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Description: The hydrocarbon content of leaf fossils from Iceland has been investigated by gas chromatography-mass spectrometry. The distribution patterns of normal hydrocarbons, branched hydrocarbons, and cyclic hydrocarbons are compared to those of present-day living organisms. The diagenetic pathways of these hydrocarbons are discussed.
Date: October 1, 1970
Creator: Han, Jerry & Calvin, Melvin.
Partner: UNT Libraries Government Documents Department

Preliminary results from the lunar prospector alpha particle spectrometer

Description: The Lunar Prospector Alpha Particle Spectrometer (LP APS) builds on Apollo heritage and maps the distribution of outgassing sites on the Moon. The APS searches for lunar surface gas release events and maps their distribution by detecting alpha particles produced by the decay of gaseous radon-222 (5.5 MeV, 3.8 day half-life) and solid polonium-210 (5.3 MeV, 138 day half-life, but remains on the surface with a 21 year half-life as lead-210), which are radioactive daughters from the decay of uranium-238. Radon is in such small quantities that it is not released directly from the lunar interior, rather it is entrained in a stream of gases and serves as a tracer for such gases. Once released, the radon spreads out by 'bouncing' across the surface on ballistic trajectories in a random-walk process. The 3.8 day half-life of radon-222 allows the gas to spread out by several 100 km before it decays and allows the APS to detect gas release events up to a few days after they occur. The long residence time (10s of years) of the lead-210 precursor to the polonium-210 allows the mapping of gas vents which have been active over the last approximately 50 years. Because radon and polonium are daughter products of the decay of uranium, the background level of alpha particle activity is a function of the lunar crustal uranium distribution. Using radioactive radon and polonium as tracers, the Apollo 15 and 16 Command Module orbital alpha particle experiments obtained evidence for the release of gases at several sites beneath the orbit tracks, especially over the Aristarchus Plateau and Mare Fecunditatis [1]. Aristarchus crater had previously been identified by ground-based observers as the site of transient optical events [2]. The Apollo 17 surface mass spectrometer showed that argon-40 is released from the lunar interior every few ...
Date: January 1, 2001
Creator: Lawson, S. L. (Stefanie L.)
Partner: UNT Libraries Government Documents Department

Influence of sample composition on aerosol organic and black carbon determinations

Description: In this paper we present results on characterization of filter-collected redwood (Sequoia sempevirens)-needle and eucalyptus smoke particles by thermal, optical, and solvent extraction methods. Our results demonstrate that organic and black carbon concentrations determined by thermal and optical methods are not only method dependent, but also critically influenced by the overall chemical composition of the samples. These conclusions are supported by the following: (1) the organic fraction of biomass smoke particles analyzed includes a component, ranging in concentration from about 6-20% of total carbon or from 16-30% of organic carbon, that is relatively non-volatile and has a combustion temperature close to that of black carbon; (2) presence of K or Na in biomass smoke samples lowers the combustion temperatures of this organic component and of black carbon, making their combustion properties indistinguishable; (3) about 20% of total organic material is nonvolatile when heated to 550{degrees}C in an inert atmosphere. Consequently, thermal methods that rely on a specific temperature to separate organic from black carbon may either underestimate or overestimate the black and organic carbon concentrations, depending on the amounts of Na and K and on the composition and concentration of organic material present in a sample. These analytical uncertainties and, under some conditions, absorption by organic material may contribute to the variability of empirically derived proportionality between light transmission through filter deposits and black carbon concentrations.
Date: July 1, 1995
Creator: Novakov, T. & Corrigan, C.E.
Partner: UNT Libraries Government Documents Department

Update to modeling soil selenium concentrations in the shallow soil profile at Kesterson Reservoir Merced County, California

Description: A mass balance model was developed to predict concentrations of water-extractable selenium in surface and subsurface soil by extrapolating the trend observed from 6 years of soil monitoring data collected at Kesterson Reservoir. Correlations between observed and calculated concentrations indicate that the major trends and year-to-year variations are well represented with the model. Results from this exercise were then used, under three climatic scenarios, to simulate the evolution of the soluble selenium inventory 25 years into the future. Based on these simulations, we expect that the availability of the soluble selenium inventory has most likely reached peak levels, and is now declining. However, year-to-year climatic variations may influence the rate of decline, and occasionally reverse this prevailing trend.
Date: January 1, 1996
Creator: Wahl, C. & Benson, S. M.
Partner: UNT Libraries Government Documents Department

