Large near-surface nitrate pools in soils capped by desert pavement in the Mojave Desert, California
Robert Graham et al., University of California-Riverside, Environmental Sciences, Soil & Water Sciences Program, Riverside, California 92521-0424, USA. Pages 259-262.
Graham et al. present exceptionally high nitrate levels (up to 12,750 kilograms per hectare) that have been found at shallow depths (less than 1 meter) in soils mantled by desert pavement, a common land surface feature in arid regions. 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.
Global frequency of magnitude 9 earthquakes
Robert McCaffrey, GNS Science, EVT, 1 Fairway Drive, PO Box 30368, Lower Hutt, New Zealand. Pages 263-266.
McCaffrey reports on the expected frequency of great earthquakes of the type that struck Sumatra in 2004. Even though we have experienced four or five in the pa
|Contact: Ann Cairns|
Geological Society of America