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Articles 61 - 90 of 587

Full-Text Articles in Oceanography and Atmospheric Sciences and Meteorology

Incorporating Recent Geochemical And Isotopic Constraints In Age Dating The Waters Of Hot Springs National Park, Arkansas, Kristina Marie Raley May 2019

Incorporating Recent Geochemical And Isotopic Constraints In Age Dating The Waters Of Hot Springs National Park, Arkansas, Kristina Marie Raley

Graduate Theses and Dissertations

Mean water age for spring discharge in Hot Springs National Park was calculated as approximately 4,400 years by Bedinger et al (1978) using carbon-14. Their analysis indicated that the water was a mixture of a small portion of cold water that was less than twenty years old with a preponderance of hot water. However, this result includes some error due to Bedinger et al. using general isotopic values for soil dissolved inorganic carbon and mineral carbon instead of obtaining actual values from the study area. A more accurate age calculation for the springs has been made possible by additional geological …


Reduced Disposal Area Performance Utilizing Secondary-Treated Effluent In Profile-Limiting Soils, David A. Meints May 2019

Reduced Disposal Area Performance Utilizing Secondary-Treated Effluent In Profile-Limiting Soils, David A. Meints

Graduate Theses and Dissertations

Onsite wastewater systems dispose of primary treated effluent by utilizing the soil for final recycling and renovation of wastewater into the environment. Soil and site limitations have become a challenge to design a wastewater system and dispose of onsite wastewater using a conventional pipe and gravel design. Using secondary-treated effluent from an advanced treatment unit applied to a reduced disposal area offers an additional alternative when developing an onsite wastewater system. The objective of this study was to determine the feasibility of hydraulically loading limiting soils with secondary-treated effluent in a reduced disposal area. A reduced disposal area was constructed …


Cool And Warm Season Climate Signals In Tree Rings From North America, Max Carl Arne Torbenson May 2019

Cool And Warm Season Climate Signals In Tree Rings From North America, Max Carl Arne Torbenson

Graduate Theses and Dissertations

Earlywood (EW) and latewood (LW) ring-width chronologies have become an increasingly important proxy in paleoclimate reconstructions. These subannual variables can provide estimates of past hydroclimate variability for seasonal windows that total ring-widths cannot resolve. The strength of the relationship between EW and LW series may influence what type of paleoclimate information is embedded within the tree-ring series. High correlations (> 0.70) between EW and LW are recorded for much of the continent but the magnitude of correlation varies greatly across space and species boundaries. Using four LW chronologies from shortleaf pine, the North American conifer species displaying the lowest EW-LW …


A Long-Term (2002 To 2017) Record Of Closed-Path And Open-Path Eddy Covariance Co2 Net Ecosystem Exchange Fluxes From The Siberian Arctic, David Holl, Christian Wille, Torsten Sachs, Peter Schreiber, Benjamin R. K. Runkle, Lutz Beckebanze, Moritz Langer, Julia Boike, Eva-Maria Pfeiffer, Irina Fedorova, Dimitry Y. Bolshianov, Mikhail N. Grigoriev, Lars Kutzbach Feb 2019

A Long-Term (2002 To 2017) Record Of Closed-Path And Open-Path Eddy Covariance Co2 Net Ecosystem Exchange Fluxes From The Siberian Arctic, David Holl, Christian Wille, Torsten Sachs, Peter Schreiber, Benjamin R. K. Runkle, Lutz Beckebanze, Moritz Langer, Julia Boike, Eva-Maria Pfeiffer, Irina Fedorova, Dimitry Y. Bolshianov, Mikhail N. Grigoriev, Lars Kutzbach

