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1.
水库近岸湿地(消落带)土壤N2O释放和反硝化作用是消落带氮的生物地球化学过程的重要组成部分.以三峡水库支流澎溪河高阳平湖库湾消落带为研究对象,于2013年落干初期,采用C2H2抑制-原状土柱培养法研究该处自然植被恢复区、农耕区和对照组等不同土地类型土壤的N2O释放速率和反硝化速率,并测定了土壤p H值、氧化还原电位、温度、有机质、总氮、铵态氮、硝态氮和土壤孔隙含水量等环境指标.结果表明,自然植被恢复区土壤N2O释放速率为9.88±6.49 g N/(hm2·d),反硝化速率为58.94±52.84 g N/(hm2·d);农耕区土壤N2O释放速率和反硝化速率分别为7.71±4.44和30.70±25.68 g N/(hm2·d).不同土地类型间N2O释放速率差异显著,落干初期土壤氧含量、含水量及氮含量对不同土地类型N2O释放和反硝化作用影响明显.土壤氧含量的升高促进了自然植被恢复区的N2O释放,并在一定程度上抑制了该区域反硝化作用.农耕区土壤含水量高于自然植被恢复区,可能致使N2O释放速率低于自然植被恢复区,而反硝化速率高于自然植被恢复区.消落带土壤氮含量降低同反硝化速率降低有一定联系.  相似文献   

2.
Organic matter mineralisation in the hypolimnion of an eutrophic Maar lake   总被引：2，自引：0，他引：2  
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3.
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4.
The spatial pattern and seasonal variation of denitrification were investigated during 2010–2011 in the Jiulong River Estuary (JRE) in southeast China. Dissolved N2 was directly measured by changes in the N2:Ar ratio. The results showed that excess dissolved N2 ranged from ?9.9 to 76.4 μmol L?1. Tidal mixing leads to a seaward decline of dissolved gaseous concentrations and water–air fluxes along the river-estuary gradient. Denitrification at freshwater sites varied between seasons, associated with changes in N input and water temperature. The denitrification process was controlled by the nitrate level at freshwater sites, and the excess dissolved N2 observed at the tidal zone largely originated from upstream water transport. Compared to other estuaries, JRE has a relative low gaseous removal efficiency (Ed = 12% of [DIN]; annual N removal = 24% of DIN load), a fact ascribed to strong tidal mixing, coarse-textured sediment with shallow depth before bedrock and high riverine DIN input.  相似文献   

5.
It have been measured the denitrification rates (DR) of sediment in Saginaw Bay, Lake Huron, by N2 production method. Triplicate samples of sediment core were collected at two GLERL long-term monitoring sites of the Bay in July and August of 1995. The DR are 48.81 -24.99 and 32.81-40.51 micromol N2 -2h-1 in the Inner and Outer regions of Saginaw Bay, respectively.The characters of DR in Saginaw Bay were studied also in this paper. The DR were influenced by the interactions between the Saginaw River as a main pollution source and the Lake Huron as a reservoir of high quality water. The impacts of zebra mussels (Dreissena Polymorpha) on denitrification in Saginaw Bay, Lake Huron, were discussed, Significant differences in NH4+ exchange fluxes were detected in the inner and outer bays. The molar ratios of N2:TIN were similar at both sampling sites. Measured DR were positively correlated to O2 consumption rates in the headspace. Additionally, a negative correlation between NH4+ and NO3- concentrations in the overlying water was found.  相似文献   

6.
Sediment cores from central Lake Constance were dated with210Pb and137Cs. A sedimentation rate of (0.11±0.02) g·cm−2·y−1 was determined with the210Pb method.137Cs measurements revealed sedimentation rates of (0.11±0.01) g·cm−2·y−1 and (0.08±0.01) g·cm−2·y−1 respectively for two different cores sampled at the same location. The lower Cs-dated value indicates incomplete core recovery and demonstrates the sensitivity of this simple dating method to small losses of material at the water/sediment interface. An unambiguous application of the137Cs method is, therefore, only possible if complete core recovery is ensured. Sedimentation rates based on particulate matter, collected in sediment traps at various water depths, agree with the results of the radioisotope methods. Estimates of 30–125 days residence times for suspended particulate matter were calculated from7Be measurements.  相似文献   