Concentrations of a water soluble, gas-phase mercury species in ambient air: Results from measurements and modeling

Description: There are few reliable data on the speciation of Hg in ambient air, although this information is critical to understanding the fate of Hg once released from point sources. The water soluble species of Hg that are thought to exist in flue gases would be subject to far greater local removal rates than is elemental Hg vapor, but methods are lacing to quantify this species. The authors developed a method using refluxing mist chambers to measure the airborne concentrations of reactive gaseous mercury (RGM) in short-term samples under ambient conditions. The method exhibits an effective detection limit of 0.02 ng/m{sup 3} and a precision for ambient concentration levels of {+-}20--30%. Using a model that simulates atmospheric transport and fate of anthropogenic mercury emissions over the contiguous United States, the authors generated 24-hr RGM concentrations to compare to the measurement data. The average RGM concentrations measured with their mist chambers at sites in Tennessee (TN) and Indiana (IN) were 0.065 ng/m{sup 3} and 0.100 ng/m{sup 3}, respectively. These averages represent about 3% of total gaseous mercury (TGM), and RGM generally exceeds regional particulate Hg. The 24-hr model-simulated RGM concentration averages in the modeling grid cells representing TN and IN are 0.051 ng/m{sup 3} and 0.098 ng/m{sup 3} respectively, in good agreement with the data. The measured concentrations at the two sites exhibit weak positive correlations with temperature, solar radiation, O{sub 3}, SO{sub 2}, and TGM. These concentrations are high enough to suggest that RGM can play an important role in both wet and dry deposition on a regional scale.
Date: December 31, 1997
Creator: Lindberg, S. E.; Stratton, W. J.; Pai, P. & Allan, M. A.
Partner: UNT Libraries Government Documents Department

Multi-Filter Rotating Shadowband Radiometer (MFRSR) retrievals of total column aerosol, water vapor, and ozone during the Arm Enhanced Shortwave Experiment (ARESE)

Description: The ARESE provided an opportunity to compare MFRSR retrievals of total column aerosol optical depth, total column water vapor, and total column ozone with independent measurements of the same quantities during this campaign in the fall of 1995. MFRSR ozone was compared to ozonesondes that reached altitudes of at least 30 km. MFRSR water vapor was compared to microwave radiometer water vapor on several clear days during the campaign. Aerosol was measured by the ARM MFRSR and the Penn State Reagan sun photometer at high time resolution on a few days of the experiment. Only total column measurements of these constituents were compared. These comparisons were part of an effort to validate MFRSR retrievals that date from 1992. The daily total column aerosol optical depth record since that year illustrates the archival data and the variability of aerosol seasonally and during the decay of the Mt. Pinatubo stratospheric aerosol layer.
Date: December 31, 1996
Creator: Michalsky, J.J.; Min, Qilong & Harrison, L.C.
Partner: UNT Libraries Government Documents Department

Toxicological benchmarks for screening potential contaminants of concern for effects of terrestrial plants: 1995 Revision

Description: The purpose of this technical memorandum is to present plant toxicity data and discuss their utility as benchmarks for determining the hazard to terrestrial plants caused by contaminants in soil. This work was performed under Work Breakdown Structure (Activity Data Sheet 8304). This report presents a standard method for deriving benchmarks, a set of data concerning effects of chemicals in soil or soil solution on plants, and a set of phytotoxicity benchmarks for 38 chemicals potentially associated with United States Department of Energy sites. In addition, background information on the phytotoxicity and occurrence of the chemicals in soils is presented, and literature describing the experiments from which data were drawn for benchmark derivation is reviewed.
Date: September 1, 1995
Creator: Will, M.E. & Suter, G.W. II
Partner: UNT Libraries Government Documents Department

Atmospheric pre-corrected differential absorption techniques to retrieve columnar water vapor: Theory and simulations

