Agron. Sustain. Dev.
Volume 26, Number 4, October-December 2006
Page(s) 263 - 267
Published online 23 January 2007
Agron. Sustain. Dev. 26 (2006) 263-267
DOI: 10.1051/agro:2006025

Assessing the source of nitrate pollution in water using stable N and O isotopes

Barbara Deutscha, Petra Kahleb and Maren Vossa

a  Baltic Sea Research Institute, Seestr. 15, 18119 Rostock, Germany
b  University of Rostock, Institute of Land Use, Justus-von-Liebig-Weg 6, 18059 Rostock, Germany

(Accepted 31 August 2006; published online 23 January 2007)

Abstract - We used the isotopic composition of nitrogen ($\delta$15N) and oxygen ($\delta$18O) in water nitrate (NO3-) to assess water pollution. $\delta$15N and $\delta$18O values in drainage water nitrate of a conventionally managed field and the adjacent surface waters were measured for 6 weeks during the main discharge period of the hydrological year 2003/2004. We hypothesized that this approach could provide more information about the impact of drainage water containing high nitrate loads on the following surface water bodies than common measurements of concentrations. The nitrate concentrations ranged between 686 and 2040 µM in the tile drain outlets and were positively correlated to the tile drain discharge. The low $\delta$18O-NO3- values, from 1.8 to 4.3°/°°, indicated that most of the nitrate derived from the nitrification process in the agricultural soils. The high $\delta$15N-NO3- values, from 8.5 to 15.0°/°°, reflected the long-term fertilizing practice which was carried out for several years with inorganic as well as organic fertilizers. In the adjacent ditch and the brook nitrate concentrations were lower but showed a similar development to the tile drain outlet. The $\delta$15N-NO3- values (7.2-12.1°/°°) and $\delta$18O-NO3- values (2.4-9.1°/°°) in the ditch and the brook indicated that the nitrate from tile drain discharge is the major N source for the adjacent surface water bodies.

Key words: tile drainage / nitrate / eutrophication / $\delta$15N / $\delta$18O

Corresponding author: Barbara Deutsch

© INRA, EDP Sciences 2006