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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Optical Properties and Distributions of Dissolved Organic Matter in the Kaoping Estuary and Coastal Zone

Yang, Hsin-mei 11 September 2006 (has links)
Chromophoric dissolved organic matter (CDOM) is a part of total dissolved organic matter (DOM), playing an important role in marine carbon cycling. Thus, a better description of the fates of DOM may increase our understanding of DOM sources and sinks in the coastal zone. This study aims to explore the distributions, transformation and transport of CDOM in the Kaoping Estuary-Canyon system. The water exchange time (£n) of Kaoping estuarine water ranged from 0.1 to 2.2 day, being much shorter in the wet season than in the dry season. The riverine materials may be flushed out of the estuary without significant transformation in the estuary during the wet season, thus, distributions of nutrients and dissolved organic carbon(DOC) were largely determined by the mixing process. However, distributions of materials may be controlled by biogeochemical processes during the dry season, due to longer water residence time. In early spring, higher temperature and longer water residence time may be responsible for the effective decay of organic matter and nitrate reduction and/or denitrification in the estuary. Nonconcervative distribution (addition) of protein-like CDOM in early spring appeared to be derived from biological and/or sewage sources. In the wet season, the distribution of terrestrial humic-like CDOM was not only controlled by the conservative mixing between river water and coastal water, but also influenced by a release from total suspended matter (TSM). In the dry season, the CDOM was slightly removed from the photobleaching process occurring around the river mouth, which may be regarded as the major sink process of CDOM. In the Kaoping Canyon, the addition of terrestrial humic-like CDOM from TSM resuspension is significant only in the deep water. The photobleaching reaction occurred only in the limited area during the dry season, and gave little impact on CDOM concentration. There were no significant in-situ addition and removal in the coastal surface waters suggesting that the terrestrial humic-like CDOM could be a conservative tracer of terrestrial DOM in the coastal zone. The terrestrial inputs of DOM may play a minor role in determining distributions of protein-like CDOM in the Kaoping Canyon. On the contrary, distributions were primarily controlled by biological sources. Nutrient inputs from the Kaoping River may be responsible for increasing the primary production in the surface water of coastal zone, linking to a potential source of protein-like CDOM. Significant correlations were found between DOC and tryptophan for those surface waters with higher fluorescence intensity. The results suggested that tryptophan may be derived from biological origins. DOC released from phytoplanktons generally contains lower Tyrosine/Tryptophan ratio than that released from microbes. The Tyrosine/Tryptophan ratio may be used as an indicator for the condition of microbial community.
2

Effects of forestry on stream water chemistry during autumn : A before and after comparison between a reference and two streams with clear-cut watershed areas

Linda, Engström January 2013 (has links)
Forestry is a large-scale business in many countries, and in northern Sweden a large portion of the Boreal forests is cut. Yet very few studies have investigated the impacts of forestry on the vast number of receiving stream waters. This study has therefore investigated the impacts of forestry, through clear-cutting, on stream water chemistry during autumn conditions in northern Sweden. The study compares the parameters water height, absorbance, dissolved organic carbon, total dissolved nitrogen and total phosphorus in two inlet streams in recently deforested sites, <1 year ago, and an undisturbed reference inlet stream. The disturbed inlet streams are compared to the reference inlet stream the year before and after clear-cutting. This study shows that during a 15- day period from late August to the beginning of September, water height was increased in both disturbed inlet streams, indicative of a higher run-off post-harvest. Absorbance showed a large decrease post-harvest in the disturbed inlet streams. Total dissolved nitrogen and total phosphorus concentrations decreased slightly after clear-cut in both disturbed inlet streams. The effect was probably larger for phosphorus, since the seasonal variation in the reference was larger in 2013. DOC concentrations increased slightly in one of the disturbed inlet streams in 2013, but decreased slightly in the other disturbed inlet stream. The increased run-off was therefore not followed by a higher DOC and nutrient leakage. Results suggest that during a short period in the autumn, harvest does not seem to lead to increased DOC and nutrient losses to receiving stream waters.
3

