Nitrate in Soils Capped by Desert Pavement, Mojave Desert, California

We have found exceptionally high nitrate levels (up to 12,750 kg/ha) at shallow depths (?1 m) in soils mantled by desert pavement. Nearby soils without desert pavement had nitrate contents that were one to two orders of magnitude lower. The soil conditions coincident with desert pavement (i.e., stability, antiquity, and virtually no leaching) favor the retention and accumulation of nitrate delivered by atmospheric deposition or fixed in situ. The nitrate stored in soils under desert pavement is a previously unrecognized pool of nitrogen with the potential to increase the global nitrogen inventory for near-surface desert soils to five times the previous estimates. Its near-surface occurrence makes this labile nitrogen pool particularly susceptible to mobilization by climate change or human disturbance, risking contamination of surface and ground waters.