Stream Dynamics Research Articles

The entropy of cancer cell migration: Bioenergetics and cell proliferation support invasive migration in 3D

Many cancer cells invade into the surrounding tissues in the form of a stream-like 3D collective structure, with distinct leader and follower cells. We previously demonstrated that leading cancer cells adopt a “drafting” strategy to efficiently overcome the barrier of migration imposed by the surrounding matrices. However, it is not clear how biophysical cues are integrated at follower positions to give rise to this collective streaming. Here, we show for the first time that energetic difference that arises from cell cycle progression drives forward motion of high-energy follower cells to the leader position to support 3D collective invasion. ATP energy, which powers numerous cellular processes, increases with cell cycle progression and peaks at the G2/M phase. With iterative experimental measurements and physical modeling based on a reaction-advection-diffusion framework, we demonstrated that the high energy in G2 cells drives their forward streaming dynamics to support 3D collective invasion, which also shifted the distribution of G2 cells toward the leader position. The accumulation or dissemination of high-energy G2 cells toward the leader position increases the disorder of cancer cell distribution thus increasing the “entropy” of the tumor-matrix system. Hence, this energy-driven cell streaming may be a fundamental characteristic of 3D collective dynamics governed by thermodynamic principles and may provide new insights to our understanding of not only cancer invasion but also tissue morphogenesis.

Long-term forecast of flow dynamics of Chirchik basin

Global climate change is undoubtedly one of the main threats to the world community among existing environmental problems. This problem has a particularly severe impact on water resources. Changes in hydrological processes or flows in river basins directly or indirectly affect the dynamics of changes in gross domestic product (GDP) in this region. Chirchik basin provides about 16% of GDP of the republic, and more than 70% of water resources are used for irrigation of crops [1-5]. For this reason, any factors affecting hydrological processes and flow dynamics in the river basin, especially climate change, immediately affect all aspects of life in the region, including the social level of society and economic stability. Assessing the impact of climate differences on river basin flow dynamics is important for ensuring sustainable agricultural productivity for river basins in the future, as well as reducing the ecological and environmental impacts of climate change. This situation calls for urgent and concerted action in several areas: technology, infrastructure, politics, economy, ecology and environmental protection. The article assessed the impact of changes in precipitation intensity on stream dynamics based on the Global Circulation Model (GCM) coordination scenarios, RCP4.5 and RCP8.5 for the years 2030, 2050 and 2070 using the delta approach method. The results of the study provided strong evidence for changes in stream dynamics in the Chirchik basin for the near and far future.

Litter inputs and standing stocks in riparian zones and streams under secondary forest and managed and abandoned cocoa agroforestry systems.

Cocoa is an important tropical tree crop that is mainly cultivated in agroforestry systems (AFS). This system, known as cabruca in northeastern Brazil, holds promise to reconcile biodiversity conservation and economic development. However, since cocoa AFS alters forest structure composition, it can affect litter dynamics in riparian zones and streams. Thus, our objective was to determine litter inputs and standing stocks in riparian zones and streams under three types of forest: managed cocoa AFS, abandoned cocoa AFS, and secondary forest. We determined terrestrial litter fall (TI), vertical (VI) and lateral (LI) litter inputs to streams, and litter standing stocks on streambeds (BS) in the Atlantic Forest of northeastern Brazil. Litter was collected every 30 days from August 2018 to July 2019 using custom-made traps. The litter was dried, separated into four fractions (leaves, branches, reproductive organs, and miscellaneous material) and weighed. Terrestrial litter fall was similar in all forests, ranging from 89 g m-2 month-1 in secondary forest (SF) to 96 g m-2 month-1 in abandoned cocoa AFS (AC). Vertical input were higher in AC (82 g m-2 month-1) and MC (69 g m-2 month-1) than in SF (40 g m-2 month-1), whereas lateral input were higher in MC (43 g m-2 month-1) than in AC (15 g m-2 month-1) and SF (24 g m-2 month-1). Standing stocks followed the order SF > AC > MC, corresponding to 425, 299 and 152 g m-2. Leaves contributed most to all litter fractions in all forests. Reproductive plant parts accounted for a larger proportion in managed AFS. Branches and miscellaneous litter were also similar in all forests, except for higher benthic standing stocks of miscellaneous litter in the SF. Despite differences in the amounts of litter inputs and standing stocks among the forests, seasonal patterns in the abandoned AFS (AC) were more similar to those of the secondary forest (SF) than the managed AFS, suggesting potential of abandoned AFS to restore litter dynamics resembling those of secondary forests.

