No description available.

Over a hundred million people across the globe, and particularly in Asia, are chronicallyexposed to high concentrations (>10 ppb) of geogenic arsenic (As) in shallow reducinggroundwaters utilised as drinking water. It is widely accepted that As mobilisation fromsediments into these groundwater requires active metal-reducing microbes and electrondonors such as organic matter (OM). Although OM have been characterised in fewaquifers, there is a dearth of data on other As rich aquifers.In this work, we further investigate the correlation between As release from aquifers andthe OM/microbial communities present. The key findings of this work are:i. OM in Vietnamese and Taiwanese As hotspot areas originates from multiple sources.This is comparable to previous studies in Cambodia and West Bengal, indicating thatOM originates from similar sources in all the areas studied up to date, regardless ofthe age (Holocene/Pleistocene) and the sediment source (Himalayas/non-Himalayas).This suggests that similar electron donors, such as petroleum derived HMW nalkanes,are present in all these groundwater aquifer sediments.ii. No noticeable differences in OM biomarker distribution patterns were observedbetween sediments from two contrasting groundwater As concentration sites (e.g. <10 ppb; Pleistocene and up to 600 ppb; Holocene) in Vietnam, suggesting thatarsenic mobilisation is not associated with a specific OM source at these sites. Inaddition, no microbial activity was determined in these two sites suggesting thatother abiotic factors could lead to As release.iii. Microbiological process of dissimilatory As(V) reduction is active in microcosmexperiments using non-Himalayan Taiwanese sediments, despite low groundwaterAs concentrations, causing the release of As into the groundwater. However, Asrelease in these sediment slurries is not controlled by a specific source of the lipidderived OM, suggesting that other electron donors, not analysed in present studycould be contributing/controlling the rate of As release; and/or that multiple fractionsof the lipid derived OM are used as electron donors in this process.iv. Artificial maturation experiments indicated that a fully 13C-lablled kerogen analoguecan be obtained by using 13C-labelled cyanobacteria biomass as a starting material.However, this kerogen analogue had some differences when compared to the naturalmaterial, suggesting that an artificial degradation precursor step, prior to the actualmaturation process, might be required to generate analogues that better resemble thenatural kerogen.v. 13C-labelled substrates (hexadecane and kerogen) incubation experiments revealedthat As(III) release in all microcosms was microbially driven. Very low 13C-n-alkaneincorporation was observed in association with As release, suggesting that otherelectron donors could be mediating this process. In contrast, kerogen did not haveany effect on As release. Moreover, As(V) amendments enhanced the degradation ofthe shorter carbon chain length n-alkanes more than the longer ones, suggesting thatthese are more important electron donors in the process of As release than the longerones.

