Download or read book Assessing the effect of dissolved organic matter DOM quality on degradation kinetics in the Vesdre River Belgium written by D.T. Dibar and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Assessing the effect of dissolved organic matter quality on denitrification in the Vesdre catchment in Wallonia region Province of Liege Belgium written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Characterization of dissolved organic matter DOM in the Vesdre river catchment Belgium during autumn leaf fall written by A.K. Weldemariam and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Characterisation of dissolved organic matter in the Vesdre river Belgium using flourescence spectroscopy written by L. Moatlhodi and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Dissolved Organic Matter in the Anthropogenically Impacted Grand River and Natural Burnt River Watersheds written by Ryan H. S. Hutchins and published by . This book was released on 2011 with total page 99 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dissolved organic carbon (DOM) is one of the largest cycled organic carbon pools on Earth and an important biogeochemical factor in aquatic systems. DOM can act as an energy source for microorganisms, alter the depth of the photic zone for photosynthesis, absorb harmful ultraviolet radiation, as well as alter the transport and toxicity of contaminants. The purpose of this research project was to characterize DOM in the Grand River watershed in Ontario, Canada using a wide range of qualitative and quantitative techniques and determine the impact of anthropogenic activities as well as seasonal and longitudinal changes on DOM processes. To reach the study objectives, historical data was analyzed to determine the seasonal cycle in the Grand River watershed. Intensive longitudinal sampling surveys were undertaken to evaluate the DOM characteristics and processes in the Grand River. Surveys of the less impacted Burnt River watershed were used as a comparison watershed to the Grand River to evaluate allochthonous and autochthonous indicators of DOM source and human impacts on DOM processes. Drinking water surveillance data was used to evaluate the effect of DOM in the Grand River on formation of disinfection by-products (DBPs). Different trends were seen in the Grand River in terms of longitudinal area and season. The headwaters of the river showed more autochthonous DOM in the spring and winter compared to the fall and summer. The lower-central river peaked in autochthonous DOM in the summer and was more allochthonous in the winter. DOM generally became more autochthonous downstream in the Grand River and was most autochthonous below the large sewage treatment plants (STPs) in the central portion. Protein content, measured as protein-like fluorescence normalized to DOC concentration, was strongly related to [delta]15N of DON; both are associated with autochthonous DOM in the Grand River and show the effects of the major STPs. The increase in autochthonous DOM below the STPs is likely associated with nutrient enrichment stimulating primary production and macrophyte growth. Based on the comparison of the Burnt River with the more impacted Grand River, the effect of lakes and photodegradation can make discrimination of autochthonous and allochthonous DOM more difficult. The ratio of DOC/DON and protein-like fluorescence proved to be robust indicators despite photodegradation. Human impacts on the Grand River watershed result in a greater seasonal cycle, high primary production in the summer and a downstream trend of increasing autochthonous DOM compared to the Burnt River. Based on drinking water surveillance data and literature review, autochthonous DOM caused greater DBPs in the drinking waters fed by the Grand River. This is currently a threat to human health and DBPs in sewage treatment plant effluent may be a threat to ecosystem health.

Download or read book Variations in Size and Optical Properties of Dissolved Organic Matter During Mixing at Large River Confluences written by Jinping Xue and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The functionality of dissolved organic matter (DOM) in natural waters depends on its size and composition. Identifying the sources and associated properties of DOM is vital to understand its effects on downstream ecosystems. River mixing has great potential to alter DOM quality, but its role in large boreal river confluences remains largely unknown, which limits our ability to realize the exact magnitude and composition of DOM exported to the ocean. Using asymmetrical flow field-flow fractionation (AF4) with offline excitation emission matrices (EEMs) measurements and parallel factor (PARAFAC) analysis, we found that inputs of DOM from the major tributaries shifted DOM quality in a typical large boreal river, namely, the lower Athabasca River (LAR). Flowing downstream, DOM tended to be higher in concentrations of dissolved organic carbon (DOC) and degrees of humification and aromaticity. Seasonal variations of DOM as a result of spring freshet were observed, during which times DOM tended to be higher in molecular mass (e.g., size) and richer in protein-like (i.e., tryptophan-like) relative to humic-like components. Source discrimination of DOM was more apparent under base flow conditions compared with the snowmelt period. In addition, conservative mixing behaviors of DOM at river confluences were observed. Contrasting mixing patterns among mixing zones suggest that both hydrological conditions and river geomorphology affect mixing patterns of DOM between the LAR and its tributaries. Our results demonstrate that DOM could be used as a quasi-conservative tracer during mixing at large river confluences. Findings from this study will enhance our ability to determine sources of DOM and to distinguish trends of mixing between the mainstem and the tributaries for DOM-associated trace elements in the boreal zone.

