Modeling of biogeochemical processes in a barrier island freshwater lens (Spiekeroog, Germany)

Stephan L. Seibert, Janek Greskowiak, Henning Prommer, Michael E. Böttcher, Gudrun Massmann

Research output: Contribution to journalArticle

Abstract

Freshwater lenses present valuable water resources on barrier islands. Yet, the biogeochemical processes that control the groundwater quality of these freshwater lenses and how they are affected by the prevailing groundwater dynamics is largely unexplored. In this study we investigated the biogeochemistry of a barrier island freshwater lens with a focus on understanding and quantifying organic matter mineralization, sulfur cycling, and chemical fluxes to the land-ocean interface. We analyzed a comprehensive set of hydrogeochemical field data from Spiekeroog Island (Germany), including stable sulfur isotope signatures of dissolved sulfur species, with a reactive transport modeling approach. Tritium-Helium groundwater ages were used to constrain the hydrogeochemistry as a function of residence time. Our results revealed that freshwater lenses can act as archives for anthropogenic pollution, conserving the high sulfur loads associated with historic atmospheric deposition. We observed two distinct (hydro)biogeochemical patterns, which we attribute to a heterogeneous distribution of reactive organic matter. Those patterns were well replicated by two separate reactive transport models that considered the variations in organic matter reactivity. Simulation and field results demonstrated that net sulfur cycling is dominated by microbial sulfate reduction and subsequent iron sulfide precipitation. In the absence of dissolved oxidants, we attribute the observed high stable sulfur isotope fractionation between dissolved sulfate and sulfide of up to 67‰ to low (<20 pmol mL−1 d−1) microbial sulfate reduction rates. We show that older groundwater becomes progressively enriched in ammonium and phosphate due to the mineralization of organic matter, and we speculate that lens-derived nutrient fluxes may be important for the benthic zone at local groundwater discharge sites, at least seasonally in spring and summer.

Original languageEnglish
Pages (from-to)1133-1144
Number of pages12
JournalJournal of Hydrology
Volume575
DOIs
Publication statusPublished - 1 Aug 2019

Fingerprint

barrier island
groundwater
sulfur
organic matter
reactive transport
modeling
sulfur isotope
sulfate
stable isotope
mineralization
hydrogeochemistry
iron sulfide
tritium
biogeochemistry
atmospheric deposition
oxidant
helium
residence time
ammonium
fractionation

Cite this

Seibert, Stephan L. ; Greskowiak, Janek ; Prommer, Henning ; Böttcher, Michael E. ; Massmann, Gudrun. / Modeling of biogeochemical processes in a barrier island freshwater lens (Spiekeroog, Germany). In: Journal of Hydrology. 2019 ; Vol. 575. pp. 1133-1144.
@article{17fbf592d44040caadd68875c6db204a,
title = "Modeling of biogeochemical processes in a barrier island freshwater lens (Spiekeroog, Germany)",
abstract = "Freshwater lenses present valuable water resources on barrier islands. Yet, the biogeochemical processes that control the groundwater quality of these freshwater lenses and how they are affected by the prevailing groundwater dynamics is largely unexplored. In this study we investigated the biogeochemistry of a barrier island freshwater lens with a focus on understanding and quantifying organic matter mineralization, sulfur cycling, and chemical fluxes to the land-ocean interface. We analyzed a comprehensive set of hydrogeochemical field data from Spiekeroog Island (Germany), including stable sulfur isotope signatures of dissolved sulfur species, with a reactive transport modeling approach. Tritium-Helium groundwater ages were used to constrain the hydrogeochemistry as a function of residence time. Our results revealed that freshwater lenses can act as archives for anthropogenic pollution, conserving the high sulfur loads associated with historic atmospheric deposition. We observed two distinct (hydro)biogeochemical patterns, which we attribute to a heterogeneous distribution of reactive organic matter. Those patterns were well replicated by two separate reactive transport models that considered the variations in organic matter reactivity. Simulation and field results demonstrated that net sulfur cycling is dominated by microbial sulfate reduction and subsequent iron sulfide precipitation. In the absence of dissolved oxidants, we attribute the observed high stable sulfur isotope fractionation between dissolved sulfate and sulfide of up to 67‰ to low (<20 pmol mL−1 d−1) microbial sulfate reduction rates. We show that older groundwater becomes progressively enriched in ammonium and phosphate due to the mineralization of organic matter, and we speculate that lens-derived nutrient fluxes may be important for the benthic zone at local groundwater discharge sites, at least seasonally in spring and summer.",
keywords = "Atmospheric sulfur deposition, Microbial sulfate reduction, Reactive transport modeling, Subterranean estuary, Sulfur isotope fractionation",
author = "Seibert, {Stephan L.} and Janek Greskowiak and Henning Prommer and B{\"o}ttcher, {Michael E.} and Gudrun Massmann",
year = "2019",
month = "8",
day = "1",
doi = "10.1016/j.jhydrol.2019.05.094",
language = "English",
volume = "575",
pages = "1133--1144",
journal = "Journal of Hydrology",
issn = "0022-1694",
publisher = "Pergamon",

}

Modeling of biogeochemical processes in a barrier island freshwater lens (Spiekeroog, Germany). / Seibert, Stephan L.; Greskowiak, Janek; Prommer, Henning; Böttcher, Michael E.; Massmann, Gudrun.

