Showing papers on "Water flow published in 1996"

Promises and Prospects of Phytoremediation

Abstract: We often think of plants primarily as a source of wood, food, and fiber Secondarily we may also appreciate their presence for aesthetic reasons as well as for "altruistically" providing habitat for other species Increasingly, however, their value as an environmental counterbalance to industrialization processes is being appreciated These processes include the burning of fossil fuels, generation of wastes (sewage, inorganic and organic solids, and effluents), and general water flow and processing Plants have long been recognized for their consumption of CO2 and, more recently, of other gaseous industrial byproducts (Simonich and Hites, 1994) Recently, their role in slowing the rate of global warming has been further appreciated in both the scientific and popular press Their use as a final water treatment and for disposal of sludge resulting from waste water treatment is centuries old (Hartman, 1975) The extensive literature concerning water and sludge treatment and the emerging field of air pollution abatement with plants will not be discussed here Instead, we focus on an emerging concept, "phytoremediation," the use of plants to remediate contamination of soil with organic or inorganic wastes Remediation of soil contamination by conventional engineering techniques often costs between $50 and $500 per ton Certain specialized techniques can exceed costs of $1000 per ton With an acre of soil (to a 3-foot depth) weighing approximately 4500 tons, this translates to a minimum cost of about a quarter million dollars per acre (Cunningham et al, 1995) It is not surprising that the cleanup of contaminated sites has not been proceeding at a rapid pace There is an active effort to develop new, more costeffective technologies to remediate contamination of such soils For the most part these efforts are being led by engineers and microbiologists More recently, however, green plant-based processes have begun receiving greater attention It has long been known that the life cycle of a plant has profound effects on the chemical, physical, and biological processes that occur in its immediate vicinity In the process of shoot and root growth, water and mineral acquisition, senescence, and eventual decay, plants can profoundly alter the surrounding soil The effects of many of these processes are apparent on the restoration of land at physically and chemically altered sites, ranging from road cuts to the site of the Mount St Helen's eruption These same plant-driven processes also occur in areas heavily impacted by industrial, mining, and urban activities One of the greatest forces driving increased emphasis on research in this area is the potential economic benefit of an agronomybased technology Growing a crop on an acre of land can be accomplished at a cost ranging from 2 to 4 orders of magnitude less than the current engineering cost of excavation and reburial There have been perhaps two dozen field tests to date; however, in many ways phytoremediation is still at its initial stages of research and development A comforting thought for plant biologists is that much of the research effort will be expected to center on a deeper understanding of basic plant processes So how do we envision phytoremediation working? The theory appears to be simple Agronomic techniques will be used to ready the contaminated soil for planting and to ameliorate chemical and physical limitations to plant growth Plants will then directly or indirectly absorb, sequester, and/or degrade the contaminant Plants and irrigation, fertilization, and cropping schemes will be managed to maximize this remedial effect By growing plants over a number of years, the aim is to either remove the pollutant from the contaminated matrix or to alter the chemical and physical nature of the contaminant within the soil so that it no longer presents a risk to human health and the environment As people who work in the remediation, herbicide development, and farming industries will attest, many weed species are remarkably tolerant of a wide range of organic and inorganic toxins Plants can thrive in soil contaminated to levels that are often orders of magnitude higher than current regulatory limits These limits are often set relatively independent of plant tolerance limits and are most often derived from human health and aquatic toxicology end points Ironically, many remediation plans begin with the destruction of the existing vegetation

Cotransport of Water by the Na + /glucose Cotransporter

Abstract: Water is transported across epithelial membranes in the absence of any hydrostatic or osmotic gradients. A prime example is the small intestine, where 10 liters of water are absorbed each day. Although water absorption is secondary to active solute transport, the coupling mechanism between solute and water flow is not understood. We have tested the hypothesis that water transport is directly linked to solute transport by cotransport proteins such as the brush border Na+/glucose cotransporter. The Na+/glucose cotransporter was expressed in Xenopus oocytes, and the changes in cell volume were measured under sugar-transporting and nontransporting conditions. We demonstrate that 260 water molecules are directly coupled to each sugar molecule transported and estimate that in the human intestine this accounts for 5 liters of water absorption per day. Other animal and plant cotransporters such as the Na+/Cl−/γ-aminobutyric acid, Na+/iodide and H+/amino acid transporters are also able to transport water and this suggests that cotransporters play an important role in water homeostasis.