Download or read book Dissolved Organic Matter DOM written by Oleg S. Pokrovsky and published by . This book was released on 2017 with total page 339 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Measuring the Influence of Environmental Conditions on Dissolved Organic Matter Biodegradability and Optical Properties written by Maxwell Landsman-Gerjoi and published by . This book was released on 2019 with total page 118 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dissolved organic matter (DOM) plays a vital role in biogeochemical processes and can flux CO2 to the atmosphere when labile fractions are degraded, hence DOM degradation is increasingly studied. Some studies have suggested that fluorescence-derived substrate characteristics are useful metrics for estimating bioavailability (as prerequisite condition for biodegradability), however, recent findings on soil organic matter emphasize the importance of ecosystem scale factors such as physical separation of substrate from soil microbial communities and soil physiochemical cycles driving organic matter stability. I extend this principle to soil derived DOM and hypothesize that such environmental conditions, covariant with season, land use and landscape position, impact the composition of soil DOM and activity and abundance of the microbial community, which together govern DOM biodegradability. As a result, DOM bioavailability may not reliably be predicted using substrate characteristics alone. To test these hypotheses, I assessed aqueous soil extracts for water extractable organic carbon (WEOC) content, biodegradability, microbial biomass and fluorescence spectroscopy on water extractable organic matter (WEOM) across a range of environmental conditions in northern Vermont, USA. My results indicate that changes in environmental conditions affect composition, quantity, and biodegradability of DOM. WEOC concentrations were highest in the fall and lowest in the summer, while no significant differences were found between land covers or landscape position, however, DOM biodegradability was significantly higher in the agricultural (AG) site across seasons. Despite a shift in utilized substrate from less aromatic DOM in summer to more aromatic DOM in winter, biodegradability was similar for all seasons. The only exception were cold temperature incubations where microbial activity was depressed, and processing was halted. These results indicate that bioavailability cannot be reliably predicted based on fluorescence-based metric alone, rather, my core findings illustrate a complex picture of how environmental conditions, landscape characteristics, and substrate composition interact to drive the biodegradability of labile carbon pools in the soil environment. This thesis includes i) a background and comprehensive review of literature to inform the reader of any relevant topics, ii) a paper submitted for publication to Biogeochemistry (Chapter 2), and iii) supplemental information containing figures and tables pertinent to the paper.

Download or read book Dissolved Organic Matter Fluctuations in an Intermittent Headwater Stream written by Alba Guarch Ribot and published by . This book was released on 2017 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Dissolved organic matter (DOM) is an important source of carbon for aquatic microorganisms and it regulates many biogeochemical processes. Therefore, changes in river DOM concentration and properties could notably affect the functioning of fluvial and coastal ecosystems and alter the global carbon cycle. The DOM in headwater streams is strongly influenced by hydrology, as a consequence of the modification of catchment flow paths with high discharges. During storm events, the catchment hillsides are washed and terrigenous DOM is transported to rivers. In the Mediterranean region, the precipitation regime and evapotranspiration strongly modulate fluvial hydrology, which shows low discharges in summer and even flow disappearance. These dry–wet cycles of conditions affect many ecological and biogeochemical processes. In this thesis, I analyse a long time series of discharge and DOM data from Fuirosos, an intermittent headwater stream in NE Spain. My aim is to examine the relationship between DOM and hydrology at different temporal scales. First, I characterise the hydrological regime of this Mediterranean stream. A decrease in discharge was revealed, although trends in temperature and precipitation were not significant. In contrast, I did not find a clear temporal trend in dry period duration. However, rewetting has been significantly delayed, moving from September to October. The frequency of storm events decreased over the interval 1998–2015, showing a significant positive relationship with solar activity with a 2-year lag. Dissolved