怀柔山地油松林氮、磷、硫生物--地球化学循环的研究

海河流域怀柔山地油松林生态系统N,P,S元素生物地球化学循环研究结果表明,生态系统氮素输入输出基本平衡。氮素、磷素在未来一段时间内将在植物凋落层中累积,硫则在凋落物层、土壤中累积。这种情况形成了城市郊区森林生态系统元素循环的独特特性。     

Experimental study and steady-state simulation of biogeochemical processes in laboratory columns with aquifer material

Packed bed laboratory column experiments were performed to simulate the biogeochemical processes resulting from microbially catalyzed oxidation of organic matter. These included aerobic respiration, denitrification, and Mn(IV), Fe(III) and SO(4) reduction processes. The effects of these reactions on the aqueous- and solid-phase geochemistry of the aquifer material were closely examined. The data were used to model the development of alkalinity and pH along the column. To study the independent development of Fe(III)- and SO(4)-reducing environments, two columns were used. One of the columns (column 1) contained small enough concentrations of SO(4) in the influent to render the reduction of this species unimportant to the geochemical processes in the column.The rate of microbially catalyzed reduction of Mn(IV) changed with time as evidenced by the variations in the initial rate of Mn(II) production at the head of the column. The concentration of Mn in both columns was controlled by the solubility of rhodochrosite (MnCO(3(S))).In the column where significant SO(4) reduction took place (column 2), the concentration of dissolved Fe(II) was controlled by the solubility of FeS. In column 1, where SO(4) reduction was not important, maximum dissolved Fe(II) concentrations were controlled by the solubility of siderite (FeCO(3(S))). Comparison of solid-phase and aqueous-phase data suggests that nearly 20% of the produced Fe(II) precipitates as siderite in column 1. The solid-phase analysis also indicates that during the course of experiment, approximately 20% of the total Fe(III) hydroxides and more than 70% of the amorphous Fe(III) hydroxides were reduced by dissimilatory iron reduction.The most important sink for dissolved S(-II) produced by the enzymatic reduction of SO(4) was its direct reaction with solid-phase Fe(III) hydroxides leading initially to the formation of FeS. Compared to this pathway, precipitation as FeS did not constitute an important sink for S(-II) in column 2. In this column, the total reacted S(-II) estimated from the concentration of dissolved sulfur species was in good agreement with the produced Cr(II)-reducible sulfur in the solid phase. Solid-phase analysis of the sulfur species indicated that up to half of the originally produced FeS may have possibly transformed to FeS(2).     

Integrated Crop–livestock Management Systems in Sub-saharan Africa

This paper outlines the advantages of integrated crop–livestock systems and unsolved problems that need to be studied further. The discussion is subdivided by ecozone with consideration of arid and dry semi-arid areas with extensive livestock management; moist semi-arid and semi-humid areas where integrated crop–livestock systems are common; and humid areas where swine and poultry often predominate. To maintain soil organic matter in all ecozones, efficient recovery and use of nutrients from animal manures, crop residues and green manures is essential. In extensive systems in dry zones, animals transport nutrients from grazing areas to cropland, while in moister regions that are more intensively farmed, the emphasis is on the efficiency of nutrient recovery. Specific research questions relating to the overall ecosystem, nutrient cycling, plants, and animals are posed.     

循环经济理论指导下上海闵行区水资源现状分析

上海闵行区水资源总量丰富但水体污染严重,3/4监测断面水质达不到水环境功能目标的要求,原因主要在于大量污水直排和受上游来水影响。基于循环经济理论,运用生态效率的概念对闵行水资源进行分析,发现水资源生产率水平和水环境生产率水平都有待提高。鉴于用水量大和污水处理设施能力不足导致闵行直排污水量增加的客观实际,结合降低资源输入（降低水耗）、废物输出（减少污染物排放）的循环经济指导思想,总结了实现闵行水资源可持续利用的途径。     

某城市湖泊中磷的循环特征及富营养化发生潜势

通过对浙江省临海市东湖水体磷元素的输入与输出途径与通量、磷元素在湖泊环境中的循环特征以及磷循环对水温上升的响应分析,并基于对该水体从2000年开始隔年进行各参数的观测,表明2000年以来磷输入年平均增量为0.007～0.009mg/L,水中叶绿素a平均年增0.14～0.56μg/L,透明度年平均下降0.38～0.49m,溶解氧年平均下降0.21～0.71mg/L.并依此建立了反映湖泊富营养化发生潜势的这些主要代表性参数与湖水中总磷含量之间的相关关系,揭示了可以通过从磷物质单因子的变化预测所引起的其它因子变化之间的关系来综合判断湖泊的营养状态,从而为减少湖泊富营养化的发生、提高湖泊水质提供科学依据.     

