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1.
The exact solution of the Maxwell-Stefan equations for steady state diffusion in a stagnant film due to Krishna and Standart
(1976) is compared to the approximate solutions of Toor (1964) and Stewart and Prober (1964) for osmotic diffusion of oxygen
in the three physiological gas mixtures He−N2−O2, He−SF6−O2, N2−SF6−O2. It is found that the predicted fluxes of He, N2 and SF6 are usually in excellent agreement but that the two methods could predict differing directions of transfer of oxygen. Concentration
profiles obtained from the linearized equations may be significantly different from the profiles calculated from an exact
solution of the film model. 相似文献
2.
Large Greenhouse Gas Emissions from a Temperate Peatland Pasture 总被引:2,自引:0,他引:2
Yit Arn Teh Whendee L. Silver Oliver Sonnentag Matteo Detto Maggi Kelly Dennis D. Baldocchi 《Ecosystems》2011,14(2):311-325
Agricultural drainage is thought to alter greenhouse gas emissions from temperate peatlands, with CH4 emissions reduced in favor of greater CO2 losses. Attention has largely focussed on C trace gases, and less is known about the impacts of agricultural conversion on
N2O or global warming potential. We report greenhouse gas fluxes (CH4, CO2, N2O) from a drained peatland in the Sacramento-San Joaquin River Delta, California, USA currently managed as a rangeland (that
is, pasture). This ecosystem was a net source of CH4 (25.8 ± 1.4 mg CH4-C m−2 d−1) and N2O (6.4 ± 0.4 mg N2O-N m−2 d−1). Methane fluxes were comparable to those of other managed temperate peatlands, whereas N2O fluxes were very high; equivalent to fluxes from heavily fertilized agroecosystems and tropical forests. Ecosystem scale
CH4 fluxes were driven by “hotspots” (drainage ditches) that accounted for less than 5% of the land area but more than 84% of
emissions. Methane fluxes were unresponsive to seasonal fluctuations in climate and showed minimal temporal variability. Nitrous
oxide fluxes were more homogeneously distributed throughout the landscape and responded to fluctuations in environmental variables,
especially soil moisture. Elevated CH4 and N2O fluxes contributed to a high overall ecosystem global warming potential (531 g CO2-C equivalents m−2 y−1), with non-CO2 trace gas fluxes offsetting the atmospheric “cooling” effects of photoassimilation. These data suggest that managed Delta
peatlands are potentially large regional sources of greenhouse gases, with spatial heterogeneity in soil moisture modulating
the relative importance of each gas for ecosystem global warming potential. 相似文献
3.
Winter production of CO2 and N2O from alpine tundra: environmental controls and relationship to inter-system C and N fluxes 总被引:15,自引:0,他引:15
Fluxes of CO2 and N2O were measured from both natural and experimentally augmented snowpacks during the winters of 1993 and 1994 on Niwot Ridge
in the Colorado Front Range. Consistent snow cover insulated the soil surface from extreme air temperatures and allowed heterotrophic
activity to continue through much of the winter. In contrast, soil remained frozen at sites with inconsistent snow cover and
production did not begin until snowmelt. Fluxes were measured when soil temperatures under the snow ranged from –5°C to 0°C,
but there was no significant relationship between flux for either gas and temperature within this range. While early developing
snowpacks resulted in warmer minimum soil temperatures allowing production to continue for most of the winter, the highest
CO2 fluxes were recorded at sites which experienced a hard freeze before a consistent snowpack developed. Consequently, the seasonal
flux of CO2
–C from snow covered soils was related both to the severity of freeze and the duration of snow cover. Over-winter CO2
–C loss ranged from 0.3 g C m−2 season−1 at sites characterized by inconsistent snow cover to 25.7 g C m−2 season−1 at sites that experienced a hard freeze followed by an extended period of snow cover. In contrast to the pattern observed
with C loss, a hard freeze early in the winter did not result in greater N2O–N loss. Both mean daily N2O fluxes and the total over-winter N2O–N loss were related to the length of time soils were covered by a consistent snowpack. Over-winter N2O–N loss ranged from less 0.23 mg N m−2 from the latest developing, short duration snowpacks to 16.90 mg N m−2 from sites with early snow cover. These data suggest that over-winter heterotrophic activity in snow-covered soil has the
potential to mineralize from less than 1% to greater than 25% of the carbon fixed in ANPP, while over-winter N2O fluxes range from less than half to an order of magnitude higher than growing season fluxes. The variability in these fluxes
suggests that small changes in climate which affect the timing of seasonal snow cover may have a large effect on C and N cycling
in these environments.
