In 2004, the U. S. Department of Agriculture (USDA) issued the first report of Phakopsora pachyrhizi, or Asian Soybean Rust (ASR) in the continental U.S. ASR is a fungal parasite that can cause significant losses in soybean and other crops. NADP partnered with the USDA Cereal Disease Laboratory (USDA-CDL) to look for ASR spores in NTN samples. From mid-May through mid-September 2008, the CDL found that 8 percent of the tested precipitation samples were positive for ASR. Weekly counts ranged from a few spores to more than 250 spores per square meter. The figure below shows the sites that had deposition of ASR during the year, along with counties where the disease was present during 2008. These data show the spread of ASR spores, and the usefulness of collaborative monitoring efforts in agricultural applications. The NADP measures wet deposition. The Clean Air Status and Trends Network (CASTNET) focuses on dry deposition. Collaboratively they yield total deposition estimates. For example, the map on the cover shows scaled pie charts depicting the 2008 total nitrogen deposition in kilograms per hectare (kg N/ha) at CASTNET sites. Wet deposition data (blue) are from NTN “total inorganic nitrogen” measurements [(nitrate + ammonium) ions expressed as nitrogen]. Dry deposition data (pink) are from CASTNET estimates of ammonium and nitrate dry deposition [(nitric acid + nitrate + ammonium) expressed as nitrogen]. A summation of these two components, “Total Inorganic Nitrogen Deposition”, is indicated with each chart. Dry deposition was estimated using the Multilayer Model (MLM). Inputs to the MLM include atmospheric concentrations, meteorological data, and information on land use, vegetation, and surface conditions. Only sites meeting completeness criteria for both networks appear on the map. For more information on CASTNET, see http://www.epa.gov/castnet.In addition to ammonium and nitrate, other nitrogen compounds are present in precipitation. Based on preliminary data, the organic nitrogen fraction may be as high as one-third of total N deposition. Scientists at the U.S. Environmental Protection Agency (USEPA) and the NADP have begun tests to determine whether organic nitrogen deposition can be measured reliably and accurately in weekly NTN samples. Preliminary results from these tests are promising. This added information is particularly important to our understanding of nitrogen deposition patterns. In 2006, the NADP Executive Committee formed the Critical Loads Ad-Hoc Committee (CLAD). This committee coordinates the efforts of multiple federal and state agencies, scientists, and other partners related to the science of critical loads (http://nadp.isws.illinois.edu/clad). CLAD provides a venue for discussion of current and emerging issues regarding the science and application of critical loads for atmospheric deposition in the United States.
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