Case Studies
Dr. Isabel Reche
Tracing biophysical and biological transformations of organic matter using spectroscopy
Characterization of dissolved organic matter (DOM) using absorption and fluorescence techniques has been used to describe its origin, composition, and bio- y photoreactivity across systems and seasons. However, their uses as tracers of processes have been less explored. Now, it is well-known that a significant portion of DOM can behave as a polymer gel. This polymeric DOM undergoes transitions from condensed to hydrated (swollen) phase and it can also assemble spontaneously promoting transformations in size and shape. These two processes appear to be mostly controlled by pH, ionic composition (calcium), and dielectric properties of the solvent. We have linked pH- phase transitions to DOM optical properties (absorption and photobleaching). We have experimentally observed that an increase in pH from acidic (5.4) to alkaline (8.2) conditions led to phase changes from condensed, less chromophoric and less photoreactive DOM to swollen, more chomophoric and more photoreactive DOM. These transformations have significant consequences to understand water transparency in inland waters.
In addition, we explored biological processes as krill excretion and bacterial carbon processing under different scenarios of substrate quality (availability of photoproducts and mineral nutrients) and viral lysis pressure. We monitored changes over time in absorption spectra and fluorescence excitation-emission matrices (EEMs) and we processed the data to search for unique signatures under these diverse experimental conditions. Antarctic krill excretion was a direct source of chromophoric DOM (CDOM). In short (hourly) incubations, krill excretion showed distinctive peaks at short wavelengths that disappeared at longer (daily) incubations, suggesting the release of very labile compounds. CDOM was generated by bacteria in all experiments, and the presence of photoproducts influenced both the quantity and the spectral quality of the resultant CDOM. We confirmed a direct link between bacterial production (3H-leucine incorporation) and CDOM generation. The availability of mineral nutrients and viral lysis pressure also affected significantly CDOM and EEMs signatures. In this talk, I will underline the versatility of spectroscopy to trace processes from biophysics to biology.
Dr. Eva Ortega-Retuerta
Observations of chromophoric dissolved and detrital organic matter distribution using remote sensing in the Southern Ocean: Validation, dynamics and regulation
Chromophoric dissolved and detrital organic matter (CDM), the optically active fraction of organic matter, affects significantly the underwater light environment and interferes with ocean color algorithms. Here, we studied the distribution and dynamics of CDM in waters around the Antarctic Peninsula, Southern Ocean, using remotely sensed data in austral summers from 1997 to 2005. First, we validated the global semi-analytic algorithm Garver-Siegel-Maritorena (GSM) by comparing simultaneous field and satellite measurements of CDM. These comparisons confirmed the validity of CDM satellite measurements obtained by the GSM algorithm (r2= 0.74, slope value= 1.01 ± 0.16, n=15).We found a higher (20%) contribution of detrital particles to the CDM signal than in lower latitudes (average 12%). Patches of higher CDM were observed in coastal areas and zones with recent ice melting. The seasonal variability of CDM, with maximum values at the end of austral summer, appeared to be ultimately controlled by the dynamics of ice, both directly and indirectly through the growth of phytoplankton and other organisms which are potential sources of CDM. At an interannual timescale, CDM dynamics may be driven by climatic forcing such as the Antarctic Oscillation.
