首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
Constructed wetlands (CWs) are considered important sources of nitrous oxide (N2O). Various reports in the literature indicate that CWs have high N2O emission rates. The release of N2O from CWs treating wastewater emissions range from ?16.7 to 188 mg N2O m?2day?1. N2O in CWs is produced mainly by nitrification, denitrification, nitrifier denitrification, and nitrate-ammonification. Denitrification is considered the major source of N2O under most conditions. In recent years, two main methods of sampling N2O gas in CWs have been employed, including the headspace equilibration technique and the closed static chambers technique. N2O emission may be affected by various operating parameters and environmental conditions. One of the main environmental factors affecting the removal of nitrogen in CWs is dissolved oxygen, which affects nitrification and denitrification processes, thus greatly influencing N2O emission. CW gas dynamics is affected mainly by season and weather conditions, especially temperature and moisture. Aquatic plants, flow regime, oxidation–reduction potential, nitrate concentration, C/N ratio and other factors can affect N2O emission in CWs.  相似文献   

2.
Nitrous oxide supersaturation was measured in the Bothnian Bay, Bothnian Sea and four depth zones of the Baltic proper along with O2, NO?3, NO?2 and other parameters useful in interpreting the sources of the N2O. In the Baltic Sea supersaturation of N2O (123%) was found in the surface water of 0 to 0.5 m. The supersaturation resulted in a flux of N2O to the atmosphere of 2.8 × 10?2Tg N · yr?1 which was 5% of the estimated total nitrogen loss for the Baltic. For the entire photic zone (0 to 20 m) the N2O saturation was 135%. The source of the N2O is not clear, as the nitrification and denitrification were ruled out as sources. The N2O saturation was the lowest (118%) in the intermediate zone. Nitrification appears to be the likely N2O sorce in this region. At the halocline zone, an increasing oversaturation of N2O (200 to 300%) correlated with decreasing O2 concentrations and increasing NO?3 concentrations, indications of nitrification. Of the NH+4 that was oxidized to NO?3, 0.56% was produced as N2O. In the deep water zone, the supersaturation of N2O remained very high (150 to 200%). Sufficient O2, high NO?3 and the presence of nitrifying activity suggested nitrification as most likely source, however in deeper waters of this zone where oxygen was less than 2% saturation the N2O production could be due to denitrification. In anoxic waters the N2O concentrations rapidly decreased to zero suggesting N2O consumption by denitrification, further evidenced by a developing nitrate anomaly.  相似文献   

3.
Methods were developed for determining rates of denitrification in coastal marine sediments by measuring the production of N2 from undisturbed cores incubated in gas-tight chambers. Denitrification rates at summer temperatures (23°C) in sediment cores from Narragansett Bay, Rhode Island, were about 50μmol N2m?2 hr?1. This nitrogen flux is equal to approximately one-half of the NH+4flux from the sediments at this temperature and is of the magnitude necessary to account for the anomalously low N/P and anomalously high O/N ratios often reported for benthic nutrient fluxes. The loss of fixed nitrogen as N2 during the benthic remineralization of organic matter, coupled with the importance of benthic remineralization processes in shallow coastal waters may help to explain why the availability of fixed nitrogen is a major factor limiting primary production in these areas. Narragansett Bay sediments are also a source of N2O, but the amount of nitrogen involved was only about 0.2 μmol m?2 hr?1 at 23°C.  相似文献   

4.
Nitrous oxide evolution may contribute to partial destruction of the ozone layer in the stratosphere. A two year study of the release of N2O from adjoining salt, brackish, and fresh marsh sediment indicates that the annual emission was 31, 48, and 55 mg N m?2 respectively. Emission from open water area was less than the corresponding emission from the marsh sediment. In vitro experiments indicate that the N2O emission was increased when the sediment was drained for extended periods of time. The addition of NO3? significantly increased the rate of N2O evolution, indicating that a large potential for denitrification exists in the anoxic sediment. Appreciable losses of N2O would only be expected when the marshes receive an extraneous source of nitrate such as sewage and/or wastewater.The contribution of the Gulf Coast wetlands to the atmospheric N2O balance is estimated to be 3.3 × 109 g N2O. The maximum average daily emission was equivalent to 1.5 g N2O-N ha?1, which is less than the measured emission from uncultivated soils (Mosieret al., 1981) but greater than the estimates from noncropped land (CAST, 1976).  相似文献   