Biological and Agricultural Engineering Faculty Publications and Presentations

Ground-based observations of land–atmosphere fluxes are necessary to progressively improve global climate models. Observed data can be used for model evaluation and to develop or tune process models. In arctic permafrost regions, climate–carbon feedbacks are amplified. Therefore, increased efforts to better represent these regions in global climate models have been made in recent years. We present a multi-annual time series of land–atmosphere carbon dioxide fluxes measured in situ with the eddy covariance technique in the Siberian Arctic (72◦220 N, 126◦300 E). The site is part of the international network of eddy covariance flux observation stations (FLUXNET; site ID: Ru-Sam). The …


Constituent Loads And Trends In The Upper Illinois River Watershed And Upper White River Basin: 2015 October Through 2018 September, Erin E. Scott, Brian E. Haggard Feb 2019

Constituent Loads And Trends In The Upper Illinois River Watershed And Upper White River Basin: 2015 October Through 2018 September, Erin E. Scott, Brian E. Haggard

Arkansas Water Resources Center Technical Reports

The Arkansas Natural Resources Commission (ANRC) identified two priority hydrologic unit code (HUC) 8 watersheds, the Upper White River Basin (UWRB; HUC 11010001) and the Upper Illinois River Watershed (UIRW; 11110103), in northwest Arkansas. Nonpoint source (NPS) pollution is a concern in these watersheds, such as excess nutrients from agriculture and sediment from changes in land uses. Several NPS pollution projects have been funded by ANRC, including streambank restoration on Sager Creek and best management practices (BMP) to control urban sediment in Fayetteville. The purpose of this project was to collect water samples at 15 sites in the UWRB and …


Methanogens, Plausible Extraterrestrial Life Forms On Mars, And Their Tolerance To Increasing Concentrations Of Illite Clay, Chandler Kern Dec 2018

Methanogens, Plausible Extraterrestrial Life Forms On Mars, And Their Tolerance To Increasing Concentrations Of Illite Clay, Chandler Kern

Biological Sciences Undergraduate Honors Theses

Methanogens, some of Earth’s most primitive prokaryotic organisms, are candidates for possible life forms capable of inhabiting Mars. Specifically, four different species (Methanobacterium formicicum, Methanococcus maripaludis, Methanosarcina barkeri, Methanothermobacter wolfeii) were analyzed for their tolerance to the presence of illite clay. Illite is a crystalline mineral that has been identified from regions of Mars’s surface. Results indicated that all four species grew with some success in the illite at different concentrations. This experimentation with methanogens’ abilities to survive and reproduce in the presence of illite allows for a more accurate understanding of the potential capability of microbial …


Margaret White Springs Recharge Study, Buffalo National River, North-Central Arkansas, Usa, Ashlon Elizabeth Leonard Dec 2018

Margaret White Springs Recharge Study, Buffalo National River, North-Central Arkansas, Usa, Ashlon Elizabeth Leonard

Graduate Theses and Dissertations

Margaret White Springs (MWS) is one of the largest springs in the middle section of the Buffalo National River (BNR) and contributes several tens of cubic feet per second of flow to river discharge on average, yet the source of the water has not been fully studied or documented. The spring is located approximately 4 miles downstream from Robertson Hole, a losing reach of the river. At Robertson Hole the river loses a significant amount of flow to groundwater, which during the dry season (summer) can be as much as 100%. Flow in the main channel is re-established at MWS; …


Managing Lake Fertility Within The Guidelines Of A Nutrient Management Plan And Based On Algal Nutrient Limitation, Bradley J. Austin, J. Thad Scott, Brian E. Haggard Nov 2018

Managing Lake Fertility Within The Guidelines Of A Nutrient Management Plan And Based On Algal Nutrient Limitation, Bradley J. Austin, J. Thad Scott, Brian E. Haggard

Arkansas Water Resources Center Technical Reports

The specific objectives were to first, monitor nutrients, algal biomass, and water clarity in lakes Cove, Spring, and Wedington. Second, evaluate whether algal growth in each of the lakes was limited by N, P, or both N and P. This research was conducted to help USFS better manage lake fertilization to maximize algal growth and improve the fisheries within these lakes.


