Keith R Lassey - Profile on Academia.edu (original) (raw)

Papers by Keith R Lassey

$Research paper thumbnail of The atmospheric cycling of radiomethane and the ''fossil fraction'' of the methane source$

The cycling of 14 CH 4 ("radiomethane") through the atmosphere has been strongly perturbed in the... more The cycling of 14 CH 4 ("radiomethane") through the atmosphere has been strongly perturbed in the industrial era by the release of 14 C-free methane from geologic reservoirs ("fossil methane" emissions), and in the nuclear era, especially since ca 1970, by the direct release of nucleogenic radiomethane from nuclear power facilities. Contemporary measurements of atmospheric radiomethane have been used to estimate the proportion of fossil methane in the global methane source (the "fossil fraction"), but such estimates carry high uncertainty due to the ill-determined nuclear-power source. We exploit an analysis in a companion paper of the global radiomethane budget through the nuclear era, using contemporary measurements of atmospheric radiomethane since 1986 to quantify both the fossil fraction and the strength of the nuclear power source. We deduce that 28.6±1.9% (1 s.d.) of the global methane source has fossil origin, a fraction which may include some 14 C-depleted refractory carbon fraction such as in aged peat deposits. The co-estimated strength of the global nuclear-power source of radiomethane is consistent with values inferred independently from local nuclear facilities.

Environmental sciences, Jun 1, 2005

The global methane source to the atmosphere from human activities is determined only to within ab... more The global methane source to the atmosphere from human activities is determined only to within about 20%, and its evolution over recent decades is essentially undetermined. IPCC Assessment Reports adjudge the contemporary global anthropogenic source to be in the range 300-450 Tg year 71 based on a 'bottom-up' inventory that aggregates the best literature-based estimates for identified sources. This source strength is compatible with, but not tightly constrained by, a 'top-down' analysis in which a global source of 495-700 Tg year 71 is inferred from a global sink estimated at 460-660 Tg year 71. While such an inventory could in principle be compiled from national emission inventories reported to the United Nations Framework Convention on Climate Change, such inventories can be incomplete or based on sparse data. As an approach towards reconciling aggregated national inventories with top-down assessments, we apply a simple model of budget evolution that incorporates constraints from carbon isotope information. Our analysis suggests that aggregated inventories probably understate anthropogenic emissions, especially isotopically heavy emissions such as from fossil sources or biomass combustion. This could be due either to emission underestimation from recognized sources or to significant unrecognized sources, both of which should be remedied with ongoing inventory improvement.

The 14CH4 Measurement Record, Geologic Sources of Methane, and a new Reconciliation of the Global Methane Budget

AGUFM, Dec 1, 2007

ABSTRACT An enduring consensus of the global methane budget, as expressed in recent IPCC Assessme... more ABSTRACT An enduring consensus of the global methane budget, as expressed in recent IPCC Assessment Reports, is that about 20%\ of emissions have geologic origin (ie, are free of 14CH4). Based on atmospheric 14CH4 measurements and confounded by ill-quantified 14CH4 emissions from the nuclear- power industry, this "fossil fraction" estimate is quite uncertain, typically 18± 9%. A very recent re-determination of 30± 5%\ (± 2sigma) for the fossil fraction which does not require that the nuclear-power emission be specified may still be compatible with the earlier assessment despite an upward revision by 50%. Anthropogenic emissions via identified pathways of fossil-fuel exploitation are assessed in the Fourth IPCC Assessment Report at 90± 16 Tg~yr-1. Natural emissions extrapolated conservatively from new and widespread measurements of terrestrial seeps are 50± 10 Tg~yr-1, at least three times larger than previously accepted. The aggregate fossil emission of 140± 19 Tg~yr-1 is conservative yet still accounts for 24± 5%\ of the global source of 582± 87 Tg~yr-1, a value that is compatible with both 14CH4-based estimates of the fossil fraction. Nevertheless, while the fossil contribution to the methane source inventory remains incompletely determined the currently accepted estimate of ~20%\ for the fossil fraction may need to be revised upward, with substantial consequences for pre-industrial and contemporary source inventories.

