Using stable isotopes of nitrogen to study its source and transformation in a heavily farmed watershed

作者：Gautam S; Iqbal M Z^*

来源：Environmental Earth Sciences, 2010, 60(1): 11-20.

DOI：10.1007/s12665-009-0165-7

• Nitrogen
• Fertilizers
• Isotopes
• Groundwater
• Watershed

Twenty private wells and ten stream locations were sampled to assess the source and fate of dissolved nitrate in the Cedar River watershed of Iowa, USA. The average levels of nitrate in groundwater decreased from 39.5 mg/L in May, to 38 mg/L in July, to 30 mg/L in September. Although several surface water samples exceeded MCL in May, most values dropped to below 20 mg/L by July and September. The decreasing N levels were attributed to the gradual uptake of nitrate by growing crops as well as the cyanobacterial growth in the aquatic systems. The delta(15)N values of dissolved nitrate in groundwater ranged from 0.45 to 5.35aEuro degrees, whereas those in surface water ranged from 1.48 to 5.16aEuro degrees. The results suggested that commercial fertilizers and soil organic nitrogen were probably mixed up in their transport pathways. A fertilizer-only source would provide much lower delta values, whereas soil nitrogen would provide higher than observed delta values. Denitrification was considered unlikely because of the low delta(15)N values, high nitrate concentrations, and moderately high DO content in groundwater. Animal wastes were not found as a possible source of nitrate in the water. This is supported by the low chloride concentrations and lower than 10aEuro degrees delta values in the water samples. The study demonstrates that nitrogen isotope data in coordination with the dissolved nitrate levels and land use can be effectively used in nitrogen source identification and its transformation studies.

• 出版日期2010-3
• 单位Virginia Tech; 美国弗吉尼亚理工大学(Virginia Tech)