Received: 5 April 1996 / Accepted: 25 November 1996 相似文献
4.
Riparian nitrogen dynamics in two geomorphologically distinct tropical rain forest watersheds: nitrous oxide fluxes 总被引:2,自引:2,他引:0
William B. Bowden William H. McDowell Clyde E. Asbury Amy M. Finley 《Biogeochemistry》1992,18(2):77-99
Fluxes of N2O at the soil surface, dissolved N2O in near-surface groundwater, and potential N2O production rates were measured across riparian catenas in two rain forest watersheds in Puerto Rico. In the Icacos watershed,
mean N2O fluxes were highest at topographic breaks in the landscape (≃ 40–300 μg N2O-N m−2 h−1). At other locations in the riparian zone and hillslope, fluxes were lower (⩽ 2 μg N2O-N m−2 h−1). This pattern of surface N2O fluxes was persistent. In the Bisley watershed, mean suface N2O fluxes were lower (<40 μg N2O-N m−2 h−1) and no identifiable spatial or temporal pattern. Although the spatial patterns and intensities of N2O emissions differed between the two watersheds, surface soils from both sites had a high potential to reduce NO3 to N2O (and perhaps N2). This potential declined sharply with depth as did soil %C, %N, and potential N-mineralization. Simple controls on denitrification
(i.e. aeration, nitrate, and carbon) explained characteristics of potential N2O production in surface and deep soils from riparian and upslope locations. In the field, spatial patterns in these controlling
variables were defined by geomorphological differences between the two watersheds, which then explained the spatial patterns
of observed N2O flux 相似文献
5.
Jirko Holst Chunyan Liu Nicolas Brüggemann Klaus Butterbach-Bahl Xunhua Zheng Yuesi Wang Shenghui Han Zhisheng Yao Jin Yue Xingguo Han 《Ecosystems》2007,10(4):623-634
Gross rates of N mineralization and nitrification, and soil–atmosphere fluxes of N2O, NO and NO2 were measured at differently grazed and ungrazed steppe grassland sites in the Xilin river catchment, Inner Mongolia, P. R.
China, during the 2004 and 2005 growing season. The experimental sites were a plot ungrazed since 1979 (UG79), a plot ungrazed
since 1999 (UG99), a plot moderately grazed in winter (WG), and an overgrazed plot (OG), all in close vicinity to each other.
Gross rates of N mineralization and nitrification determined at in situ soil moisture and soil temperature conditions were
in a range of 0.5–4.1 mg N kg−1 soil dry weight day−1. In 2005, gross N turnover rates were significantly higher at the UG79 plot than at the UG99 plot, which in turn had significantly
higher gross N turnover rates than the WG and OG plots. The WG and the OG plot were not significantly different in gross ammonification
and in gross nitrification rates. Site differences in SOC content, bulk density and texture could explain only less than 15%
of the observed site differences in gross N turnover rates. N2O and NO
x
flux rates were very low during both growing seasons. No significant differences in N trace gas fluxes were found between
plots. Mean values of N2O fluxes varied between 0.39 and 1.60 μg N2O-N m−2 h−1, equivalent to 0.03–0.14 kg N2O-N ha−1 y−1, and were considerably lower than previously reported for the same region. NO
x
flux rates ranged between 0.16 and 0.48 μg NO
x
-N m−2 h−1, equivalent to 0.01–0.04 kg NO
x
-N ha−1 y−1, respectively. N2O fluxes were significantly correlated with soil temperature and soil moisture. The correlations, however, explained only
less than 20% of the flux variance. 相似文献
6.
