Seasonal timing of N pulses influences N capture in a saltbush scrub community   总被引：1，自引：1，他引：1  

J.J. James  Z.T. Aanderud  J.H. Richards 《Journal of Arid Environments》2006,67(4):688-700

Limiting resources are generally available in brief temporal pulses in arid systems. We compared the abilities of dominant shrubs in a saltbush scrub community to capture N from pulses and evaluated whether N capture and partitioning within this community is influenced by the seasonal timing of pulses. Based on previous research in agronomic systems we predicted that the ability of a species to capture N following a pulse would depend on when the pulse occurred in relation to plant growth rate and N demand. Supporting this hypothesis, Atriplex confertifolia and Sarcobatus vermiculatus, which had greater growth rates early in the growing season compared to Atriplex parryi, captured more N from early spring pulses than A. parryi. Atriplex parryi, which had higher growth rates later in the growing season, captured more N from mid- and late spring pulses than the other species. These temporal differences in N capture among species, however, also depended on the magnitude of the N pulse. These results suggest that temporal variation in N availability may differentially impact competitive abilities of coexisting species and potentially facilitate species coexistence in arid systems.  相似文献   

Chemical composition and the nitrogen-regulated trophic state of Patagonian lakes   总被引：5，自引：0，他引：5  

Mnica Diaz  Fernando Pedrozo  Colin Reynolds  Pedro Temporetti 《Limnologica》2007,37(1):17-27

Chemical composition and nutrient concentrations of 39 relatively poorly known Patagonian lakes (38–50°S and from 70° to 68°W) are described and analysed using principal component analysis (PCA). The general relationships between nutrients (total phosphorus, bioavailable phosphorus and dissolved inorganic nitrogen) and plankton biomass are examined.We seek to demonstrate that the extreme oligotrophy characterising many lakes and reservoirs of the Argentine Patagonian region of South America owes more to nitrogen deficiency than to a shortage of available phosphorus. The data show a range of trophic conditions with variable water chemistry characteristics.The first two axes of the PCA ordination explain most of the variance (63%). The first component of the variance in the environmental data is a trophic gradient, with positive correlations with the concentrations of nutrients (TP, SRP, DIN) and electrical conductivity and a negative correlation with transparency. For all the reservoirs considered, the calculated annual, summer and winter chlorophyll-a carrying capacities of the available phosphorus were consistently and significantly (P<0.05) in excess of observations but maximum chlorophyll-a values correlate with DIN availability. Indeed the chlorophyll-a carrying capacities, as an index of the resource-sustainable maximum biomass, of the available nitrogen gives a better predictive yield relationship than does P. Our findings are remarkable in so far as the general expectation that dinitrogen-fixing phytoplankton should thrive in the absence of dissolved inorganic nitrogen, at least to the supportive limits of the available phosphorus, is unfulfilled.  相似文献   

Recent carbon and nitrogen uptake rates of phytoplankton in Bering Strait and the Chukchi Sea     

Sang H. Lee  Terry E. Whitledge  Sung-Ho Kang 《Continental Shelf Research》2007

Cruises to Bering Strait and the Chukchi Sea in US waters from late June in 2002 to early September in 2004 and the Russian–American Long-term Census of the Arctic (RUSALCA) research cruise in 2004 covered all major water masses and contributed to a better understanding of the regional physics, nutrient dynamics, and biological systems. The integrated concentration of the high nitrate pool in the central Chukchi Sea was greater in this study than in previous studies, although the highest nitrate concentration (∼22 μM) in the Anadyr Water mass passing through the western side of Bering Strait was consistent with prior observations. The chlorophyll-a concentrations near the western side of the Diomede Islands ranged from 200 to 400 mg chl-a m⁻² and the range in the central Chukchi Sea was 200–500 mg chl-a m⁻² for the 2002–2004 Alpha Helix (HX) cruises. Chlorophyll-a concentrations for the 2004 RUSALCA cruise were lower than those from previous studies. The mean annual primary production of phytoplankton from this study, using a ¹³C–¹⁵N dual-isotope technique, was 55 g C m⁻² for the whole Chukchi Sea and 145 g C m⁻² for the plume of Anadyr–Bering Shelf Water in the central Chukchi Sea. In contrast, the averages of annual total nitrogen production were 13.9 g N m⁻² (S.D.=±16.2 g N m⁻²) and 33.8 g N m⁻² (S.D.=±14.1 g N m⁻²) for the Chukchi Sea and the plume, respectively. These carbon and nitrogen production rates of phytoplankton were consistently two-or three-fold lower than those from previous studies. We suggest that the lower rates in this study, and consequently more unused nitrate in the water column, were caused by lower phytoplankton biomass in the Bering Strait and the Chukchi Sea. However, we do not know if the lower rate of production from this study is a general decreasing trend or simply temporal variations in the Chukchi Sea, since temporal and geographical variations are substantially large and presently unpredictable.  相似文献   