Complex burrows of the mud shrimp Callianassa truncata and their geochemical impact in the sea bed

Abstract: THE biogeochemical processes and associated microbial communities in the sea floor are stratified1 and dependent on vertical transport mechanisms. The penetration of oxygen is generally only a few millimetres in coastal sediments2, regulated by the dynamic balance between diffusion from the overlying water and rapid consumption within the sea bed. Macrofauna organisms living within the sea bed affect the physical structure of the sea floor, its chemical zonations and the exchange processes across the sediment–water interface3,4. Thalassinidean mud-shrimps are often abundant in tropical and temperate coastal regions 5–7 and build burrows with a species-specific architecture. The deepest reported burrows reach down to 2.5 m sediment depth8. It is difficult to study the activities of these secretive animals and their effect on sediment biogeochemistry without disturbing the sediment system9. Here we report the use of a diver observatory within the seabed, along with in situ measurements, to assess the geochemical impact of the mud-shrimp Callianassa truncata Giard and Bonnier (Decapoda, Thalassinidea), a species that commonly inhabits sandy sediments in the Mediterranean sea.

Surface-subsurface interactions in stream ecosystems.

Abstract: Stream ecologists have recently recognized that sediments below streams play an important role in lotic ecosystems. Water flows not only across the surface of stream channels, but also through sediment interstices; consequently, surface and subsurface biogeochemical processes are linked. Recent attempts to understand the influence of subsurface processes on stream ecosystems have tried to resolve the surface-subsurface hydrologic interactions, and to gain knowledge of the ecology of subsurface organisms.

Erbium laser ablation of dental hard tissue: Effect of water cooling

Abstract: Background and Objective Several lasers have been explored for hard dental tissue applications; used alone they have resulted in potentially harmful temperature increases in the pulp chamber. Materials and Methods An Er:YAG laser (λ = 2.94 μm) was used to ablate hard dental tissues. Ablation rates with and without a water-cooling spray were measured. Subsequent experiments investigated the cooling effects of the water. Initially single channels were drilled into dentin; further studies involved ablating rectangular areas with repetition rates up to 10 Hz. Results The water spray minimally reduced the ablation rates of dentin and did not affect the ablation rates of enamel. The water spray effectively cooled the teeth; while using the maximum average power investigated (10 Hz, 360 mJ/pulse), a water flow rate of 4.5 ml/min limited the temperature rise in the pulp chamber to less than 3°C. Conclusion The studies confirm the feasibility of using an Er:YAG laser in conjunction with a water spray to safely and effectively remove hard dental tissues. © 1996 Wiley-Liss, Inc.

Principles of Early Development of Karst Conduits Under Natural and Man-Made Conditions Revealed by Mathematical Analysis of Numerical Models

Abstract: Numerical models of the enlargement of primary fissures in limestone by calcite aggressive water show a complex behavior. If the lengths of the fractures are large and hydraulic heads are low, as is the case in nature, dissolution rates at the exit of the channel determine its development by causing a slow increase of water flow, which after a long gestation time by positive feedback accelerates dramatically within a short time span. Mathematical analysis of simplified approximations yields an analytical expression for the breakthrough time, when this happens, in excellent agreement with the results of a numerical model. This expression quantifies the geometrical, hydraulic, and chemical parameters determining such karst processes. If the lengths of the enlarging channels are small, but hydraulic heads are high, as is the case for artificial hydraulic structures such as dams, it is the widening at the entrance of the flow path which determines the enlargement of the conduit. Within the lifetime of the dam this can cause serious water losses. This can also be explained by mathematical analysis of simplified approximations which yield an analytical threshold condition from which the safety of a dam can be judged. Thus in both cases the dynamic processes of karstification are revealed to gain a deeper understanding of the early development of karst systems. As a further important result, one finds that minimum conditions, below which karstification cannot develop, do not exist.

Transport in shales and the design of improved water-based shale drilling fluids

Abstract: Transport of water and ions in shales and its impact on shale stability were studied to facilitate the improvement of water-based muds as shale drilling fluids. Transport parameters associated with flows driven by gradients in pressure and chemical potential were quantified in key laboratory and full-scale experiments. The experimental results show that the low-permeability matrices of intact, clay-rich shales can act as imperfect or leaky membranes that will sustain osmotic flow of water. Moreover, the ability of shales to act as osmotic membranes is shown to provide a powerful new means for stabilizing these rocks when exposed to water-based drilling fluids. Guidelines are presented for effective exploitation of shale membrane action and induced osmotic flows through optimized water-based drilling fluid formulation. In addition, special attention is given to induced electro-osmotic water flow in shales driven by electric potential gradients, which may provide an exciting, new, environmentally benign means for stabilizing shale formations.