Description: Two different approaches exist to retrieve columnar water vapor from imaging spectrometer data: (1) Differential absorption techniques based on: (a) Narrow-Wide (N/W) ratio between overlapping spectrally wide and narrow channels (b) Continuum Interpolated Band Ratio (CIBR) between a measurement channel and the weighted sum of two reference channels; and (2) Non-linear fitting techniques which are based on spectral radiative transfer calculations. The advantage of the first approach is computational speed and of the second, improved retrieval accuracy. Our goal was to improve the accuracy of the first technique using physics based on radiative transfer. Using a modified version of the Duntley equation, we derived an {open_quote}Atmospheric Pre-corrected Differential Absorption{close_quote} (APDA) technique and described an iterative scheme to retrieve water vapor on a pixel-by-pixel basis. Next we compared both, the CIBR and the APDA using the Duntley equation for MODTRAN3 computed irradiances, transmissions and path radiance (using the DISORT option). This simulation showed that the CIBR is very sensitive to reflectance effects and that the APDA performs much better. An extensive data set was created with the radiative transfer code 6S over 379 different ground reflectance spectra. The calculated relative water vapor error was reduced significantly for the APDA. The APDA technique had about 8% (vs. over 35% for the CIBR) of the 379 spectra with a relative water vapor error of greater than {+-}5%. The APDA has been applied to 1991 and 1995 AVIRIS scenes which visually demonstrate the improvement over the CIBR technique.
Date: March 1, 1996
Creator: Borel, C.C. & Schlaepfer, D.
Partner: UNT Libraries Government Documents Department

Atmospheric pre-corrected differential absorption techniques to retrieve columnar water vapor: Application to AVIRIS 91/95 data

Description: Water vapor is one of the main forces for weather development as well as for mesoscale air transport processes. The monitoring of water vapor is therefore an important aim in remote sensing of the atmosphere. Current operational systems for water vapor detection use primarily the emission in the thermal infrared (AVHRR, GOES, ATSR, Meteosat) or in the microwave radiation bands (DMSP). The disadvantage of current satellite systems is either a coarse spatial (horizontal) resolution ranging from one to tens of kilometers or a limited insight into the lower atmosphere. Imaging spectrometry on the other hand measures total column water vapor contents at a high spatial horizontal resolution and has therefore the potential of filling these gaps. The sensors of the AVIRIS instrument are capable of acquiring hyperspectral data in 224 bands located in the visible and near infrared at 10 run resolution. This data includes information on constituents of the earth`s surface as well as of the atmosphere. The optical measurement of water vapor can be performed using sensor channels located in bands or lines of the absorption spectrum. The AVIRIS sensor has been used to retrieve water vapor and with less accuracy carbon dioxide, oxygen and ozone. To retrieve the water vapor amount, the so called differential absorption technique has been applied. The goal of this technique is to eliminate background factors by taking a ratio between channels within the absorption band and others besides the band. Various rationing methods on the basis of different channels and calculation techniques were developed. The influence of a trace gas of interest on the radiance at the sensor level is usually simulated by using radiative transfer codes. In this study, spectral transmittance and radiance are calculated by MODTRAN3 simulations with the new DISORT option. This work testS the best performing differential absorption ...
Date: March 1, 1996
Creator: Schlaepfer, D.; Borel, C.C. & Keller, J.
Partner: UNT Libraries Government Documents Department

A methodology for assessing the impact of mutagens on aquatic ecosystems. Final report

Description: Assessments of impacts of hazardous agents (i.e., chemical and physical mutagens) on human health have focused on defining the effects of chronic exposure on individuals, with cancer being the main effect of concern. In contrast, impacts on ecosystems have traditionally been gauged by the assessment of near-term organism mortality, which is clearly not a useful endpoint for assessing the long-term effects of chronic exposures. Impacts on individual organisms that affect the long-term survival of populations are much more important but are also more difficult to define. Therefore, methods that provide accurate measures of sub-lethal effects that are linked to population survival are required so that accurate assessments of environmental damage can be made and remediation efforts, if required, can be initiated. Radioactive substances have entered aquatic environments as a result of research and production activities, intentional disposal, and accidental discharges. At several DOE sites, surface waters and sediments are contaminated with radioactive and mutagenic materials. The accident at the Chernobyl power station in the former Soviet Union (FSU) has resulted in the contamination of biota present in the Kiev Reservoir. This documents presents a methodology which addresses the effects of a direct-acting mutagen (radiation) on aquantic organisms by applying sensitive techniques for assessing damage to genetic material.
Date: March 1, 1995
Creator: Knezovich, J.P. & Martinelli, R.E.
Partner: UNT Libraries Government Documents Department

Characterization of anaerobic chloroethene-dehalogenating activity in several subsurface sediments

