Effects of Contaminant Decay on the Diffusion Centre of a River

Many contaminants exhibit decay (radioactive decay, consumed by bacteria, heat loss or evaporation through the surface, dissolution by turbulence). For a non-symmetric river with non-reversing flow, the effects of decay are allowed for in specifying the diffusion centre, i.e. the optimal position for a steady discharge. Three families of exact solutions are presented that illustrate the effect on the diffusion centre of cross-channel variation in the decay (uniform, decreasing or increasing with depth). The diffusion centre is shifted to deeper or to shallower water accordingly as the temporal decay divided by flow speed decreases or increases with water depth.     

Ecological degradation and hydraulic dispersion of contaminant in wetland

For the typical case of a pulsed contaminant emission into a free surface wetland flow, a theoretical analysis is presented in this paper for the decay of the depth-averaged concentration under the combined action of ecological degradation and hydraulic dispersion. Based on a first-order reaction model extensively employed in related ecological risk assessment and environmental hydraulic design, the effect of ecological degradation is separated from the hydraulic effect via an exponential transformation for the general formulation for contaminant transport. The speed profile of a fully developed steady flow through the wetland is obtained. A hydraulic dispersion model for the depth-averaged concentration is devised as an extension of Taylor’s classical analysis on dispersion, and corresponding hydraulic dispersivity is obtained by Aris’s method of moments. Analytical solution of depth-averaged concentration is rigorously derived and characterized. For typical pollutant constituents in wastewater emission, the evolution of contaminant cloud in the wetland flow is illustrated by critical length and duration of influenced region with contaminant concentration beyond given environmental standard level, with essential implications for ecological risk assessment and environmental management.     

Deterministic particle tracking simulation of pollutant discharges in rivers and estuaries

A two-dimensional deterministic particle tracking model, in which the anisotropic-dispersive process is described by a particle strength exchange scheme, is established for the simulation of pollutant transport in vertically well-mixed rivers and estuaries. By simulating two benchmark problems with analytic solutions, the PSE scheme is shown to be accurate even if the anisotropic ratio of dispersion coefficients is very high. Further simulations of two specific problems concerning the optimal effluent discharge location and procedure are presented. The major conclusion is that in a tidal estuary with a relatively large fresh-water flow, setting the discharge position at the mixing center and making the discharge rate proportional to flow speed may minimize the peaks of concentration.     

Both evaluation of resource quality and speed of recruited leaf-cutting ants (Acromyrmex lundi) depend on their motivational state

Summary During recruitment, running velocity of both outbound and laden workers of the leaf-cutting ant Acromyrmex lundi depended on the information about resource quality they received from the first successful recruiter. In independent assays, single scout ants were allowed to collect sugar solutions of different concentrations and to recruit nestmates. Recruited workers were presented with standardized paper discs rather than the sugar solution given to the original recruiting ant. Outbound recruited workers were observed to run faster the more concentrated the solution found by the recruiter. Speed of disc-laden workers also depended on the concentration of the solution found by the recruiter, i.e. on the information about food quality they received, since they had no actual contact with the sugar solution. Disc-laden workers ran, as intuitively expected, slower than outbound workers. The reduction in speed, however, could not be attributed to the effects of the load itself, because workers collecting discs of the same weight, but with added sugar, ran as rapidly as outbound, unladen workers. Workers collecting standardized sugared discs reinforced the chemical trail on their way to the nest. The percentage of trail-layers was higher when workers were recruited to 10% than to 1% sugar solution, even though they collected the same kind of discs at the source. Their evaluation of resource quality, therefore, depended on their motivational state, which was modulated by the information they received during recruitment. Using previously published data on energetics of locomotion in leaf-cutting ants, travel costs of A. lundi workers recruited to sugar solutions of different concentration could be estimated. For workers recruited to the more concentrated solution, both speed and oxygen consumption rate increased by a roughly similar factor. Therefore, although workers ran faster to the high-quality resource, their actual energy investment per trip remained similar to that made by workers recruited to the low-quality resource. It is suggested that the more motivated workers reduced travel time without increasing energy costs during the trip. The adaptive value of these responses seems to be related to a rapid transmission of information about a newly discovered food source.     