Vascular endothelial growth factor increases hydraulic conductivity of isolated perfused microvessels.

Abstract: These experiments report the first direct measurement of microvessel permeability coefficients after exposure to vascular endothelial growth factor (VEGF). The Landis technique was extended to enable measurement of the resistance of the microvessel wall to water flow, hydraulic conductivity (Lp), on the same microvessel in the frog mesentery during the initial exposure to VEGF (acute) and 24 and 72 h after initial exposure (chronic). Control measurements of Lp showed no change either acutely or chronically. Exposure to 1 nM VEGF rapidly and transiently increased microvessel Lp within 30 s (to 7.8-fold greater than baseline values) and returned to control within 2 min. The baseline Lp was fivefold greater after 24 h than the initial baseline as a result of VEGF perfusion and returned to its original value after 72 h. These experiments confirm the hypothesis that VEGF acts both acutely (over a period of a few minutes) and chronically (over a few hours) to increase microvascular permeability.

High temperature and drought stress effects on survival of Pinus ponderosa seedlings

Abstract: We studied the effects of high temperature and drought on the survival, growth and water relations of seedlings of Pinus ponderosa (Dougl.) Lawson, one of few coniferous tree species that can successfully colonize drought-prone sites with high soil surface temperatures. Temperature profiles were measured with 0.07-mm thermocouples in a sparse ponderosa pine forest in northern Idaho. The soil surface and the adjacent 5 mm of air reached maximum temperatures exceeding 75 degrees C, well above the lethal temperature threshold for most plants. Air temperatures 50 mm above the soil surface (seedling needle height) rarely exceeded 45 degrees C. Pinus ponderosa seedlings that survived maintained basal stem temperatures as much as 15 degrees C lower than the surrounding air. The apparent threshold temperature at the seedling stem surface resulting in death was approximately 63 degrees C for less than 1 min. No correlation between seedling mortality and needle temperature was found, although some needles reached temperatures as high as 60 degrees C for periods of

Spatial variability of hydraulic properties in a multi-layered soil profile

Abstract: Unsaturated hydraulic properties of field soils are needed for water flow and solute transport calculations in variably saturated soils. The purpose of this study was to quantify the spatial variability and spatial crosscorrelation of estimated parameter values of a flexible retention model that was

Water transport in plants: Role of the apoplast

Abstract: The present state of modelling of water transport across plant tissue is reviewed. A mathematical model is presented which incorporates the cell-to-cell (protoplastic) and the parallel apoplastic path. It is shown that hydraulic and osmotic properties of the apoplast may contribute substantially to the overall hydraulic conductivity of tissues (Lpr) and reflection coefficients (67-1). The model shows how water and solutes interact with each other during their passage across tissues which are considered as a network of hydraulic resistors and capacitances (‘composite transport model’). Emphasis is on the fact that hydraulic properties of tissues depend on the nature of the driving force. Osmotic gradients cause a much smaller tissue Lpr than hydrostatic. Depending on the conditions, this results in variable hydraulic resistances of tissues and plant organs. For the root, the model readily explains the well-known phenomenon of variable hydraulic resistance for the uptake of water and non-linear force/flow relations. Along the cell-to-cell (protoplastic) path, water flow may be regulated by the opening and closing of selective water channels (aquaporins) which have been shown to be affected by different environmental factors. H Lambers Section editor

Estimates of water vapor flux and canopy conductance of Scots pine at the tree level utilizing different xylem sap flow methods