Veränderungen des gelösten organischen Kohlenstoffs (DOC) im Verlauf der Aufbereitung reduzierter Grundwässer zu Trinkwasser

Köneke, Frank January 2008 (has links)
Zugl.: Hamburg, Techn. Univ., Diss., 2008
4

Methods for reduction of trihalomethanes in the rural municipality of Macdonald potable water supply system

Cho, Steven Y. F. 13 January 2010 (has links)
Monitoring data for potable water in the R.M. of Macdonald regional water system indicates elevated levels of chlorine disinfection by-products (DBPs), trihalomethanes (THMs). Dissolved Organic Carbon (DOC) and chlorine dose are the key precursors for the formation of THMs. Currently, the DOC is not removed efficiently at the Sanford water treatment plant, which supplies the R.M.’s potable water distribution system. The raw water DOC concentration incoming to the plant varied from 8.9mg/L to 31.8mg/L during this study. Sanford treated water effluent contained an average DOC of 6.5mg/L and the THM levels ranged from 86.6ppb to 175.7ppb. One of the objectives of this study was to conduct jar tests to optimize Sanford’s water treatment process to improve removal of DOC. Optimization of the coagulation process successfully reduced the DOC level in the plant effluent by 51% during the summer and 34% in the winter. The DOC reduction resulted in a THM reduction of 73.5ppb in the summer and 59.9ppb during the winter. Results showed that removal of 1mg/L of DOC eliminates 26.8ppb of THMs in summer and 11.9ppb during the winter. Another goal of this project was to investigate the relationship between THMs and their precursors, which includes: water DOC, free chlorine residual, and the chlorine contact time. Water samples were strategically collected throughout the Sanford regional water distribution system; the samples were tested for DOC, UV254, SUVA, chlorine residual, and contact time. A linear relationship between THM formation and chlorine contact time (R2 of 0.92) was found. This indicates that the content of THMs can be decreased by reducing the amount of time the water stays in the distribution system.
5

Methods for reduction of trihalomethanes in the rural municipality of Macdonald potable water supply system

Cho, Steven Y. F. 13 January 2010 (has links)
Monitoring data for potable water in the R.M. of Macdonald regional water system indicates elevated levels of chlorine disinfection by-products (DBPs), trihalomethanes (THMs). Dissolved Organic Carbon (DOC) and chlorine dose are the key precursors for the formation of THMs. Currently, the DOC is not removed efficiently at the Sanford water treatment plant, which supplies the R.M.’s potable water distribution system. The raw water DOC concentration incoming to the plant varied from 8.9mg/L to 31.8mg/L during this study. Sanford treated water effluent contained an average DOC of 6.5mg/L and the THM levels ranged from 86.6ppb to 175.7ppb. One of the objectives of this study was to conduct jar tests to optimize Sanford’s water treatment process to improve removal of DOC. Optimization of the coagulation process successfully reduced the DOC level in the plant effluent by 51% during the summer and 34% in the winter. The DOC reduction resulted in a THM reduction of 73.5ppb in the summer and 59.9ppb during the winter. Results showed that removal of 1mg/L of DOC eliminates 26.8ppb of THMs in summer and 11.9ppb during the winter. Another goal of this project was to investigate the relationship between THMs and their precursors, which includes: water DOC, free chlorine residual, and the chlorine contact time. Water samples were strategically collected throughout the Sanford regional water distribution system; the samples were tested for DOC, UV254, SUVA, chlorine residual, and contact time. A linear relationship between THM formation and chlorine contact time (R2 of 0.92) was found. This indicates that the content of THMs can be decreased by reducing the amount of time the water stays in the distribution system.
6