Dr. Andy Baker
University of New South Wales and National Centre for Groundwater Research and Training
Co-authors: S. Thacker, E. Tipping, M. Bieroza, N. Hudson, J. Roe, J. Bridgeman
Relating dissolved organic matter fluorescence to functional properties: implications for drinking water treatment
Dissolved organic matter (DOM) has a number of ecological and geochemical functions, including light absorption, proton binding, binding of heavy metals, aluminum and radionuclides, binding of organic contaminants, adsorption at surfaces, aggregation and photochemical reactivity. Recently (1,2,3), we have described a set of functional assays for DOM; simple, reproducible measurements that provide information about the environmental roles of DOM rather than its more basic physico-chemical properties. Here, we have included the measurement of DOM fluorescence properties through the analysis of their excitation-emission matrix (EEM) matrices. Fluorescence EEM analyses are becoming widely used to characterize and source DOM (see review, (4)). Information that is contained within a fluorescence EEM and which has been shown to relate to DOM character includes, for example, fulvic-like fluorescence emission wavelength which may relate to aromacity or hydrophobicity, tryptophan-like fluorescence intensity which may relate to algal derived OM, and fulvic-like fluorescence normalised to absorbance at 340 nm to molecular weight. Fluorescence characterization of DOM is instantaneous, cheap, non-invasive, requires no sample pretreatment and possible on-line. Here, we present both fluorescence and absorbance analyses, which we use to characterize DOM samples from English river and lake waters, and then to derive relationships between fluorescence and absorbance properties and DOM function. In particular, we focus on optical properties that are relevant to the prediction of geochemical function relevant to drinking water treatment. Specifically, we investigate hydrophilicity, as this both directly relates to DOM removal through coagulation in drinking water treatment, as well as potentially relates to disinfection by-product formation upon chlorination. Calibration samples were taken from four sites, both lake and river waters, from N England (5). Multiple samples were taken from two of the sites to investigate DOM functional variability through time. These additional samples comprised approximately monthly samples at from Esthwaite Water to capture seasonal variability, and samples collected at a wide range of flow regimes at Rough Sike. All samples were prepared according to procedures detailed in (1). We find that hydrophilicity has a strong positive correlation with peak T intensity and the fluorescence : absorbance ratio, and a negative correlation with peak C emission wavelength. Multiple regression models show that that hydrophilicity is best modeled by fluorescence peak C emission wavelength (r=-0.92). We use this calibration dataset to predict the hydrophilicity of DOM from previously published fluorescence data collected from SW England, C England and NE England (6-8). We can map predicted hydrophilicity spatially across England, and temporally for individual sites. Given both the speed of fluorescence analysis and the capability to analyze without sample pretreatment; this leads to the potential for rapid and real-time measurement of this functional property. We show that the technique has potential for the real-time prediction of DOC hydrophilicity, which can be used to optimise drinking water treatment works performance, producing both cost savings and drinking water of lower DOC concentration.
Dr. Xose Alvarez-Salgado
CSIC Instituto de Investigacións Mariñas, Vigo, Spain
Co-authors: C. Romera–Castillo, C. Lønborg, M. Nieto–Cid, C. Marrasé
Optical properties of marine DOM in the NW Iberian coastal upwelling system
Coastal upwelling areas are highly dynamic marine environments where the production, consumption, transformation and export of dissolved organic matter (DOM) are magnified. The coloured fraction of DOM (CDOM) represent 36 ± 20% of the bulk DOM in the large coastal embayments of the NW Iberian upwelling system, where 2/3 of the CDOM exported to the adjacent ocean are autochthonous materials produced in situ and 1/3 are allochthonous materials introduced by continental runoff. Both in situ and in vitro approaches have been applied in this coastal upwelling system to objectively separate and quantify the effect of water mass mixing from biotic (microbial) and abiotic (photochemical) processes on the absorbance and induced fluorescence spectra of CDOM. The potential of protein- and humic-like fluorophores to trace the dynamics of the labile and refractory CDOM pools and the microbial transformation of the former into the latter have also been examined.
Dr. Rudolf Jaffé
Southeast Environmental Research Center and Department of Chemistry & Biochemistry, Florida International University, Miami, Florida.
Optical properties of natural dissolved organic matter (DOM) in aquatic ecosystems: Applications in ecosystem studies from headwater streams to the deep ocean.
The study of natural dissolved organic material (DOM) contributes to the better understanding of ecosystem function as the carbon flux between environmental compartments represents an important linkage between terrestrial and aquatic ecosystems. Within freshwater and marine ecosystems, DOM typically represents the largest pool of detrital organic carbon and greatly exceeds the organic carbon present in living biomass. Thus, the sources and fate of DOM are important terms in carbon budgets. DOM can also influence ecosystem function by controlling microbial food webs, act as a means of nutrient transport, buffer pH and influence toxicity and bioavailability of pollutants, among others. DOM composition influences its ‘quality’ and thus its photo- and bio-reactivity, both of which exert a strong control of the diagenetic reworking of this carbon pool. However, the molecular composition of DOM is highly complex and diverse, and its characterization is a serious challenge to analytical chemists. In recent years, the analysis of optical properties, including excitation emission matrix (EEM) fluorescence combined with parallel factor analysis (PARAFAC), have emerged as a practical tool for the characterization of DOM. This seminar will present examples for the application of EEM-PARAFAC in assessing environmental dynamics of DOM on both spatial and temporal scales, and in both freshwater and marine ecosystems.