Miyuki Sakaguchi Kyoko Shinzawa-Itoh Shinya Yoshikawa Takashi Ogura 《Journal of bioenergetics and biomembranes》2010,42(3):241-243
In the resting oxidized state (the fully oxidized “as-isolated” state) of cytochrome c oxidase (CcO) preparation, a resonance Raman band is observed at 755 cm-1 upon 647.1 nm excitation in resonance with an absorption band at 655 nm. Addition of cyanide eliminates the Raman band concomitant
with loss of the absorption band at 655 nm. These results strongly suggest that the Raman band at 755 cm-1 originates from the O−O stretching mode of the bridging peroxide (Fe−O-−O-−Cu) in the O2 reduction site of the fully oxidized “as-isolated” CcO. Although the peroxide bridged structure has been proposed on the basis of X-ray crystallography and reductive titration
experiments, the present vibrational spectroscopic analyses reveal conclusively the chemical nature of the bridging ligand
at the O2 reduction site of the fully oxidized “as-isolated” bovine heart CcO. 相似文献
7.
Nitrous oxide and methane fluxes of a pristine slope mire in the German National Park Harz Mountains
Nadine Tauchnitz Rainer Brumme Sabine Bernsdorf Ralph Meissner 《Plant and Soil》2008,303(1-2):131-138
Pristine peatlands covered by Histosols (bogs and fens) with high water table and a restricted oxygen (O2) availability are known to have low emissions of nitrous oxide (N2O) but may be a significant source for atmospheric methane (CH4) which are both important greenhouse gases. For the first time N2O and CH4 fluxes of a pristine slope mire in the German Harz Mountains have been monitored. Previously reported peatlands are characterised
by anaerobic conditions due to high water table levels. Slope mires monitored here receive O2 through slope water inflow. Gas fluxes have been monitored deploying closed chamber method on a central non-forested area
and a forested area at the periphery of the slope mire. By means of groundwater piezometers water table levels, ammonium and
nitrate contents as well as hydro-chemical variables like oxygen content and redox potential of the mire pore water have been
concurrently measured with trace gas fluxes at both monitoring sites of the slope mire. The slope mire took up small amounts
of atmospheric methane at a rate of −0.02 ± 0.01 kg C ha−1 year−1 revealing no significant difference between the forested and non-forested site. Higher uptake rates were observed during
low water table level. In contrast to pristine peatlands influx of oxygen containing pore water into slope mire does limit
reduction processes and resultant CH4 emission. N2O fluxes of the forested and non-forested sites of the slope mire did not differ and amounted to 0.25 ± 0.44 kg N ha−1 year−1. Higher emissions were observed at low water table levels and during thawing periods. In spite of favourable conditions N2O fluxes of the slope mire have been comparable to those of pristine peatlands. 相似文献
8.
Winter and summer nitrous oxide and nitrogen oxides fluxes from a seasonally snow-covered subalpine meadow at Niwot Ridge,Colorado 总被引:4,自引:3,他引:1
Gianluca Filippa Michele Freppaz Mark W. Williams Detlev Helmig Daniel Liptzin Brian Seok Brad Hall Kurt Chowanski 《Biogeochemistry》2009,95(1):131-149
The soil emission rates (fluxes) of nitrous oxide (N2O) and nitrogen oxides (NO + NO2 = NO
x
) through a seasonal snowpack were determined by a flux gradient method from near-continuous 2-year measurements using an
automated system for sampling interstitial air at various heights within the snowpack from a subalpine site at Niwot Ridge,
Colorado. The winter seasonal-averaged N2O fluxes of 0.047–0.069 nmol m−2 s−1 were ~15 times higher than observed NO
x
fluxes of 0.0030–0.0067 nmol m−2 s−1. During spring N2O emissions first peaked and then dropped sharply as the soil water content increased from the release of snowpack meltwater,
while other gases, including NO
x
and CO2 did not show this behavior. To compare and contrast the winter fluxes with snow-free conditions, N2O fluxes were also measured at the same site in the summers of 2006 and 2007 using a closed soil chamber method. Summer N2O fluxes followed a decreasing trend during the dry-out period after snowmelt, interrupted by higher values related to precipitation
events. These peaks were up to 2–3 times higher than the background summer levels. The integrated N2O-N loss over the summer period was calculated to be 1.1–2.4 kg N ha−1, compared to ~0.24–0.34 kg N ha−1 for the winter season. These wintertime N2O fluxes from subniveal soil are generally higher than the few previously published data. These results are of the same order
of magnitude as data from more productive ecosystems such as fertilized grasslands and high-N-cycling forests, most likely
because of a combination of the relatively well-developed soils and the fact that subnivean biogeochemical processes are promoted
by the deep, insulating snowpack. Hence, microbially mediated oxidized nitrogen emissions occurring during the winter can
be a significant part of the N-cycle in seasonally snow-covered subalpine ecosystems. 相似文献
9.
