Cellulose mass loss in ombrotrophic bogs of northeastern North America

1992 ◽  
Vol 70 (12) ◽  
pp. 2378-2383 ◽  
Author(s):  
Mary V. Santelmann
Keyword(s):  
North America ◽  
Mass Loss ◽  
Water Table ◽  
Decomposition Rates ◽  
Site Analysis ◽  
Sphagnum Bogs ◽  
Peak Mass ◽  
Sphagnum Bog ◽  
Second Peak ◽  
Loss Rates

Profiles of cellulose mass loss were measured for six Sphagnum bogs in eastern North America as an index of decomposition rates. After 2 years, mass loss rates in the upper 5 cm of the profiles averaged 49% in hummocks, 52% in hollows where the water table was more than 5 cm below the surface, and 21% in hollows where the water table was within 5 cm of the surface. Hummock profiles were of three types: (i) mass loss highest at the surface, gradually decreasing to very low rates below the water table; (ii) mass loss highest at the surface, decreasing for 10 – 20 cm, with a second peak in the region of the water table; and (iii) mass loss low at the surface with a subsurface peak. Mass loss rates for all profiles reached minimum values below the water table, averaging 3% in hummocks and 5% in hollows after 2 years. Cellulose mass loss was quite variable in upper portions of the profiles; within-site variance was almost as great as between-site variance, reflecting similarity among these bogs and heterogeneity within each site. Analysis of variance of mass loss at the hummock surface showed no significant effect of site; however, contrasts among means showed that mass loss rates at the surface of hummocks of the northern (Newfoundland) bogs were significantly lower (p < 0.05) than those from the sites farthest south (in Nova Scotia and Maine). Key words: cellulose mass loss, Sphagnum bog, decomposition.

Litter mass-loss rates in late stages of decomposition in a climatic transect of pine forests. Long-term decomposition in a Scots pine forest. IX.

1995 ◽  
Vol 73 (10) ◽  
pp. 1509-1521 ◽  
Author(s):  
Maj-Britt Johansson ◽  
Björn Berg ◽  
Vernon Meentemeyer
Keyword(s):  
Mass Loss ◽  
Scots Pine ◽  
Actual Evapotranspiration ◽  
The Arctic ◽  
Decomposition Rates ◽  
Lignin Concentration ◽  
Arctic Circle ◽  
Litter Mass ◽  
Litter Mass Loss ◽  
Loss Rates

We investigated rate-regulating factors for decomposition rates of Scots pine needle litter at 22 sites over a 2000-km long transect ranging from the Arctic Circle in Scandinavia to northern continental Europe. We found very different patterns for rate-regulating factors in the early stages of decomposition as compared to later stages (> 20% accumulated mass loss). The initial decomposition rates (measured over the 1st year) ranged from about 10.9%/year close to the Arctic Circle to about 43.7%/year in south Sweden. The dominant rate-regulating factor was climate (average annual temperature, and actual evapotranspiration), and none of the substrate-quality factors was significant. In the later stages, the annual mass loss varied from 2.2%/year to 41.5%/year. The rate-regulating factors were climate and the litter's concentration of lignin. We found that the effect of lignin concentration on litter mass-loss rate varied with site and this relative effect was negatively related with actual evapotranspiration. The effect of lignin concentration on mass-loss rates near the Arctic Circle was thus low (at low values for actual evapotranspiration) whereas in Southern Sweden and on the continent the rate-regulating effect of lignin was higher. Key words: foliar litter, decomposition, lignin, climatic transect, rate-regulating factors, climate change.

Influence of Chinese Privet (Ligustrum sinense) on Decomposition and Nutrient Availability in Riparian Forests

2011 ◽  
Vol 4 (4) ◽  
pp. 437-447 ◽  
Author(s):  
Jennifer D. Mitchell ◽  
B. Graeme Lockaby ◽  
Eve F. Brantley
Keyword(s):  
Mass Loss ◽  
N Mineralization ◽  
Native Species ◽  
Field Investigation ◽  
Riparian Forests ◽  
Controlled Study ◽  
Decomposition Rates ◽  
Chinese Privet ◽  
Ligustrum Sinense ◽  
Loss Rates