Description: Anaerobic microcosms of subsurface soils from four locations were used to investigate the separate effects of several electron donors on tetrachloroethylene (PCE) dechlorination activity. The substrates tested were methanol, formate, lactate, acetate, and sucrose. Various levels of sulfate-reducing, acetogenic, fermentative, and methanogenic activity were observed in all sediments. PCE dechlorination was detected in all microcosms, but the amount of dehalogenation varied by several orders of magnitude. Trichloroethylene was the primary dehalogenation product; however, small amounts of cis-1,2-dichloroethylene, 1,1-dichloroethylene, and vinyl chloride were also detected in several microcosms. Lactate-amended microcosms showed large amounts of dehalogenation. in three of the four sediments. One of the two sediments which showed positive activity with lactate also had large amounts of delialogenation with methanol. Sucrose, formate, and acetate also stimulated large amounts of delialogenation in one sediment that showed activity with lactate. These results suggest that lactate may be an appropriate substrate for screening sediments for PCE or TCE delialogenation activity, but that the microbial response is not sufficient for complete in situ bioremediation. A detailed study of the Victoria activity revealed that delialogenation rates were more similar to the Cornell culture than to rates measured for methanogens, or a methanol-enriched sediment culture. This may suggest that these sediments contain a highly efficient delialogenation activity similar to the Cornell culture. This assertion is supported further by the fact that an average of 3% of added reducing equivalents could be diverted to dehalogenation in tests which were conducted using PCE-saturated hexadecane as a constant source of PCE during incubation. Further evidence is needed to confirm this premise. The application of these results to in situ bioremediation of highly contaminated areas are discussed.
Date: November 1, 1996
Creator: Skeen, R.S.; Gao, J.; Hooker, B.S. & Quesenberry, R.D.
Partner: UNT Libraries Government Documents Department

Remote sensing of the atmosphere by resonance Raman LIDAR

Description: When in resonance, Raman scattering exhibits strong enhancement ranging from four to six orders of magnitude. This physical phenomenon has been applied to remote sensing of the Earth`s atmosphere. With a 16 inch Cassegrain telescope and spectrometer/ CCD-detector system, 70-150 ppm-m of SO{sub 2} in the atmosphere has been detected at a distance of 0.5 kilometer. This system can be used to detect/monitor chemical effluence in the atmosphere by their unique Raman fingerprints. Experimental result together with detailed resonance Raman and atmospheric laser propagation effects will be discussed.
Date: December 1, 1994
Creator: Sedlacek, A.J.; Harder, D.; Leung, K.P.; Zuhoski, P.B. Jr.; Burr, D. & Chen, C.L.
Partner: UNT Libraries Government Documents Department

The photosynthetic acclimation response of Lolium perenne to four years growth in a free-air CO{sub 2} enrichment (FACE) facility

Description: In this study, the photosynthetic responses of field grown Lolium perenne to ambient (354 {mu}mol mol{sup -1}) and elevated (600 {mu}mol mol{sup -1}) C{sub a} were measured. The experiment utilized the FACE facility at Eschikon, Switzerland; here the L. Perenne swards had been grown at two nitrogen treatments, with six cuts per year, for 4 years. The study revealed a significant decrease in Rubisco activity (Vcmax) in the low nitrogen FACE plots; this is consistent with the theories of source-sink imbalance resulting in feedback inhibition and down-regulation. Such negative acclimation was not wholly supported by diurnal investigations which revealed an average stimulation of 53.38% and 52.78% in the low and high nitrogen, respectively. However, light response curves and AI investigations also suggested down-regulation, especially in the low nitrogen. SI is expected to decrease in response to elevated C{sub a}, if any change is seen. This was indeed observed in the high nitrogen plots but for the low nitrogen a significant increase was found. Conclusions drawn from this project center around the implications of negative acclimation to future crop productivity. For instance, inter-specific differences in response to elevated C{sub a} may result in ecosystem changes and new management techniques may be necessary. However, real predictions cannot be made from leaf level studies alone as these may not represent the overall changes at the whole plant level.
Date: November 1, 1996
Creator: Creasey, R.
Partner: UNT Libraries Government Documents Department

Genetic and biochemical analysis of solvent formation in Clostridium acetobutylicum. Progress report, September 1, 1992--July 31, 1996

