田间施用锌肥对小麦籽粒镉累积的影响及施用风险

锌（Zn）和镉（Cd）的交互作用是近年来小麦Cd污染防治的重要研究方向.以华北地区典型小麦田为研究对象,通过田间试验,探究Zn肥对土壤-小麦系统Cd污染的控制效果和施用风险.结果表明,低用量Zn处理下,济源和开封两地小麦籽粒Cd含量均呈下降趋势,与对照相比下降幅度分别为33.4%和25.3%.高用量Zn处理下,两地小麦籽粒Cd含量不降反升,与低用量Zn处理下小麦籽粒Cd含量相比增幅为22.4%和34.2%.施Zn后两地土壤Zn总量和有效态含量均有显著升高,且造成了土壤Cd的部分活化.典型相关分析（CCA）显示,当土壤ω（Zn）小于200 mg ·kg^-1时,土壤Zn是土壤-小麦系统Cd富集的主要影响因子,而当土壤ω（Zn）大于200 mg ·kg^-1时,土壤Cd的活化是影响小麦籽粒Cd富集的主要原因.回归分析显示土壤Cd/Zn降至0.0089时（低用量Zn）,Zn和Cd表现出拮抗效应,土壤Cd/Zn降至0.0078时（高用量Zn）,Zn和Cd表现出协同效应.针对区域Cd污染特征,调整Zn肥用量可以提高污染防治效率并避免加剧Cd污染危害.     

废弃物基水热炭改良对水稻产量及氮素吸收的影响

生物炭农田回用是实现农林废弃物资源化利用和碳封存的有效手段.近年来,水热碳化技术由于在炭产率、能耗及生产过程中的烟气排放等方面显著优于常规热解碳化技术而受到关注.为实现农林废弃物的资源化利用,明确水热炭农田应用对作物生产力的影响,本研究通过原状土柱模拟试验和表征分析,研究了4种不同类型改良水热炭对两种典型土壤的水稻产量和氮素吸收的影响及可能的驱动因素.结果表明,锯末水热炭和秸秆水热炭经物理或生物改良后,在两种类型土壤上均能够增加水稻产量和氮素吸收,减少氮素损失,且其效应不受水热炭添加量影响（5‰,15‰;质量分数）.与对照相比,水热炭添加处理的产量和氮素吸收量分别提高9.2%~20.7%和7.7%~17.0%.高C/N比的锯末水热炭更有利于高肥力土壤水稻氮素吸收量的增加;而低肥力土壤由于限制性因子较多,受水热炭类型的影响较小.通过对水热炭的表征分析发现,其表面养分元素丰富;水洗或生物改良后其表面孔隙结构有较大改善,C元素相对含量明显降低,N和O元素相对含量明显增加,这对养分的固持/供应可能产生影响.因此,水热炭改良后孔隙结构的改变和N、O元素含量的增加可能是其施用后水稻产量和氮素吸收增加的关键驱动因素.结果说明,水热碳化材料改良后应用农田可以在实现农林废弃物资源化利用的同时,提高作物生产力,减少农田氮素环境损失.     

Response of C and N cycles to N fertilization in Sphagnum and Molinia-dominated peat mesocosms

Plant communities play an important role in the C-sink function of peatlands. However, global change and local perturbations are expected to modify peatland plant communities, leading to a shift from Sphagnum mosses to vascular plants. Most studies have focused on the direct effects of modification in plant communities or of global change (such as climate warming, N fertilization) in peatlands without considering interactions between these disturbances that may alter peatlands' C function. We set up a mesocosm experiment to investigate how Greenhouse Gas (CO₂, CH₄, N₂O) fluxes, and dissolved organic carbon (DOC) and total dissolved N (TN) contents are affected by a shift from Sphagnum mosses to Molinia caerulea dominated peatlands combined with N fertilization. Increasing N deposition did not alter the C fluxes (CO₂ exchanges, CH₄ emissions) or DOC content. The lack of N effect on the C cycle seems due to the capacity of Sphagnum to efficiently immobilize N. Nevertheless, N supply increased the N₂O emissions, which were also controlled by the plant communities with the presence of Molinia caerulea reducing N₂O emissions in the Sphagnum mesocosms. Our study highlights the role of the vegetation composition on the C and N fluxes in peatlands and their responses to the N deposition. Future research should now consider the climate change in interaction to plants community modifications due to their controls of peatland sensitivity to environmental conditions.     

