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1.
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
2.
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
3.
Nitrogen (N) pollution is a problem in many large temperate zone rivers, and N retention in river channels is often small
in these systems. To determine the potential for floodplains to act as N sinks during overbank flooding, we combined monitoring,
denitrification assays, and experimental nitrate (NO3− -N) additions to determine how the amount and form of N changed during flooding and the processes responsible for these changes
in the Wisconsin River floodplain (USA). Spring flooding increased N concentrations in the floodplain to levels equal to the
river. As discharge declined and connectivity between the river and floodplain was disrupted, total dissolved N decreased
over 75% from 1.41 mg l−1, equivalent to source water in the Wisconsin River on 14 April 2001, to 0.34 mg l−1 on 22 April 2001. Simultaneously NO3− -N was attenuated almost 100% from 1.09 to <0.002 mg l−1. Unamended sediment denitrification rates were moderate (0–483 μg m−2 h−1) and seasonally variable, and activity was limited by the availability of NO
3− -N on all dates. Two experimental NO3− -N pulse additions to floodplain water bodies confirmed rapid NO3− -N depletion. Over 80% of the observed NO
3− -N decline was caused by hydrologic export for addition #1 but only 22% in addition #2. During the second addition, a significant
fraction (>60%) of NO3− -N mass loss was not attributable to hydrologic losses or conversion to other forms of N, suggesting that denitrification
was likely responsible for most of the NO3− -N disappearance. Floodplain capacity to decrease the dominant fraction of river borne N within days of inundation demonstrates
that the Wisconsin River floodplain was an active N sink, that denitrification often drives N losses, and that enhancing connections
between rivers and their floodplains may enhance overall retention and reduce N exports from large basins. 相似文献
4.
Importance of point sources on regional nitrous oxide fluxes in semi-arid steppe of Inner Mongolia, China 总被引:3,自引:0,他引:3
J. Holst C. Liu Z. Yao N. Brüggemann X. Zheng X. Han K. Butterbach-Bahl 《Plant and Soil》2007,296(1-2):209-226
The aim of the present work was to estimate the contribution of different point and diffuse sources to the regional N2O emission strength of steppe in the Xilin river catchment, Inner Mongolia, People’s Republic of China. Transect studies showed
that the topographic effect on N2O emissions from upland soils was negligible and that upland steppe is only a very weak net source of N2O during the growing season (0.8 ± 0.4 μg N2O–N m−2 h−1). Slightly higher emissions were found for riparian areas (1.8 ± 0.3 μg N2O–N m−2 h−1), which cover ∼4% of the landscape. Even faeces or urine additions stimulated N2O emissions from steppe soils only weakly (<2.5 μg N2O–N m−2 h−1 for a 5 days period). Due to low moisture contents, N2O emissions from dung heaps were also rather low (6.2 ± 0.8 μg N2O–N kg−1 dry matter h−1). In contrast, three orders of magnitude higher N2O emissions were found at sheepfolds (2.45 mg N2O–N m−2 h−1 on average). By calculating N2O emissions on a landscape scale, we show that point sources, and especially sheepfolds, become the dominating regional N2O source during the growing season if stocking rates are >1 sheep ha−1. Our results indicate that the common grazing management in the Xilin river region leads to a translocation of nitrogen from
large source areas towards defined spots. This finding is further supported by measurements of NH3 concentrations at different sites. Since most of the nitrogen accumulated in these hot spots is finally lost through burning
of the dried excrements by the farmers for heating and cooking purposes, the ecosystem faces a significant human perturbation
of regional N cycling, which may contribute to an accelerated degradation of steppe in the Xilin river region.
Responsible Editor: Per Ambus. 相似文献
5.
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
6.
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
7.
