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The National Agricultural Library is one of four national libraries of the United States, with locations in Beltsville, Maryland and Washington, D.C. It houses one of the world's largest and most accessible agricultural information collections and serves as the nexus for a national network of state land-grant and U.S. Department of Agriculture field libraries. In fiscal year 2011 (Oct 2010 through Sept 2011) NAL delivered more than 100 million direct customer service transactions.

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Nutrient retention by multipond systems: mechanisms for the control of nonpoint source pollution  [1998]

Yan, W. (Research Center for Eco-Environmental Science, Beijing.); Yin, C.; Tang, H.;

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The processes of the multipond system in an experimental agricultural watershed located in southeastern China were studied during a 2-yr period (1994-1995), with the purpose of the research being the reduction of nonpoint nutrient pollution at its sources. The mechanisms studied included water storage capacity, sedimentation, denitrification, and removal of nutrients by the harvest of macrophytes from ponds and ditches. The results showed that the retention of both water and nutrients depended on the water storage capacity of the ponds, the total pond volume, rainfall, surface runoff, and irrigation amounts. For the years of 1994 and 1995, the water retention rate was 85.5%, while the nutrient retention rate reached 98.1 and 97.8% for total N (TN) and total P (TP), respectively. Sediment deposit was another important mechanism. The average sedimentation rate was 30.0 mm yr-1 (from 1985-1995). For the whole multipond system (35 ha), the average retention amounts reached 9800 kg of N and 2800 kg of P by sediment accumulation per year. The results demonstrated that denitrification in ponds and ditches was an important mechanism for removing N from the watershed. The highest possible rate was more than 0.17 mg N g-1 soil during the summer season. The results suggested that the multipond system, which kept water in balance, benefited the water, nutrient, and sediment recycling in the terrestrial ecosystem, as well as helped to reduce agricultural nonpoint pollu
tion at its sources. Therefore, the multipond system, with its low cost in construction and maintenance, is recommended as a good practice both for the control of nonpoint pollution at its sources and for sustainable agricultural development

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Journal of environmental quality (USA)

ISSN : 0047-2425