Description: Several degenerate strains were isolated and characterized by sporulation, motility and growth properties. Cell appearance and colony morphology were also recorded. Enzymatic assays revealed reduced butyraldehyde dehydrogenase and Co-A transferase enzyme activities in the degenerates. DNA analysis revealed that in complete degenerate strains the genes of the solvent locus were absent. Gyrase inhibitors slightly reduced the growth rate and decreased acetone formation preferentially. In an effort to analyze the role of sporulation sigma factors in solvent gene expression, recombination experiments were conducted and led to strains with increased solvent production. Analysis of redox systems has resulted in the sequence analysis of a cluster encoding formyl transferase proteins and an oxidoreductase-like gene. The genes for the two subunits of an apparent electron transfer flavoprotein were sequenced and suggest this factor acts to carry electrons to the butyryl-CoA dehydrogenase. The genes encoding the Fo subunits of the membrane ATPase have been sequenced.
Date: January 1, 1997
Creator: Bennett, G.N. & Rudolph, F.B.
Partner: UNT Libraries Government Documents Department

Assessing historical global sulfur emission patterns for the period 1850--1990

Description: Anthropogenic sulfur dioxide emissions from energy-producing and metal production activities have become an important factor in better understanding the relationship between humans and the environment. Concerns about (1) acid rain effects on the environment and (2) anthropogenic aerosols affecting possible global change have prompted interest in the transformation and fate of sulfur in the environment. One step in assessing the importance of sulfur emissions is the development of a reliable regional emission inventory of sulfur as a function of time. The objective of this research effort was to create a homogeneous database for historical sulfur emission estimates for the world. The time from 1850--1990 was selected to include the period of industrialization form the time the main production of fuels and minerals began until the most recent year for which complete production data exist. This research effort attempts to correct some of the deficiencies associated with previous global sulfur emission estimates by (1) identifying those production activities that resulted in sulfur emissions by country and (2) calculating historical emission trends by country across years. An important component of this study was the comparison of the sulfur emission results with those of previous studies.
Date: July 19, 1996
Creator: Lefohn, A.S.; Husar, J.D.; Husar, R.B. & Brimblecombe, P.
Partner: UNT Libraries Government Documents Department

Plutonium in human urine: Normal levels in the US public. 1991 Annual report, Volume 2

Description: A neutron induced fission track method was successfully developed for assaying {sup 239}Pu in human urine with a detection limit below 20 aCi/sample. The technique involves the co-precipitation of {sup 239}Pu with rhodizonic acid, separation of {sup 239}Pu from potentially interfering natural uranium and other inorganic materials by ion-exchange techniques, collection of the sample onto lexan detectors, irradiation of sample in MIT reactor at a fluence of 1.1 x 10{sup 17} n/cm{sup 2}, etching of the lexan slide and counting the track either manually or by some automated counting system.
Date: March 1, 1997
Creator: Wrenn, M.E.; Singh, N.P. & Xue, Ying-Hua
Partner: UNT Libraries Government Documents Department

Daytime Raman lidar measurements of water vapor during the ARM 1997 water vapor intensive observation period

Description: Because of the importance of water vapor, the ARM program initiated a series of three intensive operating periods (IOPs) at its CART (Cloud And Radiation Testbed) site. The goal of these IOPs is to improve and validate the state-of-the-art capabilities in measuring water vapor. To date, two of the planned three IOPs have occurred: the first was in September of 1996, with an emphasis on the lowest kilometer, while the second was conducted from September--October 1997 with a focus on both the upper troposphere and lowest kilometer. These IOPs provided an excellent opportunity to compare measurements from other systems with those made by the CART Raman lidar. This paper addresses primarily the daytime water vapor measurements made by the lidar system during the second of these IOPs.
Date: April 1, 1998
Creator: Turner, D.D. & Goldsmith, J.E.M.
Partner: UNT Libraries Government Documents Department

Trace gas measurements in Phoenix, Arizona (1998)

Description: The DOE Atmospheric Chemistry Program, and the Arizona Department of Environmentel Quality (DEQ) conducted a field program in the Phoenix Metropolitan area in the late spring of 1998. The experiment was composed of a linked set of aircraft and surface measurements designed to characterize the chemical and meteorological processes leading to ozone episodes. The existing network of Arizona DEQ sites in Phoenix was utilized to document ground level concentrations of ozone and its precursors. West of the downtown area, a site (Usery Pass) was set up for the detailed characterization of the mature Phoenix urban plume. Detailed measurements in the source region were made at several sites in downtown Phoenix. The DOE G-1 aircraft, equipped wih a comprehensive array of instruments to characterize atmospheric trace gas and aerosol composition, flew over the region at various times during the day. All times in the following discussion are local standard time (LST). Morning flights were typically made between 08:00 and 12:00 upwind, to measure background concentrations, and over the Phoenix source region, to characterize the sources of ozone precursors. Afternoon flights over the Phoenix source region and downwind between 15:00 and 18:00 were made to examine the chemical properties and physical distribution of the photochemically aged urban plume. The aircraft flights typically included an atmospheric sounding to circa 3 km upwind and over Phoenix in the morning, and downwind in the afternoon. A total of 22 flights were made on 14 different days during the one month program. The motivation for conducting the program was to examine ozone formation rates and efficiencies in an environment where the pollutant mix is dominated by vehicle emissions, where the contribution of biogenic hydocarbons to ozone formation is thought to be low, and where processing conditions are different than they are in the Eastern US. The ...
Date: January 9, 2000
Creator: Nunnermacker, L.J.
Partner: UNT Libraries Government Documents Department