7.
According to variations of 137Cs and clay contents, 44 flood couplets were identified in a profile of reservoir deposit with a vertical length of 28.12 m in the Yuntaishan Gully. Couplet 27 at the middle of the profile had the highest average 137Cs content of 12.65 Bq kg-1, which indicated the 1963s' deposits, then 137Cs content decreased both downward and upward in the profile. The second top and bottom couplets had average 137Cs contents of 2.15 Bq kg-1 and 0.92 Bq kg-1, respectively. By integrated analysis of reservoir construction and management history, variations of 137Cs contents over the profile, sediment yields of flood couplets and rainfall data during the period of 1958-1970, individual storms related to the flood couplets were identified. 44 floods with a total sediment yield of 2.36×104 m3 occurred and flood events in a year varied between 1 and 10 times during the period of 1960-1970. 7-10 flood events occurred during the wet period of 1961-1964 with very wet autumn, while only 1-2 events during the dry period of 1965-1969. Average annual specific sediment yield was 1.29×104 t km-2 a-1 for the Yuntaishan Gully during the period of 1960-1970, which was slightly higher than 1.11 ×104 t km-2 a-1 for the Upper Yanhe River Basin above the Ganguyi Hydrological Station and slightly lower than 1.40 ×104 t km-2 a-1 for the nearby Zhifang Gully during the same period. Annual specific sediment yields for the Yuntaishan Gully were correlated to the wet season's rainfalls well.  相似文献   

8.
Soil denitrification in reservoir shoreline wetlands is an important process for removing excess inorganic nitrogen from upland runoff and controlling eutrophication in aquatic ecosystems. As yet, little is known about the influence of vegetation characteristics on the soil denitrification potential in reservoir shoreline wetlands, although vegetation can affect both denitrifying bacteria and soil properties. In this study, we measured the spatial variability of denitrification enzyme activity (DEA) using acetylene block method in shoreline wetlands of the Danjiangkou Reservoir, a water source of the South‐to‐North Water Transfer Project in China. Results indicated that DEA ranged from 0.001 to 2.449 µg N (N2O) g?1 h?1, with a mean of 0.384 µg N (N2O) g?1 h?1. DEA varied significantly among five representative plant communities and the highest DEA (0.248–2.449 µg N (N2O) g?1 h?1) was observed in the Polygonum hydropiper community. Plant biomass and vegetation cover were significantly and positively related to DEA and together explained 44.2% of the total variance. These results suggest that vegetation characteristics should also be considered in assessing soil denitrification capacity and restoring shoreline wetlands for nitrogen pollution removal in the Danjiangkou Reservoir after dam heightening.  相似文献   

9.
Tolo Harbour has received massive discharges of municipal sewage, agricultural wastes and cottage industrial effluents, via three river systems, in the past two decades before the mid Eighties. The Harbour is almost land locked and poorly flushed. The soft sediment acted as a sink for nutrients and organic pollutants. After a decade of efforts in establishing and enforcing water pollution control legislations and upgrading wastewater treatment facilities, the sediments have turned into sources of nutrients and exert a measurable oxygen demand upon the overlying waters. In vitro measurements showed that the sediments oxygen demand (SOD) was between 17.6 and 54.3 mgo2 · m-2 · h-1. The maximum rates of release of ortho-phosphate phosphorus and ammonia nitrogen were 15.0 and 206.0 mg · m-2 · h-1, respectively.  相似文献   