5.
Aquatic ecosystems have been identified as a globally significant source of nitrous oxide (N2O) due to continuous active nitrogen involvement, but the processes and influencing factors that control N2O production are still poorly understood, especially in reservoirs. For that, monthly N2O variations were monitored in Dongfeng reservoir (DFR) with a mesotrophic condition. The dissolved N2O concentration in DFR displayed a distinct spatial–temporal pattern but lower than that in the eutrophic reservoirs. During the whole sampling year, N2O saturation ranging from 144% to 640%, indicating that reservoir acted as source of atmospheric N2O. N2O production is induced by the introduction of nitrogen (NO3 ?, NH4 +) in mesotrophic reservoirs, and is also affected by oxygen level and water temperature. Nitrification was the predominate process for N2O production in DFR due to well-oxygenated longitudinal water layers. Mean values of estimated N2O flux from the air–water interface averaged 0.19 µmol m?2 h?1 with a range of 0.01–0.61 µmol m?2 h?1. DFR exhibited less N2O emission flux than that reported in a nearby eutrophic reservoir, but still acted as a moderate N2O source compared with other reservoirs and lakes worldwide. Annual emissions from the water–air interface of DFR were estimated to be 0.32 × 105 mol N–N2O, while N2O degassing from releasing water behind the dam during power generation was nearly five times greater. Hence, N2O degassing behind the dam should be taken into account for estimation of N2O emissions from artificial reservoirs, an omission that historically has probably resulted in underestimates. IPCC methodology should consider more specifically N2O emission estimation in aquatic ecosystems, especially in reservoirs, the default EF5 model will lead to an overestimation.  相似文献   

6.
The conversion of undisturbed coastal regions to commercial and suburban developments may pose a threat to surface and groundwater quality by introducing nitrate-nitrogen (NO3 ?-N) from runoff of land-applied wastewater and fertilizers. Microbial denitrification is an important NO3 ?-N removal mechanism in coastal sediments. The objective of this study was to compare denitrification and nitrate conversion rates in coastal sediments from a golf course, suburban site, undeveloped marsh, and nonmarsh area near rapidly developing Hilton Head Island, South Carolina. Nitrous oxide was measured using gas chromatography and nitrate and ammonium concentrations were measured using a flow injection autoanalyzer in microcosms spiked, with 50 μg NO3 ?-N gdw?1. The two marsh sites had the greatest ammonium production, which was correlated with fine sediment particle size and higher background sediment nitrate and surface water sulfate concentrations. The golf course swale had greatest denitrification rates, which were correlated with higher total carbon and organic nitrogen in sediments. Nitrate was consumed in golf course sediments to a greater extent than in the undeveloped marsh and upland freshwater sites, suggesting that the undeveloped sites and receiving estuaries may be more susceptible to nitrate contamination than the golf course swale and marsh under nonstorm conditions. Construction of swales and vegetated buffers using sediments with high organic carbon content as best management practices may aid in removing nitrate and other contaminants from runoff prior to its transport to the receiving marsh and estuary.  相似文献   