AbstractAs invasive species become increasingly abundant in forests, their presence may influence a number of key nutrient cycling processes. For example, Chinese privet has become well established in southeastern forests and continues to spread. Two studies, a multisite field investigation and a controlled approach on a single site, were conducted to examine the role of Chinese privet (Ligustrum sinense) on decomposition within riparian forests of the Georgia Piedmont. The field study also investigated the effects of privet presence on soil nitrogen (N) mineralization and microbial carbon and N immobilization. Both studies utilized a litterbag approach to examine how increasing proportions of privet in foliar litter influenced mass loss rates and nutrient dynamics. The field investigation included litterbags with representative proportions of the five dominant species from 16 sites. Litterbags in the controlled study were composed of specific levels of privet litter within bags (0, 10, 20, 30, 40, and 50% Chinese privet) as treatments. The litter quality of four native species was compared to Chinese privet in the controlled study. Both studies showed significant positive relationships between percentage of Chinese privet in litterbags and decomposition rates (2.6-fold rate increase with 30% privet in litterfall). Chinese privet leaf litter had lower lignin and cellulose concentrations, higher N concentrations, lower lignin : N ratios, and narrower C : N ratios than the native species. The positive relationship between mass loss rates and the proportion of Chinese privet in litter indicates that Chinese privet enhances decomposition rates as it becomes more abundant. During summer, N mineralization showed approximately a fivefold increase; during winter, microbial biomass N increased by approximately 30% on sites with the highest levels of privet in the understory. Consequently, C and N dynamics in Piedmont riparian forests were significantly influenced in direct proportion to the amount of privet present in the understory.

scholarly journals Three-component modelling of C-rich AGB star winds – V. Effects of frequency-dependent radiative transfer including drift★

2020 ◽  
Vol 499 (2) ◽  
pp. 1531-1560
Author(s):  
Christer Sandin ◽  
Lars Mattsson
Keyword(s):  
Radiative Transfer ◽  
Mass Loss ◽  
Density Ratio ◽  
Mie Scattering ◽  
Speed Ratio ◽  
Exponential Dependence ◽  
Frequency Dependent ◽  
Wind Velocities ◽  
Drift Models ◽  
Loss Rates

ABSTRACT Stellar winds of cool carbon stars enrich the interstellar medium with significant amounts of carbon and dust. We present a study of the influence of two-fluid flow on winds where we add descriptions of frequency-dependent radiative transfer (RT). Our radiation hydrodynamic models in addition include stellar pulsations, grain growth and ablation, gas-to-dust drift using one mean grain size, dust extinction based on both the small particle limit (SPL) and Mie scattering, and an accurate numerical scheme. We calculate models at high spatial resolution using 1024 gridpoints and solar metallicities at 319 frequencies, and we discern effects of drift by comparing drift models to non-drift models. Our results show differences of up to 1000 per cent in comparison to extant results. Mass-loss rates and wind velocities of drift models are typically, but not always, lower than in non-drift models. Differences are larger when Mie scattering is used instead of the SPL. Amongst other properties, the mass-loss rates of the gas and dust, dust-to-gas density ratio, and wind velocity show an exponential dependence on the dust-to-gas speed ratio. Yields of dust in the least massive winds increase by a factor 4 when drift is used. We find drift velocities in the range $10\!-\!67\, \mbox{km}\, \mbox{s}^{-1}$, which is drastically higher than in our earlier works that use grey RT. It is necessary to include an estimate of drift velocities to reproduce high yields of dust and low wind velocities.

scholarly journals Asteroseismology of luminous red giants with Kepler. II. Dependence of mass loss on pulsations and radiation

2020 ◽  
Author(s):  
Jie Yu ◽  
Saskia Hekker ◽  
Timothy R Bedding ◽  
Dennis Stello ◽  
Daniel Huber ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Asymptotic Giant Branch Stars ◽  
Chemical Enrichment ◽  
Dust Mass ◽  
Red Giant ◽  
The Masses ◽  
Loss Rates