The usage of transfer coefficients to describe radionuclide transport from a cow's diet to its milk

PubMed, Aug 1, 1980

Animal Feed Science and Technology, Mar 1, 2013

Implementations of the sulphur hexafluoride (SF 6) tracer technique to determine methane (CH 4) e... more Implementations of the sulphur hexafluoride (SF 6) tracer technique to determine methane (CH 4) emission rates from individual ruminant animals involve measuring levels of both CH 4 and SF 6 in background air. In well-ventilated settings, including grazing, background sampling is straightforward and the algebraic correction for background levels is then usually minor. In a recent paper in this journal (Vol. 170, p. 265-276), Williams et al. drew attention to the much more careful consideration that is needed for background sampling in experiments that use the SF 6 tracer technique with housed animals when both CH 4 and SF 6 levels can build up unevenly within the housing. This note builds on that study to show specifically and rigorously: (a) what is meant by background air, and that background corrections to CH 4 emission estimates are unaffected by the recycling of CH 4 and SF 6 through inhalation of self-exhaled gases; (b) that in studies of the role of various treatments on CH 4 emission rates, the siting of background samplers can crucially impact on findings; and, in particular, (c) that reports of a possible dependence of estimated CH 4 emission rates upon the rate of SF 6 release in the rumen are called into question due to the sensitivity of those findings to the siting of background samplers.

Agricultural and Forest Meteorology, Feb 1, 2007

Methane is a potent greenhouse gas whose atmospheric abundance has grown 2.5-fold over three cent... more Methane is a potent greenhouse gas whose atmospheric abundance has grown 2.5-fold over three centuries, due in large part to agricultural expansion. The farming of ruminant livestock, which generate and emit methane during digestion ('enteric fermentation'), is a leading contributor to this growth. This paper overviews the measurement or estimation of enteric methane emissions at a range of spatial scales. Measurement of individual animal emissions focuses particularly on grazing livestock for which the SF 6 tracer technique is uniquely appropriate. Gaining insight into factors that influence methane production requires that feed intake and feed properties be determined, enabling the methane emitted to be expressed per unit of intake. The latter expression is commonly encapsulated in the 'methane conversion factor', Y m , an entity that enables small-scale methane emission estimates to be extrapolated to national and global enteric methane inventories. The principles of this extrapolation and sources of uncertainty are discussed, along with the significance of this global source within the global methane cycle. Micrometeorological and similar measurement techniques over intermediate spatial scales are also surveyed.

Water Resources Research, Mar 1, 1988

211A assessed. They are based on monitoring the downward propagation into the unit of the seasona... more 211A assessed. They are based on monitoring the downward propagation into the unit of the seasonal cycle of water table fluctuation, and observation of flow in the vicinity of a cavity excavated in the unit. Results are consistent with conventional laboratory and slug tests. Characterisation of a glacial till site is described.

Livestock methane emission and its perspective in the global methane cycle

Australian Journal of Experimental Agriculture, 2008

Science, Mar 10, 2016

Anthropogenic CH4-emissions have almost tripled [CH4] since preindustrial times (1-3). This contr... more Anthropogenic CH4-emissions have almost tripled [CH4] since preindustrial times (1-3). This contributes strongly to anthropogenic climate change through radiative forcing and impacts on atmospheric chemistry, particularly hydroxyl consumption, tropospheric ozone generation and water vapor formation in the stratosphere (4). In a positive feedback to climate change, natural sources like CH4-hydrates, tundra, and permafrost may increase (5). We must therefore understand how the CH4-budget responds to human activities and environmental change. The onset and end of the 1999-2006 [CH4]-plateau (3, 6, 7) (Fig. 1) have been studied with inverse models (top-down) (8-14), as well as process modelling (6, 8, 15-20) and emission estimates (21-23) (bottom-up). These approaches are either not emission-specific or uncertain in scaling and process representation (8). In contrast, the 13 C/ 12 C-ratio in atmospheric CH4 (δ 13 C(Atm); expressed in δ-notation relative to VPDB-standard) is controlled by the relative contributions from source types with distinctive isotope signatures δ 13 C(So) (biogenic ~-60‰, e.g., wetlands, agriculture, waste; thermogenic ~-37‰, e.g., fossil-fuels; pyrogenic ~-22‰, e.g., biomass burning) (3, 24). Large and overlapping ranges for δ 13 C(So) in field studies of the main source types and even individual sources (e.g., wetlands) (24) average out at the global scale so that δ 13 C(So) is suitable to characterize emissions. Sink processes with characteristic isotopic fractionation ε (25) (e.g., hydroxyl (OH) ε =-3.9‰, chlorine in the marine boundary layer (Cl-MBL) ε =-60‰; stratospheric loss ε =-3‰; oxidation by soils ε =-20‰) (26, 27) (table S1) also influence δ 13 C(Atm). Therefore, δ 13 C(Atm)-variations indicate changes in CH4budgets, where pertinent sources are industrial (thermogenic); agricultural, i.e., ruminants, rice (biogenic); and climate dependent, i.e., biomass burning (pyrogenic) and natural wetlands incl. freshwater and permafrost (biogenic). Other sources lack magnitude (termites, wild animals, ocean, hydrates (8)) or known processes (geologic sources) to force abrupt and sustained changes (Supplement). Changes in the dominating OH-sink may affect [CH4] and δ 13 C(Atm)-trends, while substantial changes in other sinks are unlikely or uncertain (Supplement). We reconstructed [CH4] and δ 13 C(Atm) time-series by splicing measurements from ice cores, firn air, archived air (1, 2) and global networks (3) (Fig. 1, fig. S1 and tables S2 and S3) (25). 13 C-enrichment followed by stable δ 13 C(Atm) parallels [CH4]-trends until the end of the 1999-2006 plateau. Afterwards, [CH4] increases while δ 13 C(Atm) becomes more 13 Cdepleted. This suggests that the increasing emissions before and after the plateau differ in δ 13 C(So). We use a one-box model (25, 27) to quantify changes in the CH4-budget. An inversion run derives the history of