Bakteriell produktion i humösa istäckta sjöar i norra Sverige

Magnusson, Erik January 2014 (has links)
The main purposes of this study were to 1) quantify bacterial production in winter during ice conditions, and 2) to compare these production measures with values measured from summer and open water conditions in three humic lakes situated in northern Sweden. Another purpose of this study was to 3) examine whether clear-cutting significantly affected bacterial production or water chemistry in two lakes situated in catchments were a large part of the forest had been removed through logging compared to an undisturbed reference lake. In winter (March/April 2014), the bacterial production ranged from 0, 7 - 2, 2 µgC/L/day and in the summer of 2013 the production values was 4 – 10 times higher. The main reason for lower bacterial production in winter was ascribed to lower water temperatures as well as to older and more recalcitrant DOC, as there were no significant differences in total dissolved nitrogen or DOC concentration or -quality, that could explain a lower production compared to summer. It was not possible to detect any effects of the clear-cutting using the approach of only comparing between the lakes situated in clear-cut watersheds, with an undisturbed reference lake.
7

Dissolved organic carbon in aquitard environments : properties, complexation, and transport

Reszat, Thorsten 22 May 2007
Clay-rich glacial till aquitards are widespread throughout the northern hemisphere. Due to their low hydraulic conductivity, these geologic units are commonly used to contain wastes. Dissolved Organic Carbon (DOC) in natural environments influences the speciation and mobility of contaminants, such as heavy metals and radionuclides, and is present in high concentrations in clay-rich tills (5 to 150 mg l-1). Detailed knowledge of the influence of DOC on the long-term stability, speciation, and mobility of elements is lacking. Studies in this thesis characterize the properties and function of DOC with respect to element speciation and transport at the King research site, an archetypal clay-till aquitard in Saskatchewan, Canada. Characterization of DOC using Asymmetrical Flow-Field Flow Fractionation (AsFlFFF) with on-line UV and DOC detection demonstrated the molecular weight (Mw) of DOC within the aquitard environment is low, ranging from 1160 to 1286 daltons (Da), and the relative amount of aromatic carbon in aquitard DOC is lower than in surface water DOC. These findings imply the complexation ability of DOC in aquitards is lower than surface water DOC. DOC aromaticity decreased with depth in the aquitard, while Mw remained constant. DOC Mw in other aquitards investigated was comparably low (1470-1630 Da). Coupling AsFlFFF with on-line ICP-MS analysis allowed the identification of Fe, U and Zn associated with the DOC, and demonstrated that <4% of total aqueous elements tested at the King site were complexed with DOC. Experimental and numerical modeling results demonstrate the low masses of metals (Cu, Mn, Mo, Ni, Sr, U and Zn) complexed with the DOC can be attributed to competitive complexation with carbonate and sulphate ligands naturally present in the pore water. The in-situ association constant, Kd, for U and Zn as determined by complexation experiments decreased with depth in the aquitard and was attributed to the corresponding decrease in DOC aromaticity. The maximum mass of complexation of U and Zn to DOC takes place at pH 3-6, and decreases above and below this pH range (range tested: pH 1.3-10). These results were supported by geochemical modeling and suggest the complexation of aqueous metals by DOC should be limited in ground water environments of similar chemistries. Laboratory transport studies using double reservoir diffusion cells showed DOC and other similarly sized colloidal material can diffuse through the matrix at the King site aquitard. The effective pore throat diameter in the matrix media was determined to be 2 - 2.2 nm and travel times of colloids increased with increasing colloidal diameter. Colloids >2 nm were prevented from movement in the till by sieving mechanisms, which suggests bacteria and viruses as well as larger colloids should not migrate through till aquitards. Due to preferential sieving of larger Mw DOC, DOC in aquitard environments is typified by a small diameter compared with surface water DOC, and a small range in hydrodynamic diameter and Mw.
8

Dissolved organic carbon in aquitard environments : properties, complexation, and transport