A CFD study of wind patterns over a desert dune and the effect on seed dispersion

In the Namib Desert seed distribution is greatly influenced by wind patterns. Existing literature regarding wind patterns over dunes focuses on two-dimensional simulations of flow over simplified dune structures. The three-dimensional geometries of the sand dunes suggests far more complex flow features exist, which are not captured by two-dimensional simulations. Computational fluid dynamics (CFD) was used to reproduce the three-dimensional near surface wind patterns around a dune with the aim to learn more about seed distribution. Field work included terrain mapping, wind speed, direction and temperature metering. The CFD results show the expected two-dimensional flow features of high pressure at the dune toe, low pressure at the crest and flow acceleration up windward slope. Also observed are some three-dimensional flow features such as a spiral vortex near the crest and transverse flow due to crest-line curvature of the dune. It was also observed how the wall shear stress differs due to the three-dimensional shape of the dune. The wall shear stress suggests that seed accumulation is more likely to occur behind trailing (down-wind) crest edges. Particle tracking showed how seeds tend to move over the dune crest and recirculate towards the crest on the lee-side. The study showed that adding the third dimension makes the simulations more complex, adds to computational requirements and increases simulation time but also provides vital flow information which is not possible with two-dimensional simulations.     

Influence of flow speed on the functional response of a passive suspension feeder,the spionid polychaete <Emphasis Type="Italic">Polydora cornuta</Emphasis>

Passive suspension feeders rely on surrounding flow to deliver food particles to them. Therefore, the classic conception of functional response (feeding rate vs. food concentration) may require modification to account for flow speed as a second independent variable. I compared the functional response of Polydora cornuta at different velocities and determined whether food capture was proportional to particle flux (concentration × velocity). To understand feeding responses at a mechanistic level, I measured the functional responses in terms of contact and capture rates and determined particle retention efficiency. Experiments were run separately with two sizes of food particles, and with juvenile or adult worms. For both worm sizes and both particle sizes, capture rate in weak flow was directly related to concentration, but in strong flow it was constant. Worms were therefore unable to benefit from abundant food when in strong flow. The critical velocity at which the capture rate became constant was lower for adult worms than for juvenile worms, and it was lower for small particles than for large particles. Retention efficiency was constant among all treatments, and the results for contact rate were essentially the same as for capture rate. Therefore, the mechanics of particle contact must explain the effects of velocity on the functional response. Contact rate was not a constant proportion of particle flux; treatments with similar fluxes yielded different contact rates depending on the strength of flow. The results appeared to be caused by a velocity-induced behavioral change in appendage posture that affects contact rates: in moderate flow, worms form their feeding palps into helical coils, which they tighten as the velocity increases. I suggest this behavior constrains suspension feeding rates and the mechanical selection between particle sizes when worms are in strong flow, and that the effect changes with ontogeny. Because the results are consistent with patterns in measured growth rates of P. cornuta, I hypothesize that this influence of velocity on the functional response can constrain growth and population dynamics in this species.     

三江平原典型小叶章湿地土壤中硝态氮水平运移的模拟研究

选择三江平原小叶章湿地不同水分带上草甸沼泽土和腐殖质沼泽土2种土壤类型作为研究对象，以KNO3为示踪剂，模拟研究硝态氮在湿地土壤中的水平运移过程。结果表明，2种土壤各土层硝态氮水平运移浓度和速率均与运移距离呈极显著负相关（P〈0．01），并随运移距离增加呈一阶指数衰减曲线变化，各土层硝态氮水平运移速率主要受浓度梯度、水势梯度及土壤基质势的控制；土壤各土层中硝态氮水平运移速率与土壤含水量呈显著正相关（P〈0．05），并随土壤含水量增加呈指数增长曲线变化；土壤各土层中硝态氮水平运移浓度与土壤水分扩散率呈极显著正相关（P〈0．01），0—20cm土层硝态氮水平运移浓度随水分扩散率升高呈Boltzmann曲线变化，其他土层则呈指数增长曲线变化；草甸沼泽土比腐殖质沼泽土相应土层更利于硝态氮的水平运移，这主要与土层颗粒组成和孔隙度等物理性质的显著差异有关，而湿地水文条件可能对2种土壤物理性质的塑造有着重要影响。     

Effects of symbiotic status,flow speed,and prey type on prey capture by the facultatively symbiotic temperate coral <Emphasis Type="Italic">Oculina</Emphasis><Emphasis Type="Italic">arbuscula</Emphasis>

Symbiotic temperate corals can supplement prey capture by the coelenterate host with autotrophic carbon production by endosymbiotic zooxanthellae. To test the relationship between heterotrophic consumption and photosynthetic energy, prey capture by symbiotic and aposymbiotic specimens of the temperate scleractinian coral Oculina arbuscula (Verrill) was measured in January-April 2001. Corals were tested in a laboratory flume at five flow speeds, using Artemia franciscana cysts and nauplii as prey. Per-polyp capture rate and feeding efficiency were independent of symbiotic condition. Capture rate increased with flow speed, while capture efficiency declined. The location of capture shifted from the upstream to downstream side of the coral as flow speed increased. Differences in capture rate, location, and feeding efficiency for cysts and live brine shrimp nauplii were likely due to prey size rather than swimming ability.     

