Development of a Fully Coupled Biogeochemical Reactive Transport Model to Simulate Microbial Oxidation of Organic Carbon and Pyrite Under Nitrate-Reducing Conditions

TY - JOUR

T1 - Development of a Fully Coupled Biogeochemical Reactive Transport Model to Simulate Microbial Oxidation of Organic Carbon and Pyrite Under Nitrate-Reducing Conditions

AU - Knabe,Dustin

AU - Kludt,Christoph

AU - Jacques,Diederik

AU - Lichtner,Peter

AU - Engelhardt,Irina

N1 - Score=10

PY - 2018/11/1

Y1 - 2018/11/1

N2 - In regions with intensive agriculture nitrate is one of the most relevant contaminants in groundwater. Denitrification reduces elevated nitrate concentrations in many aquifers, yet the denitrification potential is limited by the concentration of available electron donors. The aim of this work was to study the denitrification potential and its limitation in natural sediments. A column experiment was conducted using sediments with elevated concentrations of organic carbon (total organic carbon 3,247 mg C/kg) and pyrite (chromium reducible sulfur 150 mg/kg). Groundwater with high nitrate concentration (100 mg/L) was injected. Measurements were taken over 160 days at five different depths including N- and S-isotope analysis for selected samples. A reactive transport model was developed, which couples nitrate reduction with the oxidation of organic carbon (heterotrophic denitrification) and pyrite (autolithotrophic denitrification), and considers also transport and growth of denitrifying microbes. The denitrification pathway showed a temporal sequence from initially heterotrophic to autolithotrophic. However, maximum rates were lower for heterotrophic (11 mmol N/(L*a)) than for autolithotrophic denitrification (48 mmol N/(L*a)). The modeling showed that denitrifying microbes initially preferred highly reactive organic carbon as the electron donor for denitrification but were also able to utilize pyrite. The results show that after 160 days nitrate increased again to 50 mg/L. At this time only 0.5% of the total organic carbon and 46% of the available pyrite was oxidized. This indicates that denitrification rates strongly decrease before the electron donors are depleted either by a low reactivity (total organic carbon) or a diminishing reactive surface possibly due to the presence of coatings (pyrite).

AB - In regions with intensive agriculture nitrate is one of the most relevant contaminants in groundwater. Denitrification reduces elevated nitrate concentrations in many aquifers, yet the denitrification potential is limited by the concentration of available electron donors. The aim of this work was to study the denitrification potential and its limitation in natural sediments. A column experiment was conducted using sediments with elevated concentrations of organic carbon (total organic carbon 3,247 mg C/kg) and pyrite (chromium reducible sulfur 150 mg/kg). Groundwater with high nitrate concentration (100 mg/L) was injected. Measurements were taken over 160 days at five different depths including N- and S-isotope analysis for selected samples. A reactive transport model was developed, which couples nitrate reduction with the oxidation of organic carbon (heterotrophic denitrification) and pyrite (autolithotrophic denitrification), and considers also transport and growth of denitrifying microbes. The denitrification pathway showed a temporal sequence from initially heterotrophic to autolithotrophic. However, maximum rates were lower for heterotrophic (11 mmol N/(L*a)) than for autolithotrophic denitrification (48 mmol N/(L*a)). The modeling showed that denitrifying microbes initially preferred highly reactive organic carbon as the electron donor for denitrification but were also able to utilize pyrite. The results show that after 160 days nitrate increased again to 50 mg/L. At this time only 0.5% of the total organic carbon and 46% of the available pyrite was oxidized. This indicates that denitrification rates strongly decrease before the electron donors are depleted either by a low reactivity (total organic carbon) or a diminishing reactive surface possibly due to the presence of coatings (pyrite).

KW - nitrate

KW - contaminants

KW - groundwater

KW - denitrification

KW - natural sediments

UR - http://ecm.sckcen.be/OTCS/llisapi.dll/open/34494928

U2 - 10.1029/2018WR023202

DO - 10.1029/2018WR023202

M3 - Article

VL - 54

SP - 9264

EP - 9286

JO - Water Resources Research

T2 - Water Resources Research

JF - Water Resources Research

SN - 0043-1397

IS - 11

ER -