Abstract: During the Hartheim Experiment (HartX) 1992 conducted in the upper Rhine Valley, Germany, three different methods were used to measure sap flow in Scots pine trees via heating of water transported in the xylem: (1) constant heating applied radially in the sapwood (“Granier-system”-G), (2) constant heating of a stem segment (“Cermak-system”-C), and (3) regulated variable heating of a stem segment that locally maintains a constant temperature gradient in the trunk (“Cermak/Schulze-system”-CS). While the constant heating methods utilize changes in the induced temperature gradient to quantify sap flux, the CS-system estimates water flow from the variable power requirement to maintain a 2 or 3 degree Kelvin temperature gradient over a short distance between inserted electrodes and reference point. The C- and CS-systems assume that all transported water is encompassed and equally heated by the electrodes. In this case, flux rate is determined from temperature difference or energy input and the heat capacity of water. Active sapwood area need not be determined exactly. In contrast, the G-system requires an empirical calibration of the sensors that allows conversion of temperature difference into sap flow density. Estimates of sapwood area are used to calculate the total flux. All three methods assume that the natural fluctuation in temperature of the trunk near the point of insertion of heating and sensing elements is the same as that where reference thermocouples are inserted. Using all three systems, 24 trees were simultaneously monitored during the HartX campaign. Tree size within the stand ranged between 18 and 61 cm circumference at breast height, while sample trees ranged between 24 and 55 cm circumference. The smallest trees could only be measured by utilizing the G-system. Sap flow rates of individual trees measured at breast height increased rapidly in the morning along with increases in irradiance and vapor pressure deficit (D), decreased slowly during the course of the afternoon with continued increase inD, and decreased more slowly during the night. Ignoring potential effects introduced by the different methods, maximum flow rates of individual trees ranged between 0.5 and 2.5 kg H2O h−1 tree−1 or 0.3 and 0.6 mm h−1 related to projected crown area of trees and daily sums of sap flow for individual trees varied between 4.4 and 24 kg H2O tree−1 d−1 or 1.1 and 6.0 mm d−1. Maximum sap flow rates per sapwood area of trees varied least for the G-system (11–17 g cm−2 h−1) and was of similar magnitude as the C- (8–21 g cm−2 h−1) and CS-system (4–14 g cm−2 h−1). Regressions of total tree conductance (g t ) derived from sap flow estimates demonstrated the same linear increase of conductance with increasing irradiance, however decrease of conductance with increasingD under non-limiting light conditions was different for the three systems with strongest reduction ofg t measured with the CS-system followed by the C- and G-system. This led to different estimates of daily sap flow rates especially during the second part of the measurement period. Variation in sap flow rates is explained on the basis of variation in leaf area index of individual trees, heterogeneity in soil conditions, and methodological differences in sap flow measurements. Despite the highly uniform plantation forest at the scale of hectares, the heterogeneity in tree size and soil depth at the scale of square meters still make it difficult to appropriately and efficiently select sample trees and to scale-up water flux from individual trees to the stand level.

Scale‐Dependent Spatial and Temporal Variability in Biogeography of Mangrove Root Epibiont Communities

Abstract: Studies across a range of spatial and temporal scales are needed to discern multiple forces structuring communities. Subtidal prop roots of red mangroves host diverse assemblages of sessile marine epibionts that provide a model system for examining community development and maintenance at a variety of discrete spatial scales. During 1991- 1992 we twice surveyed 11 sites at four cays in Belize, Central America, to quantify spatial variability and temporal change in distribution and abundance of root-fouling organisms at five sampling scales: (1) fronts and backs of roots (1-cm scale); (2) roots close to and extending away from peat bank (0.5-m scale); (3) along linear transects parallel to shore (1-50 m scale); (4) on leeward and windward shores of cays (0.5-km scale); and (5) among cays (1-10 km scale). Although epibiont community structure differed widely among sites, all cays surveyed had similar seasonal values of water salinity, pH, and temperature. Within cays, windward sites had higher dissolved oxygen levels and water flow rates than leeward sites. At still smaller scales, outer roots and fronts of roots received significantly more light and were subject to higher water flow rates than inner roots and backs of roots. Species richness, diversity, and mosaic diversity patterns indicated that epibiont assemblages were distributed non-randomly in space: leeward sites were more speciose than windward sites, and fronts of roots were more speciose than backs. Jaccard's index of similarity, cluster analysis, and Kendall's coefficient of concordance showed hierarchical patterns of decreasing similarity with increasing sampling distance. Significant spatial autocorrelation among Jaccard values occurred at 2-3 m intervals, possibly reflecting mean larval dispersal distances. Analysis of mosaic diversity among sites indicated the absence of a clear environmental gradient and supported the hypothesis that species distributions may reflect patterns of dispersal from initial source populations. While precise identity of species was unpredictable among roots, species groups based on taxonomy, morphology, and life history showed very consistent distributions among sites that may reflect variability in local root environments: algae were most prevalent in well-lit areas and on windward sites, while sponges and ascidians predominated in leeward areas. Relative importance and dominance of both individual species and species groups changed substantially between 1991 and 1992. Representatives of four species groups were transplanted across three spatial scales to assess whether post-settlement dynamics limit distributions of these taxa. All transplants survived well for the first 6 wk of the experiment. After 6 mo, all transplants exhibited similarly high levels of mortality regardless of treatment. Overall, the results indicate that larval supply may shape epibiont community composition on short time scales and small and very large spatial scales, while variation in physical factors may influence distributions over the long term and at intermediate spatial scales.