Dissolved organic matter (DOM) is crucial to carbon and nutrient biogeochemical cycling in the marine environment because it helps fuel heterotrophic microbial activity by providing substrates for degradation and remineralization. This study shows that substantial production of DOM in Texas estuaries can result from the solar radiation-enhanced dissolution (photodissolution) of particulate organic matter (POM). Experimental results showed that 0.4-6.6 mg C L⁻¹gsed⁻¹ of dissolved organic carbon (DOC) and 0.03-0.93 mg N L⁻¹gsed⁻¹ of total dissolved nitrogen (TDN) can be produced from irradiated sediment suspensions within 24 hours, and further that photodissolution may augment DOC and TDN loads in Texas estuarine waters by as much as 3-85% and 4-75%, respectively. Photodissolution can also enhance the optical thickness of the water column via the release of chromophoric dissolved organic matter (CDOM), which may subsequently further enhance photochemical processes in surrounding waters. Photoproduced CDOM appears to be of relatively high molecular weight and dominantly exhibits humic-like fluorescence, suggesting that photodissolution primarily occurs for humic moieties. Photodissolution was also observed for sterilized sediment suspensions, indicating that photochemical degradation of POM is the primary pathway of DOM production during photodissolution, as opposed to microbial mediated degradation or stimulation of benthic primary production by benthic phytoplankton or algae. Environmental and mechanistic factors controlling the extent of photodissolution in Texas estuaries may include sediment desiccation, water organic content, and sediment characteristics (organic content and lability of POM). Desiccated-rewetted sediments suspended in artificial seawater under solar irradiation produced ~40% more DOC and TDN than wet sediments, indicating the sediment dry-wet cycle may alter the 3-D structure of sediment grain matrices and thus might be a major controlling factor of photodissolution in salt marsh systems. The organic content of water used in sediment suspensions did not significantly influence DOC or TDN photoproduction by itself, but the combined influence of water organic content and sediment dry-rewet event played a substantial role in controlling the extent of photodissolution. In contrast to the results in artificial seawater, wet sediments produced slightly more DOC ([Delta]DOC=0.10 mg C gsed⁻¹) and substantially more TDN ([Delta]TDN=0.14 mg N gsed⁻¹) than dry-rewetted sediments in organic-rich Nueces Marsh water during 24 hours of photoincubation. Photodissolution dominantly produced humic-like DOM even though biologically labile organic matter was available in sediments, indicating that photochemical reactions preferentially occur with humic-like rather than protein-like organic matter. DOC and TDN production during photodissolution was strongly proportional to the amount of POC in sediment suspensions. On average, 69.2 ± 11.0 mg C of DOC and 9 ± 3.1 mg N of TDN was produced from 1 g of organic carbon in sediment suspensions after 24 hours of photodissolution. / text

The main objective of this thesis was to develop statistical and analytical methods for untargeted analyses of complex environmental matrices like soil and sediment. Untargeted analyses are notoriously difficult to perform in matrices like soil and sediment because of the complexity of organic matter composition within these matrices. This thesis aimed to (1) Develop and compare extraction methods for untargeted analyses of soil and sediment while also developing data handling and quality control protocols; (2) Investigate novel applications of untargeted analyses for environmental classification and monitoring; and (3) Investigate the experimental factors that can influence the organic matter composition of untargeted extractions. CHAPTER TWO is a literature review of metabolomics protocols, and these protocols were incorporated into a proposed workflow for performing untargeted analysis in oil, soil, and sediment. This thesis contains the first application of untargeted analysis to freshwater lake sediment organic matter (i.e. sedimentomics) in CHAPTER THREE, and this has implications for discovering new biomarkers for paleolimnology (APPENDIX ONE). I demonstrated successful extraction methods for both sedimentomics and soil metabolomics studies in CHAPTER THREE and CHAPTER FIVE, respectively, using the proposed workflow from CHAPTER TWO. I also applied sedimentomics to the classification of lake sediments using machine learning and geostatistics based on sediment organic matter compositions in CHAPTER FOUR; this was a novel application of sedimentomics that could have implications for ecosystem classifications and advance our knowledge of organic matter cycling in lake sediments. Lastly, in CHAPTER FIVE I determined microbial activity, extraction method, and soil type can all influence the composition of soil organic matter extracts in soil metabolomics experiments. I also developed novel quality controls and quantitative methods that can help control these influences in CHAPTER FIVE and APPENDIX THREE. APPENDIX TWO was written in collaboration with multiple researchers and is a review of all “omics” types of analyses that can be performed on soil or sediment, and how methods like the untargeted analysis of soil and sediment organic matter can be linked with metagenomics, metatranscriptomics, and metaproteomics for a comprehensive metaphenomics analysis of soil and sediment ecosystems. In CHAPTER SIX the conclusions and implications for each chapter and overall for this thesis are detailed and I describe future directions for the field. In the end the overall conclusions of this thesis were: 1) Quality controls are necessary for sedimentomics and soil metabolomics studies, 2) Sedimentomics is a valid technique to highlight changes in sediment organic matter, 3) Soil metabolomics and sedimentomics yield more information about carbon cycling than traditional measurements, and 4) Soil metabolomics organic matter extractions are more variable and require more quality controls.