Reszat, Thorsten 22 May 2007 (has links)
Clay-rich glacial till aquitards are widespread throughout the northern hemisphere. Due to their low hydraulic conductivity, these geologic units are commonly used to contain wastes. Dissolved Organic Carbon (DOC) in natural environments influences the speciation and mobility of contaminants, such as heavy metals and radionuclides, and is present in high concentrations in clay-rich tills (5 to 150 mg l-1). Detailed knowledge of the influence of DOC on the long-term stability, speciation, and mobility of elements is lacking. Studies in this thesis characterize the properties and function of DOC with respect to element speciation and transport at the King research site, an archetypal clay-till aquitard in Saskatchewan, Canada. Characterization of DOC using Asymmetrical Flow-Field Flow Fractionation (AsFlFFF) with on-line UV and DOC detection demonstrated the molecular weight (Mw) of DOC within the aquitard environment is low, ranging from 1160 to 1286 daltons (Da), and the relative amount of aromatic carbon in aquitard DOC is lower than in surface water DOC. These findings imply the complexation ability of DOC in aquitards is lower than surface water DOC. DOC aromaticity decreased with depth in the aquitard, while Mw remained constant. DOC Mw in other aquitards investigated was comparably low (1470-1630 Da). Coupling AsFlFFF with on-line ICP-MS analysis allowed the identification of Fe, U and Zn associated with the DOC, and demonstrated that <4% of total aqueous elements tested at the King site were complexed with DOC. Experimental and numerical modeling results demonstrate the low masses of metals (Cu, Mn, Mo, Ni, Sr, U and Zn) complexed with the DOC can be attributed to competitive complexation with carbonate and sulphate ligands naturally present in the pore water. The in-situ association constant, Kd, for U and Zn as determined by complexation experiments decreased with depth in the aquitard and was attributed to the corresponding decrease in DOC aromaticity. The maximum mass of complexation of U and Zn to DOC takes place at pH 3-6, and decreases above and below this pH range (range tested: pH 1.3-10). These results were supported by geochemical modeling and suggest the complexation of aqueous metals by DOC should be limited in ground water environments of similar chemistries. Laboratory transport studies using double reservoir diffusion cells showed DOC and other similarly sized colloidal material can diffuse through the matrix at the King site aquitard. The effective pore throat diameter in the matrix media was determined to be 2 - 2.2 nm and travel times of colloids increased with increasing colloidal diameter. Colloids >2 nm were prevented from movement in the till by sieving mechanisms, which suggests bacteria and viruses as well as larger colloids should not migrate through till aquitards. Due to preferential sieving of larger Mw DOC, DOC in aquitard environments is typified by a small diameter compared with surface water DOC, and a small range in hydrodynamic diameter and Mw.
9

