Monte Carlo Simulations as a Decision Support to Interpret δ¹⁵N Values of Nitrate in Groundwater

Abstract

Intense farming is often associated with the excessive use of manure or fertilizers and the subsequent deterioration of the groundwater quality in many aquifers worldwide. Stable isotopes of dissolved nitrate (δ 15 N and δ 18 O) are widely used to determine sources of nitrate contamination and denitrification processes in groundwater but are often difficult to interpret. Thus, Monte Carlo simulations were carried out for a site in lower Bavaria, Germany, in order to explain δ 15 N observations in a porous groundwater system with two aquifers, the main aquifer (MA) and several smaller perched aquifers (PA). For evaluating potential contributions, frequency distributions of δ 15 N were simulated deriving from (I) the mixing of different nitrate sources, related to land use, as input to groundwater, combined with (II) transport of nitrate in groundwater and (III) microbial denitrification. Simulation results indicate a source-driven isotopic shift to heavier δ 15 N values of nitrate in groundwater, which may be explained by land use changes toward a more intensified agriculture releasing high amounts of manure. Microbial denitrification may play a role in the PA, with simulated δ 15 N distributions close to the observations. Denitrification processes are however unlikely for the MA, as reasonable simulation curve fits for such a scenario were obtained predominantly for unrealistic portions of nitrate sources and related land use. The applied approach can be used to qualitatively and quantitatively evaluate the influence of different potential contributions, which might mask each other due to overlapping δ 15 N ranges, and it can support the estimation of nitrate input related to land use.

Interprétation de l’hydrogéochimie de la Molasse d’Eau Douce Supérieure (Obere Süßwassermolasse) dans la région de Munich (Bavière, Allemagne) à l’aide d’une analyse multivariée et d’une modélisation géologique en 3D

“…Elevated contents of SO 4 2and Mg 2+ are also indicators of anthropogenic contamination due to agricultural activity and wastewater release (Senbayram et al 2015;Torres-Martínez et al 2020). Previous studies conducted in the immediate vicinity of study area have shown that elevated concentrations of nitrate are caused by release of high amounts of manure and, to a lesser extent, synthetic fertilizers due to intensified agriculture (Wild et al 2018(Wild et al , 2020.…”

Strategies to Overcome Intermediate Accumulation During in situ Nitrate Remediation in Groundwater by Hydrogenotrophic Denitrification

“…Increased amounts of reactive nitrogen (Nr) and severe anthropogenic intervention in the global nitrogen cycle induce climatic change, cause biodiversity losses, and pose direct and indirect risks to human health (Fields, 2004;Galloway et al, 2008). In groundwater, the main Nr species is dissolved nitrate (NO 3 − ) which leaches into the groundwater due to excessive use of chemical and organic fertilizers as well as leaking sewage (Zhu et al, 2019;Wild et al, 2020). The resulting NO 3 − pollution of groundwater has been a severe global environmental problem since the 1970s (Rivett et al, 2008).…”