Christian Brümmer Nicolas Brüggemann Klaus Butterbach-Bahl Ulrike Falk Jörg Szarzynski Konrad Vielhauer Reiner Wassmann Hans Papen 《Ecosystems》2008,11(4):582-600
In a combined field and laboratory study in the southwest of Burkina Faso, we quantified soil-atmosphere N2O and NO exchange. N2O emissions were measured during two field campaigns throughout the growing seasons 2005 and 2006 at five different experimental
sites, that is, a natural savanna site and four agricultural sites planted with sorghum (n = 2), cotton and peanut. The agricultural fields were not irrigated and not fertilized. Although N2O exchange mostly fluctuated between −2 and 8 μg N2O–N m−2 h−1, peak N2O emissions of 10–35 μg N2O–N m−2 h−1 during the second half of June 2005, and up to 150 μg N2O–N m−2 h−1 at the onset of the rainy season 2006, were observed at the native savanna site, whereas the effect of the first rain event
on N2O emissions at the crop sites was low or even not detectable. Additionally, a fertilizer experiment was conducted at a sorghum
field that was divided into three plots receiving different amounts of N fertilizer (plot A: 140 kg N ha−1; plot B: 52.5 kg N ha−1; plot C: control). During the first 3 weeks after fertilization, only a minor increase in N2O emissions at the two fertilized plots was detected. After 24 days, however, N2O emission rates increased exponentially at plot A up to a mean of 80 μg N2O–N m−2 h−1, whereas daily mean values at plot B reached only 19 μg N2O–N m−2 h−1, whereas N2O flux rates at plot C remained unchanged. The calculated annual N2O emission of the nature reserve site amounted to 0.52 kg N2O–N ha−1 a−1 in 2005 and to 0.67 kg N2O–N ha−1 a−1 in 2006, whereas the calculated average annual N2O release of the crop sites was only 0.19 kg N2O–N ha−1 a−1 and 0.20 kg N2O–N ha−1 a−1 in 2005 and 2006, respectively. In a laboratory study, potential N2O and NO formation under different soil moisture regimes were determined. Single wetting of dry soil to medium soil water
content with subsequent drying caused the highest increase in N2O and NO emissions with maximum fluxes occurring 1 day after wetting. The stimulating effect lasted for 3–4 days. A weaker
stimulation of N2O and NO fluxes was detected during daily wetting of soil to medium water content, whereas no significant stimulating effect
of single or daily wetting to high soil water content (>67% WHCmax) was observed. This study demonstrates that the impact of land-use change in West African savanna on N trace gas emissions
is smaller—with the caveat that there could have been potentially higher N2O and NO emissions during the initial conversion—than the effect of timing and distribution of rainfall and of the likely
increase in nitrogen fertilization in the future. 相似文献
8.
Denitrification efficiency for defining critical loads of carbon in shallow coastal ecosystems 总被引:2,自引:2,他引:0
Denitrification efficiency [DE; (N2 − N/(DIN + N2 − N) × 100%)] as an indicator of change associated with nutrient over-enrichment was evaluated for 22 shallow coastal ecosystems
in Australia. The rate of carbon decomposition (which can be considered a proxy for carbon loading) is an important control
on the efficiency with which coastal sediments in depositional mud basins with low water column nitrate concentrations recycle
nitrogen as N2. The relationship between DE and carbon loading is due to changes in carbon and nitrate (NO3) supply associated with sediment biocomplexity. At the DE optimum (500–1,000 μmol m−2 h−1), there is an overlap of aerobic and anaerobic respiration zones (caused primarily by the existence of anaerobic micro-niches
within the oxic zone, and oxidized burrow structures penetrating into the anaerobic zone), which enhances denitrification
by improving both the organic carbon and nitrate supply to denitrifiers. On either side of the DE optimum zone, there is a
reduction in denitrification sites as the sediment loses its three-dimensional complexity. At low organic carbon loadings,
a thick oxic zone with low macrofauna biomass exists, resulting in limited anoxic sites for denitrification, and at high carbon
loadings, there is a thick anoxic zone and a resultant lack of oxygen for nitrification and associated NO3 production. We propose a trophic scheme for defining critical (sustainable) carbon loading rates and possible thresholds
for shallow coastal ecosystems based on the relationship between denitrification efficiency and carbon loading for 17 of the
22 Australian coastal ecosystems. The denitrification efficiency “optimum” occurs between carbon loadings of about 50 and
100 g C m−2 year−1. Coastal managers can use this simple trophic scheme to classify the current state of their shallow coastal ecosystems and
for determining what carbon loading rate is necessary to achieve any future state.