5种沉水植物的氮、磷吸收和水质净化能力比较

选取轮叶黑藻(Hydrilla verticillata)、苦草(Vallisneria natans)、金鱼藻(Ceratophyllum demersum)、穗状狐尾藻(Myriophyllum spicatum)、微齿眼子菜(Potamogeton maackianus)等5种乡土沉水植物为研究对象,在室内静水条件下对其氮、磷吸收和水质净化能力进行比较研究.结果表明,不同沉水植物试验前后的含水率差异较小,变化范围为89.8%~92.0%,但净增生物量差异较大且均存在显著性差异,变化范围(干重计)为1.52~12.92 g·m-2,其中净增生物量最高的轮叶黑藻是最低的微齿眼子菜的8.5倍.不同沉水植物试验前后植株氮、磷含量变化范围分别为26.54~34.44 g·kg~(-1)和2.54~4.01g·kg~(-1),其中金鱼藻的植株氮、磷含量相对偏高.不同沉水植物处理的水质TN、TP去除率范围分别为63.8%~83.1%和49.2%~70.8%,均显著高于CK处理的39.9%和36.9%,去除率大小顺序均为:轮叶黑藻金鱼藻苦草穗状狐尾藻微齿眼子菜CK.不同沉水植物处理的水质TN、TP去除率与净增生物量存在较高相关性,相关性系数分别为0.994(P0.01)和0.996(P0.01).不同沉水植物氮、磷直接吸收贡献率范围分别为1.5%~13.3%和2.2%~13.2%,扣除水体自身自净能力后沉水植物的增效作用贡献率范围分别为22.5%~29.9%和10.1%~20.6%,表明水质净化氮、磷去除过程中沉水植物的增效作用要大于直接吸收作用.     

Aeration optimization through operation at low dissolved oxygen concentrations: Evaluation of oxygen mass transfer dynamics in different activated sludge systems

In wastewater treatment plants(WWTPs)using the activated sludge process,two methods are widely used to improve aeration efficiency — use of high-efficiency aeration devices and optimizing the aeration control strategy. Aeration efficiency is closely linked to sludge characteristics(such as concentrations of mixed liquor suspended solids(MLSS)and microbial communities)and operating conditions(such as air flow rate and operational dissolved oxygen(DO)concentrations). Moreover,operational DO is closely linked to effluent quality. This study,which is in reference to WWTP discharge class A Chinese standard effluent criteria,determined the growth kinetics parameters of nitrifiers at different DO levels in small-scale tests. Results showed that the activated sludge system could meet effluent criteria when DO was as low as 0.3 mg/L,and that nitrifier communities cultivated under low DO conditions had higher oxygen affinity than those cultivated under high DO conditions,as indicated by the oxygen half-saturation constant and nitrification ability. Based on nitrifier growth kinetics and on the oxygen mass transfer dynamic model(determined using different air flow rate(Q′_(air))and mixed liquor volatile suspended solids(MLVSS)values),theoretical analysis indicated limited potential for energy saving by improving aeration diffuser performance when the activated sludge system had low oxygen consumption; however,operating at low DO and low MLVSS could significantly reduce energy consumption. Finally,a control strategy coupling sludge retention time and MLVSS to minimize the DO level was discussed,which is critical to appropriate setting of the oxygen point and to the operation of low DO treatment technology.     

沈阳市城市污水处理厂现状及提标改造技术对策分析

为达到国家《城镇污水处理厂污染物排放标准》(GB18918—2002)一级A要求,对沈阳市污水处理厂实施提标改造工程。通过对沈阳市城市污水处理厂现状、处理工艺特征及运行情况调研分析,根据沈阳市城市污水处理厂需要提标改造存在的问题,提出工艺优化以及提标改造解决对策,为沈阳市城市污水处理厂提标改造的工程建设提供技术支撑。     

Sustained dynamic transience in a Lotka-Volterra competition model system for grassland species