10.
There is growing interest in rates of nitrate uptake and denitrification in restored streams to better understand the effects of restoration on nitrogen processing. This study quantified nitrate uptake in two restored and two unrestored streams in Baltimore, Maryland, USA using nitrate additions, denitrification enzyme assays, and a 15N isotope tracer addition in one of the urban restored streams, Minebank Run. Restoration included either incorporation of stormwater ponds below a storm drain and catch basins to attenuate flow or hydrologic “reconnection” of a stream channel to its floodplain. Stream restoration was conducted for restoring aging sanitary and bridge infrastructure and introducing some stormwater management in watersheds developed prior to current regulations. Denitrification potential in sediments was variable across streams, whereas nitrate uptake length appeared to be significantly correlated to surface water velocity, which was low in the restored streams during summer baseflow conditions. Uptake length of NO3 −–N in Minebank Run estimated by 15N tracer addition was 556 m. Whole stream denitrification rates in Minebank Run were 153 mg NO3 −–N m−2 day−1, and approximately 40% of the daily load of nitrate was estimated to be removed via denitrification over a distance of 220.5 m in a stream reach designed to be hydrologically “connected” to its floodplain. Increased hydrologic residence time in Minebank Run during baseflow likely influenced rates of whole stream denitrification, suggesting that hydrologic residence time may be a key factor influencing N uptake and denitrification. Restoration approaches that increase hydrologic “connectivity” with hyporheic sediments and increase hydrologic residence time may be useful for stimulating denitrification. More work is necessary, however, to examine changes in denitrification rates in restored streams across different seasons, variable N loads, and in response to the “flashy” hydrologic flow conditions during storms common in urban streams.  相似文献   

11.
This study combined water- and sediment flux measurements with mass balances of dissolved gas and inorganic matter to determine the importance of pelagic and benthic processes for whole-system metabolism in a eutrophic fluvial lake. Mass balances of dissolved O2, inorganic carbon (DIC), nitrogen (DIN), phosphorous (SRP), particulate N (PN) and P (PP) and Chl a were calculated at a nearly monthly frequency by means of repeated sampling at the lake inlet and outlet. Simultaneously, benthic fluxes of gas and nutrients, including denitrification rates, and the biomass of the dominant pleustophyte (Trapa natans) were measured, and fluxes of O2 and CO2 across the water–atmosphere interface were estimated from diel changes in outlet concentrations. On an annual scale, Middle Lake exhibited CO2 supersaturation, averaging 313% (range 86–562%), but was autotrophic with a net O2 production (6.35 ± 2.05 mol m−2 y−1), DIC consumption (−31.18 ± 18.77 mol m−2 y−1) and net export of Chl a downstream (8.38 ± 0.95 mol C m−2 y−1). Phytoplankton was the main driver of Middle Lake metabolism, with a net primary production estimated at 33.24 mol O2 m−2 y−1, corresponding to a sequestration of 4.18 and 0.26 mol m−2 y−1 of N and P, respectively. At peak biomass, T. natans covered about 18% of Middle Lake’s surface and fixed 2.46, 0.17 and 0.02 mol m−2 of C, N and P, respectively. Surficial sediments were a sink for O2 (−14.47 ± 0.65 mol O2 m−2 y−1) and a source of DIC and NH4 + (18.84 ± 2.80 mol DIC m−2 y−1 and 0.83 ± 0.16 mol NH4 + m−2 y−1), and dissipated nitrate via denitrification (1.44 ± 0.11 mol NO3 − m−2 y−1). Overall, nutrient uptake by primary producers and regeneration from sediments were a minor fraction of external loads. This work suggests that the creation of fluvial lakes can produce net autotrophic systems, with elevated rates of phytoplanktonic primary production, largely sustained by allochtonous nutrient inputs. These hypereutrophic aquatic bodies are net C sinks, although they simultaneously release CO2 to the atmosphere.  相似文献   