Guest editors: J. H. Andersen & D. J. Conley
Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of
Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark 相似文献
9.
Nitrification and denitrification response to varying periods of desiccation and inundation in a western Kansas stream 总被引:3,自引:0,他引:3
Changing environmental conditions and increased water consumption have transformed many historically perennial stream systems
into intermittent systems. Multiple drying and wetting events throughout the year might impact many stream processes including
nitrification and denitrification, key components of the nitrogen (N) cycle. During summer 2007, an experimental stream was
used to dry and then rewet stream sediments to determine the effects of desiccation and rewetting of stream sediment on nitrification
and denitrification potentials. Mean (±SE) nitrification and denitrification rates in sediment not dried (controls) were 0.431 ± 0.017 μg
NO3
−–N/cm2/h and 0.016 ± 0.002 μg N2O–N/cm2/h, respectively. As sediment samples dried, nitrification rates decreased. Rates in sediments dried less than 7 d recovered
to levels equal or greater than those in the controls within 1 d of being rewetted. Denitrification rates were not affected
by 1 d of drying, but samples dried greater than 1 d experienced reduced rates of denitrification. Denitrification in sediments
dried 7 d or less recovered by day seven of being rewetted. Nitrification and denitrification processes failed to fully recover
in sediments dried more than 7 d. These results demonstrate that alterations in stream’s hydrology can significantly affect
N-cycle processes. 相似文献
10.
The deposition and cycling of carbon and nitrogen in carbonate sediments located between coral reefs on the northern and central
sections of the Great Barrier Reef were examined. Rates of mass sediment accumulation ranged from 1.9 kg m−2 year−1 (inshore reefs) to 2.1–4.9 kg m−2 year−1 (between mid-shelf reefs); sedimentation was minimal off outer-shelf reefs. Rates of total organic carbon decomposition ranged
from 1.7 to 11.4 mol C m−2 year−1 and total nitrogen mineralization ranged from 77 to 438 mmol N m−2 year−1, declining significantly with distance from land. Sediment organic matter was highly reactive, with mineralization efficiencies
ranging from 81 to 99% for organic carbon and 64–100% for nitrogen, with little C and N burial. There was no evidence of carbonate
dissolution/precipitation in short-term incubation experiments. Rates of sulfate reduction (range 0–3.4 mmol S m−2 day−1) and methane release (range 0–12.8 μmol CH4 m−2 day−1) were minor or modest pathways of carbon decomposition. Aerobic respiration, estimated by difference between total O2 consumption and the sum of the other pathways, accounted for 55–98% of total carbon mineralization. Rates of ammonification
ranged from 150 to 1,725 μmol NH4 m−2 day−1, sufficient to support high rates of denitrification (range 30–2,235 μmol N2 m−2 day−1). N2O release was not detected and rates of NH4
+ and NO2
− + NO3
− efflux were low, indicating that most mineralized N was denitrified. The percentage of total N input removed via denitrification
averaged ≈75% (range 28–100%) with little regenerated N available for primary producers. Inter-reef environments are therefore
significant sites of energy and nutrient flow, especially in spatially complex reef matrices such as the Great Barrier Reef. 相似文献
11.