organic carbon (DOC) concentration saw a slight decrease during the study period, which was opposed to that observed in boreal systems. This pattern might respond to a reduction of terrigenous DOC input from forest hillsides as a consequence of the decrease in flushing episodes. The DOC temporal dynamics during the rewetting was regulated by dry period duration. Discharge oscillations explained up to 50% of total DOC variability during the wet period. Notably, this weight of discharge increased significantly over the years. DOM quality was also explored, and described in terms of absorbance and fluorescence properties. Most of the DOM properties were strongly related to discharge, revealing the input of allochthonous, degraded, aromatic, humic and large-molecular DOM under high flow conditions. However, these relationships were altered during drying and rewetting periods. The DOM responses at the individual storm event scale were highly heterogeneous. Multiple linear regression and commonality analyses showed that, in addition to the magnitude of storm episodes, antecedent hydrological conditions, namely pre-event basal flow and the magnitude of the previous storm event, played a significant role in regulating the trends and shapes of DOM–discharge hysteresis. Finally, I identified the differences and similarities in the DOM–discharge relationships between the intermittent Mediterranean stream analysed herein and a perennial Alpine stream with higher mean discharge (Oberer Seebach). The DOM in Fuirosos was significantly more concentrated, more terrigenous, more degraded, more aromatic and more humified. The sign of the global DOM–discharge response was the same in both streams. However, discharge was a more robust predictor of DOM variability in Oberer Seebach. In fact, low flow and rewetting periods in Fuirosos introduced considerable dispersion into the relationship. During snowmelt in Oberer Seebach the sensitivity to discharge also decreased or disappeared. The flushing/dilution patterns were essentially associated with the magnitude of storm events in Fuirosos. In contrast, the DOM quality change was more coupled to basal flow conditions in Oberer Seebach, while the storms were behind the DOC oscillations. This study attests to the importance of generating and analysing long-term and high-frequency biogeochemical series, which allow relationships between DOM and hydrology to be explored in intermittent headwater streams that are subjected to extreme hydrological regimes." -- TDX.

Download or read book Dissolved Organic Matter DOM Concentrations and Quality for Watershed Compartments in a Forested Mid Atlantic Watershed USA written by Nina Finger and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: While the importance of dissolved organic matter (DOM) constituents is well recognized we know very little about how these constituents vary across watershed compartments, influence the transport of dissolved organic carbon (DOC) and nitrogen (DON), and determine the mobility and bioavailability of DOM. We explore the concentrations and quality of DOM for ten watershed sources in a 12 ha forested catchment over a two-year period. DOM was evaluated for throughfall, litter leachate, soil water, shallow and deep groundwater, groundwater discharged from seeps, stream water and water in the hyporheic zone. Soil water samples included both free flowing soil water (using zero tension lysimeters) as well as soil pore water (using tension lysimeters). DOM quality was characterized using a suite of indices derived from UV-visible absorbance and parallel factor analysis (PARAFAC) modeling of fluorescence excitation-emission matrices (EEMs). DOM quality displayed a pronounced trend in watershed compartments especially as a function of soil depth. The humic, aromatic, and high molecular weight constituents of DOM decreased with soil depth while there was a concomitant percent increase in the protein-like DOM moieties. Principal component analyses (PCA) revealed that the differences in surficial watershed compartments were dictated by humic components while differences in groundwater sources were dictated by % total proteins. The increase in % total proteins with increasing soil depth indicated that in groundwater a greater fraction of DOM may be bioavailable compared to DOM in litter leachate and soil water. We did not find any conclusive evidence for C or N enrichment in any particular DOM quality pools. In addition, DOM quality displayed pronounced spatial differences. DOM in wetland groundwater was more aromatic and humic than that at the riparian location. This study also suggested that some spectrofluorometric indices (e.g. the humification index, HIX) may be preferable over others (e.g. specific UV absorbance, SUVA) for characterizing DOM quality.