Algal Blooms In Arkansas Streams, Ponds, And Lakes, Bradley J. Austin, Brie Olsen, Tate Wentz, Brian E. Haggard Oct 2018

Algal Blooms In Arkansas Streams, Ponds, And Lakes, Bradley J. Austin, Brie Olsen, Tate Wentz, Brian E. Haggard

Arkansas Water Resource Center Fact Sheets

Did you know that algae are a natural part of ponds, lakes, streams, and rivers? These organisms grow in the water (plankton) and on rocks, plants, and other surfaces (periphyton) and sometimes periphyton slough off into the water (seston). Most of the time these algae are hardly noticeable in waterbodies; however, sometimes they can form very noticeable algal blooms.


Evaluating Climate Change Policy Through The Endangered Species Act, Richie Donahou Aug 2018

Evaluating Climate Change Policy Through The Endangered Species Act, Richie Donahou

Graduate Theses and Dissertations

This research sets out to address a growing knowledge gap of climate change science in regards to the state of Arkansas. Within the coming chapters, the goal of this research is to examine climate data and to identify if any evidence of climate change can be detected and what are the policies in place to adapt to these potential changes. Furthermore, the scope of this research will be narrowed to a few counties over the southwest Arkansas, and a specific endangered species, the Leopard Darter. Upon examination of previous environmental and ecological climate change related research it became clear that …


Estimating Watershed Mercury Contribution To Lake Fort Smith State Park, Arkansas, Usa, William Miles Harmon Aug 2018

Estimating Watershed Mercury Contribution To Lake Fort Smith State Park, Arkansas, Usa, William Miles Harmon

Graduate Theses and Dissertations

Mercury contamination associated with human activities poses global human health and environmental risks. A fish-consumption advisory has been in effect at Lake Fort Smith in central west Arkansas for more than a decade due to observed methylmercury concentrations in fish tissue. Lake Fort Smith is an important municipal drinking water supply and recreational resource. Water samples from the majority contributing tributary stream, Frog Bayou creek, were collected periodically, under differing hydrologic conditions in order to quantify the allochthonous mercury load delivered to the lake. Temperature, specific conductance, and turbidity data were collected and used to estimate dissolved organic carbon, methylmercury …


The Energy Yield Of Global Crops 1961-2016, Quinn Montana Aug 2018

The Energy Yield Of Global Crops 1961-2016, Quinn Montana

Graduate Theses and Dissertations

It is often suggested that world food production must increase by 70%-100% or more by the year 2050 if we are to feed the anticipated world population at that time. To evaluate this claim, global crop production from 1961 to 2016 was inventoried using publicly available data from the United Nations Food and Agriculture Organization (FAO). To determine the adequacy of global crop output for humanity, annual global food crop production data (T y-1) were converted to energy yield in kilojoules (KJ y-1). These data were then compared to the annual metabolic energy requirement of the global human population. The …


Irrigation Practice Adoption: Causes And Consequences In The Arkansas Delta, Kerr James Adams May 2018

Irrigation Practice Adoption: Causes And Consequences In The Arkansas Delta, Kerr James Adams

Graduate Theses and Dissertations

Concerns about groundwater depletion from conventional irrigation agriculture in the Arkansas Delta region have led to the promotion of more efficient irrigation practices. With Arkansas being the largest producer of rice, the 10th largest producer of soybeans and the 16th largest producer of corn in the United States, the irrigation demand of these crops has put pressure on producers to find ways to irrigate more efficiently. Not only are the alternative technologies supposed to reduce water use, it is also believed that their adoption can also yield economic benefits for the producer. Despite these assumed benefits, adoption of alternative technologies …


Greenhouse Gas Emissions And Management Practices That Affect Emissions In Us Rice Systems, Bruce A. Linquist, Mathias Marcos, M. Arlene Adviento-Borbe, Merle Anders, Dustin Harrell, Steve Linscombe, Michele L. Reba, Benjamin R.K. Runkle, Lee Tarpley, Allison Thomson May 2018