R. Thomas James Wayne S. Gardner Mark J. McCarthy Stephen A. Carini 《Hydrobiologia》2011,669(1):199-212
Total nitrogen (TN) in Lake Okeechobee, a large, shallow, turbid lake in south Florida, has averaged between 90 and 150 μM
on an annual basis since 1983. No TN trends are evident, despite major storm events, droughts, and nutrient management changes
in the watershed. To understand the relative stability of TN, this study evaluates nitrogen (N) dynamics at three temporal/spatial
levels: (1) annual whole lake N budgets, (2) monthly in-lake water quality measurements in offshore and nearshore areas, and
(3) isotope addition experiments lasting 3 days and using 15N-ammonium (15NH4
+) and 15N-nitrate (15NO3
−) at two offshore locations. Budgets indicate that the lake is a net sink for N. TN concentrations were less variable than
net N loads, suggesting that in-lake processes moderate these net loads. Monthly NO3
− concentrations were higher in the offshore area and higher in winter for both offshore and nearshore areas. Negative relationships
between the percentage of samples classified as algal blooms (defined as chlorophyll a > 40 μg l−1) and inorganic N concentrations suggest N-limitation. Continuous-flow experiments over intact sediment cores measured net
fluxes (μmol N m−2 h−1) between 0 and 25 released from sediments for NH4
+, 0–60 removed by sediments for NO3
−, and 63–68 transformed by denitrification. Uptake rates in the water column (μmol N m−2 h−1) determined by isotope dilution experiments and normalized for water depth were 1,090–1,970 for NH4
+ and 59–119 for NO3
−. These fluxes are similar to previously reported results. Our work suggests that external N inputs are balanced in Lake Okeechobee
by denitrification. 相似文献
12.
Floodplain restoration has been advocated as a means to restore several ecological services associated with floodplains: water
quality improvement, fish rearing habitat, wildlife habitat, flood control, and groundwater recharge. A history of agricultural
encroachment on the lower Cosumnes River has resulted in extensive channelization and levee construction. In fall 1998, an
experimental floodplain was established by breaching a levee in order to restore the connection between the main channel and
its historic floodplain. In this study, we examined how effective this newly restored floodplain was at processing nitrate
(NO
3
−
) before reentering the main channel downstream. Two methods were used to examine nitrate loss. In December 2001, we determined
denitrification potentials of the floodplain soils before seasonal flooding inundated the floodplain. Next, we conducted a
series of field soil column (mesocosm) experiments from March to June 2002 to study NO
3
−
-N loss from the overlying water in both sandy and clayey soils and at three levels of NO
3
−
-N (ambient, +1 mg N l−1, +5 mg N l−1). In addition, we examined NO
3
−
-N loss from mesocosms with water only to determine if loss was related primarily to soil or water column processes. Denitrification
potentials were highly variable ranging from 1.6 to 769 ng N2O–N cm−3 h−1. In addition, the denitrification potential was highly correlated with the amount of bioavailable carbon indicating that
carbon was a limiting factor for denitrification. Nitrate-N loss rates from mesocosms ranged from 2.9 to 21.0 μg N l−1 h−1 over all treatments and all 3 months examined. Significant loss of NO
3
−
-N (60–93%) from the water only treatment only occurred in June when warmer temperatures and solar radiation most likely increased
NO
3
−
-N uptake by phytoplankton. When scaled up, potential NO
3
−
-N loss from the restored floodplain represented 0.6–4.4% of the annual N load from the Lower Cosumnes River during a typical
wet year and ~24% during a dry year. During dry water years, the effectiveness of the floodplain for reducing nitrate is limited
by the amount of N supplied to the floodplain. Results from this study suggest that restored floodplains can be an effective
NO
3
−
sink. 相似文献
13.