7.
Tidal freshwater wetlands (TFW) alter nitrogen concentrations in river water, but the role of these processes on a river’s downstream nitrogen delivery is poorly understood. We examined spatial and temporal patterns in denitrification in TFW of four rivers in North Carolina, USA and evaluated the relative importance of denitrification rate and inundation on ecosystem-scale N2 efflux. An empirical model of TFW denitrification was developed to predict N2 efflux using a digital topographic model of the TFW, a time series of water level measurements, and a range of denitrification rates. Additionally, a magnitude-frequency analysis was performed to investigate the relative importance of storm events on decadal patterns in N2 efflux. Spatially, inundation patterns exerted more influence on N2 efflux than did the range of denitrification rate used. Temporal variability in N2 efflux was greatest in the lower half of the tidal rivers (near the saline estuary) where inundation dynamics exerted more influence on N2 efflux than denitrification rate. N2 efflux was highest in the upper half of the rivers following storm runoff, and under these conditions variation in denitrification rate had a larger effect on N2 efflux than variability in inundation. The frequency-magnitude analysis predicted that most N2 efflux occurred during low flow periods when tidal dynamics, not storm events, affected TFW inundation. Tidal hydrology and riparian topography are as important as denitrification rate in calculating nitrogen loss in TFW; we present a simple empirical model that links nitrogen transport in rivers with loss due to denitrification in TFW.  相似文献   

8.
This study demonstrates the feasibility of using direct N2 measurements in an estuary for determination of denitrification. High precision measurements of dinitrogen: argon ratios (N2∶Ar) were made by membrane inlet mass spectrometry on water samples taken along the length of the Chesapeake Bay in July and October 2004. The N2∶Ar ratio in low salinity surface water was elevated relative to air saturation by 0.3–0.5% with no systematic change along the length of the Bay. N2∶Ar in high salinity bottom water exhibited a linear increase in the landward direction along a 144-km longitudinal section. In this section of the Bay covering 20% of the main stem, the bottom water salinity was statistically uniform and the increase in N2∶Ar was in the direction of net residual current flow. The system was analyzed as a capped river with the assumption that N2 entered the water from the underlying sediment where denitrification is known to take place. The rate of denitrification needed to support the measured increase in N2 was calculated using an average residual current velocity and water column depth. The increase in N2 with distance (0.046μmol N l−1 km−1) equated to an average denitrification flux of 73 μmol N m−2 h−1. N2 fluxes determined on sediment cores taken from the source and terminus regions of the delineated water mass were 45±23 and 83±39 μmol N m−2 hr−1, respectively, which were not statistically different from the whole system estimate. The measured change in oxygen concentration within the bottom water was used to estimate nitrogen remineralization and the efficiency of denitrification. Denitrification efficiency (nitrogen denitrified/nitrogen remineralized) was estimated to be in the range of 22–28% for the bottom water sediment system and 30–37% considering the sediment zone alone.  相似文献   

9.
Measurements of15N/14N in dissolved molecular nitrogen (N2), nitrate (NO 3 − ) and nitrous oxide (N2O) and18O/16O in N2O [expressed as δ15N and δ18O, relative to atmospheric N2 and oxygen (O2), respectively] have been made in water column at several locations in the Arabian Sea, a region with one of the thickest and most intense O2 minima observed in the open ocean. Microbially-mediated reduction of NO 3 − to N2 (denitrification) in the oxygen minimum zone (OMZ) appears to greatly affect the natural isotopic abundances. The δ15N of NO 3 − increases from 6‰ in deep waters (2500 m) to 15‰ within the core of the denitrifying layer (250–350 m); the δ15N of N2 concurrently decreases from 0.6‰ to 0.20‰ Values of the isotopic fractionation factor (ε) during denitrification estimated using simple advection-reaction and diffusion-reaction models are 22‰ and 25‰, respectively. A strong decrease in δ15N of NO 3 − is observed from ∼ 200m (> 11‰) to 80m (∼ 6‰); this is attributed to the input of isotopically light nitrogen through nitrogen fixation. Isotopic analysis of N2O reveals extremely large enrichments of both15N and18O within the OMZ, presumably due to the preferential reduction of lighter N2O to N2. However, isotopically light N2O is observed to accumulate in high concentrations above the OMZ indicating that the N2O emitted to the atmosphere from this region cannot be very heavy. The isotope data from the intense upwelling zone off the southwest coast of India, where some of the highest concentrations of N2O ever found at the sea surface are observed, show moderate depletion of15N, but slight enrichment of18O relative to air. These results suggest that the ocean-atmosphere exchange cannot counter inputs of heavier isotopes (particularly18O) associated with the stratospheric back flux, as proposed by previous workers. This calls for additional sources and/or sinks of N2O in the atmosphere. Also, the N2O isotope data cannot be explained by production through either nitrification or denitrification, suggesting a possible coupling between the two processes as an important mechanism of N2O production.  相似文献   

