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Papers by Boris Koch
Biogeosciences, 2012
ABSTRACT Dissolved organic matter (DOM) was extracted with solid phase extraction (SPE) from 137 ... more ABSTRACT Dissolved organic matter (DOM) was extracted with solid phase extraction (SPE) from 137 water samples from different climate zones and different depths along an Eastern Atlantic Ocean transect. The extracts were analyzed with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with electrospray ionization (ESI). Δ14C analyses were performed on subsamples of the SPE-DOM. In addition, the amount of dissolved organic carbon was determined for all water and SPE-DOM samples as well as the yield of amino sugars for selected samples. Linear correlations were observed between the magnitudes of 43 % of the FT-ICR mass peaks and the extract Δ14C values. Decreasing SPE-DOM Δ14C values went along with a shift in the molecular composition to higher average masses (m/z) and lower hydrogen/carbon (H/C) ratios. The correlation was used to model the SPE-DOM Δ14C distribution for all 137 samples. Based on single mass peaks a degradation index was developed to compare the degradation state of marine SPE-DOM samples analyzed with FT-ICR MS. A correlation between Δ14C, degradation index, DOC values and amino sugar yield supports that SPE-DOM analyzed with FT-ICR MS reflects trends of bulk DOM. A relative mass peak magnitude ratio was used to compare aged SPE-DOM and fresh SPE-DOM regarding single mass peaks. The magnitude ratios show a continuum of different reactivities for the single compounds. Only few of the compounds present in the FT-ICR mass spectra are expected to be highly degraded in the oldest water masses of the Pacific Ocean. All other compounds should persist partly thermohaline circulation. Prokaryotic (bacterial) production, transformation and accumulation of this very stable DOM occurs probably primarily in the upper ocean. This DOM is an important contribution to very old DOM, showing that production and degradation are dynamic processes.
Biogeochemistry, 2014
ABSTRACT Large Arctic rivers discharge significant amounts of dissolved organic matter (DOM) into... more ABSTRACT Large Arctic rivers discharge significant amounts of dissolved organic matter (DOM) into the Arctic Ocean. We sampled natural waters of the Lena River, the Buor-Khaya Bay (Laptev Sea), permafrost melt water creeks, ice complex melt water creeks and a lake. The goal of this study was to characterize the molecular DOM composition with respect to different water bodies within the Lena Delta. We aimed at an identification of source-specific DOM molecular markers and their relative contribution to DOM of different origin. The molecular characterization was performed for solid-phase extracted DOM by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Average dissolved organic carbon concentrations in the original samples were 490 ± 75 µmol C L−1 for riverine and bay samples and 399 ± 115 µmol C L−1 for permafrost melt water creeks. Average TDN concentrations were elevated in the permafrost melt waters (19.7 ± 7.1 µmol N L−1) in comparison to the river and the bay (both 13.2 ± 2.6 µmol N L−1). FT-ICR MS and statistical tools demonstrated that the origin of DOM in the Lena Delta was systematically reflected in its molecular composition. Magnitude weighted parameters calculated from MS data (O/Cwa, H/Cwa, C/Nwa) highlighted preliminary sample discrimination. The highest H/Cwa of 1.315 was found for DOM in melt water creeks in comparison to 1.281 for river and 1.230 for the bay samples. In the bay samples we observed a higher fraction of oxygen-rich components which was reflected in an O/Cwa ratio of 0.445 in comparison to 0.425 and 0.427 in the river and creeks, respectively. From the southernmost location to the bay a relative depletion of nitrogenous molecular markers and an enrichment of oxidized DOM components occurred. The highest contribution of nitrogenous components was indicative for creeks reflected in a C/Nwa of 104 in comparison to 143 and 176 in the river and bay, respectively. These observations were studied on a molecular formula level using principal component and indicator value analyses. The results showed systematic differences with respect to water origin and constitute an important basis for a better mechanistic understanding of DOM transformations in the changing Arctic rivers.
Marine Ecology Progress Series
Alexandrium tamarense is a common harmful algal bloom species that can cause high concentrations ... more Alexandrium tamarense is a common harmful algal bloom species that can cause high concentrations of paralytic shellfish poisoning toxins (PSTs) in marine coastal waters. PSTs are nitrogen-rich alkaloids, and their production has been shown to depend on resource conditions as well as on growth rate. We hypothesized that PST content in A. tamarense depends on the nitrogen availability and will increase with cellular N:P ratios and arginine content. To test this hypothesis, we first grew A. tamarense cells under nitrogen-starved, phosphorus-starved and nutrient-replete conditions. Subsequently, we transferred cells into a nutrient-rich medium and followed dynamic changes in growth, elemental stoichiometry, as well as amino acid and PST content and composition. Our results illustrate that PST content was lowest under nitrogen starvation, intermediate under nutrient-replete conditions, and highest under phosphorus starvation. As expected, PST content correlated well with cellular N:P rat...
Ecological Studies, 2010
Mangrove biogeochemistry addresses the interrelation between primary production and nutrient cycl... more Mangrove biogeochemistry addresses the interrelation between primary production and nutrient cycles, material fluxes and secondary production. It requires data on source identification, quantification and turnover of organic matter and inorganic nutrients in sediments, porewater and in the water column. This information can be derived from organic biomarkers, and it is one of the important tasks in the field of biogeochemistry
... To forecast the effects of different resource-use scenarios, MAIS can make a contribution. ..... more ... To forecast the effects of different resource-use scenarios, MAIS can make a contribution. ... Tools for Integration of Ecosystem Studies towards the Development of Management Strategies Summaries ... M. and Fuhr, D.: Scenario Development as a Tool for Integrated Analysis and ...