Abstract Mass loss by red giants is an important process to understand the final stages of stellar evolution and the chemical enrichment of the interstellar medium. Mass-loss rates are thought to be controlled by pulsation-enhanced dust-driven outflows. Here we investigate the relationships between mass loss, pulsations, and radiation, using 3213 luminous Kepler red giants and 135000 ASAS–SN semiregulars and Miras. Mass-loss rates are traced by infrared colours using 2MASS and WISE and by observed-to-model WISE fluxes, and are also estimated using dust mass-loss rates from literature assuming a typical gas-to-dust mass ratio of 400. To specify the pulsations, we extract the period and height of the highest peak in the power spectrum of oscillation. Absolute magnitudes are obtained from the 2MASS Ks band and the Gaia DR2 parallaxes. Our results follow. (i) Substantial mass loss sets in at pulsation periods above ∼60 and ∼100 days, corresponding to Asymptotic-Giant-Branch stars at the base of the period-luminosity sequences C′ and C. (ii) The mass-loss rate starts to rapidly increase in semiregulars for which the luminosity is just above the red-giant-branch tip and gradually plateaus to a level similar to that of Miras. (iii) The mass-loss rates in Miras do not depend on luminosity, consistent with pulsation-enhanced dust-driven winds. (iv) The accumulated mass loss on the Red Giant Branch consistent with asteroseismic predictions reduces the masses of red-clump stars by 6.3%, less than the typical uncertainty on their asteroseismic masses. Thus mass loss is currently not a limitation of stellar age estimates for galactic archaeology studies.

scholarly journals Evolution of O stars and the WR connection

1979 ◽  
Vol 83 ◽  
pp. 431-445 ◽  
Author(s):  
Peter S. Conti
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
High Luminosity ◽  
Loss Mechanism ◽  
Evolutionary Scenario ◽  
Processed Material ◽  
Dominant Process ◽  
Highly Evolved ◽  
Loss Rates ◽  
Enriched Composition

The stellar wind mass loss rates of at least some single Of type stars appear to be sufficient to remove much if not all of the hydrogen-rich envelope such that nuclear processed material is observed at the surface. This highly evolved state can then be naturally associated with classic Population I WR stars that have properties of high luminosity for their mass, helium enriched composition, and nitrogen or carbon enhanced abundances. If stellar wind mass loss is the dominant process involved in this evolutionary scenario, then stars with properties intermediate between Of and WR types should exist. The stellar parameters of luminosity, temperature, mass and composition are briefly reviewed for both types. All late WN stars so far observed are relatively luminous like Of stars, and also contain hydrogen. All early WN stars, and WC stars, are relatively faint and contain little or no hydrogen. The late WN stars seem to have the intermediate properties required if a stellar wind is the dominant mass loss mechanism that transforms an Of star to a WR type.

scholarly journals Carbon star wind models at solar and sub-solar metallicities: a comparative study

2019 ◽  
Vol 623 ◽  
pp. A119 ◽  
Author(s):  
S. Bladh ◽  
K. Eriksson ◽  
P. Marigo ◽  
S. Liljegren ◽  
B. Aringer
Keyword(s):  
Mass Loss ◽  
Agb Stars ◽  
Carbon Stars ◽  
Dust Production ◽  
Grain Sizes ◽  
Solar Metallicity ◽  
Effective Temperatures ◽  
Carbon Excess ◽  
Thermal Pulses ◽  
Loss Rates

Context. The heavy mass loss observed in evolved stars on the asymptotic giant branch (AGB) is usually attributed to dust-driven winds, but it is still an open question how much AGB stars contribute to the dust production in the interstellar medium, especially at lower metallicities. In the case of C-type AGB stars, where the wind is thought to be driven by radiation pressure on amorphous carbon grains, there should be significant dust production even in metal-poor environments. Carbon stars can manufacture the building blocks needed to form the wind-driving dust species themselves, irrespective of the chemical composition they have, by dredging up carbon from the stellar interior during thermal pulses. Aims. We investigate how the mass loss in carbon stars is affected by a low-metallicity environment, similar to the Large and Small Magellanic Clouds (LMC and SMC). Methods. The atmospheres and winds of C-type AGB stars are modeled with the 1D spherically symmetric radiation-hydrodynamical code Dynamic Atmosphere and Radiation-driven Wind models based on Implicit Numerics (DARWIN). The models include a time-dependent description for nucleation, growth, and evaporation of amorphous carbon grains directly out of the gas phase. To explore the metallicity-dependence of mass loss we calculate model grids at three different chemical abundances (solar, LMC, and SMC). Since carbon may be dredged up during the thermal pulses as AGB stars evolve, we keep the carbon abundance as a free parameter. The models in these three different grids all have a current mass of one solar mass; effective temperatures of 2600, 2800, 3000, or 3200 K; and stellar luminosities equal to logL*∕L⊙ = 3.70, 3.85, or 4.00. Results. The DARWIN models show that mass loss in carbon stars is facilitated by high luminosities, low effective temperatures, and a high carbon excess (C–O) at both solar and subsolar metallicities. Similar combinations of effective temperature, luminosity, and carbon excess produce outflows at both solar and subsolar metallicities. There are no large systematic differences in the mass-loss rates and wind velocities produced by these wind models with respect to metallicity, nor any systematic difference concerning the distribution of grain sizes or how much carbon is condensed into dust. DARWIN models at subsolar metallicity have approximately 15% lower mass-loss rates compared to DARWIN models at solar metallicity with the same stellar parameters and carbon excess. For both solar and subsolar environments typical grain sizes range between 0.1 and 0.5 μm, the degree of condensed carbon varies between 5 and 40%, and the gas-to-dust ratios between 500 and 10 000. Conclusions. C-type AGB stars can contribute to the dust production at subsolar metallicities (down to at least [Fe∕H] = −1) as long as they dredge up sufficient amounts of carbon from the stellar interior. Furthermore, stellar evolution models can use the mass-loss rates calculated from DARWIN models at solar metallicity when modeling the AGB phase at subsolar metallicities if carbon excess is used as the critical abundance parameter instead of the C/O ratio.