10.
Biologically available nitrogen (fixed N) is removed from the oceans by metabolic conversion of inorganic N forms (nitrate and ammonium) to N2 gas. Much of this removal occurs in marine sediments, where reaction rates are thought to be limited by diffusion. We measured the concentration and isotopic composition of major dissolved nitrogen species in anoxic sediments off the coast of California. At depths below the diffusive penetration of nitrate, we found evidence of a large nitrate pool transported into the sediments by motile microorganisms. A ∼20‰ enrichment in 15N and 18O of this biologically transported nitrate over bottom water values and elevated [N2] and δ15N-N2 at depth indicate that this nitrate is consumed by enzymatic redox reactions with the production of N2 as the end product. Elevated N2O concentrations in pore waters below the nitrate diffusion depth confirm that these reactions include the denitrification pathway. A data-constrained model shows that at least 31% of the total N2 production in anoxic sediments is linked to nitrate bio-transport. Under suboxic/anoxic regimes, this nitrate bio-transport augments diffusive transport, thus increasing benthic fixed nitrogen losses and the reducing burial efficiency of sedimentary organic matter.  相似文献   

11.
The biological and physical controls on microbial processes that produce and consume N2O in soils are highly complex. Isotopomer ratios of N2O, with abundance of 14N15N16O, 15N14N16O, and 14N14N18O relative to 14N14N16O, are promising for elucidation of N2O biogeochemistry in an intact ecosystem. Site preference, the nitrogen isotope ratio of the central nitrogen atom minus that of the terminal nitrogen atom, is useful to distinguish between N2O via hydroxylamine oxidation and N2O via nitrite reduction.We applied this isotopomer analysis to a groundwater system in a temperate coniferous-forested ecosystem. Results of a previous study at this location showed that the N2O concentration in groundwater varied greatly according to groundwater chemistry, i.e. NO3−, DOC, and DO, although apportionment of N2O production to nitrification or denitrification was ambiguous. Our isotopic analysis (δ15N and δ18O) of NO3− and N2O implies that denitrification is the dominant production process of N2O, but definitive information is not derived from δ15N and δ18O analysis because of large variations in isotopic fractionations during production and consumption of N2O. However, the N2O site preference and the difference in δ15N between NO3− and N2O indicate that nitrification contributes to total N2O production and that most measured N2O has been subjected to further N2O reduction to N2. The implications of N2O biogeochemistry derived from isotope and isotopomer data differ entirely from those derived from conventional concentration data of DO, NO3−, and N2O. That difference underscores the need to reconsider our understanding of the N cycle in the oxic-anoxic interface.  相似文献   