No description available.

The movement of organisms and resources within ecosystems are essential elements in the productivity, stability, and distribution of communities. This thesis examines how water velocity, a defining factor of lotic systems, influences the dispersion of benthic organisms and particulate organic matter in small stream ecosystems. Variation in movement-related behaviours in two rheophilous (‘flow-loving’) mayflies (Epeorus and Baetis) and two rheophobic (‘flow-avoiding’) mayflies (Ameletus and Paraleptophlebia) were compared to determine how benthic organisms disperse between and within habitat patches in hydrodynamically complex landscapes. The degree to which water velocity and particle shape influence the retention of organic matter (including deciduous leaves, conifer needles, red-cedar fronds, and branch fragments) was examined to determine how physical factors determine detrital resource availability in streams. Although water velocity did not influence the crawling rates of Baetis and Ameletus in daylight conditions, both mayflies dispersed rapidly upstream in low-velocity flows in dark conditions. Drift rates of both mayflies were lower in daylight than dark conditions, and were generally inversely related to their habitat preferences. Escape responses in grazing Epeorus, Baetis, and Ameletus larvae in a range of flow conditions showed that retreat distance was more sensitive than flight initiation distance to variation in water velocity, suggesting that hydrodynamics mediate the risks of predation and the costs of flight in stream systems. Comparisons of the transport distances of live larvae, dead larvae, and passive tracer particles in low and high water velocities showed that drift distance varied substantially among taxa, and that behavioural control over drift distance generally declined as water velocity increased. While organic matter particles generally travelled further in high-velocity reaches, leaves were retained in riffles when they impacted on protruding clasts, while ‘stiff’ particles were retained when they settled into streambed interstices. Leaves placed in high-velocity microhabitats were broken down more slowly than leaves in low-flow areas, likely due to the exclusion of large-bodied detritivores. In conclusion, this thesis supports the view that hydrodynamic forces control trophic interactions and local population dynamics in stream ecosystems by directly altering the physical – and sometimes behavioural – processes of particle entrainment, transport, and deposition.

The importance of microbial biomass of low concentration, regular additions of soluble organic substrate to carbon-limited soils, such as might occur with throughfall, has been studied. The conclusions depended upon the method used to measure C concentrations. Using a TOCsin automated analyser, the high level treatment enhanced biomass C, whereas the lower level treatment had small and variable effects, but using dichromate oxidation led to the conclusion that the low level treatment had a negative effect, and even the high level treatment had no beneficial effect. A further evaluation showed that the TOCsin procedure gave low recoveries of biomass C for bacterial monoculture suspension, an effect attributed to transport-related phenomena, and could not cope with continuous SO₄^2- inputs. However, use of Cl^- to extract C before and after fumigation altered the amount of C obtained. Therefore dichromate oxidation was used subsequently. The changes in microbial biomass, ATP concentration and respired CO₂ for glucose-amended soil have been measured over 9 days, and the dynamic responses shown to differ. The large changes in ATP-to-biomass C ratio show that ATP should not be used as a surrogate for biomass C determination after fresh substrate addition. Subsequently, ¹⁴C-labelled pea plant residues have been used to study differences in response of the three determinants to incorporation of water-soluble (WS), water-insoluble (WI), and unwashed (UW) plant residue materials. For plant materials too, ATP-to-biomass C ratios changed in response to substrate additions, increasing substantially (as for glucose) for WS additions, but decreasing after W1 residue incorporation. In the shorter term, higher biomass C was favoured more by incorporation of WI than of WS plant residues.