In vivo inhibition of transcellular water channels (aquaporin-1) during acute peritoneal dialysis in rats.

Abstract: During peritoneal dialysis (PD), a major portion of the osmotically induced water transport to the peritoneum can be predicted to occur through endothelial water-selective channels. Aquaporin-1 (AQP-1) has recently been recognized as the molecular correlate to such channels. Aquaporins can be inhibited by mercurials. In the present study, HgCl2 was applied locally to the peritoneal cavity in rats after short-term tissue fixation, used to protect the tissues from HgCl2 damage. Dianeal (3.86%) was employed as dialysis fluid, 125I-albumin as an intraperitoneal volume marker, and 51Cr-EDTA (constantly infused intravenously) to assess peritoneal small-solute permeability characteristics. Immunocytochemistry and immunoelectron microscopy revealed abundant AQP-1 labeling in capillary endothelium in peritoneal tissues, representing sites for HgCl2 inhibition of water transport. HgCl2 treatment reduced water flow and inhibited the sieving of Na+ without causing any untoward changes in microvascular permeability, compared with that of fixed control rats, in which the peritoneal cavity was exposed to tissue fixation alone. In fixed control rats, the mean intraperitoneal volume (IPV) increased from 20.5 +/- 0.15 to 25.0 +/- 0.52 ml in 60 min, whereas in the HgCl2-treated rats, the increment was only from 20.7 +/- 0.23 to 23.5 +/- 0.4 ml. In fixed control rats, the dialysate Na+ fell from 135.3 +/- 0.97 to 131.3 +/- 1.72 mM, whereas in the HgCl2-treated rats the dialysate Na+ concentration remained unchanged between 0 and 40 min, further supporting that water channels had been blocked. Computer simulations of peritoneal transport were compatible with a 66% inhibition of water flow through aquaporins. The observed HgCl2 inhibition of transcellular water channels strongly indicates a critical role of aquaporins in PD and provides evidence that water channels are crucial in transendothelial water transport when driven by crystalloid osmosis.

Flow trace analysis to access water use

Abstract: Precise information about water use patterns can be gathered by analyzing flow traces obtained from residential customer water meters that are fitted with portable data loggers. Flow traces are precise enough that signatures associated with all major water use categories can be identified. For this study, more than 10,000 water use events were recorded, classified, and entered into a database. The technique is both accurate and reliable and can be used to collect time-specific and disaggregated water use data. Measuring directly instead of inferring measurements from aggregated data is a quick and cost-effective way to analyze water use patterns and directly assess how conservation measures influence water demand.

Sustainability of irrigated agriculture.

