The impact of biogeochemical processes on the composition of dissolved organic matter in marine subsurface sediments

Organic matter in marine sediments is one of the largest pools of reduced carbon on Earth. It had been known as recalcitrant carbon pool with scarce living biomasses. The findings of microbes at several kilometers below seafloor suggest there is a substantial amount of living biomasses in the subsurface sediments under extreme conditions, for example, decreasing labile biomolecules as carbon sources, electron acceptors, and thermal conditions at deeper layers. Those microbes might drive a slow but extensive carbon flow and play an important role in the carbon cycle in deep Earth. It is not known how the microbes could survive on the recalcitrant organic matter (ROM) leftover . The gap of knowledge is especially in the initial step of degradation process: how the ROM is degraded to assimilable substrates. Dissolved organic matter (DOM) encompasses the analytical window for the initial degradation of ROM. However, the DOM pool is complex and comprises tens of thousands of formulae. Therefore, this study focused on firstly the method of DOM characterization, secondly the DOM cycling and degradation process in subseafloor sediment. In further, this study aims to answer the questions: how the degradation patterns of organic matter change with environmental condition in the subsurface sediments, which are highly stratified by redox conditions and thermal gradients. In summary, this dissertation addressed the interactions between microbes and DOM in stratified anaerobic sediments by combinations of EEMs and FT-ICR MS. It is indicated that the metabolism of microbes is sensitive and adaptive to environmental conditions, which ultimately influence the carbon and nitrogen flow in subsurface sediments due to the change of microbial metabolisms and abiotic processes

Molecular Composition of Dissolved Organic Matter in the Changjiang (Yangtze River) – Imprints of Anthropogenic Impact

Understanding the biogeochemical transformation of dissolved organic matter (DOM) across fluvial networks will ultimately help to predict anthropogenic influences. To date, few studies have evaluated the anthropogenic impact on the spatial and temporal changes of DOM composition in large river systems. Here, FT-ICR-MS combined with excitation-emission matrix spectroscopy (EEMs) and biomarkers were applied to resolve chemical differences of DOM collected from the Changjiang basin at different hydrological and environmental conditions. PCA and cluster analysis illustrated that samples collected from lake systems and northern and southern tributaries differed from the two batches of main stream samples, particularly due to higher contribution of nitrogen and sulfur containing compounds. Correlation of land-use information along the tributaries with different PCA loadings indicated that agricultural, forest and wetland areas and wastewater discharge control the composition of DOM within these subregions. Higher heteroatom content (especially CHONx) in the low discharge period (2009) may be contributed by paddy soil leaching into groundwater. The relative peak magnitude of sulfur containing formulas was elevated during flood season (2010), which may be related to pollutions in areas of high population density. In addition, lignin phenol concentrations were higher in the flood season because of elevated soil erosion. Consequently, land use and human activities can strongly alter the quality and composition of DOM in watersheds flowing through densely populated regions, which may also impact or influence the riverine carbon flux in anthropogenically disturbed river systems

Der Einfluss biogeochemischer Prozesse auf die Zusammensetzung gelöster organischer Stoffe in marinen Untergrundsedimenten

Organic matter in marine sediments is one of the largest pools of reduced carbon on Earth. It had been known as recalcitrant carbon pool with scarce living biomasses. The findings of microbes at several kilometers below seafloor suggest there is a substantial amount of living biomasses in the subsurface sediments under extreme conditions, for example, decreasing labile biomolecules as carbon sources, electron acceptors, and thermal conditions at deeper layers. Those microbes might drive a slow but extensive carbon flow and play an important role in the carbon cycle in deep Earth. It is not known how the microbes could survive on the recalcitrant organic matter (ROM) leftover . The gap of knowledge is especially in the initial step of degradation process: how the ROM is degraded to assimilable substrates. Dissolved organic matter (DOM) encompasses the analytical window for the initial degradation of ROM. However, the DOM pool is complex and comprises tens of thousands of formulae. Therefore, this study focused on firstly the method of DOM characterization, secondly the DOM cycling and degradation process in subseafloor sediment. In further, this study aims to answer the questions: how the degradation patterns of organic matter change with environmental condition in the subsurface sediments, which are highly stratified by redox conditions and thermal gradients. In summary, this dissertation addressed the interactions between microbes and DOM in stratified anaerobic sediments by combinations of EEMs and FT-ICR MS. It is indicated that the metabolism of microbes is sensitive and adaptive to environmental conditions, which ultimately influence the carbon and nitrogen flow in subsurface sediments due to the change of microbial metabolisms and abiotic processes

DataSheet_2_Molecular Composition of Dissolved Organic Matter in the Changjiang (Yangtze River) – Imprints of Anthropogenic Impact.pdf

Understanding the biogeochemical transformation of dissolved organic matter (DOM) across fluvial networks will ultimately help to predict anthropogenic influences. To date, few studies have evaluated the anthropogenic impact on the spatial and temporal changes of DOM composition in large river systems. Here, FT-ICR-MS combined with excitation-emission matrix spectroscopy (EEMs) and biomarkers were applied to resolve chemical differences of DOM collected from the Changjiang basin at different hydrological and environmental conditions. PCA and cluster analysis illustrated that samples collected from lake systems and northern and southern tributaries differed from the two batches of main stream samples, particularly due to higher contribution of nitrogen and sulfur containing compounds. Correlation of land-use information along the tributaries with different PCA loadings indicated that agricultural, forest and wetland areas and wastewater discharge control the composition of DOM within these subregions. Higher heteroatom content (especially CHONx) in the low discharge period (2009) may be contributed by paddy soil leaching into groundwater. The relative peak magnitude of sulfur containing formulas was elevated during flood season (2010), which may be related to pollutions in areas of high population density. In addition, lignin phenol concentrations were higher in the flood season because of elevated soil erosion. Consequently, land use and human activities can strongly alter the quality and composition of DOM in watersheds flowing through densely populated regions, which may also impact or influence the riverine carbon flux in anthropogenically disturbed river systems.</p

DataSheet_1_Molecular Composition of Dissolved Organic Matter in the Changjiang (Yangtze River) – Imprints of Anthropogenic Impact.csv

Understanding the biogeochemical transformation of dissolved organic matter (DOM) across fluvial networks will ultimately help to predict anthropogenic influences. To date, few studies have evaluated the anthropogenic impact on the spatial and temporal changes of DOM composition in large river systems. Here, FT-ICR-MS combined with excitation-emission matrix spectroscopy (EEMs) and biomarkers were applied to resolve chemical differences of DOM collected from the Changjiang basin at different hydrological and environmental conditions. PCA and cluster analysis illustrated that samples collected from lake systems and northern and southern tributaries differed from the two batches of main stream samples, particularly due to higher contribution of nitrogen and sulfur containing compounds. Correlation of land-use information along the tributaries with different PCA loadings indicated that agricultural, forest and wetland areas and wastewater discharge control the composition of DOM within these subregions. Higher heteroatom content (especially CHONx) in the low discharge period (2009) may be contributed by paddy soil leaching into groundwater. The relative peak magnitude of sulfur containing formulas was elevated during flood season (2010), which may be related to pollutions in areas of high population density. In addition, lignin phenol concentrations were higher in the flood season because of elevated soil erosion. Consequently, land use and human activities can strongly alter the quality and composition of DOM in watersheds flowing through densely populated regions, which may also impact or influence the riverine carbon flux in anthropogenically disturbed river systems.</p