Modeling nitrogen–carbon cycling and oxygen consumption in bottom sediments     

Mohamed M. Hantush 《Advances in water resources》2007

A model framework is presented for simulating nitrogen and carbon cycling at the sediment–water interface, and predicting oxygen consumption by oxidation reactions inside the sediments. Based on conservation of mass and invoking simplifying assumptions, a coupled system of diffusive–reactive partial differential equations is formulated for two-layer conceptual model of aerobic–anaerobic sediments. Oxidation reactions are modeled as first-order rate processes and nitrate is assumed to be consumed entirely in the anoxic portion of the sediments. The sediments are delineated into a thin oxygenated surface layer whose thickness is equal to the oxygen penetration depth, and a lower, but much thicker anoxic layer. The sediments are separated from the overlying water column by a relatively thin boundary layer through which mass transfer is diffusion controlled. Transient solutions are derived using the method of Laplace transform and Green’s function, which relate pore-water concentrations of the constituents to their concentrations in the bulk water and to the flux of decomposable settling organic matter. Steady-state pore-water concentrations are also obtained including expressions for the extent of methane saturation zone and methane gas flux. A relationship relating the sediment oxygen demand (SOD) to bulk water oxygen is derived using the two-film concept, which in combination with the depth-integrated solutions forms the basis for predicting the extent of oxygen penetration in the sediment. Iterative procedure and simplification thereof are proposed to estimate the extent of methane saturation zone and thickness of the aerobic layer as functions of time. Sensitivity of steady-state solutions to key parameters illustrates sediment processes interactions and synergistic effects. Simulations indicate that for a relatively thin diffusive boundary layer, d, oxygen uptake is limited by biochemical processes inside the sediments, whereas for a thick boundary layer oxygen transfer through the diffusive boundary layer is limiting. The results show an almost linear relationship between steady-state sediment oxygen demand and bulk water oxygen. For small d methane and nitrogen fluxes are sediment controlled, whereas for large d they are controlled by diffusional transfer through the boundary layer. It is shown that the two-layer model solution converges to the one-layer model (anaerobic layer) solution as the thickness of the oxygenated layer approaches zero, and that the transient solutions approach asymptotically their corresponding steady-state solutions.  相似文献   

Emission of nitrogen oxides (NO x ) from a flooded soil fertilized with urea: Relation to other nitrogen loss processes     

I. E. Galbally  J. R. Freney  W. A. Muirhead  J. R. Simpson  A. C. F. Trevitt  P. M. Chalk 《Journal of Atmospheric Chemistry》1987,5(3):343-365

Emissions of nitric oxide and other odd nitrogen oxides (NO _x ) from a flooded rice field were studied after urea had been broadcast into the floodwater.The NO _x flux from the fertilized area was very low (0.2×10^-9 g N m^-2 s^-1) for the first few days after application of urea and was high (0.95×10^-9 g N m^-2 s^-1) in the subsequent period when significant nitrite and nitrate were present in the floodwater. At night, little if any NO _x was exhaled but ambient NO₂ was absorbed by the floodwater. An uptake velocity for NO₂ of 3×10^-4 m s^-1 was measured during one night. Maximum NO _x losses were observed near 1300 h when temperature and solar ultraviolet light were maximum.While the amounts of nitrogen oxides emitted are of little agronomic importance (2×10^-3 per cent of the fertilizer nitrogen was lost as NO _x during the 10-day study period), they may well be of significance as a source for some gas reactions in the atmosphere and for the global nitrogen cycle.Of the fertilizer nitrogen applied (as urea) approximately 30% was lost to the atmosphere by NH₃ volatilization, 15% by denitrification, presumably as N₂, and the remainder, less minor losses of NO and N₂O, remained in the plant/soil/water system.Now at Forestry Department, Australian National University, G.P.O. Box 4, ACT 2601, Australia.  相似文献   

Nitrogen dioxide column content measurements made from an aircraft between 5° and 82°N     