Download or read book The Influence of Dissolved Organic Matter Composition on Its Reactivity in Natural and Engineered Systems written by Reid Milstead and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dissolved organic matter (DOM) is a complex heterogeneous mixture of organic compounds that is found in all water systems. DOM is derived from both terrestrial and microbial sources. The composition of DOM can vary greatly depending on a number of variables, including time of year, surrounding groundcover type, and water column depth. The characterization of DOM composition is increasingly performed using high-resolution mass spectrometry, although different instrumentation and techniques may yield different results. Importantly, DOM plays a key role in a number of chemical processes in both natural and engineered systems, such as the generation of carbon dioxide (CO2) from surface waters, the degradation of aquatic contaminants, and the formation of disinfection byproducts (DBPs) during drinking water treatment. The composition of DOM determines its reactivity in all of these processes. Using both bulk and high-resolution analytical techniques, the photooxidation of DOM can be explored. DOM compounds that are more oxidized and aromatic tend to be associated with the consumption of oxygen and the production of CO2. Bulk scale measurements show that DOM becomes less aromatic and lower in molecular weight as a result of partial photooxidation. High-resolution mass spectrometry also provides evidence of oxygen addition and the loss of CO2 from DOM during irradiation experiments. However, the chemical formulas that are most photolabile vary depending on the initial composition of DOM. Using light exposure experiments the kinetics of degradation of four contaminants were quantified for a large set of diverse waters. Using this information, we evaluated the relationships between indirect photolysis rate constants and the formation of photochemically produced reactive intermediates (PPRI) using linear regression analysis. Additionally, quencher experiments were performed to identify the PPRI associated with the degradation of each contaminant in all waters. Triplet state DOM (3DOM) and singlet oxygen (1O2) were identified as critical for atorvastatin, carbamazepine, and sulfadiazine, while hydroxyl radical (•OH) is important for benzotriazole. Our results suggest that quenching experiments should be used with caution due to the non-targeted nature of quenching compounds and the interconnection of PPRI. All of these factors result in probe compounds possibly overstating the importance of PPRI in the indirect photolysis of common contaminants. The characterization of DOM in drinking waters reveals a high degree of variability in DOM composition and reactivity with chlorine, particularly in groundwater samples. Despite the variability in DOM composition, novel DBPs with up to three halogen substituents are compositionally similar among all waters. These novel DBPs are positively correlated with trihalomethane and, to a lesser extent, the formation of haloacetonitriles. This suggests that some low molecular weight DBPs and novel DBPs detected via high-resolution mass spectrometry share similar aromatic precursors, providing evidence that low molecular weight DBPs are useful proxies for the formation of unknown, unidentified high molecular weight DBPs. Compared to Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS), Orbitrap MS yields significantly fewer formula matches and appears to have a bias towards sulfur-containing formulas and against nitrogen-containing formulas. Additionally, the choice of calibration method is particularly important for the less powerful Orbitrap MS. The matched formulas yielded from Orbitrap MS tend to be more oxidized and less highly saturated than those yielded by FT-ICR MS. Despite these differences, the formulas produced by both instruments tend to yield similar relative differences between samples, suggesting that Orbitrap MS is an acceptable replacement for FT-ICR MS in some cases.

Download or read book The Influence of Dissolved Organic Matter Composition on Its Reactivity in Natural and Engineered Systems written by Reid Milstead and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dissolved organic matter (DOM) is a complex heterogeneous mixture of organic compounds that is found in all water systems. DOM is derived from both terrestrial and microbial sources. The composition of DOM can vary greatly depending on a number of variables, including time of year, surrounding groundcover type, and water column depth. The characterization of DOM composition is increasingly performed using high-resolution mass spectrometry, although different instrumentation and techniques may yield different results. Importantly, DOM plays a key role in a number of chemical processes in both natural and engineered systems, such as the generation of carbon dioxide (CO2) from surface waters, the degradation of aquatic contaminants, and the formation of disinfection byproducts (DBPs) during drinking water treatment. The composition of DOM determines its reactivity in all of these processes. Using both bulk and high-resolution analytical techniques, the photooxidation of DOM can be explored. DOM compounds that are more oxidized and aromatic tend to be associated with the