Biogeosciences, 2012
ABSTRACT Dissolved organic matter (DOM) was extracted with solid phase extraction (SPE) from 137 ... more ABSTRACT Dissolved organic matter (DOM) was extracted with solid phase extraction (SPE) from 137 water samples from different climate zones and different depths along an Eastern Atlantic Ocean transect. The extracts were analyzed with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with electrospray ionization (ESI). Δ14C analyses were performed on subsamples of the SPE-DOM. In addition, the amount of dissolved organic carbon was determined for all water and SPE-DOM samples as well as the yield of amino sugars for selected samples. Linear correlations were observed between the magnitudes of 43 % of the FT-ICR mass peaks and the extract Δ14C values. Decreasing SPE-DOM Δ14C values went along with a shift in the molecular composition to higher average masses (m/z) and lower hydrogen/carbon (H/C) ratios. The correlation was used to model the SPE-DOM Δ14C distribution for all 137 samples. Based on single mass peaks a degradation index was developed to compare the degradation state of marine SPE-DOM samples analyzed with FT-ICR MS. A correlation between Δ14C, degradation index, DOC values and amino sugar yield supports that SPE-DOM analyzed with FT-ICR MS reflects trends of bulk DOM. A relative mass peak magnitude ratio was used to compare aged SPE-DOM and fresh SPE-DOM regarding single mass peaks. The magnitude ratios show a continuum of different reactivities for the single compounds. Only few of the compounds present in the FT-ICR mass spectra are expected to be highly degraded in the oldest water masses of the Pacific Ocean. All other compounds should persist partly thermohaline circulation. Prokaryotic (bacterial) production, transformation and accumulation of this very stable DOM occurs probably primarily in the upper ocean. This DOM is an important contribution to very old DOM, showing that production and degradation are dynamic processes.
Biogeochemistry, 2014
ABSTRACT Large Arctic rivers discharge significant amounts of dissolved organic matter (DOM) into... more ABSTRACT Large Arctic rivers discharge significant amounts of dissolved organic matter (DOM) into the Arctic Ocean. We sampled natural waters of the Lena River, the Buor-Khaya Bay (Laptev Sea), permafrost melt water creeks, ice complex melt water creeks and a lake. The goal of this study was to characterize the molecular DOM composition with respect to different water bodies within the Lena Delta. We aimed at an identification of source-specific DOM molecular markers and their relative contribution to DOM of different origin. The molecular characterization was performed for solid-phase extracted DOM by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Average dissolved organic carbon concentrations in the original samples were 490 ± 75 µmol C L−1 for riverine and bay samples and 399 ± 115 µmol C L−1 for permafrost melt water creeks. Average TDN concentrations were elevated in the permafrost melt waters (19.7 ± 7.1 µmol N L−1) in comparison to the river and the bay (both 13.2 ± 2.6 µmol N L−1). FT-ICR MS and statistical tools demonstrated that the origin of DOM in the Lena Delta was systematically reflected in its molecular composition. Magnitude weighted parameters calculated from MS data (O/Cwa, H/Cwa, C/Nwa) highlighted preliminary sample discrimination. The highest H/Cwa of 1.315 was found for DOM in melt water creeks in comparison to 1.281 for river and 1.230 for the bay samples. In the bay samples we observed a higher fraction of oxygen-rich components which was reflected in an O/Cwa ratio of 0.445 in comparison to 0.425 and 0.427 in the river and creeks, respectively. From the southernmost location to the bay a relative depletion of nitrogenous molecular markers and an enrichment of oxidized DOM components occurred. The highest contribution of nitrogenous components was indicative for creeks reflected in a C/Nwa of 104 in comparison to 143 and 176 in the river and bay, respectively. These observations were studied on a molecular formula level using principal component and indicator value analyses. The results showed systematic differences with respect to water origin and constitute an important basis for a better mechanistic understanding of DOM transformations in the changing Arctic rivers.
Marine Ecology Progress Series
Alexandrium tamarense is a common harmful algal bloom species that can cause high concentrations ... more Alexandrium tamarense is a common harmful algal bloom species that can cause high concentrations of paralytic shellfish poisoning toxins (PSTs) in marine coastal waters. PSTs are nitrogen-rich alkaloids, and their production has been shown to depend on resource conditions as well as on growth rate. We hypothesized that PST content in A. tamarense depends on the nitrogen availability and will increase with cellular N:P ratios and arginine content. To test this hypothesis, we first grew A. tamarense cells under nitrogen-starved, phosphorus-starved and nutrient-replete conditions. Subsequently, we transferred cells into a nutrient-rich medium and followed dynamic changes in growth, elemental stoichiometry, as well as amino acid and PST content and composition. Our results illustrate that PST content was lowest under nitrogen starvation, intermediate under nutrient-replete conditions, and highest under phosphorus starvation. As expected, PST content correlated well with cellular N:P rat...
Ecological Studies, 2010
Mangrove biogeochemistry addresses the interrelation between primary production and nutrient cycl... more Mangrove biogeochemistry addresses the interrelation between primary production and nutrient cycles, material fluxes and secondary production. It requires data on source identification, quantification and turnover of organic matter and inorganic nutrients in sediments, porewater and in the water column. This information can be derived from organic biomarkers, and it is one of the important tasks in the field of biogeochemistry
... To forecast the effects of different resource-use scenarios, MAIS can make a contribution. ..... more ... To forecast the effects of different resource-use scenarios, MAIS can make a contribution. ... Tools for Integration of Ecosystem Studies towards the Development of Management Strategies Summaries ... M. and Fuhr, D.: Scenario Development as a Tool for Integrated Analysis and ...