Wetlands are often highly effective nitrogen (N) sinks. In the Lake Waco Wetland (LWW), near Waco, Texas, USA, nitrate (NO3−) concentrations are reduced by more than 90% in the first 500 m downstream of the inflow, creating a distinct gradient in
NO3− concentration along the flow path of water. The relative importance of sediment denitrification (DNF), dissimilatory NO3− reduction to ammonium (DNRA), and N2 fixation were examined along the NO3− concentration gradient in the LWW. “Potential DNF” (hereafter potDNF) was observed in all months and ranged from 54 to 278 μmol N m−2 h−1. “Potential DNRA” (hereafter potDNRA) was observed only in summer months and ranged from 1.3 to 33 μmol N m−2 h−1. Net N2 flux ranged from 184 (net denitrification) to −270 (net N2 fixation) μmol N m−2 h−1. Nitrogen fixation was variable, ranging from 0 to 426 μmol N m−2 h−1, but high rates ranked among the highest reported for aquatic sediments. On average, summer potDNRA comprised only 5% (±2%
SE) of total NO3− loss through dissimilatory pathways, but was as high as 36% at one site where potDNF was consistently low. Potential DNRA
was higher in sediments with higher sediment oxygen demand (r
2 = 0.84), and was related to NO3− concentration in overlying water in one summer (r
2 = 0.81). Sediments were a NO3− sink and accounted for 50% of wetland NO3− removal (r
2 = 0.90). Sediments were an NH4+ source, but the wetland was often a net NH4+ sink. Although DNRA rates in freshwater wetlands may rival those observed in estuarine systems, the importance of DNRA in
freshwater sediments appears to be minor relative to DNF. Furthermore, sediment N2 fixation can be extremely high when NO3− in overlying water is consistently low. The data suggest that newly fixed N can support sustained N transformation processes
such as DNF and DNRA when surface water inorganic N supply rates are low. 相似文献
10.
Nitrous oxide (N2O) emissions from grazed grasslands are estimated to be approximately 28% of global anthropogenic N2O emissions. Estimating the N2O flux from grassland soils is difficult because of its episodic nature. This study aimed to quantify the N2O emissions, the annual N2O flux and the emission factor (EF), and also to investigate the influence of environmental and soil variables controlling
N2O emissions from grazed grassland. Nitrous oxide emissions were measured using static chambers at eight different grasslands
in the South of Ireland from September 2007 to August 2009. The instantaneous N2O flux values ranged from -186 to 885.6 μg N2O-N m−2 h−1 and the annual sum ranged from 2 ± 3.51 to 12.55 ± 2.83 kg N2O-N ha−1 y−1 for managed sites. The emission factor ranged from 1.3 to 3.4%. The overall EF of 1.81% is about 69% higher than the Intergovernmental
Panel on Climate Change (IPCC) default EF value of 1.25% which is currently used by the Irish Environmental Protection Agency
(EPA) to estimate N2O emission in Ireland. At an N applied of approximately 300 kg ha−1 y−1, the N2O emissions are approximately 5.0 kg N2O-N ha−1 y−1, whereas the N2O emissions double to approximately 10 kg N ha−1 for an N applied of 400 kg N ha−1 y−1. The sites with higher fluxes were associated with intensive N-input and frequent cattle grazing. The N2O flux at 17°C was five times greater than that at 5°C. Similarly, the N2O emissions increased with increasing water filled pore space (WFPS) with maximum N2O emissions occurring at 60–80% WFPS. We conclude that N application below 300 kg ha−1 y−1 and restricted grazing on seasonally wet soils will reduce N2O emissions. 相似文献
11.
Contribution of plants to N
2
O emissions in soil-winter wheat ecosystem: pot and field experiments 总被引:1,自引:0,他引:1
Outdoor pot and field experiments were conducted to assess the role of growing plants in agricultural ecosystem N2O emissions. N2O emissions from plants were quantified as the difference in soil-crop system N2O emissions before and immediately after cutting plants during the main growth stages in 2001–02 and 2002–03 winter wheat
seasons. Emissions of N2O from plants depended on biomass within the same plant developmental status. Field results indicated that the seasonal contribution
of N2O emissions from plants to ecosystem fluxes averaged 25%, ranging from 10% at wheat tillering to 62% at the heading stage.