We assessed the effect of whole-stream nitrate enrichment on decomposition of three substrates differing in nutrient quality
(alder and oak leaves and balsa veneers) and associated fungi and invertebrates. During the 3-month nitrate enrichment of
a headwater stream in central Portugal, litter was incubated in the reference site (mean NO3-N 82 μg l−1) and four enriched sites along the nitrate gradient (214–983 μg NO3-N l−1). A similar decomposition experiment was also carried out in the same sites at ambient nutrient conditions the following
year (33–104 μg NO3-N l−1). Decomposition rates and sporulation of aquatic hyphomycetes associated with litter were determined in both experiments,
whereas N and P content of litter, associated fungal biomass and invertebrates were followed only during the nitrate addition
experiment. Nitrate enrichment stimulated decomposition of oak leaves and balsa veneers, fungal biomass accrual on alder leaves
and balsa veneers and sporulation of aquatic hyphomycetes on all substrates. Nitrate concentration in stream water showed
a strong asymptotic relationship (Michaelis–Menten-type saturation model) with temperature-adjusted decomposition rates and
percentage initial litter mass converted into aquatic hyphomycete conidia for all substrates. Fungal communities did not differ
significantly among sites but some species showed substrate preferences. Nevertheless, certain species were sensitive to nitrogen
concentration in water by increasing or decreasing their sporulation rate accordingly. N and P content of litter and abundances
or richness of litter-associated invertebrates were not affected by nitrate addition. It appears that microbial nitrogen demands
can be met at relatively low levels of dissolved nitrate, suggesting that even minor increases in nitrogen in streams due
to, e.g., anthropogenic eutrophication may lead to significant shifts in microbial dynamics and ecosystem functioning.
Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at . 相似文献
14.
We examined the hydrologic controls on nitrogen biogeochemistry in the hyporheic zone of the Tanana River, a glacially-fed
river, in interior Alaska. We measured hyporheic solute concentrations, gas partial pressures, water table height, and flow
rates along subsurface flowpaths on two islands for three summers. Denitrification was quantified using an in situ 15NO3− push–pull technique. Hyporheic water level responded rapidly to change in river stage, with the sites flooding periodically
in mid−July to early−August. Nitrate concentration was nearly 3-fold greater in river (ca. 100 μg NO3−–N l−1) than hyporheic water (ca. 38 μg NO3−–N l−1), but approximately 60–80% of river nitrate was removed during the first 50 m of hyporheic flowpath. Denitrification during
high river stage ranged from 1.9 to 29.4 mg N kg sediment−1 day−1. Hotspots of methane partial pressure, averaging 50,000 ppmv, occurred in densely vegetated sites in conjunction with mean
oxygen concentration below 0.5 mgO2 l−1. Hyporheic flow was an important mechanism of nitrogen supply to microbes and plant roots, transporting on average 0.41 gNO3−–N m−2 day−1, 0.22 g NH4+–N m−2 day−1, and 3.6 g DON m−2 day−1 through surface sediment (top 2 m). Our results suggest that denitrification can be a major sink for river nitrate in boreal
forest floodplain soils, particularly at the river-sediment interface. The stability of the river hydrograph and the resulting
duration of soil saturation are key factors regulating the redox environment and anaerobic metabolism in the hyporheic zone. 相似文献
15.
Shannon KE Saleh-Lakha S Burton DL Zebarth BJ Goyer C Trevors JT 《Antonie van Leeuwenhoek》2011,100(2):183-195
The effect of glucose addition (0 and 500 μg C g−1 soil) and nitrate (NO3) addition (0, 10, 50 and 500 μg NO3–N g−1 soil) on nitric oxide reductase (cnorB) gene abundance and mRNA levels, and cumulative denitrification were quantified over 48 h in anoxic soils inoculated with
Pseudomonas mandelii. Addition of glucose-C significantly increased cnorB
p
(P. mandelii and related species) mRNA levels and abundance compared with soil with no glucose added, averaged over time and NO3 addition treatments. Without glucose addition, cnorB
p
mRNA levels were higher when 500 μg NO3–N g−1 soil was added compared with other NO3 additions. In treatments with glucose added, addition of 50 μg NO3–N g−1 soil resulted in higher cnorB
p
mRNA levels than soil without NO3 but was not different from the 10 and 500 μg NO3–N g−1 treatments. cnorB
p
abundance in soils without glucose addition was significantly higher in soils with 500 μg NO3–N g−1 soil compared to lower N-treated soils. Conversely, addition of 500 μg NO3–N g−1 soil resulted in lower cnorB
p
abundance compared with soil without N-addition. Over 48 h, cumulative denitrification in soils with 500 μg glucose-C g−1 soil, and 50 or 500 μg NO3–N g−1 was higher than all other treatments. There was a positive correlation between cnorB
p
abundance and cumulative denitrification, but only in soils without glucose addition. Glucose-treated soils generally had
higher cnorB
p
abundance and mRNA levels than soils without glucose added, however response of cnorB
p
abundance and mRNA levels to NO3 supply depended on carbon availability. 相似文献
16.