Abstract: Preface. Research Agenda L.S. Pereira, et al. Part I: Sustainability Concerns in Irrigated Agriculture. Irrigated Agriculture at the Crossroads M.E. Jensen. Economics of Irrigation I. Carruthers. Institutional Questions and Social Challenges H. Hill, L. Tollefson. Health Impacts of Agricultural Development I. Hespanol. Vulnerability of Soils under Irrigation J. Porta, J. Herrero. Sustainability Concerns of Irrigated Agriculture L.K. Smedema. Part II: Soil and Water Conservation and Water Harvesting (Or Rainfed Systems). Sustainability of Soil and Water Conservation in Sub-Saharan Africa C. Reij, W. Critchley. Soil and Water Conservation in Tunisia H. Missaoui. Water Harvesting - Past and Future D. Prinz. Part III: On-Farm Water Management. Measurement and Estimation of Evapotranspiration B. Itier. Water Use Efficiency P. Steduto. Modeling of Water Flow and Solute Transport for Irrigation and Drainage J.C. van Dam, R.A. Feddes. Irrigation Scheduling D.F. Heermann. Irrigation Scheduling in the Agronomic Practice A. Yazar, et al. Part IV: On-Farm Irrigation and Drainage Systems. Surface Irrigation Systems L.S. Pereira. Sprinkler Irrigation Systems J.R. Gilley. Micro-Irrigation Systems and Fertigation I. Papadopoulos. Drainage of Irrigated Land S. Bouarfa, et al. Part V: Water Quality Management. Salinity Management in Irrigated Agriculture N.K. Tyagi. Use and Management of Saline Water for Irrigation Towards Sustainable Development A. Hamdy. Agrochemicals and Water Management R.S. Kanwar. Water and Nitrate Balance in Irrigated Soils G. Vachaud, et al. Nitrate Leaching Under Irrigated Agriculture F. Moreno, et al. Waste-water Reuse S. Kyritsis. Part VI: Irrigation Scheme Management. Sustainability Concerns in the Operation and Maintenance of Irrigation Systems J.A. Sagardoy. Performance Parameters for a Decentralized and Participatory Water Administration J. Chambouleyron. Remote Sensing, GIS and Hydrological Modelling for Irrigation Management M. Menenti, et al. Regulation and Control in Irrigation Systems J. Goussard. Remote Control and Management of Irrigation Delivery Systems P. Kosuth. Part VII: Capacity Building. Role of Consulting Services J. Hennessy. Professional Training Requirements J. Feyen. North-South Cooperative Research on Sustainability of Water Resources Utilization in Agriculture M. Catizzone. Technology Transfer for Sustainable Water Resources Development M. Smith. Part VIII: Regional Perspectives. Sustainability Concerns in Asian Irrigation K. Mohtadullah, et al. Sustaining Irrigated Agriculture in China L. Cai, et al. Sustainability Concerns in African Irrigation F.N. Gichuki. Assessment of Impacts of Irrigated Agriculture: A Case Study A. Poulovassilis, et al. Annex I: Format of the Workshop. Annex II: List of Papers Presented to the Workshop. Annex III: List of Participants.

Developmental patterns of above‐ground hydraulic conductance in a Scots pine (Pinus sylvestris L.) age sequence

Abstract: Hydraulic resistance to water flow was measured in branches and stems of Scots pine trees ranging from 7 to 59 years of age in Thetford (East Anglia, UK). On the basis of these measurements, tree above-ground conductance was calculated and related to the amount of leaf area sustained by each tree. Branches at the crown bottom had a lower proportion of sapwood area and a lower total hydraulic conductance than branches of the same diameter at the tree top. Within branches, most of the hydraulic resistance was located near the needles. Tree above-ground conductance was positively related to tree diameter and inversely related to tree height. Compared with young trees, mature trees had about 4 times less above-ground conductance per unit of leaf area. Apparently, the increase in pathway length associated with tree height growth could be only partially compensated for by the increase in conductive capacities resulting from diameter growth. We argue that this reduction may account for reported decreases of stomatal conductance with tree age. It is suggested that the increase in branchiness associated with tree maturation may represent a compensation mechanism to reduce the overall resistance to water flow in the crowns.

Preferential water flow in a frozen soil - A two-domain model approach

Abstract: Earlier modelling studies have shown the difficulty of accurately simulating snowmelt infiltration into frozen soil using the hydraulic model approach. Comparison of model outputs and field measurements have inferred the occurrence of rapid flow even during periods when the soil is still partly frozen. A one-dimensional, physically based soil water and heat model (SOIL) has been complemented with a new two-domain approach option to simulate preferential flow through frozen layers. The ice is assumed to be first formed at the largest water filled pore upon freezing. Infiltrating water may be conducted rapidly through previously air-filled pores which are not occupied by ice. A minor fraction of water is slowly transferred within the liquid water domain, which is absorbed by the solid particles. A model validation with field measurements at a location in the middle-east of Sweden indicated that the two-domain approach was suitable for improving the prediction of drainage during snowmelting. In particular, the correlation between simulated and observed onset of drainage in spring was improved. The validation also showed that the effect of the high flow domain was highly sensitive to the degree of saturation in the topsoil during freezing, as well as to the hydraulic properties at the lower frost boundary regulating the upward water flow to the frozen soil and ice formation.