The fluxes of N2O emissions from plants varied between 0.3 and 3.9 mg N2O-N m−2 day−1 and its seasonal amount was equivalent to 0.23% of plant N released as N2O. A N2O emission coefficient (N2OE, mg N2O-N g−1 C day−1), defined as N2O-N emission in milligrams from per gram carbon of plant dry matter within a day, was represented by a 5-fold variation ranging
from 0.021 to 0.004 mg N2O-N g C−1 day−1. A linear relationship (y=0.4611x+0.0015, r
2=0.9352, p < 0.001) between N2OE (y) and plant dark respiration rate (x, mg CO2-C g C−1 day−1) suggested that in the absence of photosynthesis, some N2O production in plant N assimilation was associated with plant respiration. Although this study could not show whether N2O was produced or transferred by winter wheat plants, these results indicated an important role for higher plant in N2O exchange. Identifying its potential contribution is critical for understanding agricultural ecosystem N2O sources. 相似文献
12.
N2O, CH4 and CO2 emissions from seasonal tropical rainforests and a rubber plantation in Southwest China 总被引:2,自引:1,他引:1
Christian Werner Xunhua Zheng Janwei Tang Baohua Xie Chunyan Liu Ralf Kiese Klaus Butterbach-Bahl 《Plant and Soil》2006,289(1-2):335-353
The main focus of this study was to evaluate the effects of soil moisture and temperature on temporal variation of N2O, CO2 and CH4 soil-atmosphere exchange at a primary seasonal tropical rainforest (PF) site in Southwest China and to compare these fluxes with fluxes from a secondary forest (SF) and a rubber plantation (RP) site. Agroforestry systems, such as rubber plantations, are increasingly replacing primary and secondary forest systems in tropical Southwest China and thus effect the N2O emission in these regions on a landscape level. The mean N2O emission at site PF was 6.0 ± 0.1 SE μg N m−2 h−1. Fluxes of N2O increased from <5 μg N m−2 h−1 during dry season conditions to up to 24.5 μg N m−2 h−1 with re-wetting of the soil by the onset of first rainfall events. Comparable fluxes of N2O were measured in the SF and RP sites, where mean N2O emissions were 7.3 ± 0.7 SE μg N m−2 h−1 and 4.1 ± 0.5 SE μg N m−2 h−1, respectively. The dependency of N2O fluxes on soil moisture levels was demonstrated in a watering experiment, however, artificial rainfall only influenced the timing of N2O emission peaks, not the total amount of N2O emitted. For all sites, significant positive correlations existed between N2O emissions and both soil moisture and soil temperature. Mean CH4 uptake rates were highest at the PF site (−29.5 ± 0.3 SE μg C m−2 h−1), slightly lower at the SF site (−25.6 ± 1.3 SE μg C m−2 h−1) and lowest for the RP site (−5.7 ± 0.5 SE μg C m−2 h−1). At all sites, CH4 uptake rates were negatively correlated with soil moisture, which was also reflected in the lower uptake rates measured in the watering experiment. In contrast to N2O emissions, CH4 uptake did not significantly correlate with soil temperature at the SF and RP sites, and only weakly correlated at the PF site. Over the 2 month measurement period, CO2 emissions at the PF site increased significantly from 50 mg C m−2 h−1 up to 100 mg C m−2 h−1 (mean value 68.8 ± 0.8 SE mg C m−2 h−1), whereas CO2 emissions at the SF and RP site where quite stable and varied only slightly around mean values of 38.0 ± 1.8 SE mg C m−2 h−1 (SF) and 34.9 ± 1.1 SE mg C m−2 h−1 (RP). A dependency of soil CO2 emissions on changes in soil water content could be demonstrated for all sites, thus, the watering experiment revealed significantly higher CO2 emissions as compared to control chambers. Correlation of CO2 emissions with soil temperature was significant at the PF site, but weak at the SF and not evident at the RP site. Even though we demonstrated that N and C trace gas fluxes significantly varied on subdaily and daily scales, weekly measurements would be sufficient if only the sink/ source strength of non-managed tropical forest sites needs to be identified. 相似文献
13.
