Investigation of Nitrate Contamination Sources Under the Conventional and Organic Agricultural Systems Using Nitrogen Isotope Ratios

摘要

Nitrate contamination in water system is a critical environmental problem caused by excessive application of chemical fertilizer and concentration of livestock. In order to prevent further contamination, therefore, ,it is necessary to understand the origin of nitrate in nitrogen loading sources and manage the very/source of contamination. The objective of this study was to examine the nitrate contamination sources in different agricultural system by using nitrogen isotope ratios. Groundwater and runoff water samples were collected on a monthly basis from February 2003 to November 2003 and analyzed for nitrogen isotopes. The nitrate concentrations of groundwater in livestock farming area were higher than those in conventional and organic farming areaand exceeded the national drinking water standard of lOmg N/l . The 3 15N ranges of chemical fertilizer and animal manure were -3.7-+2.3%0 and +12.5~26.1%, respectively. The higher 515N of animal manure than those of chemical fertilizer reflected isotope fractionation and volatilization of 14N. The different agricultural systems and corresponding average nitrate concentrations and 15N values were: conventional farming, 5.47 mg/L, 8.31/1000; organic farming, 5.88 mg/EUR, 10.1%; crop-livestock farming, 12.5 mg/1, 11.1%. These data indicated that whether conventional or organic agriculture effected groundwater and runoff water quality. In conclusions, relationship between nitrate concentrations and 8 15N value could be used to make a distinction betweennitrate derived from chemical fertilizer and from animal manure. Additional investigation is required to monitor long-term impact on water quality in accordance with agricultural systems.