Biogeochemical Cycling in a Headwater Stream and Riparian Zone

Several teams of researchers at multiple universities are currently measuring annual and seasonal fluxes of carbon dioxide and other greenhouses gases (nitrous oxide and methane) in riparian wetlands and upland forests in the Tenderfoot Creek Experimental Forest (TCEF), a subalpine watershed in the Little Belt Mountains, Montana. In the current thesis, the author characterized the geochemistry and stable carbon isotope composition of shallow groundwater, soil water, and stream water in upper Stringer Creek, near sites that are being investigated for gas chemistry and microbial studies. It was hypothesized that if methanogenesis were a dominant process in the riparian wetlands of upper Stringer Creek, then this should impart a characteristic signal in the measured stable isotopic composition of dissolved inorganic carbon in shallow groundwater. For the most part, the major solute composition of shallow groundwater in upper Stringer Creek was similar to that of the stream. However, several wells completed in wetland soil had highly elevated concentrations of Fe2+ and Mn2+ which were absent in the well-oxygenated surface water. Use of sediment pore-water samplers (peepers) demonstrated a rapid increase in Fe2+ and Mn2+ with depth, most feasibly explained by microbial reduction of Fe- and Mn-oxide minerals. In general, the pH of shallow groundwater was lower than that of the stream. Since concentrations of CO2 in the groundwater samples were consistently greater than atmospheric pCO2, exchange of CO2 gas across the stream/air interface occurred in one direction, from stream to air. Evasion of CO2 partly explains the higher pH values in the stream. Microbial processes involving breakdown of organic carbon, including aerobic respiration, anaerobic respiration, and methanogenesis, explain the occurrence of excess CO2 in the groundwater. In general, the isotopic composition of total dissolved inorganic carbon (DIC) decreased with increasing DIC concentration, consistent with aerobic and/or anaerobic respiration being the dominant metabolic process in shallow groundwater. However, a minority of wells contained high DIC concentrations that were anomalously heavy in u13C, and these same wells had elevated concentrations of dissolved methane. It is concluded that the wells with isotopically-heavier DIC have likely been influenced by acetoclastic methanogenesis. Results from shallow groundwater wells and one of the peeper samplers suggest a possible link between methanogenesis and bacterial iron reduction.

A study of environmental and management drivers of non-co2 greenhouse gas emissions in Australian agro-ecosystems

Australian climate, soils and agricultural management practices are significantly different from those of the northern hemisphere nations. Consequently, experimental data on greenhouse gas production from European and North American agricultural soils and its interpretation are unlikely to be directly applicable to Australian systems.

A study of environmental and management drivers of non-CO2 greenhouse gas emissions in Australian agro-ecosystems

Australian climate, soils and agricultural management practices are significantly different from those of the northern hemisphere nations. Consequently, experimental data on greenhouse gas production from European and North American agricultural soils and its interpretation are unlikely to be directly applicable to Australian systems. A programme of studies of non-CO2 greenhouse gas emissions from agriculture has been established that is designed to reduce uncertainty of non-CO2 greenhouse gas emissions in the Australian National Greenhouse Gas Inventory and provide outputs that will enable better on-farm management practices for reducing non-CO2 greenhouse gas emissions, particularly nitrous oxide. The systems being examined and their locations are irrigated pasture (Kyabram Victoria), irrigated cotton (Narrabri, NSW), irrigated maize (Griffith, NSW), rain-fed wheat (Rutherglen, Victoria) and rain-fed wheat (Cunderdin, WA). The field studies include treatments with and without fertilizer addition, stubble burning versus stubble retention, conventional cultivation versus direct drilling and crop rotation to determine emission factors and treatment possibilities for best management options. The data to date suggest that nitrous oxide emissions from nitrogen fertilizer, applied to irrigated dairy pastures and rain-fed winter wheat, appear much lower than the average of northern hemisphere grain and pasture studies. More variable emissions have been found in studies of irrigated cotton/vetch/wheat rotation and substantially higher emissions from irrigated maize.

CO2 capture and gas separation on boron carbon nanotubes

Concern about the increasing atmospheric CO2 concentration and its impact on the environment has led to increasing attention directed toward finding advanced materials and technologies suited for efficient CO2 capture, storage and purification of clean-burning natural gas. In this letter, we have performed comprehensive theoretical investigation of CO2, N2, CH4 and H2 adsorption on B2CNTs. Our study shows that CO2 molecules can form strong interactions with B2CNTs with different charge states. However, N2, CH4 and H2 can only form very weak interactions with B2CNTs. Therefore, the study demonstrates B2CNTs could sever as promising materials for CO2 capture and gas separation.

Effect of functional groups on separating carbon dioxide from CO2/N-2 gas mixtures using edge functionalized graphene nanoribbons

Development of microporous adsorbents for separation and sequestration of carbon dioxide from flue gas streams is an area of active research. In this study, we assess the influence of specific functional groups on the adsorption selectivity of CO2/N-2 mixtures through Grand Canonical Monte Carlo (GCMC) simulations. Our model system consists of a bilayer graphene nanoribbon that has been edge functionalized with OH, NH2, NO2, CH3 and COOH. Ab initio Moller-Plesset (MP2) calculations with functionalized benzenes are used to obtain binding energies and optimized geometries for CO2 and N-2. This information is used to validate the choice classical forcefields in GCMC simulations. In addition to simulations of adsorption from binary mixtures of CO2 and N-2, the ideal adsorbed solution theory (IAST) is used to predict mixture isotherms. Our study reveals that functionalization always leads to an increase in the adsorption of both CO2 and N-2 with the highest for COOH. However, significant enhancement in the selectivity for CO2 is only seen with COOH functionalized nanoribbons. The COOH functionalization gives a 28% increase in selectivity compared to H terminated nanoribbons, whereas the improvement in the selectivity for other functional groups are much Enure modest. Our study suggests that specific functionalization with COOH groups can provide a material's design strategy to improve CO2 selectivity in microporous adsorbents. Synthesis of graphene nanoplatelets with edge functionalized COOH, which has the potential for large scale production, has recently been reported (Jeon el, al., 2012). (C) 2014 Elsevier Ltd. All rights reserved,

Fast response CO2 sensor for automotive exhaust gas analysis

A fast response sensor for measuring carbon dioxide concentration has been developed for laboratory research and tested on a spark ignition engine. The sensor uses the well known infra-red absorption technique with a miniaturized detection system and short capillary sampling tubes, giving a time constant of approximately 5 milliseconds; this is sufficiently fast to observe changes in CO2 levels on a cycle-by-cycle basis under normal operating conditions. The sensor is easily located in the exhaust system and operates continuously. The sensor was tested on a standard production four cylinder spark-ignition engine to observe changes in CO2 concentration in exhaust gas under steady state and transient operating conditions. The processed sensor signal was compared to a standard air-to-fuel ratio (AFR) sensor in the exhaust stream and the results are presented here. The high frequency response CO2 measurements give new insights into both engine and catalyst transient operation. Copyright © 1999 Society of Automotive Engineers, Inc.

Ab initio investigation of C2H2/X Van der Waals complexes (X=Noble gas, CO2, N2O)

info:eu-repo/semantics/nonPublished