Nitrogen removal in a wastewater treatment plant through biofilters: nitrous oxide emissions during nitrification and denitrification 总被引:1,自引:0,他引:1
In order to estimate N2O emissions from immersed biofilters during nitrogen removal in tertiary treatments at urban wastewater treatment plants (WWTPs), a fixed culture from the WWTP of “Seine Centre” (Paris conurbation) was subjected to lab-scale batch experiments under various conditions of oxygenation and a gradient of methanol addition. The results show that during nitrification, N2O emissions are positively related to oxygenation (R
2 = 0.99). However, compared to the rates of ammonium oxidation, the percentage of emitted N2O is greater when oxygenation is low (0.5–1 mgO2 L−1), representing up to 1% of the oxidized ammonium (0.4% on average). During denitrification, the N2O emission reaches a significant peak when the quantity of methanol allows denitrification of between 66% and 88%. When methanol concentrations lead to a denitrification of close to 100%, the flows of N2O are much lower and represent on average 0.2% of the reduced nitrate. By considering these results, we can estimate, the emissions of N2O during nitrogen removal, at the “Seine Centre” WWTP, to approximately 38 kgN-N2O day−1. 相似文献
14.
Elongation growth of plant cells occurs by stretching of cell walls under turgor pressure when intermolecular bonds in the
walls are temporarily loosened. The acid-growth theory predicts that wall loosening is the result of wall acidification because
treatments (including IAA and fusicoccin) that cause lowered wall pH cause elongation. However, conclusive evidence that IAA
primarily reduces wall pH has been lacking. Calcium has been reported to stiffen the cell walls. We have used a microelectrode
ion-flux measuring technique to observe directly, and non-invasively, the net fluxes of protons and calcium from split coleoptiles
of oats (Avena sativa L.) in unbuffered solution. Normal net fluxes are 10 nmol · m−2 · s−1 proton efflux and zero calcium flux. The toxin fusicoccin (1 μM) causes immediate efflux from tissue not only of protons,
but also of calcium, about 110 nmol · m−2 · s−1 in each case. The data fit the “weak acid Donnan Manning” model for ion exchange in the cell wall. Thus we associate the
known “acid-growth” effect of fusicoccin with the displacement of calcium from the wall by exchange for protons extruded from
the cytoplasm. Application of 10 μM IAA causes proton efflux to increase transiently by about 15 nmol · m−2 · s−1 with a lag of about 10 min. The calcium influx decreases immediately to an efflux of about 20 nmol · m−2 · s−1. It appears that auxin too causes an “acid-growth” effect, with extruded protons exchanging for calcium in the cell walls.
I. Arif is currently recieving an AIDAB scholarship. This work was supported by an Australian Research Council grant to I.A.
Newman. 相似文献
15.
A method to estimate net community metabolism (NCM) in natural waters using vertical profiles of water temperature, salinity,
dissolved O2, gas tension, and calculated dissolved N2 is presented. The method utilizes the disparate biological activity of dissolved O2 and N2 to estimate metabolism at different depths in the water column. For well-mixed surface waters, N2 saturation levels are assumed to be the result of a quasi steady state balance of net warming or cooling and air–water gas
exchange. Dissolved O2 levels are assumed to maintain a similar balance, subject to net biological activity, and NCM is then calculated based on
the difference between N2 and O2 saturation levels and the estimated timescale required to equilibrate the layer with the atmosphere. For deeper stratified
layers of water that warmed after layer formation in isolation from the atmosphere, the temperature at formation is calculated
using the measured N2 concentration and an assumed N2 saturation level of 100% at formation. By assuming that initial N2 and O2 saturation levels were equal, the initial O2 concentration is calculated based on solubility relationships. NCM of the deeper waters is then estimated based on this information
and knowledge of the general seasonal heating cycle of the waters. Daily mean water temperature and dissolved gas levels are
used in the calculations. The method was assessed using profile measurements collected at Long Pond, Plymouth, Massachusetts,
USA, on 23 August 2002. Oxygen was supersaturated relative to N2 by approximately 4% in the 0–6 m deep epilimnion, and undersaturated relative to N2 by approximately 7% in the stratified water at 9 m depth. The estimated 4-day average NCM for the epilimnion was 140 ± 70 mgC m−2day−1. For waters at 9 m depth, the temperature at formation was calculated to be 6.58 °C, and the estimated 100-day average NCM
was −2.5 ± 0.6 mgC m−3 day−1. An independent estimate of −4.6 ± 0.9 mgC m−3 day−1 was derived from the measured O2 decline at 9 m depth over the same period of 2003. 相似文献
16.