consumption of oxygen and the production of CO2. Bulk scale measurements show that DOM becomes less aromatic and lower in molecular weight as a result of partial photooxidation. High-resolution mass spectrometry also provides evidence of oxygen addition and the loss of CO2 from DOM during irradiation experiments. However, the chemical formulas that are most photolabile vary depending on the initial composition of DOM. Using light exposure experiments the kinetics of degradation of four contaminants were quantified for a large set of diverse waters. Using this information, we evaluated the relationships between indirect photolysis rate constants and the formation of photochemically produced reactive intermediates (PPRI) using linear regression analysis. Additionally, quencher experiments were performed to identify the PPRI associated with the degradation of each contaminant in all waters. Triplet state DOM (3DOM) and singlet oxygen (1O2) were identified as critical for atorvastatin, carbamazepine, and sulfadiazine, while hydroxyl radical (•OH) is important for benzotriazole. Our results suggest that quenching experiments should be used with caution due to the non-targeted nature of quenching compounds and the interconnection of PPRI. All of these factors result in probe compounds possibly overstating the importance of PPRI in the indirect photolysis of common contaminants. The characterization of DOM in drinking waters reveals a high degree of variability in DOM composition and reactivity with chlorine, particularly in groundwater samples. Despite the variability in DOM composition, novel DBPs with up to three halogen substituents are compositionally similar among all waters. These novel DBPs are positively correlated with trihalomethane and, to a lesser extent, the formation of haloacetonitriles. This suggests that some low molecular weight DBPs and novel DBPs detected via high-resolution mass spectrometry share similar aromatic precursors, providing evidence that low molecular weight DBPs are useful proxies for the formation of unknown, unidentified high molecular weight DBPs. Compared to Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS), Orbitrap MS yields significantly fewer formula matches and appears to have a bias towards sulfur-containing formulas and against nitrogen-containing formulas. Additionally, the choice of calibration method is particularly important for the less powerful Orbitrap MS. The matched formulas yielded from Orbitrap MS tend to be more oxidized and less highly saturated than those yielded by FT-ICR MS. Despite these differences, the formulas produced by both instruments tend to yield similar relative differences between samples, suggesting that Orbitrap MS is an acceptable replacement for FT-ICR MS in some cases.

Download or read book Dissolved Organic Matter Sources and Dynamics in an Agricultural Watershed written by Sandrine Journet Matiasek and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Agriculture is a dominant land use on Earth, but its impacts on dissolved organic matter (DOM) sources, processing, and fate remain relatively unclear. The goal of this research was to study DOM sources and dynamics in an irrigated agricultural watershed of Central Valley, California by 1) assessing the quantitative and qualitative impacts of organic matter (OM) desorption from sediments and soils, and by 2) generating an amino acids time series to link seasonal processes (natural and anthropogenic) to changes in stream DOM chemistry and reactivity. Abiotic desorption experiments revealed that mineral-bound organic carbon (OC) desorption is a predictable and finite process in agricultural surface waters, contributing 5 - 7% of the annual dissolved OC (DOC) export, with local maxima up to 50% of typical field runoff concentrations and 20% of winter storm DOC concentrations. The relevance of OM desorption was even more evident at the molecular level. Relative to mineral-bound OM, desorbed DOM was nitrogen-poor and depleted in amino acids and lignin. Distinct fractionation patterns of amino acids and lignin phenols led to a more acidic DOM pool that appeared substantially more degraded than particulate OM, with decreased mole fractions of basic amino acids, increased molar contributions of non-protein amino acids, decreased degradation index values, and increased proportions of acidic lignin phenols. If unaccounted for, the profound alteration of DOM composition incurred by desorption could lead to misinterpretations of indicators commonly used to assess the diagenetic state of OM. At the watershed scale, the role of land use and hydrologic controls on labile DOM dynamics was evidenced by elevated total hydrolyzable amino acid (THAA) concentrations throughout the low-discharge irrigation season and by seasonal compositional differences. DOM during winter baseflow was the most degraded, with the lowest THAA content and the lowest degradation index (DI), while winter storms and summer irrigation were two critical hydrologic regimes for DOM cycling with the largest amino acid contents, the largest proportions of basic amino acids, and the largest DI values, indicative of a relatively fresh DOM pool. The biogeochemical relevance of irrigation practices was therefore demonstrated by the mobilization of DOM similar in concentration and reactivity to DOM during winter storms.

