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Vast nitrogen reserves hidden beneath desert soils

A University of California scientist working at the Laboratory in collaboration with researchers from the U.S. Geological Survey, New Mexico Institute of Mining and Technology in Socorro, the University of Nevada, the University of Arkansas and Desert Research Institute in Reno, Nev., has recently found evidence that there may be significantly more amounts of nitrogen, in the form of nitrates, than previously estimated in desert landscapes. The discovery of these vast subsoil nitrate reservoirs could have implications for groundwater quality in arid/semi-arid environments worldwide, as mobilization of the nitrates could adversely affect drinking water supplies.

High nitrate concentrations in drinking water have been linked by the Environmental Protection Agency to a blood disease called methaemoglobinaemia, miscarriages and non-Hodgkin's lymphoma.

In findings published in today's issue of the journal Science, the team of scientists theorize that the nitrate reservoirs have been accumulating in subsoil zones of arid regions throughout the world over the last 11,000 years, during a period of geologic time called the Holocene Epoch, when the onset of arid Holocene climatic conditions and succession to vegetation requiring scant amounts of moisture triggered subsoil nitrogen retention.

The desert landscapes that cover approximately one-fourth of the continental United States and one-third of the land surface worldwide had previously been thought to be relatively low in nitrates as mechanisms such as plant uptake, wind erosion and denitrification robbed the soil of nitrogen. These new studies challenge this assumption with the idea that large quantities of nitrogen have been leached into deeper, subsoil levels.

According to Brent Newman, the Los Alamos scientist working on the project, "this discovery could have some significant implications for humankind. The discovery of the subsoil nitrate reservoirs could raise previous estimates of nitrogen soil and subsoil inventories by as much as 71 percent in warm deserts and arid shrub lands and up to 16 percent in global nitrogen totals. These large nitrate inventories could adversely affect water quality if the nitrate becomes mobilized by land use change, such as conversion of natural deserts and shrub lands to irrigated agriculture, or by wetter climatic conditions. Nitrate also is an important nutrient and the finding of large nitrate inventories in the subsoil has important implications for understanding nutrient cycling in arid and semiarid ecosystems around the world."

Newman, of Atmospheric, Climate and Environmental Dynamics (EES-2), conducted some of the nitrate profile analyses based on the Mesita del Buey and Technical Area 16 regions of Laboratory property. This data turned out to be particularly important as Los Alamos appears to be something of a borderland in a climate regime, falling between areas that seem to develop more or less subsurface nitrate accumulation depending on the amount of moisture the region gets. In other words, if a region has a climate wetter than Los Alamos, the sub-soils probably won't accumulate as much nitrate when compared to drier climates.

The nitrogen reservoir studies were funded by the Laboratory Material Disposal Area G Performance Assessment and Environmental Restoration projects, the U.S. Geological Survey and the National Science Foundation.

-- Todd Hanson

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