Greenhouse Gas Emissions And Management Practices That Affect Emissions In Us Rice Systems, Bruce A. Linquist, Mathias Marcos, M. Arlene Adviento-Borbe, Merle Anders, Dustin Harrell, Steve Linscombe, Michele L. Reba, Benjamin R.K. Runkle, Lee Tarpley, Allison Thomson

Biological and Agricultural Engineering Faculty Publications and Presentations

Previous reviews have quantified factors affecting greenhouse gas (GHG) emissions from Asian rice (Oryza sativa L.) systems, but not from rice systems typical for the United States, which often vary considerably particularly in practices (i.e., water and carbon management) that affect emissions. Using meta‐analytic and regression approaches, existing data from the United States were examined to quantify GHG emissions and major practices affecting emissions. Due to different production practices, major rice production regions were defined as the mid‐South (Arkansas, Texas, Louisiana, Mississippi, and Missouri) and California, with emissions being evaluated separately. Average growing season CH4 emissions for the mid‐South and …


A Geospatial Study Of The Drought Impact On Surface Water Reservoirs: Study Cases From Texas And California, Zachary Asbury May 2018

A Geospatial Study Of The Drought Impact On Surface Water Reservoirs: Study Cases From Texas And California, Zachary Asbury

Graduate Theses and Dissertations

Drought in Texas and California has been a long-term problem. Over the past 60 years reservoir construction has occurred to remedy the situation. Satellite imagery has been used historically to measure and monitor fluctuations in surface water reservoirs. This investigation integrates remote sensing and geographic information system (GIS) technologies to study the impact of drought on selected surface water reservoirs in San Angelo and Dallas in Texas, and Lake Oroville in California. Expansion and shrinkage over the 2005-2016 period reveal the concrete impact that drought, along with other factors, have on the selected lakes. Fluctuations in reservoir sizes during summer …


How College Campuses Are Using Social Media During Severe Weather Events, Emmale Davis May 2018

How College Campuses Are Using Social Media During Severe Weather Events, Emmale Davis

Graduate Theses and Dissertations

This study explores how college campuses are using social media during severe weather events. This topic surfaced after a tornado devastated Moore, Oklahoma in May 2013 and those displaced flocked to the University of Oklahoma campus after a post made on Twitter went viral prior to an official message being sent out by the university. In order to further explore this topic, a qualitative phenomenological case study was conducted at the following sites: University of Alabama, Missouri Southern State University, University of Oklahoma, and Florida State University. This study included observations of social media posts on Facebook and Twitter on …


Gis Modeling Of The Prominent Geohazards In Arkansas, Kyle Walker Rowden May 2018

Gis Modeling Of The Prominent Geohazards In Arkansas, Kyle Walker Rowden

Graduate Theses and Dissertations

The State of Arkansas is prone to numerous geohazards. This thesis is a twofold study of prominent geohazards in Arkansas: the first fold includes a novel triggerless approach for mass wasting susceptibility modeling applied to the Boston Mountains in NW Arkansas, and the second fold is a GIS-based regression modeling of the extreme weather patterns at the state level. Each study fold is presented in this thesis as a separate chapter embracing a published peer-reviewed paper. In the first paper, I have used the analytical hierarchy process to assign preliminary statistical weights to the most cogent variables influencing mass wasting …


Applications Of Reservoir Limnology Theory And Steady-State Modeling To Eutrophication Management In Beaver Lake, Arkansas, Matthew Rich May 2018

Applications Of Reservoir Limnology Theory And Steady-State Modeling To Eutrophication Management In Beaver Lake, Arkansas, Matthew Rich