12.
Backwaters connected to large rivers retain nitrate and may play an important role in reducing downstream loading to coastal marine environments. A summer nitrogen (N) inflow-outflow budget was examined for a flow-regulated backwater of the upper Mississippi River in conjunction with laboratory estimates of sediment ammonium and nitrate fluxes, organic N mineralization, nitrification, and denitrification to provide further insight into N retention processes. External N loading was overwhelmingly dominated by nitrate and 54% of the input was retained (137 mg m−2 day−1). Ammonium and dissolved organic N were exported from the backwater (14 and 9 mg m−2 day−1, respectively). Nitrate influx to sediment increased as a function of increasing initial nitrate concentration in the overlying water. Rates were greater under anoxic versus oxic conditions. Ammonium effluxes from sediment were 26.7 and 50.6 mg m−2 day−1 under oxic and anoxic conditions, respectively. Since anoxia inhibited nitrification, the difference between ammonium anoxic–oxic fluxes approximated a nitrification rate of 29.1 mg m−2 day−1. Organic N mineralization was 64 mg m−2 day−1. Denitrification, estimated from regression relationships between oxic nitrate influx versus initial nitrate concentration and a summer lakewide mean nitrate concentration of 1.27 mg l−1, was 94 mg m−2 day−1. Denitrification was equivalent to only 57% of the retained nitrate, suggesting that another portion was assimilated by biota. The high sediment organic N mineralization and ammonium efflux rate coupled with the occurrence of ammonium export from the system suggested a possible link between biotic assimilation of nitrate, mineralization, and export.  相似文献   

13.
东巢湖沉积物水界面氮、磷、氧迁移特征及意义   总被引：2，自引：0，他引：2  
以东巢湖近城市湖湾沉积物为研究对象,在沉积物氮、磷营养盐分析的基础上,采用沉积物柱状芯样静态释放模拟法定量评估研究区域沉积物—水界面氨氮、溶解性活性磷酸盐营养盐释放潜力,利用微电极非损伤测定技术获得沉积物—水微界面溶解氧(DO)剖面分布及微界面DO消耗和扩散特征.结果表明:东巢湖近城市湖湾沉积物氮、磷污染物蓄积量较高,受TN、TP污染程度较重.沉积物内源氨氮、磷酸盐释放明显,平均释放速率分别达到32.44 mg/(m~2·d)和1.25mg/(m~2·d),区域内沉积物已成为水柱中氮、磷营养盐的污染源.研究区域上覆水体处于好氧状态,沉积物—水微界面平均DO穿透深度(OPD)达到5.3 mm,平均DO扩散通量为4.56 mmol/(m~2·d),表现出良好的DO扩散能力.沉积物内源氨氮和磷酸盐释放能力与表层沉积物TN/TP物质含量及沉积物—水微界面DO穿透深度有关,在沉积物氮、磷污染较重的情况下,DO穿透深度越低越有利于氮、磷污染物从沉积物向上覆水体释放.  相似文献   

14.
2 and approximately 85% SO2 of the total sulfur gas. Relative amounts of He, Ar, and N2 show a distinct hot-spot signature ( ). The δ13C–CO2 is approximately −3.6‰ and δ34ST is approximately +3.3‰. The δD/δ18O of fumarole H2O indicates steam separation from local meteoric waters whose estimated minimum mean residence time from 3H analyses is ≤40 years. Fumarolic activity at Alcedo is controlled by a caldera-margin fault containing at least seven hydrothermal explosion craters, and by an intracaldera rhyolite vent. Two explosion craters which formed in 1993–1994 produce approximately 15 m3/s of steam, yet discharge temperatures are ≤97°C. Water content of the total gas is 95–97 mol.%, noncondensible gas is 92–98 mol.% CO2, and sulfur gas is dominated by H2S. Relative amounts of He, Ar, and N2 show extensive mixing between hot spot and air or air-saturated meteoric water components but the average . The δ13C–CO2 is approximately −3.5‰ and δ34ST is approximately −0.8‰. The δD/δ18O of fumarole steam indicates separation from a homogeneous reservoir that is enriched 3–5‰ in 18O compared with local meteoric water. 3H indicates that this reservoir water has a maximum mean residence time of approximately 400 years and empirical gas geothermometry indicates a reservoir temperature of 260–320°C. The intracaldera hydrothermal reservoir in Alcedo is probably capable of producing up to 150 MW; however, environmental concerns as well as lack of infrastructure and power users will limit the development of this resource. Received: 19 April 1999 / Accepted: 23 October 1999  相似文献   

