Flow Pathways (flow + pathway)

Distribution by Scientific Domains

Selected Abstracts

Dependence of the surface fractal dimension of soil pores on image resolution and magnification

A. Dathe
Summary Two recent investigations have reported contradictory trends concerning the effect of image resolution on the surface fractal dimension of soil pores, evaluated via image analysis. In one case, dealing with a preferential flow pathway and an ideal fractal, image resolution had no influence on the estimated fractal dimension, whereas in the other case, involving images of soil thin sections, the surface fractal dimension decreased significantly with image resolution. In the present paper, we try to determine the extent to which these conflicting observations may have been due to the different ways in which image resolution was varied. By narrowing down (up to 400 times) the field of view on progressively smaller portions of a textbook surface fractal, the von Koch island, one causes its apparent surface fractal dimension to decrease significantly. On the other hand, changing the resolution of images of soil thin sections (up to 6 times), while keeping the magnification constant, does not lead to appreciable changes in the surface fractal dimension. These results demonstrate that there is no real conflict in earlier reports, as long as both the resolution and the magnification of images are taken into account in image-based evaluations of surface fractal dimensions of soil pores. [source]

A study of D-lactate and extracellular methylglyoxal production in lactate Re-Utilizing CHO cultures

Tomas Paoli
Abstract In large-scale mammalian cell culture, the key toxic by-products assessed and monitored are lactate and ammonia. Often no distinction between the two isoforms of lactate is made. Here, we present profiles of both D - and L -lactate. D -Lactate is the end molecule of the methylglyoxal pathway. D -Lactate unlike L -lactate is not re-utilized, and although during normal culture time frames it represents one-tenth of total lactate, during lactate re-use it represents nearly 35%. This indicates significant carbon flow through pathways not associated with primary metabolites. We have observed that the behavior of D -lactate is radically different from that of L -lactate with the level of one isoform changing, whilst the concentration of the other remains constant. This is an example of an alternate carbon flow pathway containing metabolic intermediates that may potentially have a detrimental effect on cells. The activity of the methylglyoxal pathway when measured as a proportion of glucose consumption in this study far exceeds any previously reported. This highlights the potential importance of "non-primary" metabolisms to long lifespan mammalian fermentation practices. Biotechnol. Bioeng. 2010;107: 182,189. 2010 Wiley Periodicals, Inc. [source]

Spatial and temporal patterns of microcrustacean assemblage structure and secondary production in a wetland ecosystem

Summary 1. In contrast to extensive studies of zooplankton in lakes, the role of microcrustaceans in wetlands is not well studied. In this study, spatial and temporal patterns of microcrustacean assemblage structure and secondary production were quantified over a 2-year period in a southeastern U.S.A. wetland. 2. Thirty-two species, including 19 cladocerans, 10 copepods and three ostracods, generated different temporal patterns of density and production between vegetated (Nymphaea) and non-vegetated (open-water) zones reflecting species-specific differences in life histories. 3. Summer assemblages were dominated by small, planktonic filter-feeders, typified by high annual production/biomass (P/B) and daily production. In contrast, winter assemblages were dominated by larger, epibenthic detritivores with low P/B and high biomass. Seasonal shifts in the relative importance of planktonic species in the warmer months to benthic and epiphytic species in the cooler months suggest that energy flow pathways through microcrustaceans may vary seasonally. 4. Total annual production was higher during both years in the Nymphaea zone (13.0 g and 13.6 g DM m,2 year,1) than the open-water (8.2 and 6.3 g DM m,2 year,1), and was similar between years for the entire wetland pond (12.3 and 12.2 g DM m,2 year,1). 5. Although wetland ecosystems have been the subject of considerable ecological research in the past 20 years, our study is one of the few to demonstrate a highly diverse and relatively productive microcrustacean assemblage. Such comprehensive production studies can be used to quantify the ecological importance of microcrustaceans in freshwater wetland ecosystems. [source]

Mechanisms and pathways of lateral flow on aspen-forested, Luvisolic soils, Western Boreal Plains, Alberta, Canada

