Agricultural Chemical Movement through a Field-Size Watershed in Iowa: Surface Hydrology and Nitrate Losses in Discharge

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• 作者：Thomas R. Steinheimer ; Kenwood D. Scoggin ; and Larry A. Kramer
• 刊名：Environmental Science & Technology
• 出版年：1998
• 出版时间：April 15, 1998
• 年：1998
• 卷：32
• 期：8
• 页码：1048 - 1052
• 全文大小：156K
• 年卷期：v.32,no.8(April 15, 1998)
• ISSN：1520-5851

文摘

Nonpoint source pollution of surface water by nitrate fromagricultural activities is a national problem. Anagricultural watershed in the Iowa Loess Hills with a 23-year history of annual corn production with average Nfertilization is studied. Headcut seepage istransportedthrough a natural riparian zone and observed as weirbaseflow; surface runoff is measured separately.Nitraterunoff graphs illustrate the importance of high-frequencysampling of each event to permit quantitative estimationofchemical loss. The concentration of nitrate carriedfromthe field in basin drainage steadily increased from <1 mgL^-1 in 1969 to >20 mgL^-1 in 1991. The rate ofcumulativeincrease in the amount of applied N is greater than therateof removal by the crop. Over the 23-year record, 23%of the mean annual application of N remains stored andavailable for leaching or chemical conversion by soilmicrobes. Nitrate removal during early springsnowmeltsurface runoff shows a diurnal pattern that correspondsto the daily freezing and thawing of the surface soil inearlyMarch. Contribution to the load of nitrate depositedonthe soil surface by rainfall is very small in comparison totheamount applied by fertilizer application. Measurablechanges in water quality within various hydrogeologiccompartments are seldom observed in just a few years ofmonitoring. Therefore, these results emphasize theimportance of long-term data sets incorporating temporalvariability when evaluating the impact of agriculturalpractices on surface water resources.