The movement of organisms and resources within ecosystems are essential elements in the productivity, stability, and distribution of communities. This thesis examines how water velocity, a defining factor of lotic systems, influences the dispersion of benthic organisms and particulate organic matter in small stream ecosystems. Variation in movement-related behaviours in two rheophilous (‘flow-loving’) mayflies (Epeorus and Baetis) and two rheophobic (‘flow-avoiding’) mayflies (Ameletus and Paraleptophlebia) were compared to determine how benthic organisms disperse between and within habitat patches in hydrodynamically complex landscapes. The degree to which water velocity and particle shape influence the retention of organic matter (including deciduous leaves, conifer needles, red-cedar fronds, and branch fragments) was examined to determine how physical factors determine detrital resource availability in streams. Although water velocity did not influence the crawling rates of Baetis and Ameletus in daylight conditions, both mayflies dispersed rapidly upstream in low-velocity flows in dark conditions. Drift rates of both mayflies were lower in daylight than dark conditions, and were generally inversely related to their habitat preferences. Escape responses in grazing Epeorus, Baetis, and Ameletus larvae in a range of flow conditions showed that retreat distance was more sensitive than flight initiation distance to variation in water velocity, suggesting that hydrodynamics mediate the risks of predation and the costs of flight in stream systems. Comparisons of the transport distances of live larvae, dead larvae, and passive tracer particles in low and high water velocities showed that drift distance varied substantially among taxa, and that behavioural control over drift distance generally declined as water velocity increased. While organic matter particles generally travelled further in high-velocity reaches, leaves were retained in riffles when they impacted on protruding clasts, while ‘stiff’ particles were retained when they settled into streambed interstices. Leaves placed in high-velocity microhabitats were broken down more slowly than leaves in low-flow areas, likely due to the exclusion of large-bodied detritivores. In conclusion, this thesis supports the view that hydrodynamic forces control trophic interactions and local population dynamics in stream ecosystems by directly altering the physical – and sometimes behavioural – processes of particle entrainment, transport, and deposition.

Examensarbete. / Graduate thesis in soil science 2004.

The movement of organisms and resources within ecosystems are essential elements in the productivity, stability, and distribution of communities. This thesis examines how water velocity, a defining factor of lotic systems, influences the dispersion of benthic organisms and particulate organic matter in small stream ecosystems. Variation in movement-related behaviours in two rheophilous (‘flow-loving’) mayflies (Epeorus and Baetis) and two rheophobic (‘flow-avoiding’) mayflies (Ameletus and Paraleptophlebia) were compared to determine how benthic organisms disperse between and within habitat patches in hydrodynamically complex landscapes. The degree to which water velocity and particle shape influence the retention of organic matter (including deciduous leaves, conifer needles, red-cedar fronds, and branch fragments) was examined to determine how physical factors determine detrital resource availability in streams. Although water velocity did not influence the crawling rates of Baetis and Ameletus in daylight conditions, both mayflies dispersed rapidly upstream in low-velocity flows in dark conditions. Drift rates of both mayflies were lower in daylight than dark conditions, and were generally inversely related to their habitat preferences. Escape responses in grazing Epeorus, Baetis, and Ameletus larvae in a range of flow conditions showed that retreat distance was more sensitive than flight initiation distance to variation in water velocity, suggesting that hydrodynamics mediate the risks of predation and the costs of flight in stream systems. Comparisons of the transport distances of live larvae, dead larvae, and passive tracer particles in low and high water velocities showed that drift distance varied substantially among taxa, and that behavioural control over drift distance generally declined as water velocity increased. While organic matter particles generally travelled further in high-velocity reaches, leaves were retained in riffles when they impacted on protruding clasts, while ‘stiff’ particles were retained when they settled into streambed interstices. Leaves placed in high-velocity microhabitats were broken down more slowly than leaves in low-flow areas, likely due to the exclusion of large-bodied detritivores. In conclusion, this thesis supports the view that hydrodynamic forces control trophic interactions and local population dynamics in stream ecosystems by directly altering the physical – and sometimes behavioural – processes of particle entrainment, transport, and deposition. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate