Simulation and analysis of solute transport in 2D fracture/pipe networks: the SOLFRAC program

The Time Domain Random Walk (TDRW) method has been recently developed by Delay and Bodin [Delay, F. and Bodin, J., 2001. Time domain random walk method to simulate transport by advection-dispersion and matrix diffusion in fracture networks. Geophys. Res. Lett., 28(21): 4051-4054.] and Bodin et al. [Bodin, J., Porel, G. and Delay, F., 2003c. Simulation of solute transport in discrete fracture networks using the time domain random walk method. Earth Planet. Sci. Lett., 6566: 1-8.] for simulating solute transport in discrete fracture networks. It is assumed that the fracture network can reasonably be represented by a network of interconnected one-dimensional pipes (i.e. flow channels). Processes accounted for are: (1) advection and hydrodynamic dispersion in the channels, (2) matrix diffusion, (3) diffusion into stagnant zones within the fracture planes, (4) sorption reactions onto the fracture walls and in the matrix, (5) linear decay, and (6) mass sharing at fracture intersections. The TDRW method is handy and very efficient in terms of computation costs since it allows for the one-step calculation of the particle residence time in each bond of the network. This method has been programmed in C++, and efforts have been made to develop an efficient and user-friendly software, called SOLFRAC. This program is freely downloadable at the URL (labo.univ-poitiers.fr/hydrasa/intranet/telechargement.htm). It calculates solute transport into 2D pipe networks, while considering different types of injections and different concepts of local dispersion within each flow channel. Post-simulation analyses are also available, such as the mean velocity or the macroscopic dispersion at the scale of the entire network. The program may be used to evaluate how a given transport mechanism influences the macroscopic transport behaviour of fracture networks. It may also be used, as is the case, e.g., with analytical solutions, to interpret laboratory or field tracer test experiments performed in single fractures.     

Determination of the potential for release of mercury from combustion product amended soils: Part 1--Simulations of beneficial use

This paper describes a project that assessed the potential for mercury (Hg) release to air and water from soil amended with combustion products to simulate beneficial use. Combustion products (ash) derived from wood, sewage sludge, subbituminous coal, and a subbituminous coal-petroleum coke mixture were added to soil as agricultural supplements, soil stabilizers, and to develop low-permeability surfaces. Hg release was measured from the latter when intact and after it was broken up and mixed into the soil. Air-substrate Hg exchange was measured for all materials six times over 24 hr, providing data that reflected winter, spring, summer, and fall meteorological conditions. Dry deposition of atmospheric Hg and emission of Hg to the atmosphere were both found to be important fluxes. Measured differences in seasonal and diel (24 hr) fluxes demonstrated that to establish an annual estimate of air-substrate flux from these materials data on both of these time steps should be collected. Air-substrate exchange was highly correlated with soil and air temperature, as well as incident light. Hg releases to the atmosphere from coal and wood combustion product-amended soils to simulate an agricultural application were similar to that measured for the unamended soil, whereas releases to the air for the sludge-amended materials were higher. Hg released to soil solutions during the Synthetic Precipitation Leaching Procedure for ash-amended materials was higher than that released from soil alone. On the basis of estimates of annual releases of Hg to the air from the materials used, emissions from coal and wood ash-amended soil to simulate an agricultural application could simply be re-emission of Hg deposited by wet processes from the atmosphere; however, releases from sludge-amended materials and those generated to simulate soil stabilization and disturbed low-permeability pads include Hg indigenous to the material.     

Air-surface exchange of mercury with soils amended with ash materials

Air-surface exchange of mercury (Hg) was measured from soil low in Hg (0.013 mg/kg) amended with four different ash materials: a wood ash containing -10% coal ash (0.070 mg/kg Hg), a mixture of two subbituminous coal fly ashes (0.075 mg/kg Hg), a subbituminous coal ash containing -10% petroleum coke ash (1.2 mg/kg Hg), and an ash from incinerated municipal sewage sludge (4.3 mg/kg Hg) using a dynamic flux chamber. Ash was added to soil to simulate agricultural supplements, soil stabilization, and pad layers used in livestock areas. For the agricultural amendment, -0.4% ash was well mixed into the soil. To make the stabilized soil that could be used for construction purposes, -20% ash was mixed into soil with water. The pad layer consisted of a wetted 1-cm layer of ash material on the soil surface. Diel trends of Hg flux were observed for all of the substrates with significantly higher Hg emissions during the day and negligible flux or deposition of Hg during the night. Hg fluxes, which were measured in the summer months, were best correlated with solar radiation, temperature, and air O3 concentrations. Mean Hg fluxes measured outdoors for unamended soils ranged from 19 to 140 ng/m2 day, whereas those for soil amended with ash to simulate an agricultural application ranged from 7.2 to 230 ng/m2 day. Fluxes for soil stabilized with ash ranged from 77 to 530 ng/m2 day and for soil with pads constructed of ash ranged from -50 to 90 ng/m2 day. Simple analytical tests (i.e., total Hg content, synthetic precipitation leaching procedure, heating, and indoor gas-exchange experiments) were performed to assess whether algorithms based on these tests could be used to predict Hg fluxes observed outdoors using the flux chamber. Based on this study, no consistent relationships could be developed. More work is needed to assess long-term and seasonal variations in Hg flux from (intact and disturbed) substrates before annual estimates of emissions can be developed.     

Mercury accumulation in grass and forb species as a function of atmospheric carbon dioxide concentrations and mercury exposures in air and soil

The goal of this study was to investigate the potential for atmospheric Hg degrees uptake by grassland species as a function of different air and soil Hg exposures, and to specifically test how increasing atmospheric CO(2) concentrations may influence foliar Hg concentrations. Four common tallgrass prairie species were germinated and grown for 7 months in environmentally controlled chambers using two different atmospheric elemental mercury (Hg major; 3.7+/-2.0 and 10.2+/-3.5 ng m(-3)), soil Hg (<0.01 and 0.15+/-0.08 micro g g(-1)), and atmospheric carbon dioxide (CO(2)) (390+/-18, 598+/-22 micro mol mol(-1)) exposures. Species used included two C4 grasses and two C3 forbs. Elevated CO(2) concentrations led to lower foliar Hg concentrations in plants exposed to low (i.e., ambient) air Hg degrees concentrations, but no CO(2) effect was apparent at higher air Hg degrees exposure. The observed CO(2) effect suggests that leaf Hg uptake might be controlled by leaf physiological processes such as stomatal conductance which is typically reduced under elevated CO(2). Foliar tissue exposed to elevated air Hg degrees concentrations had higher concentrations than those exposed to low air Hg degrees , but only when also exposed to elevated CO(2). The relationships for foliar Hg concentrations at different atmospheric CO(2) and Hg degrees exposures indicate that these species may have a limited capacity for Hg storage; at ambient CO(2) concentrations all Hg absorption sites in leaves may have been saturated while at elevated CO(2) when stomatal conductance was reduced saturation may have been reached only at higher concentrations of atmospheric Hg degrees . Foliar Hg concentrations were not correlated to soil Hg exposures, except for one of the four species (Rudbeckia hirta). Higher soil Hg concentrations resulted in high root Hg concentrations and considerably increased the percentage of total plant Hg allocated to roots. The large shifts in Hg allocation patterns-notably under soil conditions only slightly above natural background levels-indicate a potentially strong role of plants in belowground Hg transformation and cycling processes.     

Sperm morphology, swimming velocity, and longevity in the house sparrow Passer domesticus

Sperm competition exerts strong selection on males to produce spermatozoa with an optimal morphology that maximizes their fertilization success. Long sperm were first suggested to be favored because they should swim faster. However, studies that investigated the relationship between sperm length and sperm competitive ability or sperm swimming velocity yielded contradictory results. More recently, ratios of the different sections of a spermatozoon (the head, midpiece, and flagellum) were suggested to be more crucial in determining swimming velocity. Additionally, sperm ability to remain and survive in the female storage organs may also influence fertilization success, so that optimal sperm morphology may rather maximize sperm longevity than velocity. In this study, we investigated how sperm morphology is related to sperm velocity and sperm longevity in the house sparrow Passer domesticus. Sperm velocity was found to be correlated with head/flagellum ratio. Sperm with small heads relative to their flagellum showed higher swimming velocity. Additionally, shorter sperm were found to live longer. Finally, we found sperm morphological traits to vary substantially within males and the head/flagellum ratio to be unrelated to total sperm length. We discuss the hypothesis that the substantial within-male variation in sperm morphology reflects a male strategy to produce a diversity of sperm from long, fast-swimming to short, long-living sperm to maximize their fertilization success in a context of sperm competition.     