scholarly journals IRAS observations of classical cepheids

1987 ◽  
Vol 122 ◽  
pp. 227-228
Author(s):  
C. J. Butler ◽  
H. P. Deasy ◽  
P. A. Wayman
Keyword(s):  
Mass Loss ◽  
Classical Cepheids ◽  
Cepheid Variables ◽  
Loss Rates

IRAS observations of sources identified with cepheid variables are used to give estimates of observed mass-loss rates for those stars.

scholarly journals Two-dimensional modeling of density and thermal structure of dense circumstellar outflowing disks

2018 ◽  
Vol 613 ◽  
pp. A75 ◽  
Author(s):  
P. Kurfürst ◽  
A. Feldmeier ◽  
J. Krtička
Keyword(s):  
Mass Loss ◽  
Optical Depth ◽  
Massive Stars ◽  
Thermal Structure ◽  
Time Dependent ◽  
Navier Stokes ◽  
Viscous Heating ◽  
Two Dimensional ◽  
Dense Region ◽  
Loss Rates

Context. Evolution of massive stars is affected by a significant loss of mass either via (nearly) spherically symmetric stellar winds or by aspherical mass-loss mechanisms, namely the outflowing equatorial disks. However, the scenario that leads to the formation of a disk or rings of gas and dust around massive stars is still under debate. It is also unclear how various forming physical mechanisms of the circumstellar environment affect its shape and density, as well as its kinematic and thermal structure. Aims. We study the hydrodynamic and thermal structure of optically thick, dense parts of outflowing circumstellar disks that may be formed around various types of critically rotating massive stars, for example, Be stars, B[e] supergiant (sgB[e]) stars or Pop III stars. We calculate self-consistent time-dependent models of temperature and density structure in the disk’s inner dense region that is strongly affected by irradiation from a rotationally oblate central star and by viscous heating. Methods. Using the method of short characteristics, we specify the optical depth of the disk along the line-of-sight from stellar poles. Within the optically thick dense region with an optical depth of τ > 2∕3 we calculate the vertical disk thermal structure using the diffusion approximation while for the optically thin outer layers we assume a local thermodynamic equilibrium with the impinging stellar irradiation. For time-dependent hydrodynamic modeling, we use two of our own types of hydrodynamic codes: two-dimensional operator-split numerical code based on an explicit Eulerian finite volume scheme on a staggered grid, and unsplit code based on the Roe’s method, both including full second-order Navier-Stokes shear viscosity. Results. Our models show the geometric distribution and contribution of viscous heating that begins to dominate in the central part of the disk for mass-loss rates higher than Ṁ ≳ 10−10 M⊙ yr−1. In the models of dense viscous disks with Ṁ > 10−8 M⊙ yr−1, the viscosity increases the central temperature up to several tens of thousands of Kelvins, however the temperature rapidly drops with radius and with distance from the disk midplane. The high mass-loss rates and high viscosity lead to instabilities with significant waves or bumps in density and temperature in the very inner disk region. Conclusions. The two-dimensional radial-vertical models of dense outflowing disks including the full Navier-Stokes viscosity terms show very high temperatures that are however limited to only the central disk cores inside the optically thick area, while near the edge of the optically thick region the temperature may be low enough for the existence of neutral hydrogen, for example.

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