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Contamination of groundwater (GW) by nitrate from agricultural sources is of particularimportance in Prince Edward Island (Canada), where agricultural lands dominate thelandscape and GW is the sole source of potable water. In this region and in many others,the transfer of N compounds from agricultural soils to aquifers is a key process, and it isimportant to assess if values coming from residual soil nitrate estimations, and associatedestimates of N loading to aquifers match estimations based on GW concentrationsmeasured at the top of the aquifer. The nitrate "dual isotope" characterization is gainingpopularity in the field of hydrogeochemistry, and such study promises to shed importantinsights into the processes involved in the transport of nitrogen from agricultural soils toGW. The current watershed scale sampling program indicates that nitrate concentrationsin the region are relatively stable throughout the year, as are the water isotopecharacteristics in both surface water (SW) and GW. In contrast,values in dissolved nitrate in both GW and SW display distinct seasonal characteristics.The differing behavior of the water and nitrate oxygen isotopes can be resolved byinvoking mixtures of recent recharge water (soil leachate) characterized by high nitrateconcentrations and seasonally distinct isotopic characteristics, with deeper and oldermulti-year GW having lower nitrate concentrations and practically uniform isotopiccharacteristics. Mixing 25% or less of seasonal recharge with older, less impacted GWaccounts for the observed characteristics of GW from domestic wells, implying that thegreatest proportion of N flux in GW is at this time restricted to relatively shallow portionsof the aquifer. This same rationale also helps explain why currently observed nitrateconcentrations in well water in the watershed are below those that would otherwise beexpected based on calculated estimates of nitrate loading to the aquifer. Includes 17 references, tables, figures.

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Edition: Vol. - No. Published: 01/01/2008 Number of Pages: 13File Size: 1 file , 470 KB