Graduate Theses and Dissertations

Reservoir limnology theory predicts that phytoplankton biomass (PB) is greatest in riverine-transition zones and least in lacustrine zones leading to an inverse pattern in water clarity. These theoretical patterns were utilized to create a statistical model of chlorophyll-a (Chl-a), an indicator of PB, and Secchi transparency (ST), an indicator of Chl-a, in Beaver Lake, Arkansas, a 12,800-ha reservoir, in order to hindcast historical conditions. Sampling for Chl-a, ST, and photic depth occurred semimonthly at 12 locations along a 78-km transect from the river inflow to the dam during the 2015 growing season. The ratio of Chl-a and ST measured at …


How To Sample: Collecting Water Samples Is So Easy, Anyone Can Do It!, Mike Daniels, Bradley J. Austin, Brian E. Haggard Apr 2018

How To Sample: Collecting Water Samples Is So Easy, Anyone Can Do It!, Mike Daniels, Bradley J. Austin, Brian E. Haggard

Arkansas Water Resource Center Fact Sheets

The Arkansas Water Resources Center (AWRC) runs a water quality lab that anyone can use to have their water sample tested. The AWRC Lab is certified for the analysis of water samples, but the quality (and meaningfulness) of the data generated by the Lab is also dependent on you – the client. This fact sheet provides you some general guidance on how to properly collect your water sample.


Watershed Investigative Support To The Poteau Valley Improvement Authority: Stream Water Quality To Support Huc 12 Prioritization In The Lake Wister Watershed, Oklahoma, Bradley J. Austin, Brina A. Smith, Brian E. Haggard Feb 2018

Watershed Investigative Support To The Poteau Valley Improvement Authority: Stream Water Quality To Support Huc 12 Prioritization In The Lake Wister Watershed, Oklahoma, Bradley J. Austin, Brina A. Smith, Brian E. Haggard

Arkansas Water Resources Center Technical Reports

Nonpoint source pollution associated with human land use (agriculture and urbanization) is one of the leading causes of impairment to waterways in the United States (EPA, 2000). The primary pollutants associated with agricultural and urban land use are sediment and nutrients which enter nearby streams during rain events and are then carried downstream. These sediments and nutrients may result in water quality issues in the downstream water bodies like increased algal growth or decreased water clarity (e.g. Smith et al., 1999).


Arkansas Bulletin Of Water Research - Issue 2018, Erin E. Scott, Brian E. Haggard Jan 2018

Arkansas Bulletin Of Water Research - Issue 2018, Erin E. Scott, Brian E. Haggard

Arkansas Bulletin of Water Research

The Arkansas Bulletin of Water Research is a publication of the Arkansas Water Resources Center (AWRC). This bulletin is produced in an effort to share water research relevant to Arkansas water stakeholders in an easily searchable and aesthetically engaging way. This is the second publication of the bulletin and will be published annually. The submission of a paper to this bulletin is appropriate for topics at all related to water resources, by anyone conducting water research or investigations. This includes but is not limited to university researchers, consulting firms, watershed groups, and other agencies. Prospective authors should read the “Introduction …


Tree Ring Dating Of The Ficklin-Imboden Log Structures, Powhatan Historic State Park, Arkansas, Kaylee R. Mcadoo, David W. Stahle Jan 2018

Tree Ring Dating Of The Ficklin-Imboden Log Structures, Powhatan Historic State Park, Arkansas, Kaylee R. Mcadoo, David W. Stahle

Journal of the Arkansas Academy of Science

Powhatan Historic State Park in Powhatan, Arkansas preserves and interprets five historical structures from 19th century Arkansas, including the Ficklin-Imboden Log House. This structure, which is actually two separate log buildings with uncertain construction dates and functions, is believed to be the earliest surviving structure at Powhatan State Park and is on the National Register of Historic Places. Powhatan State Park contracted with the University of Arkansas Tree-Ring Laboratory to develop a more accurate dating and interpretation of the log structures.