Temporal trends of N2O fluxes across the soil–atmosphere interface were determined using continuous flux chamber measurements over an entire growing season of a subsurface aerating macrophyte (Phalaris arundinacea) in a nonmanaged Danish wetland. Observed N2O fluxes were linked to changes in subsurface N2O and O2 concentrations, water level (WL), light intensity as well as mineral‐N availability. Weekly concentration profiles showed that seasonal variations in N2O concentrations were directly linked to the position of the WL and O2 availability at the capillary fringe above the WL. N2O flux measurements showed surprisingly high temporal variability with marked changes in fluxes and shifts in flux directions from net source to net sink within hours associated with changing light conditions. Systematic diurnal shifts between net N2O emission during day time and deposition during night time were observed when max subsurface N2O concentrations were located below the root zone. Correlation (P < 0.001) between diurnal variations in O2 concentrations and incoming photosynthetically active radiation highlighted the importance of plant‐driven subsoil aeration of the root zone and the associated controls on coupled nitrification/denitrification. Therefore, P. arundinacea played an important role in facilitating N2O transport from the root zone to the atmosphere, and exclusion of the aboveground biomass in flux chamber measurements may lead to significant underestimations on net ecosystem N2O emissions. Complex interactions between seasonal changes in O2 and mineral‐N availability following near‐surface WL fluctuations in combination with plant‐mediated gas transport by P. arundinacea controlled the subsurface N2O concentrations and gas transport mechanisms responsible for N2O fluxes across the soil–atmosphere interface. Results demonstrate the necessity for addressing this high temporal variability and potential plant transport of N2O in future studies of net N2O exchange across the soil–atmosphere interface. 相似文献
17.
The carbon cycle was quantified in the catchment of Doe House Gill, which drains high-relief moorland, with thin organic-rich
soils (leptosols and podzols) 10–25 cm deep, in northern England. The soil C pool of 8,300 g m-2 is due mainly to humic acid and older humin. If steady state is assumed, and a single soil C pool, the average 14C content of the whole soil (93% modern) yields a mean carbon residence time of 800 years, although this varied from 300 to
1,600 years in the four samples studied. Stream water fluxes of dissolved and particulate organic carbon (DOC, POC) were 2.5
and 0.4 g m−2 a−1 respectively in 2002–2003, lower than values for some other upland streams in the UK. The C pool, flux, and isotope data
were used, with the assumption of steady state, to calibrate DyDOC, a model that simulates the soil carbon cycle, including
the generation and transport of DOC. According to DyDOC, the litter pool (ca. 100 gC m−2) turns over quickly, and most (>90%) of the litter carbon is rapidly mineralised. The soil is calculated to gain only 16 gC m−2 a−1, and to lose the same amount, about 80% as CO2 and 20% as DOC. From the DO14C content of 107.5% modern (due to “bomb carbon”) the model could be calibrated by assuming all DOC to come directly from
litter, but DOC is more likely a mixture, derived from more than one soil C pool. The seasonal variability exhibited by stream
water DOC concentration (maximum in September, minimum in January) is attributed mainly to variations in rainfall and evapotranspiration,
rather than in the metabolic production rate of “potential DOC”. The model predicts that, for a Q
10 of 2, the total soil organic C pool would decrease by about 5% if subjected to warming over 200 years. DyDOC predicts higher
DOC fluxes in response to increased litter inputs or warming, and can simulate changes in DOC flux due to variations in sorption
to soil solids, that might occur due to acidification and its reversal. 相似文献
18.