15.
We present an uncertainty analysis of ecological process parameters and CO2 flux components (R eco, NEE and gross ecosystem exchange (GEE)) derived from 3 years’ continuous eddy covariance measurements of CO2 fluxes at subtropical evergreen coniferous plantation, Qianyanzhou of ChinaFlux. Daily-differencing approach was used to analyze the random error of CO2 fluxes measurements and bootstrapping method was used to quantify the uncertainties of three CO2 flux components. In addition, we evaluated different models and optimization methods in influencing estimation of key parameters and CO2 flux components. The results show that: (1) Random flux error more closely follows a double-exponential (Laplace), rather than a normal (Gaussian) distribution. (2) Different optimization methods result in different estimates of model parameters. Uncertainties of parameters estimated by the maximum likelihood estimation (MLE) are lower than those derived from ordinary least square method (OLS). (3) The differences between simulated Reco, NEE and GEE derived from MLE and those derived from OLS are 12.18% (176 g C·m−2·a−1), 34.33% (79 g C·m−2·a−1) and 5.4% (92 g C·m−2·a−1). However, for a given parameter optimization method, a temperature-dependent model (T_model) and the models derived from a temperature and water-dependent model (TW_model) are 1.31% (17.8 g C·m−2·a−1), 2.1% (5.7 g C·m−2·a−1), and 0.26% (4.3 g C·m−2·a−1), respectively, which suggested that the optimization methods are more important than the ecological models in influencing uncertainty in estimated carbon fluxes. (4) The relative uncertainty of CO2 flux derived from OLS is higher than that from MLE, and the uncertainty is related to timescale, that is, the larger the timescale, the smaller the uncertainty. The relative uncertainties of Reco, NEE and GEE are 4%−8%, 7%−22% and 2%−4% respectively at annual timescale. Supported by the National Natural Science Foundation of China (Grant No. 30570347), Innovative Research International Partnership Project of the Chinese Academy of Sciences (Grant No. CXTD-Z2005-1) and National Basic Research Program of China (Grant No. 2002CB412502)  相似文献   

16.
以三峡水库香溪河库湾为研究对象,采用原位加密采样(2021年5月)和室内培养方法,结合沉积物特性与水环境因子分析,探讨了香溪河库湾沉积物甲烷(CH4)释放潜力、沉积物-水界面CH4产生和氧化通量空间分布规律及其影响因素。结果表明:三峡水库泄水期间,香溪河库湾沉积物CH4释放潜力的变化范围是6.35-2029.37 mg/(kg·d),沉积物-水界面CH4产生通量和氧化通量的变化范围分别为0.04～0.73、0.03～0.62 mmol/(m2·d);空间上,沉积物CH4释放潜力、沉积物-水界面CH4产生及氧化通量在香溪河库湾和各典型横切面(XX02、XX05和XX06)间表现出空间差异性,主要受水深、TOC和温度的影响。垂向上,CH4产生速率随沉积物深度的增加而减小,表层20 cm沉积物CH4释放潜力占整柱沉积物的70%,可以用于估算库湾沉积物CH4释放潜力。此外,沉积...  相似文献   

