Volcanic investigations in the Commonwealth of the Northern Mariana Islands, April to May 1994

Open-File Report 94-705

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Hydrologic and water-quality data were collected from a test plot instrumented to determine the quantity of nitrogen (N) fertilizer in surface runoff from, and in ground water below, a continuous corn cropping system with conventional tillage. This report presents the sampling design and data- collection techniques at the test plot and includes a compilation of the rainfall-, surface-, ground-, and unsaturated-zone water-quality data, soils, grain and stover data, and the quality-assurance data. Background data were collected at the plot for one year prior to the application in May 1992 of a fertilizer enriched with 15N to +3,080 per mil. The movement of the fertilizer through the hydrologic system was monitored through September 1993. The first runoff event after the application of the spiked fertilizer had the largest 15N enrichment from the spike. The spiked fertilizer was detected in the shallowest suction lysimeters less than one month after application and in shallow wells six days after substantial ground-water recharge from fall rains in November 1992. The 15N enrichment in water samples collected from gravity lysimeter in November 1992 ranged from +297 to +1.145 per mil. Grain harvested in 1992 had 15N enrichment of +648 per mil. In 1993, the 15N enrichment in runoff increased in late spring and early summer and then declined through the summer. The 15N enrichment in ground-water samples continued to increase through August 1993, while 15N enrichment in the water samples from suction and gravitv lysimeters gradually declined. The 15N enrichment in grain was +188 per mil in 1993.

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Volcanic investigations in the Commonwealth of the Northern Mariana Islands, April to May 1994
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Open-File Report
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U.S. Geological Survey,
57 leaves :ill., maps ;28 cm.