Todd Redding
Abstract Rainfall simulation experiments by Redding and Devito (2008, Hydrological Processes 23: 4287,4300) on two adjacent plots of contrasting antecedent soil moisture storage on an aspen-forested hillslope on the Boreal Plain showed that lateral flow generation occurred only once large soil storage capacity was saturated combined with a minimum event precipitation of 15,20 mm. This paper extends the results of Redding and Devito (2008, Hydrological Processes 23: 4287,4300) with detailed analysis of pore pressure, soil moisture and tracer data from the rainfall simulation experiments, which is used to identify lateral flow generation mechanisms and flow pathways. Lateral flow was not generated until soils were wet into the fine textured C horizon. Lateral flow occurred dominantly through the clay-rich Bt horizon by way of root channels. Lateral flow during the largest event was dominated by event water, and precipitation intensity was critical in lateral flow generation. Lateral flow was initiated as preferential flow near the soil surface into root channels, followed by development of a perched water table at depth, which also interacted with preferential flow pathways to move water laterally by the transmissivity feedback mechanism. The results indicate that lateral flow generated by rainfall on these hillslopes is uncommon because of the generally high available soil moisture storage capacity and the low probability of rainfall events of sufficient magnitude and intensity. Copyright 2010 John Wiley & Sons, Ltd. [source]

Assessing the impact of mixing assumptions on the estimation of streamwater mean residence time

Fabrizio Fenicia
Abstract Catchment streamwater mean residence time (Tmr) is an important descriptor of hydrological systems, reflecting their storage and flow pathway properties. Tmr is typically inferred from the composition of stable water isotopes (oxygen-18 and deuterium) in observed rainfall and discharge. Currently, lumped parameter models based on convolution and sinewave functions are usually used for tracer simulation. These traditional models are based on simplistic assumptions that are often known to be unrealistic, in particular, steady flow conditions, linearity, complete mixing and others. However, the effect of these assumptions on Tmr estimation is seldom evaluated. In this article, we build a conceptual model that overcomes several assumptions made in traditional mixing models. Using data from the experimental Maimai catchment (New Zealand), we compare a complete-mixing (CM) model, where rainfall water is assumed to mix completely and instantaneously with the total catchment storage, with a partial-mixing (PM) model, where the tracer input is divided between an ,active' and a ,dead' storage compartment. We show that the inferred distribution of Tmr is strongly dependent on the treatment of mixing processes and flow pathways. The CM model returns estimates of Tmr that are well identifiable and are in general agreement with previous studies of the Maimai catchment. On the other hand, the PM model,motivated by a priori catchment insights,provides Tmr estimates that appear exceedingly large and highly uncertain. This suggests that water isotope composition measurements in rainfall and discharge alone may be insufficient for inferring Tmr. Given our model hypothesis, we also analysed the effect of different controls on Tmr. It was found that Tmr is controlled primarily by the storage properties of the catchment, rather than by the speed of streamflow response. This provides guidance on the type of information necessary to improve Tmr estimation. Copyright 2010 John Wiley & Sons, Ltd. [source]

Dynamics of stream nitrate sources and flow pathways during stormflows on urban, forest and agricultural watersheds in central Pennsylvania, USA

Anthony R. Buda
Abstract Understanding the influence of storm events on nitrate (NO3,) dynamics is important for efficiently managing NO3, pollution. In this study, five sites representing a downstream progression of forested uplands underlain by resistant sandstone to karst lowlands with agricultural, urban and mixed land-use were established in Spring Creek, a 201 km2 mixed land-use watershed in central Pennsylvania, USA. At each site, stream water was monitored during six storm events in 2005 to assess changes in stable isotopes of NO3, (,15N-NO3, and ,18O-NO3,) and water (,18O-H2O) from baseflow to peakflow. Peakflow fractions of event NO3, and event water were then computed using two-component mixing models to elucidate NO3, flow pathway differences among the five sites. For the forested upland site, storm size appeared to affect NO3, sources and flow pathways. During small storms (<35 mm rainfall), greater event NO3, fractions than event water fractions indicated the prevalence of atmospheric NO3, source contributions at peakflow. During larger storms (>35 mm rainfall), event NO3, fractions were less than event water fractions at peakflow suggesting that NO3, was flushed from stored sources via shallow subsurface flow pathways. For the urbanized site, wash-off of atmospheric NO3, was an important NO3, source at peakflow, especially during short-duration storms where event water contributions indicated the prevalence of overland flow. In the karst lowlands, very low fractions of event water and even lower fractions of event NO3, at peakflow suggested the dominance of ground water flow pathways during storms. These ground water flow pathways likely flushed stored NO3, sources into the stream, while deep soils in the karst lowlands also may have promoted NO3, assimilation. The results of this study illustrated how NO3, isotopes and ,18O-H2O could be combined to show key differences in water and NO3, delivery between forested uplands, karst valleys and fully urbanized watersheds. Copyright 2009 John Wiley & Sons, Ltd. [source]