Organic Carbon Biogeochemistry Around the Area of Luzon Strait

Hsiang, Chin-Ying 11 September 2006 (has links)
Luzon Strait is the deepest channel for water exchange between the Northern South China Sea (NSCS) and the West Philippine Sea (WPS). It is important to investigate the seasonal and spatial distributions and the biogeochemical processes of organic carbon, nitrogen and phosphorus in Luzon Strait. During the summer season, the flow of Kuroshio water into the SCS through the Bashi Channel was restricted due to the prevailing southwest monsoon. However, during the winter season, the flow of Kuroshio water into the SCS through the Bashi Channel was enhanced due to the prevailing northeast monsoon. The characteristics of water types across the Bashi Channel depend highly upon the water exchange between the WPS and the NSCS. Distributions of dissolved organic carbon (DON), nitrogen (DON) and phosphorus (DOP) in the euphotic zone generally show an increasing trend from the WPS to the NSCS. The same distribution was pattern found for particulate organic carbon (POC) and nitrogen (PN). The stichomythic ratio (C/N/P) of dissolved organic matter in the euphotic layer was lower in spring than in autumn. The reason may be that the Kuroshio water flowing through the Luzon Strait is much less in spring than in autumn. The ratios of DIN/DIP were much lower than the Redfield ratio (16) suggesting a status of N-limitation in the euphotic zone. The DOC/DON ratios, however, were much higher than the Redfield ratio (6.6). These results implied that DOM might have played an important role in modulating nutrient cycling and food web dynamics in the euphotic zone of study area. The subsurface water (100-600m) of the NSCS, west of Luzon, was more enriched with POM than that of the WPS. However, the situation was reversed in the intermediate water (600-1500m). Correlations are significant between POC and Chl-a in spring and summer, suggesting that phytoplankton abundance may primarily control the distribution of POC in the euphotic zone. The DOC/POC ratio was inversely correlated with Chl-a in both spring and summer. The ratios generally decreased to a constant value as the Chl-a concentration increased to a higher level, implying a higher biological contribution for POC than for DOC. Correlations were also significant between TEP/POC and Chl-a. The ratio of TEP-C/POC in the euphotic layer showed a decreasing trend from the NSCS to the WPS, implying a significant influence of phytoplankton productivity on TEP distribution. During the study period, the integrated gross production (IGP) and integrated dark community respiration (IDCR) in the study area were in the range of 3056~7094 mg C m-2 d-1 and 3372~8901 mg C m-2 d-1 in autumn, respectively; 1740~5338 mg C m-2 d-1 and 2628~7685 mg C m-2 d-1 in spring, respectively; 2149~6110 mg C m-2 d-1 and 4391~8896 mg C m-2 d-1 in summer, respectively. During the autumn and summer season, there were no significant correlations between GP (DCR) and temperature, PAR, salinity, Chl-a, DOC and POC, possibly resented from the effect of typhoon. During the spring season without the typhoon effect, there were significant correlations between GP (DCR) and salinity, Chl-a, DOC and POC. The ratio of IGP/IDCR is an indicator of net ecosystem production, with>1 for the autotrophic system and <1 for the heterotrophic system. The ratio was <1 for all stations indicating a heterotrophic system. However, the ratio was slightly higher in autumn than in spring and summer.
10

Biologically relevant characteristics of dissolved organic carbon (DOC) from soil