Theoretical approaches, such as the Lotka-Volterra framework, enable predictions about long term species coexistence based on stability criteria, but generally assume temporal constancy of system equations and parameters. In real world systems, temporal variability may interfere with the attainment of stable states. Managed grassland ecosystems in Northwestern Europe experience structural periodic fluctuations in environmental conditions: the seasons. In addition, periodic disturbances such as cutting are very common. Here we show, using a Lotka-Volterra system applied to grassland species with empirically derived parameters, that seasonal variability can result in a time dependent equilibrium and redirection of displacement processes.Parameter estimates differed between species and - in most cases - between the seasons. As a result, five of the fifteen tested species combinations had different outcomes of species interactions between seasons. This indicates that systems remain in dynamic transience over the year as the equilibrium changes and the species composition of the system follows the equilibrium without ever attaining it. The non-attainment of the steady state enables coexistence of species even if there is competitive exclusion in one of the seasons. For three of the fifteen species combinations, cutting frequency affected the long-term coexistence patterns. Cutting resets the biomass of competing species and favours during regrowth those species that have a high growth rate, which can alter species coexistence in comparison to a Lotka-Volterra model without cutting. The Lotka-Volterra framework with seasonally changing empirical parameters predicts coexistence as a possible outcome of systems that in component seasons are characterised by exclusion, and vice versa.     

我国中亚热带人工林水热通量对干旱差异响应的模拟研究

季节性干旱现象在我国中亚热带地区时有发生,为了研究该区域大气-生态系统之间的相互作用关系及其碳水收支状况,2002年起在江西省千烟洲（26.7°N,115.1°E）人工林生态系统建立了通量观测塔。2003年7月该人工林生态系统遭遇了历史上少有的高温少雨天气,本研究应用基于生理生态学过程的EALCO（Ecological Assimilation of Land and Climate Observation）模型及2003和2004年通量观测数据对该生态系统的水热通量进行了模拟,同时分析了干旱胁迫对它们产生的影响。结果显示,模型能够很好的模拟该生态系统的能量通量的日变化,净辐射、显热和潜热通量模拟值与实测值相关系数的平方（R2）及标准差分别为0.99和8.05 W.m-2;0.81和41.02 W.m-2;0.90和31.49 W.m-2,模型可以解释87%的日蒸散量的变化。从模拟结果看,2003年7月下旬（发生较严重干旱胁迫）较2004年同期（干旱程度轻）相比,冠层及土壤水势下降约2倍,植物蒸腾的日变化形式改变,根系吸水滞后冠层蒸腾的时间缩短约半小时,冠层导度下降40%～60%。模拟与观测结果均表明,2003年7月下旬每天正午的波文比大都介于1～2.2,而2004年同期正午的波文比则介于0.2～0.6。EALCO模型通过Ball模型将植物碳水过程耦合在一起,从而可以很好的模拟植物的气孔行为,进而准确的模拟植物水热过程对干旱的响应。土壤水分匮乏对冠层导度的限制是2003年干旱期间冠层潜热通量模拟值下降的根本原因。     

A botanical importance rating system for estuaries

In many semi-arid areas, estuaries are threatened because of freshwater impoundment. Estuaries are important sites for ecological diversity and, increasingly, for recreation. A system has been developed which rates estuaries according to their botanical importance. A formula allows a single numerical importance score to be calculated. The area cover of each estuarine plant community type (i.e. intertidal salt marsh, submerged macrophytes, reed/sedge swamps and supratidal salt marsh) and its importance in the estuary forms the basis of the score. The ‘ecological condition’ of the plant community and the community richness within the estuary are incorporated into the formula. The formula is effective in determining the botanical importance of estuaries. Further methods to determine the zoological, physical and socio-economic importance of estuaries need to be developed to allow the overall importance of estuaries to be determined.     

Macroalgal growth in nutrient-enriched estuaries: A biogeochemical and evolutionary perspective

Increased nutrient loading of a body of water leads to an increase in macroalgal growth. It is generally observed, however, that certain species thrive more than others, capitalising on the increased nutrient availability. These are usually small, fast-growing, ephemeral algae that often appear as nuisance blooms. This article discusses the correlation between nutrient increase and macroalgal bloom formation. From a historical perspective, the evolutionary history of nuisance macroalgae, and the habits available to them prior to anthropogenic influences on estuarine geochemistry are considered. The occurrence of macroalgal genera whose distribution is commonly related to estuaries with high nutrient loading is discussed, along with evidence suggesting that the ecophysiological traits of r-selected, ephemeral algae largely contribute to their ecological success and bloom-formation at nutrient-enriched sites.