12.
Anaerobic incubations of upland and wetland temperate forest soils from the same watershed were conducted under different moisture and temperature conditions. Rates of nitrous oxide (N2O) production by denitrification of nitrate () and the stable isotopic composition of the N2O (δ15N, δ18O) were measured. In all soils, N2O production increased with elevated temperature and soil moisture. At each temperature and moisture level, the rate of N2O production in the wetland soil was greater than in the upland soil. The 15N isotope effect (ε) (product − substrate) ranged from −20‰ to −29‰. These results are consistent with other published estimates of 15N fractionation from both single species culture experiments and soil incubation studies from different ecosystems.A series of incubations were conducted with 18O-enriched water (H2O) to determine if significant oxygen exchange (O-exchange) occurred between H2O and N2O precursors during denitrification. The exchange of H2O-O with nitrite () and/or nitric oxide (NO) oxygen has been documented in single organism culture studies but has not been demonstrated in soils prior to this study. The fraction of N2O-O derived from H2O-O was confined to a strikingly narrow range that differed between soil types. H2O-O incorporation into N2O produced from upland and wetland soils was 86% to 94% and 64% to 70%, respectively. Neither the temperature, soil moisture, nor the rate of N2O production influenced the magnitude of O-exchange. With the exception of one treatment, the net 18O isotope effect (εnet) (product-substrate) ranged from +37‰ to +43‰.Most previous studies that have reported 18O isotope effects for denitrification of to N2O have failed to account for the effect of oxygen exchange with H2O. When high amounts of O-exchange occur after fractionation during reductive O-loss, the 18O-enrichment is effectively lost or diminished and δ18O-N2O values will be largely dictated by δ18O-H2O values and subsequent fractionation. The process and extent of O-exchange, combined with the magnitude of oxygen isotope fractionation at each reduction step, appear to be the dominant controls on the observed oxygen isotope effect. In these experiments, significant oxygen isotope fractionation was observed to occur after the majority of water O-exchange. Due to the importance of O-exchange, the net oxygen isotope effect for N2O production in soils can only be determined using δ18O-H2O addition experiments with δ18O-H2O close to natural abundance.The results of this study support the continued use of δ15N-N2O analysis to fingerprint N2O produced from the denitrification of . The utilization of 18O/16O ratios of N2O to study N2O production pathways in soil environments is complicated by oxygen exchange with water, which is not usually quantified in field studies. The oxygen isotope fractionation observed in this study was confined to a narrow range, and there was a clear difference in water O-exchange between soil types regardless of temperature, soil moisture, and N2O production rate. This suggests that 18O/16O ratios of N2O may be useful in characterizing the actively denitrifying microbial community.  相似文献   

13.
With rapidly industrial and agricultural development,more and more fertilizers,chemicals and heavy ions will be discharged into lakes and rivers,which would cause lake eutrophication and quality deterioration in drinking water sources.Therefore,denitrification is essential for controlling the amounts of nitrogen,During the transformation process from nitrate to the end products-nitrogen and several intermediated[e.g.nitrite(NO2^-),nitrous oxide(N2O) and nitric oxide(NO)]may be accumulated,which have more toxic influences on the environment.in This study,the denitrification effect of Paracoccus Denitrificans was examined on the changes between oxic and anoxic conditions at varying pH.At pH=7.5,denitrification proceeded well after 3 switches from oxic to anoxic conditions and vice versa,Production of N2 was constant and the amounts of NO2-,N2O and NO were extremely low.How ever,at pH=6.8,denitrification activity was inhitied and there large amounts of the intermaediates.The denitrifying bacteria decreased violently in dry weight and were washed out.  相似文献   

14.
Sediment denitrification is a microbial process that converts dissolved inorganic nitrogen in sediment porewaters to N2 gas, which is subsequently lost to the atmosphere. In coastal waters, it represents a potentially important loss pathway for fixed nitrogen which might otherwise be available to primary producers. Currently, data are lacking to adequately assess the role of denitrification in reducing or remediating the effects of large anthropogenic nitrogen loads to the coastal zone. This study describes the results of 88 individual measurements of denitrification (as a direct flux of N2 gas) in sediment cores taken over a 3-yr period (1991–1994) from six stations in Boston Harbor, nine stations in Massachusetts Bay, and two stations in Cape Cod Bay. The dataset is unique in its extensive spatial and temporal coverage and includes the first direct measurements of denitrification for North Atlantic shelf sediments. Results showed that rates of denitrification were significantly higher in Boston Harbor (mean=54, range<5–206 μmol N2 m?2 h?1) than in Massachusetts Bay (mean=23, range<5–64 μmol N2 m?2 h?1). Highest rates occurred in areas with organic-rich sediments in the harbor, with slower rates observed for low-organic sandy sediments in the harbor and at shallow shelf stations in the bay. Lowest rates were found at the deepest shelf stations, located in Stellwagen Basin in Massachusetts Bay. Observed rates were correlated with temperature, sediment carbon content, and benthic macrofaunal activity. Seasonally, highest denitrification rates occurred in the summer in Boston Harbor and in the spring and fall in Massachusetts Bay, coincident with peak phytoplankton blooms in the overlying water column. Despite the fact that sediment denitrification rates were high relative to rates reported for other East Coast estuaries, denitrification losses accounted for only 8% of the annual total nitrogen load to Boston Harbor, a consequence perhaps, of the short water-residence times (2–10 d) of the harbor.  相似文献   