Dr. Natalie Mladenov
INSTAAR, University of Colorado, Boulder, CO, USA
Using optical spectroscopy to examine organic matter in remote lakes and the atmosphere
Alpine and other remote lakes are sentinels of global change owing to the limited vegetation in their catchments and their location outside of the realm of human disturbance. In a global sampling of remote lakes from the Atlas, Sierra Nevada, Patagonia, Pyrenees, Tyrolian Alps, Antarctic, and Arctic sites, we found that DOM optical properties were strongly influenced by UV radiation, hydraulic residence time, amount of vegetation in the catchment, and bacterial abundance. As expected, greater clear sky UV radiation and longer solar exposure resulted in lower absorption at 250 nm. Meanwhile, greater bacterial abundance resulted in higher absorption and DOC concentrations.
Fluorescence spectroscopy and PARAFAC modeling provided an additional level of information about DOM provenance and transformation. Recently deglaciated lakes in the Tyrolian Alps showed a gradient of increasing terrestrial humic-like fluorescence with age. The fluorescence of DOM in Sierra Nevada lakes resembled that of organic matter in Saharan-derived wet and dry deposition. Both lakes located above treeline in rocky, unvegetated catchments and wet and dry deposition contained substantial amounts of amino acid-like fluorescence, owing most probably to the strong microbial influence in these pristine aquatic and atmospheric settings. In contrast, organic matter in urban aerosols was dominated by humic-like fluorescent components. Saharan dust aerosols could be differentiated from urban pollution aerosols based on the distribution of fluorescent components, the fluorescence index, and the humification index.
Tracing biophysical and biological transformations of organic matter using spectroscopy
Characterization of dissolved organic matter (DOM) using absorption and fluorescence techniques has been used to describe its origin, composition, and bio- y photoreactivity across systems and seasons. However, their uses as tracers of processes have been less explored. Now, it is well-known that a significant portion of DOM can behave as a polymer gel. This polymeric DOM undergoes transitions from condensed to hydrated (swollen) phase and it can also assemble spontaneously promoting transformations in size and shape. These two processes appear to be mostly controlled by pH, ionic composition (calcium), and dielectric properties of the solvent. We have linked pH- phase transitions to DOM optical properties (absorption and photobleaching). We have experimentally observed that an increase in pH from acidic (5.4) to alkaline (8.2) conditions led to phase changes from condensed, less chromophoric and less photoreactive DOM to swollen, more chomophoric and more photoreactive DOM. These transformations have significant consequences to understand water transparency in inland waters.
In addition, we explored biological processes as krill excretion and bacterial carbon processing under different scenarios of substrate quality (availability of photoproducts and mineral nutrients) and viral lysis pressure. We monitored changes over time in absorption spectra and fluorescence excitation-emission matrices (EEMs) and we processed the data to search for unique signatures under these diverse experimental conditions. Antarctic krill excretion was a direct source of chromophoric DOM (CDOM). In short (hourly) incubations, krill excretion showed distinctive peaks at short wavelengths that disappeared at longer (daily) incubations, suggesting the release of very labile compounds. CDOM was generated by bacteria in all experiments, and the presence of photoproducts influenced both the quantity and the spectral quality of the resultant CDOM. We confirmed a direct link between bacterial production (3H-leucine incorporation) and CDOM generation. The availability of mineral nutrients and viral lysis pressure also affected significantly CDOM and EEMs signatures. In this talk, I will underline the versatility of spectroscopy to trace processes from biophysics to biology.