17.
Dajing Cu-Sn-Ag-Pb-Zn ore deposit, in the Inner Mongolia Autonomous Region of China, is a fissure-filling hydrothermal ore deposit. The δD values of quartz-hosted inclusion water are centered at −100%.– −130%.. The δ34S values of sulfide ore minerals and δ13 C values of carbonate gangue minerals vary from −0.3%. to 2.6%. and from −2.9%. to −7.0%., respectively. Integrated isotopic data point to two major contributions to the mineralizing fluid that include a dominant meteoric-derived groundwater, and sulfur and carbon species from hypogene magma. Linear trends are exhibited on the gaseous H2O versus CO2 plot, and plots of CO, N2, CH4, and C2H6. It is shown by quantitative simulation that magma degassing cannot explain the linear trends. Hence, these linear trends are interpreted in terms of mixing of CO2-rich magmatic fluid with meteoric-derived groundwater. The groundwater circulated in Paleozoic sedimentary rocks and absorbed CO, N2, CH4, C2H6 and radiogenic Ar from organic matter. Cooling effects resulting from mixing have caused the precipitation of ore minerals.  相似文献   

18.
The release of nitrous oxide during denitrification in activated sludge is influenced by various environmental factors. Experiments with different electron acceptors showed that under anoxic conditions increasing concentrations of nitrate as well as nitrite enhance the production of N2O. The N2O concentration in the gas phase increases for 2 h, then decreases. Nitrite causes a higher release of N2O than nitrate. Acetate in high concentration can stimulate N2O-release. Without addition of acetate nitrate and nitrite reduction are delayed, and hence N2O-release and consumption are much slower. In activated sludge sulfide can play a role as an inhibitor of the nitrous oxide reductase (like in soil and pure cultures), but is inactivated very rapidly. Repeated addition of sulfide can cause a new release of nitrous oxide. At low pH (less than 6.5) denitrification is slightly inhibited and N2O-release is 100 times higher than at pH 7.0 to 8.0. Under oxygen-limiting conditions N2O-release and denitrification starts at 0.5–1.0 mg/L DO, but it is not always accompanied by accumulation of nitrite. Further reduction of the oxygen concentration reduces N2O-release.  相似文献   

19.
The sediment macro-distribution patterns and their evolutionary characteristics in the South China Sea (SCS) are discussed based on a quantification of the sediment mass from the be- ginning of seafloor spreading in the Oligocene to the Present. Above the pre-Oligocene base, the total sediment mass for the whole SCS is estimated to be 1.44×1016 t, with the highest average accumulation rate of ~22 g·cm-2·ka-1 in the Oligocene. Having no large abyssal fans but fast accumulation in sedimentary basins on the continental shelf and slope, the SCS shows quite different sedimentary characters not only from the open ocean but also from small backarc basins along the marginal West Pacific, apparently controlled by the coupling between local tectonics and global climate changes.  相似文献   

20.
We measured SO2 emission rate from six volcanoes in Latin America (Santa Ana, El Salvador; San Cristóbal and Masaya, Nicaragua; Arenal and Poás, Costa Rica; Tungurahua and Sierra Negra, Ecuador) and from Mt. Etna, Italy, using two different remote sensing techniques: COSPEC (COrrelation SPECtrometer) and miniDOAS (miniaturized Differential Optical Absorption Spectroscopy). One of the goals of this study was to evaluate the differences in SO2 emission rates obtained by these two methods. The observed average SO2 emission rates measured during this study were 2688 t·d−1 from Tungurahua in July 2006, 2375 t·d−1 in September 2005 and 480 t·d−1 in February 2006 from Santa Ana, 1200 t·d−1 in May 2005 from Etna, 955 t·d−1 in March 2006 and 1165 t·d−1 in December 2006 from Masaya, 5400 t·d−1 of March 7, 2006 and 265 t·d−1 in March 2006 from San Cristobal, 113 t·d−1 in April 2006 from Arenal, 104 t·d−1 in April 2006 from Poás and 11 t·d−1 in July 2006 from Sierra Negra volcano. Most of the observed relative differences of SO2 emission measurements from COSPEC and miniDOAS were lower than 10%.  相似文献   

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