15.
《Quaternary Science Reviews》2007,26(1-2):201-212
Temporal changes in oceanic denitrification, the bacterial reduction of nitrate under suboxic conditions, highlight the potential importance of N inventory changes and the production of N2O on the climate system. At the same time, the cause of the globally observed variation in denitrification remains unclear. High-resolution benthic foraminiferal oxygen isotope and bulk sediment nitrogen isotope records from ODP Site 1234 on the Chile Margin record integrated denitrification changes within the Peru–Chile Upwelling system over the last ∼70 ka. Denitrification changes in the southeast Pacific are coherent with Antarctic climate changes recorded by the Byrd ice core δ18O record, and lead northern hemisphere climate events. The southern-hemisphere character of the Chile margin δ15N record suggests that episodes of reduced denitrification in the SE Pacific represent times when more oxygen was supplied as the result of changes in the ventilation and preformed nutrient content of Subantarctic Mode Water (SAMW), which forms in the Subantarctic zone of the Southern Ocean and feeds into the low-latitude thermocline.  相似文献   

16.
Laboratory scale studies were conducted in an up-flow anoxic bioreactor using synthetic fertilizer wastewater for ascertaining the denitrification efficiency. The performance of the reactor was compared using ethanol and topioca starch as the carbon source. The initial No3-N concentrations (50–250 mg/L) and hydraulic retention time (FTRT, 12–24 h) were varied to evaluate the COD and No3-N removal. The results from this study shows that ethanol gave very good denitrification efficiency (78–98%) compared to topioca starch (68–96%).  相似文献   

17.
Coastal ocean primary productivity is often limited by nitrogen (N) availability, which is determined by the balance between N sources (e.g., N-fixation, groundwater, river inputs, etc.) and sinks (e.g., denitrification, sediment burial, etc.). Historically, heterotrophic N-fixation in sediments was excluded as a significant source of N in estuarine budgets, based on low, indirectly measured rates (e.g., acetylene reduction assay) and because it was unnecessary to achieve mass balance. Many recent studies using net N2 flux measurements have shown that sediment N-fixation can equal or exceed N2 loss. In an effort to quantify N2 production and consumption simultaneously, we measured N-fixation and denitrification directly in sediment cores from a temperate estuary (Waquoit Bay, MA). N-fixation, dissimilatory nitrate reduction to ammonium, and denitrification occurred simultaneously, and the net N2 flux shifted from uptake (N-fixation) to efflux (denitrification) over the 120-h incubation. Evidence for N-fixation included net 28N2 and 30N2 uptake, 15NH4 + production from 30N2 additions, 15Norganic matter production, and nifH expression. N-fixation from 30N2 was up to eight times higher than potential denitrification. However, N-fixation calculated from 15NO3 ? was one half of the measured fixation from 30N2, indicating that 15NO3-isotope labeling calculations may underestimate N-fixation. These results highlight the dynamic nature of sediment N cycling and suggest that quantifying individual processes allows a greater understanding of what net N2 fluxes signify and how that balance varies over time.  相似文献   