不同环境场所夏季空气负离子浓度分布特征及其与环境因子的关系

大气离子是由许多自然和人为的原因产生,并且它们的浓度在不同环境场所下差别很大。以我国南部沿海某省份作为研究区域,挑选了近10处有代表性的环境场所进行为期一周的实测和研究,收集了空气正、负离子浓度、风速、空气温度、相对湿度等数据。研究显示,空气负离子浓度与风速、水、植物、相对湿度等有较为密切的关系,其中最主要的影响因素是水,其次是风,最小的是气温。为了改善城市生态环境,建议在城市规划建设中采取有效措施以提高空气负离子浓度。     

Manipulating decay time for efficient large-mammal density estimation: gorillas and dung height

Large-mammal surveys often rely on indirect signs such as dung or nests. Sign density is usually translated into animal density using sign production and decay rates. In principle, such auxiliary variable estimates should be made in a spatially unbiased manner. However, traditional decay rate estimation methods entail following many signs from production to disappearance, which, in large study areas, requires extensive travel effort. Consequently, decay rate estimates have tended to be made instead at some convenient but unrepresentative location. In this study we evaluated how much bias might be induced by extrapolating decay rates from unrepresentative locations, how much effort would be required to implement current methods in a spatially unbiased manner, and what alternate approaches might be used to improve precision. To evaluate the extent of bias induced by unrepresentative sampling, we collected data on gorilla dung at several central African sites. Variation in gorilla dung decay rate was enormous, varying by up to an order of magnitude within and between survey zones. We then estimated what the effort-precision relationship would be for a previously suggested "retrospective" decay rate (RDR) method, if it were implemented in a spatially unbiased manner. We also evaluated precision for a marked sign count (MSC) approach that does not use a decay rate. Because they require repeat visits to remote locations, both RDR and MSC require enormous effort levels in order to gain precise density estimates. Finally, we examined an objective criterion for decay (i.e., dung height). This showed great potential for improving RDR efficiency because choosing a high threshold height for decay reduces decay time and, consequently, the number of visits that need to be made to remote areas. The ability to adjust decay time using an objective decay criterion also opens up the potential for a "prospective" decay rate (PDR) approach. Further research is necessary to evaluate whether the temporal bias inherent in such an approach is small enough to ignore, given the 10-20-fold increases in precision promised by a PDR approach.     

城市街道内机动车排放污染物NO对流扩散的特征

采用现场观测和数值模拟的方法研究了城市街道内机动车排放污染物中的NO扩散特征。结果表明:城市街道中机动车排放污染物的对流扩散取决于屋顶风向和风速,随着建筑物顶部气流速度的增大,街道内同样位置的污染物浓度相对减小;当风向垂直于街道轴线时,街道内同样位置的污染物浓度最大;同时街道内机动车排放的污染物浓度与车流量成正比关系,即机动车流量越大污染物浓度越高。     

PIV experimental study on the flow characteristics upstream of a floating intake in nonlinear stratified ambient conditions

Selective withdrawal is commonly implemented in nonlinearly stratified ambient, which typically has stratified ambient conditions, for purposes of controlling quality. A floating intake is applied as an effective facility of selective withdrawal. However, the outflow dynamics of a floating intake in a nonlinearly stratified ambient have been disregarded, which has a significant effect on the outflow water quality of a reservoir. Experiments were conducted to investigate the effect of thermal stratification on the flow characteristics using particle image velocimetry at three temperature distributions (no stratification, weak stratification and strong stratification). The flow fields upstream of the floating intake showed that the withdrawal layer was formed inhibited by the thermal stratification. And strong stratification produced the thinner withdrawal layer thickness, leading to a larger nonuniform coefficient of the velocity profile. To quantitatively describe the velocity profiles, formulas of dimensionless velocity profiles were proposed. The flow developments were analysed, and the virtual control points located 0.56d above the floating intake (where d is the straight pipe diameter of the floating intake) were obtained. The positions of virtual control points mainly depended on the withdrawal discharge. The decay rate of the velocity along the horizontal line passing through the virtual control point was inversely proportional to the stratification intensity.

     

Fungi and wind strongly influence the temporal availability of logs in an old-growth spruce forest.

