Using O-17 to Investigate Nitrate Sources and Sinks in a Semi-Arid Groundwater System

作者：Dejwakh Navid Rene; Meixner Thomas^*; Michalski Greg; McIntosh Jennifer

来源：Environmental Science & Technology, 2012, 46(2): 745-751.

DOI：10.1021/es203450z

We apply a triple isotope approach for nitrate that utilizes Delta O-17 as a conservative tracer, in combination with delta O-18 and delta N-15, to assess source/sink dynamics of groundwater nitrate beneath alluvial washes in a semiarid urban setting. Other studies have used delta O-18 and delta N-15 to determine nitrate sources and cycling, but the atmospheric delta O-18 signature can be overprinted by biogeochemical processes. In this study, delta O-18 and delta N-15 values of nitrate were coupled with delta O-17 values of nitrate to quantify atmospheric nitrate inputs and denitrification amounts. Results show generally low groundwater nitrate concentrations (<0.2 mmol/L) throughout the basin; high nitrate concentrations (up to 1 mmol/L) with evidence for some denitrification were detected in areas where effluent was the predominant source of recharge to groundwater. Furthermore, the denitrification was inferred from elevated delta O-18 and delta N-15 values which were reinforced by increases in observed delta O-17 values. Finally, relatively low, but significant atmospheric nitrate concentrations were measured in groundwater (up to 6% of total nitrate). This study concludes that the triple isotope approach improves determination of the proportion of atmospheric nitrate and the significance of denitrification in natural waters, allowing us to develop a conceptual model of the biogeochemical processes controlling nitrogen in an urban setting.

• 出版日期2012-1-17