TY - THES

T1 - Systematic analysis of sediments, gas seeps and sludge gas at Lake Neusiedl

AU - Bähr, Christoph

N1 - no embargo

PY - 2024

Y1 - 2024

N2 - Permanent gas seeps at Lake Neusiedl are indicated in literature, but not very well characterized in terms of their origin. This study aimed at analysing the source of the apparently permanent seeps and comparing their geochemical signature with sludge gas that is a common by-product of organic matter degradation in the lake sediments. The main research questions were if a thermogenic gas source exists, and if all gases of biogenic origin share a common source or can be distinguished by their organic-geochemical signature. Molecular and stable carbon and hydrogen isotope compositions were measured to analyse the origin of the gas. Methane was the only hydrocarbon that was detected, indicating the absence of a thermogenic contribution of higher hydrocarbon components. Stable hydrogen and carbon isotope signature of methane and CO¿ confirm a purely biogenic source for seep gas and sludge gas. A systematic difference in isotope composition between these two types could not be detected, so a common origin of all gases, presumably associated with organic matter degradation in the lake sediments, is indicated. It is still under question why some of the gas shows seem to occur permanently at the same spot, and if this observation holds true at all. No evidence was found that permanent shows are related to a shallow microbial reservoir associated with organic-rich strata underlying the recent lake sediments. Another point of investigation were systematic changes of mineralogy and bulk geochemical parameters across the W-E lake axis. Sediment samples along two profiles between Breitenbrunn and Podersdorf were analysed via X-ray diffraction, as well as for their total organic carbon (TOC) content and pH. The composition of the lake sediments is dominated by quartz, feldspar, clay minerals and varying carbonate minerals. Carbonate minerals present are calcite, low magnesium calcite, high magnesium calcite and protodolomite. The X-ray diffractograms showed broadened peaks for low magnesium calcite, and protodolomite. The formation of high magnesium calcite and protodolomite is currently only occurring in specific regions of the lake. The pH decreases towards the lake centre, while TOC increases accordingly, arguing for more favourable conditions for organic matter preservation.

AB - Permanent gas seeps at Lake Neusiedl are indicated in literature, but not very well characterized in terms of their origin. This study aimed at analysing the source of the apparently permanent seeps and comparing their geochemical signature with sludge gas that is a common by-product of organic matter degradation in the lake sediments. The main research questions were if a thermogenic gas source exists, and if all gases of biogenic origin share a common source or can be distinguished by their organic-geochemical signature. Molecular and stable carbon and hydrogen isotope compositions were measured to analyse the origin of the gas. Methane was the only hydrocarbon that was detected, indicating the absence of a thermogenic contribution of higher hydrocarbon components. Stable hydrogen and carbon isotope signature of methane and CO¿ confirm a purely biogenic source for seep gas and sludge gas. A systematic difference in isotope composition between these two types could not be detected, so a common origin of all gases, presumably associated with organic matter degradation in the lake sediments, is indicated. It is still under question why some of the gas shows seem to occur permanently at the same spot, and if this observation holds true at all. No evidence was found that permanent shows are related to a shallow microbial reservoir associated with organic-rich strata underlying the recent lake sediments. Another point of investigation were systematic changes of mineralogy and bulk geochemical parameters across the W-E lake axis. Sediment samples along two profiles between Breitenbrunn and Podersdorf were analysed via X-ray diffraction, as well as for their total organic carbon (TOC) content and pH. The composition of the lake sediments is dominated by quartz, feldspar, clay minerals and varying carbonate minerals. Carbonate minerals present are calcite, low magnesium calcite, high magnesium calcite and protodolomite. The X-ray diffractograms showed broadened peaks for low magnesium calcite, and protodolomite. The formation of high magnesium calcite and protodolomite is currently only occurring in specific regions of the lake. The pH decreases towards the lake centre, while TOC increases accordingly, arguing for more favourable conditions for organic matter preservation.

KW - permanente Gausaustritte

KW - Kochbrunnen

KW - Schlammgas

KW - thermogen

KW - biogen

KW - Kohlenstoff

KW - Wasserstoff

KW - Isotope

KW - TOC

KW - pH

KW - Neusiedlersee

KW - Rust

KW - Breitenbrunn

KW - Podersdorf

KW - Sediment

KW - Methan

KW - Schwefelwasserstoff

KW - XRD

KW - Protodolomit

KW - LMC

KW - HMC

KW - CO2

KW - Kalzit

KW - Magnesium

KW - Lake Neusiedl

KW - sediments

KW - gas seeps

KW - sludge gas

KW - mineralogy

KW - geochemical parameters

KW - XRD

KW - TOC

KW - pH

KW - biogenic

KW - thermogenic

KW - lake sediments

KW - Rust

KW - Breitenbrunn

KW - Podersdorf

KW - calcite

KW - protodolomite

KW - LMC

KW - HMC

KW - methane

KW - hydrogen sulfide

KW - carbon isotope

KW - hydrogen isotope

KW - CO2

U2 - 10.34901/mul.pub.2025.013

DO - 10.34901/mul.pub.2025.013

M3 - Master's Thesis

ER -