Ecological Modelling, 1983

Environmental assessment methodologies and studies of element cycling in ecosystems require a qua... more Environmental assessment methodologies and studies of element cycling in ecosystems require a quantitative description of each transfer process contributing to the mobility of the entity (or element) under scrutiny. A conceptually simple filtration model is put forward as a candidate description of such a transfer process, appropriate when mobility is impeded by continual capture and release (possibly only partial release) by an interacting medium through which the entity passes. Three variants of the model are described, according to the saturability of the interacting medium and of the mobile host. Their presentation should make them particularly amenable to descriptions of a wide variety of processes which may be perceived in terms of filtration or exchange.

Journal of Integrative Environmental Sciences, Aug 1, 2010

The doubling of atmospheric methane (CH 4) during the twentieth century due largely to growth in ... more The doubling of atmospheric methane (CH 4) during the twentieth century due largely to growth in anthropogenic emissions has made CH 4 the second largest contributor behind carbon dioxide to anthropogenic forcing of climate change. However, the global CH 4 budget and its decadal evolution remain poorly quantified despite re-evaluations that include the IPCC Fourth Assessment Report. Potentially, the aggregation of national anthropogenic emission inventories as reported to the United Nations Framework Convention on Climate Change could document the changing anthropogenic emission since 1990, as could other ''bottom-up'' inventories such as EDGAR. As an examination of the recent CH 4 budget evolution, we compare two constructions of CH 4 source history, one based on an aggregation of national emission inventories, the other version 4 of EDGAR, each in combination with alternative natural CH 4 emissions, for consistency with observed atmospheric mixing ratio and carbon isotope content (d 13 C(CH 4)). We conclude that despite the utility of isotopic constraints on budget evolution, the level of uncertainty in sink strengths and their isotopic fractionation limits the confidence in constructing anthropogenic emission histories over recent decades.

The sulphur hexafluoride tracer technique for estimating enteric methane emissions from ruminants

New Zealand Journal of Agricultural Research, Oct 1, 2002

Methane emission was measured from 10 dairy cows and 12 wether sheep grazing kikuyu grass-(Pennis... more Methane emission was measured from 10 dairy cows and 12 wether sheep grazing kikuyu grass-(Pennisetum clandestinum) dominant pastures at Waimate North, Northland, in February 1997 and March 1999, and from 10 dairy cows grazing summer grass-(Digitaria sanguinalis) dominant pasture at Edgecumbe, Bay of Plenty, in March 2000. Methane emission was measured from each animal for 5 consecutive days in each measurement period using the sulphur hexafluoride (SF 6) tracer gas technique. Analysis of variance of the kikuyu grass chemical composition with sheep and cow data combined showed that the 1999 pastures were significantly higher in protein (P < 0.01), soluble sugars (P < 0.001), lipid (P < 0.01), and dry matter (DM) digestibility (P < 0.001) and lower in ash (P = 0.023), acid detergent fibre (ADF) (P < 0.001), and neutral detergent fibre (NDF) (P < 0.001) than the 1997 pastures, presumably as a consequence of urea topdressing in 1999. The A02022;

Parity violating observables in low energy nucleon-nucleon scattering

Physical review, Feb 1, 1978

We have calculated the parity violating observables in p-p and n-p scattering using a number of s... more We have calculated the parity violating observables in p-p and n-p scattering using a number of strong nucleon-nucleon potentials for a large class of weak parity violating potentials.