Dr. Eva Ortega-Retuerta
Observations of chromophoric dissolved and detrital organic matter distribution using remote sensing in the Southern Ocean: Validation, dynamics and regulation
Chromophoric dissolved and detrital organic matter (CDM), the optically active fraction of organic matter, affects significantly the underwater light environment and interferes with ocean color algorithms. Here, we studied the distribution and dynamics of CDM in waters around the Antarctic Peninsula, Southern Ocean, using remotely sensed data in austral summers from 1997 to 2005. First, we validated the global semi-analytic algorithm Garver-Siegel-Maritorena (GSM) by comparing simultaneous field and satellite measurements of CDM. These comparisons confirmed the validity of CDM satellite measurements obtained by the GSM algorithm (r2= 0.74, slope value= 1.01 ± 0.16, n=15).We found a higher (20%) contribution of detrital particles to the CDM signal than in lower latitudes (average 12%). Patches of higher CDM were observed in coastal areas and zones with recent ice melting. The seasonal variability of CDM, with maximum values at the end of austral summer, appeared to be ultimately controlled by the dynamics of ice, both directly and indirectly through the growth of phytoplankton and other organisms which are potential sources of CDM. At an interannual timescale, CDM dynamics may be driven by climatic forcing such as the Antarctic Oscillation.
Dr. Andy Baker
University of New South Wales and National Centre for Groundwater Research and Training
Co-authors: S. Thacker, E. Tipping, M. Bieroza, N. Hudson, J. Roe, J. Bridgeman
Relating dissolved organic matter fluorescence to functional properties: implications for drinking water treatment
Dissolved organic matter (DOM) has a number of ecological and geochemical functions, including light absorption, proton binding, binding of heavy metals, aluminum and radionuclides, binding of organic contaminants, adsorption at surfaces, aggregation and photochemical reactivity. Recently (1,2,3), we have described a set of functional assays for DOM; simple, reproducible measurements that provide information about the environmental roles of DOM rather than its more basic physico-chemical properties. Here, we have included the measurement of DOM fluorescence properties through the analysis of their excitation-emission matrix (EEM) matrices. Fluorescence EEM analyses are becoming widely used to characterize and source DOM (see review, (4)). Information that is contained within a fluorescence EEM and which has been shown to relate to DOM character includes, for example, fulvic-like fluorescence emission wavelength which may relate to aromacity or hydrophobicity, tryptophan-like fluorescence intensity which may relate to algal derived OM, and fulvic-like fluorescence normalised to absorbance at 340 nm to molecular weight. Fluorescence characterization of DOM is instantaneous, cheap, non-invasive, requires no sample pretreatment and possible on-line. Here, we present both fluorescence and absorbance analyses, which we use to characterize DOM samples from English river and lake waters, and then to derive relationships between fluorescence and absorbance properties and DOM function. In particular, we focus on optical properties that are relevant to the prediction of geochemical function relevant to drinking water treatment. Specifically, we investigate hydrophilicity, as this both directly relates to DOM removal through coagulation in drinking water treatment, as well as potentially relates to disinfection by-product formation upon chlorination. Calibration samples were taken from four sites, both lake and river waters, from N England (5). Multiple samples were taken from two of the sites to investigate DOM functional variability through time. These additional samples comprised approximately monthly samples at from Esthwaite Water to capture seasonal variability, and samples collected at a wide range of flow regimes at Rough Sike. All samples were prepared according to procedures detailed in (1). We find that hydrophilicity has a strong positive correlation with peak T intensity and the fluorescence : absorbance ratio, and a negative correlation with peak C emission wavelength. Multiple regression models show that that hydrophilicity is best modeled by fluorescence peak C emission wavelength (r=-0.92). We use this calibration dataset to predict the hydrophilicity of DOM from previously published fluorescence data collected from SW England, C England and NE England (6-8). We can map predicted hydrophilicity spatially across England, and temporally for individual sites. Given both the speed of fluorescence analysis and the capability to analyze without sample pretreatment; this leads to the potential for rapid and real-time measurement of this functional property. We show that the technique has potential for the real-time prediction of DOC hydrophilicity, which can be used to optimise drinking water treatment works performance, producing both cost savings and drinking water of lower DOC concentration.