采用Pt、Dy改性粘结层的铈酸镧/氧化锆双陶瓷层抗氧化行为研究

目的研究Pt、Dy改性粘结层的铈酸镧/氧化锆双陶瓷层的抗氧化行为。方法采用电镀+EB-PVD的方式在高温合金表面制备带有Pt、Dy掺杂NiAl粘结层的热障涂层(Thermal Barrier Coatings TBCs)。采用双陶瓷层结构设计,顶层为铈酸镧(La_2Ce_2O_7),底层为氧化锆(YSZ)。对涂层在1200℃条件下的热循环行为、微观组织以及失效机制进行了研究。结果经过500次循环后,不掺杂涂层YSZ层与热生长氧化物(TGO)处出现了大量裂纹,Pt/Dy共掺杂的涂层经过1000次循环后界面处结合良好,仅仅是在La_2Ce_2O_7陶瓷顶层中出现了少量的微裂纹。结论在粘结层中加入Pt元素,能有效抑制互扩散区难溶相的析出,延缓涂层的蜕化。     

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

In this paper we investigate the seasonal autochthonous sources of dissolved organic carbon (DOC) and nitrogen (DON) in the euphotic zone at a station in the upper Chesapeake Bay using a new mass-based ecosystem model. Important features of the model are: (1) carbon and nitrogen are incorporated by means of a set of fixed and varying C:N ratios; (2) dissolved organic matter (DOM) is separated into labile, semi-labile, and refractory pools for both C and N; (3) the production and consumption of DOM is treated in detail; and (4) seasonal observations of light, temperature, nutrients, and surface layer circulation are used to physically force the model. The model reasonably reproduces the mean observed seasonal concentrations of nutrients, DOM, plankton biomass, and chlorophyll a. The results suggest that estuarine DOM production is intricately tied to the biomass concentration, ratio, and productivity of phytoplankton, zooplankton, viruses, and bacteria. During peak spring productivity phytoplankton exudation and zooplankton sloppy feeding are the most important autochthonous sources of DOM. In the summer when productivity peaks again, autochthonous sources of DOM are more diverse and, in addition to phytoplankton exudation, important ones include viral lysis and the decay of detritus. The potential importance of viral decay as a source of bioavailable DOM from within the bulk DOM pool is also discussed. The results also highlight the importance of some poorly constrained processes and parameters. Some potential improvements and remedies are suggested. Sensitivity studies on selected parameters are also reported and discussed.     

Phosphorus mobility in dam reservoir affected by redox oscillations: An experimental study

The internal sedimentary phosphorus(P) load of aquatic systems is able to support eutrophication, especially in dam–reservoir systems where sedimentary P stock is high and where temporary anaerobic conditions occur. The aim of this study therefore is to examine the response of sedimentary P exposed to redox oscillations. Surface sediments collected in the Champsanglard dam–reservoir(on the Creuse River, France) were subjected to two aerobic phases(10 and 12 days) alternated with two anaerobic periods(21 and 27 days)through batch incubations. The studied sediment contained 77 ± 3 μmol/g DW of P, mainly associated with the ascorbate fraction(amorphous Fe/Mn oxyhydroxides). The used sediment was rich in organic matter(OM)(21% ± 1%) with primarily allochthone signature.Our results showed that redox oscillations enhance dissolved inorganic phosphorus release at sediment/water interface. During the first anaerobic stage, the P release was mainly controlled by the dissolution/precipitation of iron minerals. The more pronounced increase of P release during the second anaerobic stage(44%) was due to various mechanisms related to the change in quality of dissolved organic matter(DOM), namely a higher SUVA254 and humification indices. The release of more refractory DOM(rDOM) served to lower the microbial metabolism activity, possibly favored iron oxyhydroxide aggregation and thus limiting iron reduction. In addition, rDOM is able to compete for mineral P sorption sites,leading to a greater P release. In reservoir with predominant allochthone OM input, the release of more aromatic DOM therefore plays an important role in P mobility.     

The balance of acidity and redox capability over modified CeO2 catalyst for the selective catalytic reduction of NO with NH3

The effect of acidity and redox capability over sulfuric acid-modified CeO_2 catalysts were studied for the selective catalytic reduction of NO_x with NH_3(NH_3-SCR). The deposition of sulfate significantly enhanced the catalytic performance over CeO_2. NO_x conversion over4H_2SO_4/CeO_2 at 230–440 °C was higher than 90%. The strong redox capability of CeO_2 could result in unselective NH_3 oxidation and decrease high temperatures catalytic activity and N_2 selectivity. The deposition of sulfate increased the acidity and weakened the redox capability, and then increased the high temperature NO_x conversion and N_2 selectivity. An appropriate level of acidity also promoted the activity at 190–250 °C over ceria-based catalysts, and with further increase in the acidity, the SCR activity decreased slightly. Weak redox capability lowered the low-temperature catalytic activity. Excellent SCR activity requires a balance of acidity and redox capability on the catalysts.     

Nutrient fluxes at the landscape level and the R* rule

Nutrient cycling in terrestrial ecosystems involves not only the vertical recycling of nutrients at specific locations in space, but also biologically driven horizontal fluxes between different areas of the landscape. This latter process can result in net accumulation of nutrients in some places and net losses in others. We examined the effects of such nutrient-concentrating fluxes on the R* rule, which predicts that the species that can survive in steady state at the lowest level of limiting resource, R*, can exclude all competing species. To study the R* rule in this context, we used a literature model of plant growth and nutrient cycling in which both nutrients and light may limit growth, with plants allocating carbon and nutrients between foliage and roots according to different strategies. We incorporated the assumption that biological processes may concentrate nutrients in some parts of the landscape. We assumed further that these processes draw nutrients from outside the zone of local recycling at a rate proportional to the local biomass density. Analysis showed that at sites where there is a sufficient biomass-dependent accumulation of nutrients, the plant species with the highest biomass production rates (roughly corresponding to the best competitors) do not reduce locally available nutrients to a minimum concentration level (that is, minimum R*), as expected from the R* rule, but instead maximize local nutrient concentration. These new results require broadening of our understanding of the relationships between nutrients and vegetation competition on the landscape level. The R* rule is replaced by a more complex criterion that varies across a landscape and reduces to the R* rule only under certain limiting conditions.