Process-level controls on CO<Subscript>2</Subscript> fluxes from a seasonally snow-covered subalpine meadow soil,Niwot Ridge,Colorado 总被引:4,自引:4,他引:0
Daniel Liptzin Mark W. Williams Detlev Helmig Brian Seok Gianluca Filippa Kurt Chowanski Jacques Hueber 《Biogeochemistry》2009,95(1):151-166
Fluxes of CO2 during the snow-covered season contribute to annual carbon budgets, but our understanding of the mechanisms controlling the
seasonal pattern and magnitude of carbon emissions in seasonally snow-covered areas is still developing. In a subalpine meadow
on Niwot Ridge, Colorado, soil CO2 fluxes were quantified with the gradient method through the snowpack in winter 2006 and 2007 and with chamber measurements
during summer 2007. The CO2 fluxes of 0.71 μmol m−2 s−1 in 2006 and 0.86 μmol m−2 s−1 in 2007 are among the highest reported for snow-covered ecosystems in the literature. These fluxes resulted in 156 and 189 g C m−2 emitted over the winter, ~30% of the annual soil CO2 efflux at this site. In general, the CO2 flux increased during the winter as soil moisture increased. A conceptual model was developed with distinct snow cover zones
to describe this as well as the three other reported temporal patterns in CO2 flux from seasonally snow-covered soils. As snow depth and duration increase, the factor controlling the CO2 flux shifts from freeze–thaw cycles (zone I) to soil temperature (zone II) to soil moisture (zone III) to carbon availability
(zone IV). The temporal pattern in CO2 flux in each zone changes from periodic pulses of CO2 during thaw events (zone I), to CO2 fluxes reaching a minimum when soil temperatures are lowest in mid-winter (zone II), to CO2 fluxes increasing gradually as soil moisture increases (zone III), to CO2 fluxes decreasing as available carbon is consumed. This model predicts that interannual variability in snow cover or directional
shifts in climate may result in dramatically different seasonal patterns of CO2 flux from seasonally snow-covered soils. 相似文献
19.
Claus Orendt Georg Wolfram Zdeněk Adámek Pavel Jurajda Mechthild Schmitt-Jansen 《Biologia》2012,67(1):180-199
Macroinvertebrate communities were investigated along a gradient of heavy industrial and municipal pollution in the highland
Bílina River (Czech Republic). Physico-chemical determinants and ions were monitored and community analysis performed focusing
on taxonomic composition, ecological functioning (feeder and dweller guilds) and water quality metrics, including saprobity
index, BMWP and diversity. Impacted sites differed significantly from reference and from recovered stretches. Chemical data
revealed two main pollution factors, (1) a “salinity determinant”, described best by conductivity and SO42−, and (2) an “organic pollution determinant”, represented best by O2 concentrations and NO2−, all varying locally and temporally. Some metrics and taxa showed significant correlations to abiotic parameters. Functional
communities showed a stronger relationship to the “organic pollution determinant”, suggesting that elevated organic pollution
had a dominating influence on functional community metrics; though other variables may also have an influence in this multistress
environment. On the other hand, there were indications that the taxonomic community was more influenced by ion concentrations
(“salinity determinant”). The gradient from reference sites to polluted sites was weaker in the final sampling campaign. The
results presented here can be used as a reference for assessing future changes in environmental impact from pollution, being
finer and more detailed than assessment according to the EU’s WFD. 相似文献
20.
A simple procedure is described for the fabrication of micrometer to nanometer-scale platinum electrodes to be used in a
vibrating oxygen-selective system. The electrode was prepared by etching a fine platinum wire and insulating it with an electrophoretic
paint. The dimensions allowed this electrode to be used with the “vibrating probe technique” in exploratory studies aimed
at mapping and measuring the patterns of net influxes as well as effluxes of oxygen in Olea europaea L. leaves and roots with spatial and temporal resolutions of a few microns and a few seconds, respectively. The magnitude
and spatial localisation of O2 influxes in roots was characterised by two distinct peaks. The first, in the division zone, averaged 38 ± 5 nmol m−2 s−1; the second, in the elongation region, averaged 68 ± 6 nmol m−2 s−1. Long-term records of oxygen influx in the elongation region of the root showed an oscillatory regime characterised by a
fast oscillation with periods of about 8–9 min. In leaves, the system allowed the measurement of real-time changes in O2 evolution following changes in light. Furthermore, it was possible to obtain “topographical” images of the photosynthetically
generated oxygen diffusing through different stomata from a region of the leaf of 120 μm × 120 μm. The combination of topographic
and electrochemical information at the micrometer scale makes the system an efficient tool for studying biological phenomena
involving oxygen diffusion.
Received: 12 November 1999 / Accepted: 1 February 2000 相似文献