W. A. Matthews 《Journal of Atmospheric Chemistry》1984,2(2):125-132

In the first two weeks of May 1981, the research jet of the German Aerospace Research Establishment (DFVLR) was charted to fly a meridional section between 5° and 82°N. A scanning filter photometer, developed at the Max Planck Institut für Aeronomie to measure column content values of atmospheric ozone and nitrogen dioxide, using ultra violet and visible absorption techniques, constituted part of the experimental payload for this campaign that was called SIMOC. The vertical NO₂ column content above the aircraft, flying at approximately 10 km, was found to decrease rapidly from 6.9×10¹⁵ molecules cm^-2 to 2.5×10¹⁵ molecules cm^-2 around 50°N and then to increase again north of 75°N. A sharp rise in the NO₂ content was observed south of the subtropical jet but this could possibly be due to the increased depth of the troposphere above the aircraft in these regions.  相似文献   

Fine-scale prediction of biomass and leaf nitrogen content in sugarcane using UAV LiDAR and multispectral imaging     

《International Journal of Applied Earth Observation and Geoinformation》2020

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Domestic politics and the diffusion of international policy innovations: How does accommodation happen?     

《Global Environmental Change》2014

What happens to policy innovations after they have been adopted? What factors account for subsequent changes to these policies? These are the research questions guiding this study on the spread of and subsequent changes to limit values for nitrogen oxide emissions from large combustion plants. By comparing the processes of diffusion and follow-up policy changes, we assess whether and how policy innovations translate into policy making. In so doing, we build on the literature on the determinants of policy diffusion and transfer. We employ original data on instances of policy adoption and policy change in 24 Organisation for Economic Co-operation and Development (OECD) countries over a period of thirty years (1976–2005). The data are analysed using semi-parametric event-history models. Our empirical findings show that both international and domestic factors account for the observed variation in our data regarding both first-time adoptions and post-adoption modifications. The results reveal that the subsequent tightening of emission standards faces greater obstacles than their mere diffusion (i.e., policy adoption). While international factors and supranational integration appear to impede the subsequent tightening of existing policies, international peer pressure is a strong predictor of an on-going regulatory commitment. Overall, adoption and accommodation processes seem to follow distinctive patterns, suggesting that a promising strategy in policy innovation research would involve differentiation between the first-time adoption and subsequent modification of policies.  相似文献   

Potential of Svalbard reindeer winter droppings for emission/absorption of methane and nitrous oxide during summer     

《Polar Science》2014,8(2):196-206

Droppings of Svalbard reindeer (Rangifer tarandus platyrhynchus) could affect the carbon and nitrogen cycles in tundra ecosystems. The aim of this study was to evaluate the potential of reindeer droppings originating from the winter diet for emission and/or absorption of methane (CH₄) and nitrous oxide (N₂O) in summer. An incubation experiment was conducted over 14 days using reindeer droppings and mineral subsoil collected from a mound near Ny-Ålesund, Svalbard, to determine the potential exchanges of CH₄ and N₂O for combinations of two factors, reindeer droppings (presence or absence) and soil moisture (dry, moderate, or wet). A line transect survey was conducted to determine the distribution density of winter droppings at the study site. The incubation experiment showed a weak absorption of CH₄ and a weak emission of N₂O. Reindeer droppings originating from the winter diet had a negligible effect on the exchange fluxes of both CH₄ and N₂O. Although the presence of droppings resulted in a short-lasting increase in N₂O emissions on day 1 (24 h from the start) for moderate and wet conditions, the emission rates were still very small, up to 3 μg N₂O m⁻² h⁻¹.  相似文献   

城市污水处理厂升级改造工程设计与运行效果     

刘如玲  宋美芹 《海洋湖沼通报》2015,(1):134-140

为保护海洋环境,改善胶州湾的水污染现状,根据青岛市政府的要求对污水处理厂进行升级改造。主体生化工艺采用A2/O+移动床生物膜(MBBR)工艺,通过投加SPR-1生物填料,将好氧段改造为生物膜—活性污泥复合工艺。同时新建混凝、沉淀、过滤等深度处理设施。运行四年来,效果良好,抗冲击负荷能力强,可同时强化脱氮除磷,主要水质指标均稳定达到《城镇污水处理厂污染物排放标准》(GB18918-2002)一级A标准。实践证明,该工艺可大幅减少工程量,具有运行管理简便、处理效率稳定等特点,较好地解决了市政污水厂升级改造中的难题,可为其他污水厂的升级改造提供借鉴。同时,污染物年减排量明显提高,团岛海域水质环境质量将得到进一步改善。  相似文献