Towards an energy-based runoff generation theory for tundra landscapes

William L. Quinton
Abstract Runoff hydrology has a large historical context concerned with the mechanisms and pathways of how water is transferred to the stream network. Despite this, there has been relatively little application of runoff generation theory to cold regions, particularly the expansive treeless environments where tundra vegetation, permafrost, and organic soils predominate. Here, the hydrological cycle is heavily influenced by 1) snow storage and release, 2) permafrost and frozen ground that restricts drainage, and 3) the water holding capacity of organic soils. While previous research has adapted temperate runoff generation concepts such as variable source area, transmissivity feedback, and fill-and-spill, there has been no runoff generation concept developed explicitly for tundra environments. Here, we propose an energy-based framework for delineating runoff contributing areas for tundra environments. Aerodynamic energy and roughness height control the end-of-winter snow water equivalent, which varies orders of magnitude across the landscape. Radiant energy in turn controls snowmelt and ground thaw rates. The combined spatial pattern of aerodynamic and radiant energy control flow pathways and the runoff contributing areas of the catchment, which are persistent on a year-to-year basis. While ground surface topography obviously plays an important role in the assessment of contributing areas, the close coupling of energy to the hydrological cycles in arctic and alpine tundra environments dictates a new paradigm. Copyright 2008 John Wiley & Sons, Ltd. [source]

Hydrological versus biogeochemical controls on catchment nitrate export: a test of the flushing mechanism

Carlos J. Ocampo
Abstract Deciphering the connection between streamflows and nitrate (NO,3) discharge requires identification of the various water flow pathways within a catchment, and the different time-scales at which hydrological and biogeochemical processes occur. Despite the complexity of the processes involved, many catchments around the world present a characteristic flushing response of NO,3 export. Yet the controls on the flushing response, and how they vary across space and time, are still not clearly understood. In this paper, the ,flushing response' of NO,3 export from a rural catchment in Western Australia was investigated using isotopic (deuterium), chemical (chloride, NO,3), and hydrometric data across different antecedent conditions and time-scales. The catchment streamflow was at all time-scales dominated by a pre-event water source, and the NO,3 discharge was correlated with the magnitude of areas contributing to saturation overland flow. The NO,3 discharge also appeared related to the shallow groundwater dynamics. Thus, the antecedent moisture condition of the catchment at seasonal and interannual time-scales had a major impact on the NO,3 flushing response. In particular, the dynamics of the shallow ephemeral perched aquifer drove a shift from hydrological controls on NO,3 discharge during the ,early flushing' stage to an apparent biogeochemical control on NO,3 discharge during the ,steady decline' stage of the flushing response. This temporally variable control hypothesis provides a new and alternative description of the mechanisms behind the commonly seen flushing response. Copyright 2006 John Wiley & Sons, Ltd. [source]

Defining hydrochemical evolution of streamflow through flowpath dynamics in Kawakami headwater catchment, Central Japan

Kasdi Subagyono
Abstract The hydrochemical behaviour of catchments is often investigated by inferring stream chemistry through identification of source areas involved in hydrograph separation analysis, yet its dynamic evolution of hydrologic pathways has received little attention. Intensive hydrometric and hydrochemical measurements were performed during two different storms on March 29, 2001 and August 21,22, 2001 to define hydrochemical evolution under the dynamic of flow pathways in a 52 ha first-order drainage of the Kawakami experimental basin (KEB), Central Japan, a forested headwater catchment with various soil depths (18 to 5 m) overlying late Neogene of volcanic bedrocks. The hydraulic potential distribution and flow lines data showed that the change in flow direction, which was controlled by rainfall amount and antecedent wetness of the soil profile, agreed well with the hydrochemical change across the slope segment during the storm. Hydrograph separation predicted by end-member mixing analysis (EMMA) using Ca2+ and SiO2 showed that near surface riparian, hillslope soil water and deep riparian groundwater were important in stream flow generation. The evidence of decrease in solutes concentration at a depth of 1 m in the hillslope and 06 m in the near surface riparian during peak storm suggested a flushing of high solutes concentration. Most of the solutes accumulated in the deep riparian groundwater zone, which was due to prominent downward flow and agreed well with the residence time. The distinct flow pathways and chemistry between the near surface riparian and deep riparian groundwater zones and the linkage hillslope aquifer and near surface riparian reservoir, which controls rapid flow and solutes flushing during the storm event, are in conflict with the typical assumption that the whole riparian zone resets flow pathways and chemical signature of hillslope soil water, as has been reported in a previous study. Copyright 2005 John Wiley & Sons, Ltd. [source]