Impact of Physiological State on Surface Thermodynamics and Adhesion of Pseudomonas aeruginosa

Abstract: A quantitative understanding of microorganism migration in geological formations is critical to predict the dissemination of microorganisms in the environ ment and to evaluate the efficacy of microbially mediated in situ pollutant degradation. The key event that retards the movement of microorganisms in the saturated zone with respect to the convective water flow is the interaction between microorganisms and the matrix surfaces. This interaction may result in adhesion and concomitant retardation. Interactions are determined by the surface thermodynamics of the microorganism and the matrix. Whereas the nature of the matrix substratum surface may be considered temporally invariant, the nature of bacterial cell surfaces is a function of its physiological state. The work presented here explored quantitatively the impact of the physiological state of Pseudomonas aeruginosa Olin on its surface thermodynamic characteristics and its adhesion to dolomite. Lewis acid/base (hydrophobic), Lifshitz−van der Waals (elec...

Transport of conservative chemical through an unsaturated two‐dimensional Miller‐similar medium with steady state flow

Abstract: Numerical simulation of water flow in a two-dimensional, macroscopically homogeneous, Miller-similar medium showed the existence of a network of flow channels with two complementary states separated by a critical point [Roth, 1995]. The consequences of this for solute transport are explored by numerical simulations using particle tracking. It is found that many experimentally observed features of transport through soil are reproduced qualitatively by these simulations. Analyzing the results reveals that in the corresponding effective medium the travel distance for the transition to convection-dispersion and the effective dispersivity depend on the water flux. In particular, the effective longitudinal dispersivity, which is often assumed to be a material constant of the porous structure, is found to vary by more than an order of magnitude with a minimum near the critical point. The simulations further demonstrate that the local structure of the velocity field and the subscale hydrodynamic dispersion are of minor importance for the field-averaged transport process.

Site conditions limit pioneer tree recruitment after logging of dipterocarp forests in sabah, malaysia

Abstract: In Sabah, Malaysia, logging operations leave substantial areas denuded of vegetation and topsoil. These sites are prone to erosion and slow to become reforested. Stands of pioneer trees established in these heavily disturbed sites may provide environmental conditions that foster recruitment of persistent forest species. Results of a field experiment indicate that recruitment of pioneer trees in recently logged sites is limited more by site conditions than by availability of seeds. In lightly disturbed areas, where the canopy is open and soils are uncompacted, seed addition does not increase the density of pioneer tree seedlings; resprouting vegetation covers such gaps within 3 mo following logging. On landings and skid trails, pioneer seedling densities increase initially following seed addition but by 12 mo after seeding, densities of pioneer seedlings are similar to those on unseeded areas. High seedling mortality in seed addition plots on skid trails and landings indicate that conditions on these compacted and nutrient poor sites during the first year after logging are unfavorable for the persistence of pioneer seedlings. On log landings, seedlings recruit adjacent to debris and bark fragments more frequently than expected by chance. Eighty percent of artificial seeds sown on landings and skid trails were washed away by overland water flow after three storms. The scattering of bark fragments and other small debris over denuded sites may assist seed capture and increase seedling survival temporarily, but many seedlings die within a year. Improving harvesting practices to minimize the area scraped and compacted by heavy machinery will be more effective management than attempting to rehabilitate these areas following logging. The broadcasting of seeds of pioneer trees onto landings and skid trails immediately after logging may be a reasonable management option for hastening tree cover in denuded areas, but only if it is combined with site preparations that improve conditions for the survival of pioneer tree seedlings.

Colloid‐enhanced transport of chemicals in subsurface environments: A review

Abstract: Ample published evidence demonstrates that colloidal particles can act as carriers to enhance the transport of contaminants in subsurface environments. Conventionally, soil and aquifer porous media are considered to have two phases: an immobile solid matrix and a mobile liquid. Published reports indicate that biocolloids, aluminosilicate clay minerals, and organic colloids can migrate to considerable distances during water flow in soils and aquifers. In the presence of such carriers, the system should be perceived as consisting of three phases: a stationary solid matrix phase, a carrier phase, and an aqueous phase. Particle transport through porous media has been clearly demonstrated in filtration studies, but a need exists to investigate the role of colloidal carriers upon contaminant transport in porous media and to model carrier‐enhanced migration of contaminants accurately. In order to assess the potential role of colloidal carriers in facilitating chemical transport in porous media, this rev...