Bowen, Susan January 2006 (has links)
Of the organic matter in soils typically < 1% by weight is dissolved in the soil solution (dissolved organic matter; DOM). DOM is a continuum of molecules of various sizes and chemical structures which has largely been operationally defined as the fraction of total organic carbon in an aqueous solution that passes through a 0.45 µm filter. Although only representing a relatively small proportion, it represents the most mobile part of soil organic carbon and is probably enriched with highly labile compounds. DOM acts as a source of nutrients for both soil and aquatic micro-organisms, influences the fate and transport of organic and inorganic contaminants, presents a potential water treatment problem and may indicate the mobilisation rate of key terrestrial carbon stores. The objective of this research was to ascertain some of the biologically relevant characteristics of soil DOM and specifically to determine: (1) the influence of method and time of extraction of DOM from the soil on its biochemical composition and concentration; (2) the dynamics of DOM biodegradation; and, (3) the effects of repeated applications of trace amounts of DOM on the rate of soil carbon mineralization. To examine the influence of method and time of extraction on the composition and concentration of DOM, soil solution was collected from a raised peat bog in Central Scotland using water extraction, field suction lysimetry, and centrifugation techniques on a bimonthly basis over the period of a year (Aug 2003 – Jun 2004). Samples were analysed for dissolved organic carbon (DOC), dissolved organic nitrogen (DON), protein, carbohydrate and amino acid content. For all of the sampled months except June the biochemical composition of DOC varied with extraction method, suggesting the biological, chemical and/or physical influences on DOC production and loss are different within the differently sized soil pores. Water-extractable DOC generally contained the greatest proportion of carbohydrate, protein and/or amino acid of the three extraction methods. Time of extraction had a significant effect on the composition of water- and suction-extracted DOC: the total % carbohydrate + protein + amino acid C was significantly higher in Oct than Dec, Feb and Jun for water-extracted DOC and significantly greater in Dec than Aug, Apr and Jun for suction-extracted DOC. There was no significant change in the total % carbohydrate + protein + amino acid C of centrifuge-extracted DOC during the sampled year. Time of extraction also had a significant effect on the % protein + amino acid N in water- and centrifuge-extracted DON: Oct levels were significantly higher than Feb for water-extracted DON and significantly higher in Aug and Apr for centrifuge-extracted DON. Concentrations of total DOC and total DON were also found to be dependent on time of extraction. DOC concentrations showed a similar pattern of variation over the year for all methods of extraction, with concentrations relatively constant for most of the year, rising in April to reach a peak in Jun. DON concentrations in water- and centrifuge-extracted DON peaked later, in Aug. There were no significant seasonal changes in the concentration of suction-extracted DON. A lack of correlation between DOC and DON concentrations suggested that DOC and DON production and/or loss are under different controls. Laboratory-based incubation experiments were carried out to examine the dynamics of DOC biodegradation. Over a 70 day incubation period at 20oC, the DOM from two types of peat (raised and blanket) and four samples of a mineral soil (calcaric gleysol), each previously exposed to a different management strategy, were found to be comprised of a rapidly degradable pools (half-life: 3 – 8 days) and a more stable pool (half-life: 0.4 to 6 years). For all soil types/treatments, excepting raised peat, the total net loss of DOC from the culture medium was greater than could be accounted for by the process of mineralization alone. A comparison between net loss of DOC and loss of DOC to CO2 and microbial biomass determined by direct microscopy suggested that at least some of the differences between DOC mineralised and net DOC loss were due to microbial assimilation and release. Changes in the microbial biomass during the decomposition process showed proliferation followed by decline over 15 days. The protein and carbohydrate fractions showed a complex pattern of both degradation and production throughout the incubation. The effects of repeated applications of trace amounts of litter-derived DOC on the rate of carbon mineralization over a 35 day period were investigated in a laboratory based incubation experiment. The addition of trace amounts of litter-derived DOC every 7 and 10.5 days appeared to ‘trigger’ microbial activity causing an increase in CO2 mineralisation such that extra C mineralised exceeded DOC additions by more than 2 fold. Acceleration in the rate of extra C mineralised 7 days after the second addition suggested that either the microbial production of enzymes responsible for biodegradation and/or an increase in microbial biomass, are only initiated once a critical concentration of a specific substrate or substrates has been achieved. The addition of ‘DOC + nutrients’ every 3.5 days had no effect on the total rate of mineralization. To date DOC has tended to be operationally defined according to its chemical and physical properties. An understanding of the composition, production and loss of DOC from a biological perspective is essential if we are to be able to predict the effects of environmental change on the rate of mineralization of soil organic matter. This research has shown that the pools of DOC extracted, using three different methods commonly used in current research, are biochemically distinct and respond differently to the seasons. This suggests some degree of compartmentalisation of biological processes within the soil matrix. The observed similarities between the characteristics of the decomposition dynamics of both peatland and agricultural DOC suggests that either there is little difference in substrate quality between the two systems or that the microbial community have adapted in each case to maximise their utilisation of the available substrate. The dependency of the concentration and biochemical composition of DOC on the seasons requires further work to ascertain which biotic and/or abiotic factors are exerting control. Published research has focussed on factors such as temperature, wet/dry cycles, and freeze/thawing. The effect of the frequency of doses of trace amounts of DOC on increasing the rate of soil organic C mineralization, evident from this research, suggests that the interval between periods of rainfall may be relevant. It also emphasises how it can be useful to use knowledge of a biological process as the starting point in determining which factors may be exerting control on DOC production and loss.

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