Infiltration and solute transport under a seasonal wetland: bromide tracer experiments in Saskatoon, Canada

David F. Parsons
Abstract In the northern glaciated plain of North America, the duration of surface water in seasonal wetlands is strongly influenced by the rate of infiltration and evaporation. Infiltration also plays important roles in nutrient exchange at the sediment,water interface and groundwater recharge under wetlands. A whole-wetland bromide tracer experiment was conducted in Saskatchewan, Canada to evaluate infiltration and solute transport processes. Bromide concentrations of surface water, groundwater, sediment pore water and plant tissues were monitored as the pond water-level gradually dropped until there was no surface water. Hydraulic head gradients showed strong lateral flow from under the wetland to the treed riparian zone during the growing season. The bromide mass balance analysis showed that in early spring, almost 50% of water loss from the wetland was by infiltration, and it increased to about 70% in summer as plants in and around the wetland started to transpire more actively. The infiltration contributed to recharging the shallow, local groundwater under the wetland, but much of it was taken up by trees without recharging the deeper groundwater system. Emergent plants growing in the wetlands incorporated some bromide, but overall uptake of bromide by vegetation was less than 10% of the amount initially released. After one summer, most of the subsurface bromide was found within 40,80 cm of the soil surface. However, some bromide penetrated as deep as 2,3 m, presumably owing to preferential flow pathways provided by root holes or fractures. Copyright 2004 Crown in the Right of Canada. Published by John Wiley & Sons, Ltd. [source]

Hillslope-swamp interactions and flow pathways in a hypermaritime rainforest, British Columbia

D. F. Fitzgerald
Abstract The process of water delivery to a headwater stream in a hypermaritime rainforest was examined using a variety of physical techniques and tracing with dissolved organic carbon (DOC) and the stable isotopes of water. Headwater swamps, often the major discharge zones for water draining off steep forest slopes, strongly affect the physical and chemical character of streamflow in the region. The headwater swamp selected for detailed investigation was sustained by relatively constant groundwater input from the steep colluvial slopes that maintained the water table above the ground surface. During significant storm events the water table rose quickly and the swamp expanded to engulf marginal pools that developed rapidly on the adjacent ground surfaces. The corresponding release of surface water directly to the stream typically comprised up to 95% of total stream discharge. The proportion of groundwater seepage to the stream by matrix flow (<1%) and via macropore-fed springs (up to 73%) increased during the recession period, but could not be sustained over the longer term. In more protracted drying periods, deep groundwater contributions to the stream were routed first to the headwater swamp. Dissolved organic carbon (DOC) in the stream, measured daily or more frequently during storm events, was found to be directly proportional to discharge, owing to the domination of DOC-rich headwater-swamp water sources. Although ,18O and ,2H composition of rainwater, groundwater and stream flow were found to be similar, deuterium excess (d ,2H , 8,18O) of water components was often found to be distinct, and suggested short water residence times of roughly 12 days for one event. Overall, observations of a typical headwater swamp reveal that the groundwater regime is dominated by rapid infiltration and short, emergent flow paths. With a relatively short turnover time, potential disturbances to the system by harvesting of upslope areas can be expected to occur rapidly. Forest managers can mitigate some of the harmful effects of logging operations by respecting the integrity of headwater wetland systems. The nature and magnitude of such perturbations will require further study. Copyright 2003 John Wiley & Sons, Ltd. [source]

Using time-domain reflectometry to characterize shallow solute transport in an oak woodland hillslope in northern California, USA

