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Fate of nitrate during groundwater recharge in a fractured karst aquifer in Southwest Germany (2021)

Visser, Anna-Neva ; Lehmann, Moritz F. ; Rügner, Hermann ; [et al.]

Springer Berlin Heidelberg

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Publication Date: 2023-08-08

Description: Over the past decades, fractured and karst groundwater systems have been studied intensively due to their high vulnerability to nitrate (NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉) contamination, yet nitrogen (N) turnover processes within the recharge area are still poorly understood. This study investigated the role of the karstified recharge area in NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 transfer and turnover by combining isotopic analysis of NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 and nitrite (NO〈sub〉2〈/sub〉〈sup〉−〈/sup〉) with time series data of hydraulic heads and specific electrical conductivity from groundwater monitoring wells and a karstic spring in Germany. A large spatial variability of groundwater NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 concentrations (0.1–0.8 mM) was observed, which cannot be explained solely by agricultural land use. Natural-abundance N and O isotope measurements of NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 (δ〈sup〉15〈/sup〉N and δ〈sup〉18〈/sup〉O) confirm that NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 derives mainly from manure or fertilizer applications. Fractional N elimination by denitrification is indicated by relatively high δ〈sup〉15〈/sup〉N- and δ〈sup〉18〈/sup〉O-NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 values, elevated NO〈sub〉2〈/sub〉〈sup〉−〈/sup〉 concentrations (0.05–0.14 mM), and δ〈sup〉15〈/sup〉N-NO〈sub〉2〈/sub〉〈sup〉−〈/sup〉 values that were systematically lower than the corresponding values of δ〈sup〉15〈/sup〉N-NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉. Hydraulic and chemical response patterns of groundwater wells suggest that rain events result in the displacement of water from transient storage compartments such as the epikarst or the fissure network of the phreatic zone. Although O〈sub〉2〈/sub〉 levels of the investigated groundwaters were close to saturation, local denitrification might be promoted in microoxic or anoxic niches formed in the ferrous iron-bearing carbonate rock formations. The results revealed that (temporarily) saturated fissure networks in the phreatic zone and the epikarst may play an important role in N turnover during the recharge of fractured aquifers.

Description: Projekt DEAL

Keywords: ddc:551.49 ; Nitrate ; Karst ; Groundwater recharge ; Stable isotopes ; Germany

Language: English

Type: doc-type:article

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Incubation experiments with 15N tracers in the water column of Lake La Cruz, Spain (2022)

Tischer, Jana ; Zopfi, Jakob ; Frey, Claudia ; [et al.]

PANGAEA

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Publication Date: 2023-12-15

Keywords: 15N-tracer; 15N tracer incubations, calulated (Trimmer et al. 2016); 15N tracer incubations (Wenk et al. 2013); Ammonium-15, production; Ammonium-15, production, standard error; anoxia; Calculated; chemodenitrification; DATE/TIME; Denitrification; DEPTH, water; Experimental treatment; ferruginous; IRMS, hypobromite method (Robertson et al. 2016); Lake_LaCruz; Measurement conducted; meromixis; MULT; Multiple investigations; N2O production rates; N2O site preference; nitrification; nitrifier denitrification; Nitrite, production; Nitrite, production, standard error; Nitrogen-15, tracer; Nitrogen-15, tracer, fraction; Nitrogen-15, tracer, reduction; Nitrogen-15, tracer, reduction, standard error; Nitrogen gas, 29N2, production; Nitrogen gas, 29N2, production, standard error; Nitrogen gas, 30N2, production; Nitrogen gas, 30N2, production, standard error; nitrogen isotopes; nitrous oxide; Nitrous oxide, production; Nitrous oxide, production, standard error; Nitrous oxide/Nitrogen-15 tracer reduction ratio; Oxic condition; oxycline; Photometrical detection, Griess reagent method (Hansen and Koroleff 1999); Spain; Various methods; water column

Type: Dataset

Format: text/tab-separated-values, 303 data points

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DATA PANGAEA

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Microbial and abiotic nitrous oxide cycling in the water column of meromictic, iron-rich Lake La Cruz, Spain, 2015-2017 (2022)

Tischer, Jana ; Zopfi, Jakob ; Frey, Claudia ; [et al.]

PANGAEA

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Publication Date: 2024-02-12

Description: We investigated the microbial and abiotic N2O cycle in the water column of iron-rich, meromictic Lake La Cruz, Spain, during two sampling campaigns in March 2015 and March 2017. At the deepest point of the lake, we used a profiling in situ analyzer equipped with several probes and optodes to detect physicochemical parameters. In addition, we collected water column samples via an in situ pump in order to analyze concentrations of N, S, and Fe species as well as isotope characteristics of several N species. In 2017, we used a Niskin bottle to take water samples from 8.0 and 14.5 m depth for two types of incubation experiments. In the first set of experiments, we added 15N-labeled substrates, and in some incubations Fe2+, to filtered and unfiltered lake water, and analyzed the produced N2O, N2, and NH4+. In the other experiment, we determined the N and O isotope effects of NO2- and N2O during chemodenitrification (reaction of NO2- and Fe2+) in anoxic and sterile lake water from 14.5 m depth.

Keywords: 15N-tracer; anoxia; chemodenitrification; Denitrification; ferruginous; Lake_LaCruz; meromixis; MULT; Multiple investigations; N2O production rates; N2O site preference; nitrification; nitrifier denitrification; nitrogen isotopes; nitrous oxide; oxycline; Spain; water column

Type: Dataset

Format: application/zip, 4 datasets

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