Coarse woody debris (CWD) is a key habitat for many species in forest ecosystems. To ensure the long-term survival of such species, forest management regimes must include measures that promote dead wood dynamics similar to those of natural forests. Thus, information on CWD dynamics under natural conditions is required, including data pertaining to the underlying agents of disturbance. This study examines modes of mortality, decay rates, and temporal patterns in the availability of Picea abies logs in a Swedish old-growth forest affected by internal, small-scale disturbance. All 684 logs in a 6.6-ha plot were mapped and classified into one of six decay classes. Logs in the early stages of decay were examined for the presence of heart-rot fungi. Six years later all logs were re-inventoried, including newly formed logs. Matrix models based on the transition rates between decay classes showed that it took about 60 years for 90% of the logs to decay beyond class 6 (a deformed trunk with soft wood). Large logs (> 26 cm) decayed 40% more slowly than small logs (< 25 cm). The initial volume of logs was 37.6 m3/ha but increased to 44.8 m3/ha after six years. In addition, there was a large shift in the decay-class distribution. The volume of logs in early and late decay classes increased by 71% and 45%, respectively, while the volume of logs in the intermediate decay classes decreased by 32%. The fluctuations appear to result from pulses in mortality, driven by a combination of strong winds and the heart-rot fungus, Phellinus chrysoloma, which was present in more than 30% of all logs at an early stage of decay. These results show that large temporal fluctuations in dead wood also occur in the absence of large-scale disturbance, and that heart-rot fungi are important factors driving the overall dynamics of dead wood. Since many wood-inhabiting species are naturally rare and have very specific substrate demands, such temporal variability in dead wood availability may have effects on biodiversity and should be taken into account when designing small, protected forest areas.     

A model of savanna litter decomposition

A model of litter decomposition in a South African savanna is described. Decomposing material is divided into a number of particle classes, distinguishing material of different ages, origins and size. Each particle class is further divided into a number of chemical constituents. Processes modelled include ageing, physical disintegration, consumption by termites and decay. Sources of fresh litter include tree and grass leaves. Results from a standard run of the model and a number of runs with changed parameter values to test the model's sensitivity to these are presented and discussed. From exercise of the model it appears that the most important processes relate to soil-feeding termites, with decay and physical breakdown being the background against which termites operate.     

六价铬在具有渗透性反应墙的渗流槽中迁移实验研究

地下水中六价铬的污染修复是目前地下水污染修复研究的热点课题之一。以室内模拟为基础,进行了六价铬[Cr（Ⅵ）]随水流迁移的渗流槽实验,以及利用课题组研发的新型壳聚糖材料填充渗透性反应墙（PRB）,进行六价铬吸附试验研究。结果表明：在重金属迁移实验中,地下水的流速是影响Cr（Ⅵ）在含水层中迁移的主要因素,含水层介质的变化都会对Cr（Ⅵ）的迁移发生重要的影响。实验过程中,从进水口到出水口各个取样点依次出现Cr（Ⅵ）的质量浓度峰值,并且随着时间的延长,质量浓度峰值没有减少的趋势,证明了Cr（Ⅵ）在含水介质中基本上没有吸附。Cr（Ⅵ）的质量浓度峰值在含水介质中的持续时间不长,由于弥散作用造成了在相当长的时间内的较明显的拖尾现象。模拟渗透性反应墙的实验中,在同样的流速条件下,Cr（Ⅵ）的质量浓度峰值的出现时间相对先前的实验有明显滞后,并且质量浓度也有明显的减少,说明新型壳聚糖材料对Cr（Ⅵ）有较高的吸附作用,再达到质量浓度的峰值后,墙体后面的采样口中Cr（Ⅵ）的质量浓度减少的更为平缓,说明随着水流的流动,吸附在壳聚糖材料上的Cr（Ⅵ）有缓慢的析出。     

Application of electrochemical reactor divided by cellulosic membrane for optimized simultaneous removal of phenols,chromium, and ammonia from tannery effluents

The post treatment of simulated tannery wastewater was evaluated in an electrochemical oxidation process under galvanostatic conditions. A continuous flow reactor divided by a cellulosic membrane consisted of Ti/SnO₂–Sb anodes and iron cathodes was used. Central composite design and response surface methodology (RSM) were applied to investigate the effects of six operational parameters, namely initial concentration of total phenols (TPh), total chromium (TCr), total ammonia nitrogen (TAN), flow rate (Q), current intensity (I), and electrode surface area (A). Effectiveness of the innovative cellulosic membrane was proven by considerable pH variations in the anolyte and catholyte chambers. A faster removal rate was observed for TPh and TAN, followed by TCr. The treatment level was very sensitive to Q and I in the studied ranges. RSM showed the removal efficiencies of 78.14%, 63.42%, and 86.09% for TPh, TCr, and TAN, respectively, are achieved under optimal conditions with consumption of only 9.03 kWh m^?3 electrical energy. Chlorinated compounds such as chloroform, 2,4-dichlorophenol, and chlorobenzene were detected as the degradation intermediates. According to the obtained results, electrolysis in the divided cell with cellulosic membrane is a practical, cost-effective method for advanced treatment of tannery effluents.     