In: Journal of Hydrology, Vol. 575, 01.08.2019, p. 1133-1144.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Modeling of biogeochemical processes in a barrier island freshwater lens (Spiekeroog, Germany)

AU - Seibert, Stephan L.

AU - Greskowiak, Janek

AU - Prommer, Henning

AU - Böttcher, Michael E.

AU - Massmann, Gudrun

PY - 2019/8/1

Y1 - 2019/8/1

N2 - Freshwater lenses present valuable water resources on barrier islands. Yet, the biogeochemical processes that control the groundwater quality of these freshwater lenses and how they are affected by the prevailing groundwater dynamics is largely unexplored. In this study we investigated the biogeochemistry of a barrier island freshwater lens with a focus on understanding and quantifying organic matter mineralization, sulfur cycling, and chemical fluxes to the land-ocean interface. We analyzed a comprehensive set of hydrogeochemical field data from Spiekeroog Island (Germany), including stable sulfur isotope signatures of dissolved sulfur species, with a reactive transport modeling approach. Tritium-Helium groundwater ages were used to constrain the hydrogeochemistry as a function of residence time. Our results revealed that freshwater lenses can act as archives for anthropogenic pollution, conserving the high sulfur loads associated with historic atmospheric deposition. We observed two distinct (hydro)biogeochemical patterns, which we attribute to a heterogeneous distribution of reactive organic matter. Those patterns were well replicated by two separate reactive transport models that considered the variations in organic matter reactivity. Simulation and field results demonstrated that net sulfur cycling is dominated by microbial sulfate reduction and subsequent iron sulfide precipitation. In the absence of dissolved oxidants, we attribute the observed high stable sulfur isotope fractionation between dissolved sulfate and sulfide of up to 67‰ to low (<20 pmol mL−1 d−1) microbial sulfate reduction rates. We show that older groundwater becomes progressively enriched in ammonium and phosphate due to the mineralization of organic matter, and we speculate that lens-derived nutrient fluxes may be important for the benthic zone at local groundwater discharge sites, at least seasonally in spring and summer.

AB - Freshwater lenses present valuable water resources on barrier islands. Yet, the biogeochemical processes that control the groundwater quality of these freshwater lenses and how they are affected by the prevailing groundwater dynamics is largely unexplored. In this study we investigated the biogeochemistry of a barrier island freshwater lens with a focus on understanding and quantifying organic matter mineralization, sulfur cycling, and chemical fluxes to the land-ocean interface. We analyzed a comprehensive set of hydrogeochemical field data from Spiekeroog Island (Germany), including stable sulfur isotope signatures of dissolved sulfur species, with a reactive transport modeling approach. Tritium-Helium groundwater ages were used to constrain the hydrogeochemistry as a function of residence time. Our results revealed that freshwater lenses can act as archives for anthropogenic pollution, conserving the high sulfur loads associated with historic atmospheric deposition. We observed two distinct (hydro)biogeochemical patterns, which we attribute to a heterogeneous distribution of reactive organic matter. Those patterns were well replicated by two separate reactive transport models that considered the variations in organic matter reactivity. Simulation and field results demonstrated that net sulfur cycling is dominated by microbial sulfate reduction and subsequent iron sulfide precipitation. In the absence of dissolved oxidants, we attribute the observed high stable sulfur isotope fractionation between dissolved sulfate and sulfide of up to 67‰ to low (<20 pmol mL−1 d−1) microbial sulfate reduction rates. We show that older groundwater becomes progressively enriched in ammonium and phosphate due to the mineralization of organic matter, and we speculate that lens-derived nutrient fluxes may be important for the benthic zone at local groundwater discharge sites, at least seasonally in spring and summer.

KW - Atmospheric sulfur deposition

KW - Microbial sulfate reduction

KW - Reactive transport modeling

KW - Subterranean estuary

KW - Sulfur isotope fractionation

UR - http://www.scopus.com/inward/record.url?scp=85067646471&partnerID=8YFLogxK

U2 - 10.1016/j.jhydrol.2019.05.094

DO - 10.1016/j.jhydrol.2019.05.094

M3 - Article

VL - 575

SP - 1133

EP - 1144

JO - Journal of Hydrology

JF - Journal of Hydrology

SN - 0022-1694

ER -