Using isotope fractionation of nitrate-nitrogen and nitrate-oxygen for evaluation of microbial denitrification in a sandy aquifer

verfasst von

J. Böttcher, O. Strebel, Susanne Voerkelius, H. L. Schmidt

Abstract

The nitrate input into the groundwater from forest and agricultural land in the 'Fuhrberger Feld' catchment area is virtually completely degraded by microbial denitrification in the aquifer. Five multilevel groundwater sampling wells show characteristic depth functions of nitrate, proving the denitrification process. A series of 10 samples of 'arable land groundwater' was taken from different depths at these multilevel wells and isotope ratios of ¹⁵N ¹⁴N and ¹⁸O ¹⁶O in the nitrate were measured. The sampling was based on the two-dimensional vertical-plane groundwater flownet and on the knowledge of the landuse upgradient of the multilevel wells. High nitrate concentrations are associated with low δ¹⁵N and low δ¹⁸O values, and vice versa. The δ¹⁵N δ¹⁸O ratio indicates a linear increase with a slope of 1:2.1. The microbial dentrification accords with a Rayleigh process with calculated enrichment factors of ε = -15.9‰ for ¹⁵N and ε = -8.0 ‰ for ¹⁸O. Three samples taken from groundwater recharged under coniferous forest show deviating characteristics: low nitrate concentrations with low δ¹⁵N values (1-4‰) but very high δ¹⁸O values (40-50‰). Using the previously quantified enrichment factors for ¹⁵N and ¹⁸O, an attempt was made to ascertain the significance of denitrification in specific depth sections at two other multilevel wells (7 samples). In two cases quantitative assessments on the degree of nitrate concentration decrease owing to denitrification were possible. However, in other cases the specific nitrate isotope fractionation was masked by the variability of nitrate concentration and of nitrate isotope ratios in the corresponding groundwater recharge preventing definite interpretations.

Externe Organisation(en)

Bundesanstalt für Geowissenschaften und Rohstoffe (BGR)
Technische Universität München (TUM)

Typ

Artikel

Journal

Journal of hydrology

Band

114

Seiten

413-424

Anzahl der Seiten

12

ISSN

0022-1694

Publikationsdatum

05.1990

Publikationsstatus

Veröffentlicht

Peer-reviewed

Ja

ASJC Scopus Sachgebiete

Gewässerkunde und -technologie

Ziele für nachhaltige Entwicklung

SDG 15 – Lebensraum Land

Elektronische Version(en)

https://doi.org/10.1016/0022-1694(90)90068-9 (Zugang: Geschlossen)