水体扰动对铜绿微囊藻生长影响的规律及原因

在实验室条件下模拟不同扰动状态的水体,探讨铜绿微囊藻的生长与水体扰动之间的关系.结果表明,水体的扰动对铜绿微囊藻的生长同时存在促进和抑制作用.低速度扰动时,促进作用占主导地位;高速度扰动时,抑制作用占主导地位.实验发现中营养化条件下,当温度为25℃,光照为4000 lx,光暗比为12 h∶12 h时,300 r.min-1的扰动速度是铜绿微囊藻生长的临界速度.扰动过程可以为铜绿微囊藻的光合作用提供充足的二氧化碳是其能够促进铜绿微囊藻生长的潜在原因.     

Large-eddy simulation of starting buoyant jets

A series of Large Eddy Simulations (LES) are performed to investigate the penetration of starting buoyant jets. The LES code is first validated by comparing simulation results with existing experimental data for both steady and starting pure jets and lazy plumes. The centerline decay and the growth rate of the velocity and concentration fields for steady jets and plumes, as well as the simulated transient penetration rate of a starting pure jet and a starting lazy plume, are found to compare well with the experiments. After validation, the LES code is used to study the penetration of starting buoyant jets with three different Reynolds numbers from 2000 to 3000, and with a wide range of buoyancy fluxes from pure jets to lazy plumes. The penetration rate is found to increase with an increasing buoyancy flux. It is also observed that, in the initial Period of Flow Development, the two penetrative mechanisms driven by the initial buoyancy and momentum fluxes are uncoupled; therefore the total penetration rate can be resolved as the linear addition of these two effects. A fitting equation is proposed to predict the penetration rate by combining the two independent mechanisms.     

Modification of light utilization for skeletal growth by water flow in the scleractinian coral <Emphasis Type="Italic">Galaxea fascicularis</Emphasis>

In this study, we tested the hypothesis that the importance of water flow for skeletal growth (rate) becomes higher with increasing irradiance levels (i.e. a synergistic effect) and that such effect is mediated by a water flow modulated effect on net photosynthesis. Four series of nine nubbins of G. fascicularis were grown at either high (600 μE m⁻² s⁻¹) or intermediate (300 μE m⁻² s⁻¹) irradiance in combination with either high (15–25 cm s⁻¹) or low (5–10 cm s⁻¹) flow. Growth was measured as buoyant weight and surface area. Photosynthetic rates were measured at each coral’s specific experimental irradiance and flow speed. Additionally, the instantaneous effect of water flow on net photosynthetic rate was determined in short-term incubations in a respirometric flowcell. A significant interaction was found between irradiance and water flow for the increase in buoyant weight, the increase in surface area, and specific skeletal growth rate, indicating that flow velocity becomes more important for coral growth with increasing irradiance levels. Enhancement of coral growth with increasing water flow can be explained by increased net photosynthetic rates. Additionally, the need for costly photo-protective mechanisms at low flow regimes could explain the differences in growth with flow.     

A Biosurfactant-Enhanced Soil Flushing for the Removal of Phenanthrene and Diesel in Sand

In order to examine the potential of biosurfactants in soil remediation, and to investigate the effects of several operating conditions, such as flow rate, biosurfactant concentration and surfactant type, biosurfactant-enhanced soil flushing was conducted. In the biosurfactant-enhanced soil flushing process, the removal efficiency increased as the flow rate decreased. Rhamnolipid showed no effect on the removal efficiency of phenanthrene and diesel from sand in the concentration range 0.3-0.5%. However, rhamnolipid showed higher efficiencies for the removal of phenanthrene and diesel from sand than Tween 80. Based on total recovery, following an equivalent pore volume flush, it was more difficult to remove diesel than phenanthrene. In order to obtain the specific removal efficiency, more pore volumes of surfactant solution may be required in field applications. Under optimum conditions, the biosurfactant removed as much as 70% of the phenanthrene and 60% of the diesel in the sand. These results indicate that the use of biosurfactants in the flushing process is favorable, not only with respect to the environment, but also on removal efficiencies.