Dr. Xose Alvarez-Salgado
CSIC Instituto de Investigacións Mariñas, Vigo, Spain
Co-authors: C. Romera–Castillo, C. Lønborg, M. Nieto–Cid, C. Marrasé
Optical properties of marine DOM in the NW Iberian coastal upwelling system
Coastal upwelling areas are highly dynamic marine environments where the production, consumption, transformation and export of dissolved organic matter (DOM) are magnified. The coloured fraction of DOM (CDOM) represent 36 ± 20% of the bulk DOM in the large coastal embayments of the NW Iberian upwelling system, where 2/3 of the CDOM exported to the adjacent ocean are autochthonous materials produced in situ and 1/3 are allochthonous materials introduced by continental runoff. Both in situ and in vitro approaches have been applied in this coastal upwelling system to objectively separate and quantify the effect of water mass mixing from biotic (microbial) and abiotic (photochemical) processes on the absorbance and induced fluorescence spectra of CDOM. The potential of protein- and humic-like fluorophores to trace the dynamics of the labile and refractory CDOM pools and the microbial transformation of the former into the latter have also been examined.
Dr. Rudolf Jaffé
Southeast Environmental Research Center and Department of Chemistry & Biochemistry, Florida International University, Miami, Florida.
Optical properties of natural dissolved organic matter (DOM) in aquatic ecosystems: Applications in ecosystem studies from headwater streams to the deep ocean.
The study of natural dissolved organic material (DOM) contributes to the better understanding of ecosystem function as the carbon flux between environmental compartments represents an important linkage between terrestrial and aquatic ecosystems. Within freshwater and marine ecosystems, DOM typically represents the largest pool of detrital organic carbon and greatly exceeds the organic carbon present in living biomass. Thus, the sources and fate of DOM are important terms in carbon budgets. DOM can also influence ecosystem function by controlling microbial food webs, act as a means of nutrient transport, buffer pH and influence toxicity and bioavailability of pollutants, among others. DOM composition influences its ‘quality’ and thus its photo- and bio-reactivity, both of which exert a strong control of the diagenetic reworking of this carbon pool. However, the molecular composition of DOM is highly complex and diverse, and its characterization is a serious challenge to analytical chemists. In recent years, the analysis of optical properties, including excitation emission matrix (EEM) fluorescence combined with parallel factor analysis (PARAFAC), have emerged as a practical tool for the characterization of DOM. This seminar will present examples for the application of EEM-PARAFAC in assessing environmental dynamics of DOM on both spatial and temporal scales, and in both freshwater and marine ecosystems.
Dr. Natalie Mladenov
INSTAAR, University of Colorado, Boulder, CO, USA
Using optical spectroscopy to examine organic matter in remote lakes and the atmosphere
Alpine and other remote lakes are sentinels of global change owing to the limited vegetation in their catchments and their location outside of the realm of human disturbance. In a global sampling of remote lakes from the Atlas, Sierra Nevada, Patagonia, Pyrenees, Tyrolian Alps, Antarctic, and Arctic sites, we found that DOM optical properties were strongly influenced by UV radiation, hydraulic residence time, amount of vegetation in the catchment, and bacterial abundance. As expected, greater clear sky UV radiation and longer solar exposure resulted in lower absorption at 250 nm. Meanwhile, greater bacterial abundance resulted in higher absorption and DOC concentrations.
Fluorescence spectroscopy and PARAFAC modeling provided an additional level of information about DOM provenance and transformation. Recently deglaciated lakes in the Tyrolian Alps showed a gradient of increasing terrestrial humic-like fluorescence with age. The fluorescence of DOM in Sierra Nevada lakes resembled that of organic matter in Saharan-derived wet and dry deposition. Both lakes located above treeline in rocky, unvegetated catchments and wet and dry deposition contained substantial amounts of amino acid-like fluorescence, owing most probably to the strong microbial influence in these pristine aquatic and atmospheric settings. In contrast, organic matter in urban aerosols was dominated by humic-like fluorescent components. Saharan dust aerosols could be differentiated from urban pollution aerosols based on the distribution of fluorescent components, the fluorescence index, and the humification index.