Running Head: Control and Adjustment of the Rate of Photosynthesis Above Present CO{sub 2} Levels

Description: The adjustment of photosynthesis to different environmental conditions and especially to elevated CO{sub 2} is often characterized in terms of changes in the processes that establish (limit) the net CO{sub 2} assimilation rate. At slightly above present ambient pCO{sub 2} light-saturated photosynthetic responses to CO{sub 2} depart limitation by the catalytic capacity of tissue rubisco content. An hypothesis attributing this departure to limited thylakoid reaction/electron transport capacity is widely accepted, although we find no experimental evidence in the literature supporting this proposition.. The results of several tests point to the conclusion that the capacity of the thyiakoid reactions cannot be generally responsible for the deviation from rubisco limitation. This conclusion leaves a significant gap in the interpretation of gas exchange responses to CO{sub 2}. Since the inputs to the photosynthetic carbon reduction cycle (CO{sub 2} and photon-capture/electron-transport products) do not limit photosynthesis on the shoulder of the A=f(c{sub i}) curve, the control of photosynthesis can be characterized as: due to feedback. Several characteristics of gas exchange and fluorescence that occur when steady-states in this region are perturbed by changes in CO{sub 2} or O{sub 2} suggest significant regulation by conditions other than directly by substrate RuBP levels. A strong candidate to explain these responses is the triose-phosphate flux/ inorganic phosphate regulatory sequence, although not all of the gas exchange characteristics expected with ''TPU-limitation'' are present (e.g. oxygen-insensitive photosynthesis). Interest in nitrogen allocation between rubisco and light capture/electron transport as the basis for photosynthetic adjustment to elevated CO{sub 2} may need to be reconsidered as a result of these findings. Contributors to the feedback regulation of photosynthesis (which may include sucrose phosphate synthase and fructose bisphosphatase activities, phloem loading, and ''sink-strength'') may play a large role in the adjustment of photosynthesis to elevated CO{sub 2}. The continuing rise in atmospheric CO{sub ...
Date: December 1, 1996
Creator: Ball, J. Timothy
Partner: UNT Libraries Government Documents Department

Whole System Carbon Exchange of Small Stands of Pinus Ponderosa Growing at Different CO{sub 2} concentrations in open top chambers

Description: Functional understanding of the carbon cycle from the molecular to the global level is a high scientific priority requiring explanation of the relationship between fluxes at different spatial and temporal scales. We describe methods used to convert an open top chamber into both closed and open flow gas exchange systems utilized to measure such fluxes. The systems described consist of temporary modifications to an open top chamber, and are put in place for several days on one or several open top chambers. In the closed system approach, a chamber is quickly sealed for a short, predetermined time interval, the change in gas concentrations is measured, then the chamber is unsealed and ventilated. In the open flow system approach, airflow into the open top chamber is measured by trace gas injection, and the air stream concentration of CO{sub 2} and water vapor is measured before and after injection into the chamber. The closed chamber approach can resolve smaller fluxes, but causes transient increases in chamber air temperature, and has a high labor requirement. The open flow approach reduces the deviation of measuring conditions from ambient, may be semi-automated (requiring less labor), allows a more frequent sampling interval, but cannot resolve low fluxes well. Data demonstrating the capabilities of these systems show that, in open canopies of ponderosa pine, scaling fluxes from leaves to whole canopies is well approximated from summation of leaf P{sub s} rates. Flux measurements obtained from these systems can be a valuable contribution to our understanding whole system material fluxes, and challenge our understanding of ecosystem carbon budgets.
Date: December 1, 1996
Creator: Ball, J. Timothy; Ross, Peter D.; Picone, John B.; Eichelmann, Hillar Y. & Ross, Gregory N.
Partner: UNT Libraries Government Documents Department