Impact of point source pollution on nitrogen isotope signatures (δ¹⁵N) of vegetation in SE Brazil

Abstract

This study presents novel evidence that ¹⁵N natural abundance can be used as a robust indicator to detect pollutant nitrogen in natural plant communities. Vegetation from the heavily polluted industrial area of Cubatão in São Paulo State, SE Brazil, was strongly ¹⁵N depleted compared to plants at remote sites. Historic herbarium samples from Cubatão were significantly less ¹⁵N depleted than extant plants, indicating that ¹⁵N depletion of vegetation is associated with present-day nitrogen pollution in Cubatão. The heavy load of nitrogenous atmospheric pollutants in Cubatão provides a nitrogen source for plants, and strongly ¹⁵N depleted air NH₃ is likely to contribute to plant and soil ¹⁵N depletion. Epiphytic plants from Cubatão were extremely ¹⁵N depleted (average –10.9‰) contrasting with epiphytes at remote sites (averages –1.0‰ and –3.0‰). Nitrogen isotope composition of vegetation provides a tool to determine input of pollutant nitrogen into plant communities. The strong isotopic change of epiphytes suggests that epiphytes are particularly sensitive biomonitors for atmospheric pollutant nitrogen.