Combination of nitrate (N, O) and boron isotopic ratios with microbiological indicators for the determination of nitrate sources in karstic groundwater

Abstract

Environmental context. Nitrate contamination of drinking water quality may be critical, particularly in rural areas where agricultural practices may release large amounts of nitrogen. Knowledge of the source of such contamination, mandatory for water supply management, can be successfully acquired by combining the natural stable isotopes of nitrate, boron isotopic ratios and microbiological indicators. Nitrate produced by anthropogenic activities is an important environmental issue, particularly in agricultural regions and especially when water is used as drinking water. Determination of the source of nitrate among the many potential sources is the first step towards water quality improvement.Recent studies have proven the efficiency of the coupled use of nitrate (N and O) and boron isotope ratios to identify the origin of nitrate in water. [1][2][3] Nitrate from mineral fertilisers is characterised by atmospheric values of d

Legacy of contaminant N sources to the NO3− signature in rivers: a combined isotopic (δ15N-NO3−, δ18O-NO3−, δ11B) and microbiological investigation

“…However, the characterization of local animal pool (fresh dejection δ 11 B = −3.3‰ and poultry manure δ 11 B = +8.6‰) shows lower values than previously reported (+15.3‰ to +27.6) 19 . Globally, [B] and δ 11 B of the GR and LR samples were really close to those measured in the underlying karstic aquifer (10.5 ± 2 ppb and 25.3 ± 1‰) 38 , and in rain, and were significantly different from the WWTP end-member ( Fig. 7 ).…”

“…The [B] and δ 11 B values of the mixing end-members were measured in this study (rain and WWTP) or in a previous one (GW) 38 . Rain: [B] R = 1.6 ± 1 ppb and δ 11 B R = 27.7 ± 7‰; Groundwater: [B] GW = 10.5 ± 2 ppb and δ 11 B GW = 25.3 ± 1‰; WWTP: [B] WWTP = 83.3 ± 3 ppb and δ 11 B WWTP = 1.9 ± 2‰;…”

“…Bacteroidales are fecal bacteria with DNA sequences specific to human, cattle, pig effluents 34 35 36 37 . These host-specificity markers have rarely been applied in natural aqueous environments 38 39 , but their recent combination with δ 15 N, δ 18 O and δ 11 B has shown a great potential for determining NO 3 − origin in groundwater (GW) 38 .…”

“…2 ). Nitrate concentrations of Gabas River (GR, 150 km long) and Laudon River (LR, 15 km long) are a serious threat for the underlying karstic aquifer, used for drinking water supply 38 . To better integrate the spatial heterogeneity of N point and non-point sources of the whole watershed, a 2.5 years monitoring has been conducted in the karstified downstream part of the Gabas and Laudon catchments ( Fig.…”

Investigating Boron Isotopes for Identifying Nitrogen Sources Supplied by Submarine Groundwater Discharge to Coastal Waters

“…The large relative mass differences between 11 B and 10 B means that isotope fractionation leads to a wide range of isotopic values in nature. The combined use of δ 11 B and δ 15 N to trace NO 3 − sources has been successfully applied in terrestrial and aquatic environments (Komor, 1997;Widory et al, 2004Widory et al, , 2005Widory et al, , 2013Seiler, 2005;Bronders et al, 2012;Lindenbaum, 2012;Briand et al, 2013Briand et al, , 2017Eppich et al, 2013;Saccon et al, 2013;Ransom et al, 2016;Guinoiseau et al, 2018;Kruk et al, 2020); however, the use of δ 11 B and δ 15 N has yet to be tested in the STE of coastal systems.…”