17.
Compared to upland forests, riparian forest soils have greater potential to remove nitrate (NO3) from agricultural runoff through denitrification. It is unclear, however, whether prolonged exposure of riparian soils to nitrogen (N) loading will affect the rate of denitrification and its end products. This research assesses the rate of denitrification and nitrous oxide (N2O) emissions from riparian forest soils exposed to prolonged nutrient runoff from plant nurseries and compares these to similar forest soils not exposed to nutrient runoff. Nursery runoff also contains high levels of phosphate (PO4). Since there are conflicting reports on the impact of PO4 on the activity of denitrifying microbes, the impact of PO4 on such activity was also investigated. Bulk and intact soil cores were collected from N-exposed and non-exposed forests to determine denitrification and N2O emission rates, whereas denitrification potential was determined using soil slurries. Compared to the non-amended treatment, denitrification rate increased 2.7- and 3.4-fold when soil cores collected from both N-exposed and non-exposed sites were amended with 30 and 60 μg NO3-N g−1 soil, respectively. Net N2O emissions were 1.5 and 1.7 times higher from the N-exposed sites compared to the non-exposed sites at 30 and 60 μg NO3-N g−1 soil amendment rates, respectively. Similarly, denitrification potential increased 17 times in response to addition of 15 μg NO3-N g−1 in soil slurries. The addition of PO4 (5 μg PO4-P g−1) to soil slurries and intact cores did not affect denitrification rates. These observations suggest that prolonged N loading did not affect the denitrification potential of the riparian forest soils; however, it did result in higher N2O emissions compared to emission rates from non-exposed forest soils. 相似文献
18.
The Impact of Nitrogen Placement and Tillage on NO, N2O, CH4 and CO2 Fluxes from a Clay Loam Soil 总被引:4,自引:0,他引:4
Xuejun J. Liu Arvin R. Mosier Ardell D. Halvorson Fusuo S. Zhang 《Plant and Soil》2006,280(1-2):177-188
To evaluate the impact of N placement depth and no-till (NT) practice on the emissions of NO, N2O, CH4 and CO2 from soils, we conducted two N placement experiments in a long-term tillage experiment site in northeastern Colorado in 2004.
Trace gas flux measurements were made 2–3 times per week, in zero-N fertilizer plots that were cropped continuously to corn
(Zea mays L.) under conventional-till (CT) and NT. Three N placement depths, replicated four times (5, 10 and 15 cm in Exp. 1 and 0,
5 and 10 cm in Exp. 2, respectively) were used. Liquid urea–ammonium nitrate (UAN, 224 kg N ha−1) was injected to the desired depth in the CT- or NT-soils in each experiment. Mean flux rates of NO, N2O, CH4 and CO2 ranged from 3.9 to 5.2 μg N m−2 h−1, 60.5 to 92.4 μg N m−2 h−1, −0.8 to 0.5 μg C m−2 h−1, and 42.1 to 81.7 mg C m−2 h−1 in both experiments, respectively. Deep N placement (10 and 15 cm) resulted in lower NO and N2O emissions compared with shallow N placement (0 and 5 cm) while CH4 and CO2 emissions were not affected by N placement in either experiment. Compared with N placement at 5 cm, for instance, averaged
N2O emissions from N placement at 10 cm were reduced by more than 50% in both experiments. Generally, NT decreased NO emission
and CH4 oxidation but increased N2O emissions compared with CT irrespective of N placement depths. Total net global warming potential (GWP) for N2O, CH4 and CO2 was reduced by deep N placement only in Exp. 1 but was increased by NT in both experiments. The study results suggest that
deep N placement (e.g., 10 cm) will be an effective option for reducing N oxide emissions and GWP from both fertilized CT-
and NT-soils. 相似文献
19.