Download or read book Temporal and Spatial Variability in the Quality of Dissolved Organic Matter in Ocean Systems written by Stuart Jerome Goldberg and published by ProQuest. This book was released on 2008 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt: Oceanic DOM is an important substrate that fuels heterotrophic bacterial activity, however, there is a paucity of data regarding the composition and quality of DOM in ocean systems. I analyzed the total carbohydrate (TCHO) and dissolved combined neutral sugar (DCNS) fractions of dissolved organic carbon (DOC), and mainly used TCHO and DCNS yields (% of DOC) to assess DOM quality over large temporal and spatial scales throughout the ocean.

Download or read book Characterization of Dissolved Organic Matter and Determination of Its Biogeochemical Significance in Coastal and Inland Water Bodies written by M.S. Sankar and published by . This book was released on 2019 with total page 153 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dissolved organic matter (DOM) is a major component of natural waters and provides essential nutrients for aquatic organisms. However, excess DOM in the water results in water quality issues and affects the aquatic life negatively. The present research evaluated the source, composition, reactivity, dynamics, and the spatial distribution of DOM in diverse water bodies using spectrofluorometric methods in tandem with multivariate statistics. The study was conducted in the inland and coastal water bodies of Mississippi, Louisiana, and Alabama over a period of three years (2016 to 2018). Surface water samples were collected from spatially separated waterbodies with diverse land use and land cover classes. In addition, reactivity of DOM was assessed by conducting a series of laboratory experiments at varying magnitudes of sunlight and bacterial activity. Spatial distribution and mobility of DOM, nutrients and trace elements with respect to land cover classes and hydrology was evaluated using watershed delineation and multivariate statistics. Results suggest that microbial humic-like or protein-like DOM compositions derived from microbial/anthropogenic sources were less reactive than the terrestrial humic-like compositions originated from forests and woody wetlands. Furthermore, the sunlight was the major factor causing the degradation of DOM in the water bodies, while temperature had a minor effect. Additionally, the results also suggest that livestock fields in the pastoral and rangelands release a high amount of microbial humic-like DOM along with nutrients such as phosphates and nitrates into the water bodies. Present research identified the presence of four types of DOM in the study areas and were terrestrial humic-like, microbial humic-like, soil-derived humic-like and protein-like compositions. Additionally, trace element availability and mobility of coastal areas is influenced by local hydrology and precipitation. Research also identified forested areas as the major source of DOM to the water bodies of Mississippi. In conclusion, present research found that watershed land use and land cover, hydrology, and climate control the dynamics of DOM, other nutrients, and trace element delivery to the water bodies, while combined effects of light and bacteria are more efficient in reprocessing DOM chemistry within the waterbody.

Download or read book CHARACTERIZATION AND TRANSFORMATION OF DISSOLVED ORGANIC MATTER DOM IN ENGINEERED ULTRAVIOLET UV PHOTOLYSIS AND UV BASED ADVANCED OXIDATION PROCESSES written by and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract : Dissolved organic matter (DOM) is a complex mixture of heterogeneous surrogate organic compounds and includes natural organic matter (NOM), dissolved organic nitrogen (DON), dissolved organic phosphorous (DOP) and soluble microbial products (SMP). DOM plays a key role in moderating the aquatic biogeochemical cycle in freshwater ecosystems. Shedding light into the composition of freshwater DOM will aid in understanding the biogeochemical dynamics of freshwater ecosystems and consequently the role of DOM as a local climate regulator. An increase in de facto wastewater reuse has made the removal of DOM present in wastewater imperative, as DOM can be potentially toxic to human health. Additionally, wastewater DOM can reduce the efficiency of the treatment performances of advanced treatment techniques such as UV-advanced oxidation processes (UV-AOPs), as DOM can screen UV light and scavenge reactive radical species, thereby reducing the concentrations of reactive radical species that are available to destroy the target trace organic contaminants. Therefore, understanding the molecular composition of DOM present in wastewater as well as in the effluent to surface water is crucial, as this knowledge will aid in upgrading treatment performances and subsequently contribute towards the effective removal of target contaminants. In this regard, ultrahigh resolution mass spectrometry was used to evaluate the molecular composition of DOM present in wastewater as well as in the effluent to surface water. DOM composition is characterized in terms