Dendrochronology (tree-ring dating) was used to determine the true felling dates of logs in both buildings. Core specimens …


Comparison Of Various Mean Field Formulations For Retrieving Refractive Indices Of Aerosol Particles Containing Inclusions, Kristin S. Dooley, Jessica Deyoung Jan 2018

Comparison Of Various Mean Field Formulations For Retrieving Refractive Indices Of Aerosol Particles Containing Inclusions, Kristin S. Dooley, Jessica Deyoung

Journal of the Arkansas Academy of Science

Application of effective medium approximation (EMA) methods to two-component systems are presented. Systems studied are composed of water, sulfate, soot, and dust as these are commonly encountered atmospheric aerosol components. Atmospheric models often employ EMAs to include internally mixed aerosols without the computational burden of exact theory. In the current work, several types of mixing rules (Maxwell-Garnet, Bruggeman, and coherent potential approximation) have been applied to various two-component internally mixed particles at 550 nm using volume fractions of the minor component below 0.1. As expected, results show that the formulations tested produce very similar effective refractive indices indicating that electric …


Exploring Energy, Comfort, And Building Health Impacts Of Deep Setback And Normal Occupancy Smart Thermostat Implementation, Zachary Ethan Alderman Dec 2017

Exploring Energy, Comfort, And Building Health Impacts Of Deep Setback And Normal Occupancy Smart Thermostat Implementation, Zachary Ethan Alderman

Graduate Theses and Dissertations

As smart thermostat adoption rates continue to increase, it becomes worthwhile to explore what unanticipated outcomes may result in their use. Specific attention was paid to smart thermostat impacts to deep setback and normal occupancy states in a variety of conditions while complying with the ventilation and temperature requirements of ASHRAE 90.2-2013. Custom weather models and occupancy schedules were generated to efficiently explore a combination of weather conditions, building constructions, and occupancy states. The custom modeling approach was combined with previous experimental data within the Openstudio graphics interface to the EnergyPlus building modeling engine. Results indicate smart thermostats add the …


An Investigation Of Biological Carbon Sequestration At The Pea Ridge National Military Park, Dorine Reed Bower Dec 2017

An Investigation Of Biological Carbon Sequestration At The Pea Ridge National Military Park, Dorine Reed Bower

Graduate Theses and Dissertations

The direct correlation between increasing levels of atmospheric CO2 and global temperatures is now irrefutable. A 50% increase in atmospheric CO2 levels from a pre-industrial level of 270 ppm to a present-day level of 405 ppm, has resulted in documented record temperatures and a concomitant rising of sea levels from melting ice caps.

The ability of biological/terrestrial ecological systems to store atmospheric carbon is a viable option in the effort to mitigate the climate impacts of rising anthropogenically-caused greenhouse gas emissions. Components of the vegetation and soils in the Pea Ridge National Military Park (the Park) were examined for carbon …


Habitat Ecology, Trophic Interactions, And Distribution Of Endangered Himalayan Musk Deer In The Nepal Himalaya, Kapil Kishor Khadka Dec 2017

Habitat Ecology, Trophic Interactions, And Distribution Of Endangered Himalayan Musk Deer In The Nepal Himalaya, Kapil Kishor Khadka

Graduate Theses and Dissertations

This dissertation seeks to explore and assess the habitat selection, trophic interactions and distribution of Himalayan musk deer. Chapter one deals with seasonal diet analysis of musk deer along with the overlap in consumption with livestock during summer. Microhistological technique was employed to assess dietary consumption. Results showed that Abies spectabilis, Pinus wallichiana, and Berberis species constituted the major portion of musk deer’s diet. Dietary breadth measured by the Shannon index was found higher in winter compared to summer. Although musk deer and livestock shared a considerable number of plant species in their diets, the consumption however was significantly different …


3d Seismic Interpretation Of A Plio-Pleistocene Mass Transport Deposit In The Deepwater Taranaki Basin Of New Zealand, Francisco Jose Rusconi Dec 2017

3d Seismic Interpretation Of A Plio-Pleistocene Mass Transport Deposit In The Deepwater Taranaki Basin Of New Zealand, Francisco Jose Rusconi