Urban streams often contain elevated concentrations of nitrogen (N) which can be amplified in systems receiving effluent from
wastewater treatment plants (WWTP). In this study, we evaluated the importance of denitrification in a stream draining urban
Greensboro, NC, USA, using two approaches: (1) natural abundance of 15N–NO3− in conjunction with background NO3−–N concentrations along a 7 km transect downstream of a WWTP; and (2) C2H2 block experiments at three sites and at three habitat types within each site. Overall lack of a longitudinal pattern of δ15N–NO3− and NO3−–N, combined with high concentrations of NO3−–N suggested that other factors were controlling NO3−–N flux in the study transect. However, denitrification did appear to be significant along one portion of the transect. C2H2 block experiments showed that denitrification rates were much higher downstream of the WWTP compared to upstream, and showed
that denitrification rates were highest in erosional and depositional areas downstream of the WWTP and in erosional areas
upstream of the plant. Thus, the combination of the two methods for evaluating denitrification provided more insight into
the spatial dynamics of denitrification activity than either approach alone. Denitrification appeared to be a significant
sink for NO3−–N upstream of the WWTP, but not downstream. Approximately 46% of the total NO3−–N load was removed via denitrification in the upstream, urban section of the stream, while only 2.3% of NO3−–N was lost downstream of the plant. This result suggests that controlling NO3−–N loading from the plant could result in considerable improvement of downstream water quality. 相似文献
20.
To clarify the relationship between denitrification activity and dry–wet levels in the littoral wetland sediments of Lake
Biwa, Japan, denitrification rates and their regulating parameters (degree of dryness, redox potential, nitrate concentration)
were measured on different moisture sediments. Redox potential in sediments was higher in the exposed region in contact with
atmosphere than the flooded region covered with water. The nitrate concentration in interstitial waters was undetectable in
the flooded region. On the other hand, concentration in the exposed region increased with increase in the degree of sediment
dryness. The denitrification rate ranged from <0.001 to 0.88 μg N cm−3 h−1 in the exposed region and increased with the increase in the degree of dryness. In the flooded region, on the other hand,
no detectable rate (<0.001 μg N cm−3 h−1) was observed. This indicates that the rates in the exposed region were mainly influenced by nitrate concentration in the
interstitial waters accumulated by desiccation of sediments, whereas rates in the flooded region were strongly limited by
no accumulation of nitrate in the anaerobic conditions. The potential denitrification rate, under the application condition
of nitrate, ranged from 0.13 to 0.26 μg N cm−3 h−1 in the flooded region and from 0.77 to 1.5 μg N cm−3 h−1 in the exposed region. The potential rates in the flooded region had a tendency to be lower than those in the exposed region,
implying that the number of denitrifying bacteria in the flooded region was low due to inactivation of aerobic respiration
and denitrification in the denitrifying bacteria community. Kinetic parameters, maximum rate (V
max) and half-saturation constant (K
s) for denitrification were calculated on the experimental procedures of the wetting–drying cycles of sediments. Both parameters
decreased by the wetting treatment and increased by the drying treatment. The fluctuation of V
max values with wetting–drying cycles indicated that the number of denitrifying bacteria was influenced by aerobic respiration
and denitrification in the denitrifying bacteria community similar to the potential rates, and denitrifying enzyme was induced
by the nitrate supplied by nitrification accelerated through the drying process. On the other hand, the fluctuation of K
s values implied that members of denitrifying bacteria were shifted to members of high nitrate affinity by wetting treatment
and of low nitrate affinity by drying treatment. 相似文献