18.
In this study rates of oxygen, ammonium (NH4 +), nitrate (NO3 −), nitrite (NO2 −), and nitrous oxide (N2O) fluxes, nitrogen (N) fixation, nitrification, and denitrification were compared between two intertidal sites for which there is an abundant global literature, muddy and sandy sediments, and two sites representing the rocky intertidal zone where biogeochemical processes have scarcely been investigated. In almost all sites oxygen production rates greatly exceeded oxygen consumption rates. During daylight, NH4 + and NO3 − uptake rates together with ammonification could supply the different N requirements of the primary producer communities at all four sites; N assimilation by benthic or epilithic primary producers was the major process of dissolved inorganic nitrogen (DIN) removal; N fixation, nitrification, and denitrification were minor processes in the overall light DIN cycle. At night, distinct DIN cycling processes took place in the four environments, denitrification rates ranged from 9 ± 2 to 360 ± 30 μmol N2 m−2 h−1, accounting for 10–48% of the water column NO3 − uptake; nitrification rates varied from 0 to 1712 ± 666 μmol NH4 + m−2 h−1. A conceptual model of N cycle dynamics showed major differences between intertidal sediment and rocky sites in terms of the mean rates of DIN net fluxes and the processes involved, with rocky biofilm showing generally higher fluxes. Of particular significance, the intertidal rocky biofilms released 10 times the amount of N2O produced in intertidal sediments (up to 17 ± 6 μmol N2O m−2 h−1), representing the highest N2O release rates ever recorded for marine systems. The biogeochemical contributions of intertidal rocky substrata to estuarine and coastal processes warrant future detailed investigation.  相似文献   

19.
Freshwater marshes could be a source of greenhouse gases emission because they contain large amounts of soil carbon and nitrogen. These emissions are strongly influenced by exogenous nitrogen. We investigate the effects of exogenous nitrogen on ecosystem respiration (CO2), CH4 and N2O emissions from freshwater marshes in situ in the Sanjiang Plain Northeast of China during the growing seasons of 2004 and 2005, using a field fertilizer experiment and the static opaque chamber/GC techniques. The results show that there were no significant differences in patterns of seasonal variations of CO2 and CH4 among the fertilizer and non-fertilizer treatments, but the seasonal patterns of N2O emission were significantly influenced by the exogenous nitrogen. Seasonal averages of the CO2 flux from non-fertilizer and fertilizer were 987.74 and 1,344.35 mg m −2 h −1, respectively, in 2004, and 898.59 and 2,154.17 mg m −2 h −1, respectively, in 2005. And the CH4 from the control and fertilizer treatments were 6.05 and 13.56 mg m −2 h −1 and 0.72 and 1.88 mg m −2 h −1, respectively, in 2004 and 2005. The difference of N2O flux between the fertilizer and non-fertilizer treatments is also significant either in 2004 and 2005. On the time scale of 20-, 100-, and 500-year periods, the integrated global warming potential (GWP) of CO2 + CH4 + N2O released during the two growing seasons for the treatment of fertilizer was 97, 94 and 89%, respectively, higher than that for the control, which suggested that the nitrogen fertilizer can enhance the GWP of the CH4 and N2O either in long time or short time scale.  相似文献   

20.
One of the technologies used for wastewater nitrogen removal consists in simultaneous nitrification–denitrification. The low microbial growth rate and the low availability of organic material for the denitrification stage make it necessary to study new operational conditions and the use of microbial supports. The aim of this study was to evaluate the operational behavior of a simultaneous nitrification–denitrification process in a sequential batch reactor utilizing zeolite as a biomass support and step-feed strategy. Two reactors of 2 L were used, one with zeolite and another without zeolite, both operated at constant temperature (31 °C), varying nitrogen loading rate (NLR) from 0.041 to 0.113 kg total Kjeldahl nitrogen (TKN/m3/day). After 209 days, removals higher than 86 and 96 % in nitrogen compounds and organic matter were obtained, respectively. There was not accumulation of nitrate and nitrite in any case; this means that there was a simultaneous nitrification–denitrification in the reactors. The incorporation of zeolite in the system held higher concentration of biomass in the reactor; this led to reduce start-up to 21 days and to improve 11.31 % removal kinetic. The use of a step-feed strategy prevents events of inhibition by substrate, even duplicating tolerance to higher NLR for the same operation time.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号