Oxygen and nitrogen isotopic composition of nitrate in commercial fertilizers, nitric acid, and reagent salts

摘要

Nitrate is a key component of synthetic fertilizers that can be beneficial to crop production in agro-ecosystems, but can also cause damage to natural ecosystems if it is exported in large amounts. Stable isotopes, both oxygen and nitrogen, have been used to trace the sources and fate of nitrate in various ecosystems. However, the oxygen isotope composition of synthetic and organic nitrates is poorly constrained. Here, we present a study on the N and O isotope composition of nitrate-based fertilizers. The N-15 values of synthetic and natural nitrates were 0 +/- 2 parts per thousand similar to the air N-2 from which they are derived. The O-18 values of synthetic nitrates were 23 +/- 3 parts per thousand, similar to air O-2, and natural nitrate fertilizer O-18 values (55 +/- 5 parts per thousand) were similar to those observed in atmospheric nitrate. The O-17 values of synthetic fertilizer nitrate were approximately zero following a mass-dependent isotope relationship, while natural nitrate fertilizers had O-17 values of 18 +/- 2 parts per thousand similar to nitrate produced photochemically in the atmosphere. These narrow ranges of values can be used to assess the amount of nitrate arising from fertilizers in mixed systems where more than one nitrate source exists (soil, rivers, and lakes) using simple isotope mixing models.