Tracing atmospheric nitrate deposition in a complex semiarid ecosystem using Δ170

The isotopic composition of nitrate collected from aerosols, fog, and precipitation was measured and found to have a large (17)0 anomaly with Delta(17)0 values ranging from 20parts per thousand to 30parts per thousand (Delta(17)0 = delta(17)0 - 0.52(delta(18)0)). This (17)0 anomaly was used to trace atmospheric deposition of nitrate to a semiarid ecosystem in southern California. We demonstrate that the Delta(17)0 signal is a conserved tracer of atmospheric nitrate deposition and is a more robust indicator of N deposition relative to standard delta(18)0 techniques. The data indicate that a substantial portion of nitrate found in the local soil, stream, and groundwater is of atmospheric origin and does not undergo biologic processing before being exported from the system.