Some rumen digestion characteristics and methane emission in sheep

Verifying agricultural emissions of methane

Springer eBooks, 2000

The most direct way to establish the level of surface emissions of greenhouse gases is to measure... more The most direct way to establish the level of surface emissions of greenhouse gases is to measure and interpret concentration gradients in the atmosphere. We have tested the efficacy of this approach for inferring average methane fluxes from regions of pastoral agriculture a few tens of km in extent In its simplest form, vertical concentration profiles are measured upwind and downwind of the target region, based on air samples collected from light aircraft. Using simple mass balance models, the profile contrasts can be related to the mean surface flux over the intervening region. The inferred flux can then be compared with ‘bottom-up’ estimates based on livestock density and per-animal emissions. However, such simple models may poorly simulate air flows over the New Zealand terrain, and as an alternative, we deploy a state-of-the-art mesoscale meteorological model, RAMS, coupled to an atmospheric dispersion model. RAMS is used prognostically to guide the timing and siting of measurement campaigns, and diagnostically to simulate regional wind fields which are validated against local meteorological data. Source-oriented and receptor-oriented dispersion modelling techniques, in combination with aircraft-based sampling and laboratory gas analysis, provide ‘top-down’ methane flux estimates that compare favourably with ‘bottom-up’ estimates. These techniques thus enhance confidence in national emission inventories based on bottom-up estimation. However, the challenge for similar verification of nitrous oxide emission is more imposing.

Methane Emission By Grazing Livestock

In a series of field campaigns since 1995, a team of atmospheric and ruminantnutrition scientists... more In a series of field campaigns since 1995, a team of atmospheric and ruminantnutrition scientists have measured methane emissions directly from individual ruminant livestock freely grazing representative New Zealand pastures. The technique collects integrated ‘breath’ samples during grazing, using an implanted SF6 source as a conservative calibrated tracer, an approach pioneered by Johnson et al. [1994]. Most of these measurements have been on grazing sheep (942 animal-days to Aug 1999), others on grazing dairy cows (283), with some measurements also on sheep under controlled feeding conditions (305) [eg, Lassey et al., 1997; Ulyatt et al., 1999]. The aim is to characterise the variability of emission rates, including their dependence on pasture quality and physiological condition. The research goal is two-fold: (i) to provide a better scientific basis for assessing the national emissions inventory; and (ii) to investigate options for mitigating livestock emissions. Here, we discuss the research strategy and overview the principal research findings. We note in particular, that as a source of enterically fermented methane, sheep may not be merely ‘small cattle’.

Animal Feed Science and Technology, Jun 1, 2011

New Zealand Journal of Agricultural Research, Dec 1, 2005

Four groups of sheep were grazed on four late summer/autumn pastures: southern North Island summe... more Four groups of sheep were grazed on four late summer/autumn pastures: southern North Island summer moist hill country (Ballantrae); good quality perennial ryegrass/white clover dominant pasture in the Manawatu (Aorangi); severe late summer drought pasture in Hawke's Bay (Poukawa); and after drought conditions in Canterbury (Springston). Mature ewes were used at Springston, while young wethers were used at all the other sites. Methane emission from each animal was measured using the sulphur hexafluoride (SF 6) tracer technique and feed intake was also determined. The pastures used were chosen for their expected chemical compositions at that time of the year. However, unseasonal rain fell just before the measurements were made at Ballantrae, Aorangi, and Springston. Those three pastures, although different in botanical composition, were similar in chemical composition and dry matter (DM) digestibility. The Poukawa pasture was dead and had low protein, soluble carbohydrate and DM

Chemosphere - Global Change Science, Oct 1, 2001

Livestock farming is among the most methane-productive of human activities, contributing signi®ca... more Livestock farming is among the most methane-productive of human activities, contributing signi®cantly to the atmospheric growth of this greenhouse gas. International agreements to limit this growth require that source strengths be reliably quanti®ed. In a widely applied technique for unobtrusively measuring methane emission rates from freely grazing ruminant livestock, an inert tracer, sulfur hexa¯uoride, is released from a permeation tube pre-inserted into the rumen, also the site of methane generation. This paper presents examples of unexpected long-term changes in permeation characteristics, discusses their possible causes, and presents an empirical strategy for incorporating them into estimates of per-animal methane emission rates.