Chris G. Campbell
Abstract The natural heterogeneity of water and solute movement in hillslope soils makes it difficult to accurately characterize the transport of surface-applied pollutants without first gathering spatially distributed hydrological data. This study examined the application of time-domain reflectometry (TDR) to measure solute transport in hillslopes. Three different plot designs were used to examine the transport of a conservative tracer in the first 50 cm of a moderately sloping soil. In the first plot, which was designed to examine spatial variability in vertical transport in a 12 m2 plot, a single probe per meter was found to adequately characterize vertical solute travel times. In addition, a dye and excavation study in this plot revealed lateral preferential flow in small macropores and a transport pattern where solute is focused vertically into preferential flow pathways. The bypass flow delivers solute deeper in the soil, where lateral flow occurs. The second plot, designed to capture both vertical and lateral flow, provided additional evidence confirming the flow patterns identified in the excavation of the first plot. The third plot was designed to examine lateral flow and once again preferential flow of the tracer was observed. In one instance rapid solute transport in this plot was estimated to occur in as little as 3% of the available pore space. Finally, it was demonstrated that the soil anisotropy, although partially responsible for lateral subsurface transport, may also homogenize the transport response across the hillslope by decreasing vertical solute spreading. Copyright 2002 John Wiley & Sons, Ltd. [source]

Collateral Capillary Arterialization following Arteriolar Ligation in Murine Skeletal Muscle

Microcirculation (2010) 17, 333,347. doi: 10.1111/j.1549-8719.2010.00034.x Abstract Objective:, Chronic and acute ischemic diseases,peripheral artery disease, coronary artery disease, stroke,result in tissue damage unless blood flow is maintained or restored in a timely manner. Mice of different strains recover from arteriolar ligation (by increasing collateral blood flow) at different speeds. We quantify the spatio-temporal patterns of microvascular network remodeling following arteriolar ligation in different mouse strains to better understand inter-individual variability. Methods:, Whole-muscle spinotrapezius microvascular networks of mouse strains C57Bl/6, Balb/c and CD1 were imaged using confocal microscopy following ligation of feeding arterioles. Results:, Baseline arteriolar structures of C57Bl/6 and Balb/c mice feature heavily ramified arcades and unconnected dendritic trees, respectively. This network angioarchitecture identifies ischemia-protected and ischemia-vulnerable tissues; unlike C57Bl/6, downstream capillary perfusion in Balb/c spinotrapezius is lost following ligation. Perfusion recovery requires arterialization (expansion and investment of mural cells) of a subset of capillaries forming a new low-resistance collateral pathway between arteriolar trees. Outbred CD1 exhibit either Balb/c-like or C57Bl/6-like spinotrapezius angioarchitecture, predictive of response to arteriolar ligation. Conclusions:, This collateral capillary arterialization process may explain the reported longer time required for blood flow recovery in Balb/c hindlimb ischemia, as low-resistance blood flow pathways along capillary conduits must be formed ("arterialization") before reperfusion. [source]

Breeding behavior and its possible consequences for gene flow in Taraxacum sect.

Erythrosperma (H. Lindb.) Dahlst.
Abstract Studies of pollen, seed set and experimental hybridizations were carried out to clarify breeding behavior and gene flow pathways in Taraxacum sect. Erythrosperma. Seeds from hybridization (106 samples), open pollinated (34) and bagged (43) capitula were analyzed for breeding system using a flow,cytometric seed screen. In the section Erythrosperma, diploids are obligate sexuals, mostly allogamous; however, autogamy also occurs (in 28% of unpollinated capitula). Triploids are apomicts with residual sexuality (in 13% of capitula pollinated by pollen of diploids). Pollen of diploids in Taraxacum is usually approximately the same size (regular pollen). In our study, in the section Erythrosperma, many diploids (24%) produced pollen grains of different sizes (irregular pollen) and one plant produced no pollen. The pollen of triploids is either irregular (33%) or the triploids produce no pollen (67%). Consequently, the method of ploidy level assessment on the basis of pollen characteristics is not suitable for Taraxacum sect. Erythrosperma. Low potential for polyploid hybrid formation between diploid maternal plants and polyploid pollen donors, considerable tendency to autogamy and no evidence of the formation of diploid progeny by polyploid maternal plants (facultative apomixis) indicates low intensity of gene flow within Taraxacum sect. Erythrosperma. This, together with a lower population density and spatial isolation of ploidy levels, is expected to result in a lower rate of formation of new apomictic lineages. Thus, Taraxacum sect. Erythrosperma appears evolutionarily more stable and taxonomically less complicated than sect. Ruderalia. The present study supports the agamospecies concept of Taraxacum sect. Erythrosperma. [source]