecters of Groundwater in the Youngdong, Chungbuk Province

“…지하수의 Zn 이후 다수의 연구가 보고되었다 (Kreitler and Browning, 1983;Aravena et al, 1993;Komor and Anderson, 1993;Wilson et al, 1994;Min et al, 2003;Kellman and Hillair-Marcel, 2003;Chae et al, 2009;Jeon et al, 2011) 2) 농업 활동에 관련된 질소 비료의 사용으로부터 유 입되는 질산염의 δ 15 N nitrate 값은 일반적으로 -4~4‰이 지만, 일부 비료에서는 -8~8‰을 보이기도 한다 (Kendall and McDonnell, 1998 …”