of H/C and O/C elemental ratios and double bond equivalents (DBEs). Effluent DOM was found to comprise of a higher number of unsaturated aromatic species relative to wastewater DOM. Species with nitrogen and sulfur heteroatoms are less common among effluent DOM relative to wastewater DOM. In order to better understand the interference of DOM in the treatment performances of individual UV-AOPs, the transformation of a standard DOM isolate, i.e. Suwannee River Fulvic Acid (SRFA) as well as municipal effluent wastewater DOM (EfOM) were investigated in UV/H2O2, UV/free chlorine and UV/persulfate AOPs using ultrahigh resolution mass spectrometry. The changes in the H/C and O/C elemental ratios, DBEs, and the low-molecular-weight transformation product concentrations reveal that different DOM and EfOM transformation patterns are induced by each UV-AOP. DOM and EfOM transformation routes induced by hydroxyl, chlorine and sulfate radicals were mechanistically elucidated by comparing the known reactivities of each active radical species with specific organic compounds. In the UV/H2O2 system, distinct transformation of aliphatic components of DOM and transformation of olefinic as well as aliphatic components of EfOM was observed. In the UV/free chlorine system, transformation of aliphatic as well as olefinic species of DOM and transformation of aromatic species of EfOM was observed. Transformation of aromatic and olefinic moieties of both DOM as well as EfOM was observed in the UV/persulfate system. Transformation products of DOM such as chlorinated compounds are of concern due to their adverse health impacts. However, only a small portion of these compounds have been well-characterized, thus necessitating the characterization of the unknown compounds. Plausible structural information about chlorinated compounds produced from UV/free chlorine triggered transformation of DOM is provided through the means of tandem mass spectrometry (MS/MS) with ultrahigh resolution mass analysis. The two compounds of interest were hypothesized to be composed of alcohol, carboxylic acid and aldehyde/ketone groups.

Download or read book Watershed Export of Dissolved Organic Matter in Response to Anthropogenic and Hydroclimatic Drivers in Subtropical Streams and Rivers written by Shuo Chen and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Dissolved organic matter (DOM) is an assemblage of heterogeneous organic compounds that play important roles in terrestrial and aquatic ecosystems. In this dissertation, I investigated changes in the amount, source, composition, lability, and ecological functions of stream water DOM in response to agricultural land use, hydrological events, and downstream transport and transformation in the southeastern United States. The dissertation includes three stand-alone studies presented in Chapters 2, 3 and 4, respectively. In Chapter 2, I evaluated the effects of hurricane-induced storm events on the quantity and quality of DOM exported from ten watersheds of various physical and land-use characteristics within five Gulf and South Atlantic states. We found that large storms can significantly enhance the concentrations and yields of terrestrially-derived dissolved organic carbon (DOC) and nutrients in streams and rivers but decrease the percentage bioreactive DOC. This study demonstrates that extreme weather and climate events can lead to rapid, ecosystem-level disturbances that significantly shift energy and nutrient availability within drainage networks. The objective of Chapter 3 was to quantify the relative importance of agricultural land use and natural hydroclimatic drivers in affecting the quality and quantity of DOM in a group of 15 streams draining watersheds of a gradient of agricultural land use. The partial least square path modeling (PLS-PM) identified that agricultural land use increased stream water DOM quantity primarily through increasing allochthonous carbon sources. This study demonstrates that structural equation modeling is a powerful tool that should be more widely adopted to distinguish among multiple drivers and mechanisms regulating freshwater biogeochemistry. Chapter 4 investigated the longitudinal transformations of DOM in relation to ecosystem metabolism along a fluvial section including 3rd order, 7th and 8th order streams. From upstream to downstream, DOC concentrations and the relative contributions of freshly-produced DOM increased. The gross primary productivity was positively correlated with the contributions of autochthonous DOM, yet the ecosystem respiration did not vary with the quantity or quality of DOM. This study highlights the complexity of DOM transformations in relation to stream metabolism along the river continuum. Collectively, the three independent but connected studies reveal the complexity and sensitivity of inland water DOM in response to hydroclimatic and anthropogenic drivers. The findings provide new insights into potential shifts in energy and substrates exported across the terrestrial-aquatic boundary due to human activities and climate change and how these shifts can alter water quality and fluvial biogeochemical functions.