From IBM to IPM: Using individual-based models to design the spatial arrangement of traps and crops in integrated pest management strategies

The development of alternative pest-control strategies based on the spatial design of cropping systems requires a thorough understanding of the spatial links between the pest and its environment. Mechanistic models, especially individual-based models (IBMs), are powerful tools for integrating key behaviours, such as habitat selection and dispersal, with spatial heterogeneity. In this paper, we used an IBM calibrated and evaluated from real data to represent the spatial dynamics of the banana weevil in relation to the cropping system. We considered crop fragmentation and mass trapping as tools for suppressing pest numbers. Our simulation results showed that manipulating crop residues in the area surrounding each pheromone trap greatly improved trap efficiency. For an intensive banana plantation in fallow, traps were most effective when situated at the transition zone between banana area and fallow so as to maximize the trapping of weevils escaping the fallow. The model also showed that weevil numbers decreased when fragmentation of banana plantations was reduced.     

Contributions to eco-design of machine-to-machine product service systems: the example of waste glass collection

Efficient waste management is necessary in order to face up to increasing quantities of waste generated in modern societies. A technical solution using a Machine-to-Machine (M2M) enhanced Product-Service System (PSS) for bring-in waste glass collection is identified. Methodology based on Life Cycle Analysis (LCA) is proposed. The results help understand the mechanisms of M2M PSS. Possible improvements are explored and the study shows how the PSS infrastructure impacts the environment. It examines the influence of major organisational parameters and contributes to eco-design and dimensioning of the M2M PSS. It reveals the interest of mutualisation to reduce environmental impacts and shows the importance of limiting data exchanges. It argues for the use of multi-criteria LCA on the complete system including the telecom infrastructures and employs realistic use scenarios derived from field studies.     

Results of the first adapted design for sustainability project in a South Pacific small island developing state: Fiji

With high population densities concentrated in predominately coastal zones, the South Pacific will, in this century, be heavily impacted by global temperature and sea level rises. Small island developing states do have a number of unique problems, namely, small scale economic development together with environmental sustainability. This paper presents the lessons learnt from the implementation of the first cleaner production and design initiative project conducted in a Pacific small island developing state(s) (SIDS) using the design for sustainability (D4S) methodology. The final product was analysed using the life cycle assessment (LCA) method. Implemented within a medium-sized enterprise operating in Fiji, the Cook Islands, and Samoa, the project focused on improving an existing product and its associated life cycle to make it more environmentally friendly to manufacture, retail, and dispose of. The project outcomes revealed that D4S provides a suitable tool for a country like Fiji to pursue more intensively an eco-friendly manufacturing agenda. However, when combined with LCA, the qualitative nature of D4S shows that not all solutions produce the best overall result. Specifically, the “improved” design, whilst being less impactful on Fiji in terms of disposal, has a higher impact globally due to the production and manufacture of the new materials used. For this reason designers need to address the impact criteria and decide whether a domestic or international agenda is of greater concern within the SIDS context.     

Determination of time-dependent partition coefficients for several pesticides using diffusion theory

Diffusion-retarded partitioning of pesticides with aggregated soils results in a time-dependent partition coefficient (Kd') which is different at equilibrium from the partition coefficient derived from conventional 24-h batch studies (Kd) measured on dispersed soil. An experiment was undertaken to determine the importance of Kd' for the prediction of pesticide concentrations in solutions bathing artificial soil aggregates and to determine whether diffusion theory could accurately predict the concentrations. Two clay soils were mixed with polyacrylamide to create artificial aggregates of 0.8, 1.4 and 1.7 cm diameter when dry. After saturation, the aggregates were immersed in solutions containing isoproturon or a mixture of isoproturon, chlorotoluron and triasulfuron. The decline with time of the pesticide concentrations in the bathing solution was monitored and the results were compared with predictions from a diffusion-based model. The effective diffusion coefficients of the compounds were obtained by either fitting the non-linear diffusion model to the data (D(ef)) or by independent calculations based on the properties of the compounds and of the aggregates (D(ec)). The diffusion model was able to predict the temporal variation in pesticide concentrations in the bathing solution reasonably well whether D(ef) or D(ec) values were used. However, equilibrium concentrations in solution were sometimes overestimated due to increased sorption with time at the particle scale. Overall, the ratio between D(ef) and D(ec) ranged from 0.23 to 0.95 which was a reasonable variation when compared to the range of aggregate sizes used in the experiments and of the Kd values of the compounds.