Graduate Theses and Dissertations

A series of Plio-Pleistocene mass transport deposits (MTD) have been identified in the deepwater Taranaki Basin, in New Zealand, using the Romney 3D seismic survey, which covers an area of approximately 2000 km2. One of these MTDs has been chosen for description and interpretation based on high confidence mapping of its boundary surfaces. The deposit exhibits an array of interesting features similar to those documented by researchers elsewhere plus a unique basal feature unlike those previously observed. The basal shear surface exhibits erosional features such as grooves, “monkey fingers”, and glide tracks. Internally, the MTD is typically characterized by low …


Laboratory Quality Control Report: Why Is It Important?, Bradley J. Austin, Mike Daniels, Brian E. Haggard Oct 2017

Laboratory Quality Control Report: Why Is It Important?, Bradley J. Austin, Mike Daniels, Brian E. Haggard

Arkansas Water Resource Center Fact Sheets

The Arkansas Water Resources Center (AWRC) maintains a fee-based water quality lab that is certified through the Arkansas Department of Environmental Quality (ADEQ). The AWRC Water Quality Lab analyzes water samples for a variety of constituents, using standard methods for the analysis of water samples (APHA 2012). Whether you have one or several water samples tested, the lab generates a report of values for each parameter that you have analyzed, which is provided to the client. Included with every water quality report is a Lab Quality Control (QC) report for each of the parameters analyzed within the package. The Lab …


Variability In Methane Emissions From West Siberia's Shallow Boreal Lakes On A Regional Scale And Its Environmental Controls, Aleksandr F. Sabrekov, Benjamin R.K. Runkle, Mikhail V. Glagolev, Irina E. Terentieva, Victor M. Stephanenko, Oleg R. Kotsyurbenko, Shamil S. Maksyutov, Oleg S. Pokrovsky Aug 2017

Variability In Methane Emissions From West Siberia's Shallow Boreal Lakes On A Regional Scale And Its Environmental Controls, Aleksandr F. Sabrekov, Benjamin R.K. Runkle, Mikhail V. Glagolev, Irina E. Terentieva, Victor M. Stephanenko, Oleg R. Kotsyurbenko, Shamil S. Maksyutov, Oleg S. Pokrovsky

Biological and Agricultural Engineering Faculty Publications and Presentations

Small lakes represent an important source of atmospheric CH4 from northern wetlands. However, spatiotemporal variations in flux magnitudes and the lack of knowledge about their main environmental controls contribute large uncertainty into the global CH4 budget. In this study, we measured methane fluxes from small lakes using chambers and bubble traps. Field investigations were carried out in July–August 2014 within the West Siberian middle and southern taiga zones. The average and median of measured methane chamber fluxes were 0.32 and 0.30 mgCH4 m−2 h−1 for middle taiga lakes and 8.6 and 4.1 mgCH4 m−2 h−1 for southern taiga lakes, respectively. …


Understanding N-Nitrosodimethylamine Formation In Water: Chloramine Chemistry, Kinetics, And A Proposed Reaction Pathway, Huong Thu Pham May 2017

Understanding N-Nitrosodimethylamine Formation In Water: Chloramine Chemistry, Kinetics, And A Proposed Reaction Pathway, Huong Thu Pham

Graduate Theses and Dissertations

The formation of N-nitrosodimethylamine (NDMA) in drinking water systems is a concern because of its potential carcinogenicity and occurrence at toxicologically relevant levels. The postulated mechanism for NDMA formation involves a substitution between dichloramine and amine-based precursors to form an unsymmetrical dimethylhydrazine (UDMH), which is then oxidized by ground-state molecular oxygen to form NDMA. However, this latter reaction is spin forbidden, thus likely occurs at a slow rate. It is hypothesized that the reaction between monochloramine and hydroxylamine (a nitrification product) may form an intermediate, which is involved in the NDMA formation pathway. This intermediate may also be generated from …