Greenhouse gas dynamics in tropical montane streams of Puerto Rico and the role of watershed lithology

Greenhouse gas dynamics in tropical montane streams of Puerto Rico and the role of watershed lithology

Organic litter dynamics in headwater streams draining contrasting land uses

Climate change could alter fluxes of organic matter and macronutrients through freshwater ecosystems potentially affecting stream organisms. However, riparian controls on litter dynamics offer an opportunity to adapt headwaters to climate change by protecting or restoring riparian vegetation. We assessed how riparian land cover and climatic variability affected the supply, retention and downstream transport of particulate organic matter (POM) in headwaters—the most extensive small water bodies in temperate landscapes. Leaf litter inputs, benthic stocks and suspended organic matter were measured nominally monthly in second–third-order streams draining broadleaf woodland, conifer, acid moorland and circumneutral moorland over four years with varying discharge. Streams draining broadleaf woodland received more leaf litter from the riparian zone than conifer and moorland and transported higher concentrations of CPOM and FPOM at base flows. Broadleaf sites had higher CPOM stocks, even after hydrological events that reduced CPOM in conifer and moorland sites. In contrast, FPOM dynamics reflected hydrological conditions irrespective of land cover. These results show how some organic matter fractions in streams are sensitive to hydrological conditions, illustrating how wetter climates will influence FPOM exports. Nevertheless, riparian broadleaves have the potential to offset climatic effects on organic matter processing in headwaters through the replenishment and retention of CPOM.

Large Wood in Small Channels: A 20‐Year Study of Budgets and Piece Mobility in Two Redwood Streams

AbstractLarge wood (LW) influences geomorphic and ecological processes. However, most field data sets describing LW dynamics are conducted over the span of only a few years. We present a unique long‐term data set from northern California, USA of LW volumes, inputs, and transport in two small headwater streams, the North Fork (NF) and South Fork (SF) of Caspar Creek. We used data collected approximately every 2 years from 1998 to 2018 to assess how LW budgets change over time between catchments, what factors influence inputs from standing trees to the streams, and controls on LW piece mobility. We find that the SF, which experienced stream‐side logging and instream wood removal in the 1970s, continued to have lower LW volumes (range of 101–153 m3 km−1 over the 20‐year period) compared to the NF (range of 297–313 m3 km−1), which experienced logging in the 1980s but with buffer strips left near the channel. If current trends continue, it will likely take ∼100–200 years from the time of logging for the SF to reach NF instream wood volumes. We show that windstorms combined with precipitation events, very high winds, and hillslope steepness are strongly associated with LW piece inputs from standing trees. LW moves infrequently in the channel, with piece characteristics, the number of wood pieces per meter surrounding an LW piece, and discharge metrics influencing LW entrainment and displacement lengths. Our data set provides strong support to previously identified controls on LW dynamics in streams while also capturing variability over a 20‐year period.

Exploring the relations between sequential droughts and stream nitrogen dynamics in central Germany through catchment-scale mechanistic modelling

Like many other regions in central Europe, Germany experienced sequential summer droughts from 2015 to 2018. As one of the environmental consequences, river nitrate concentrations have exhibited significant changes in many catchments. However, catchment nitrate responses to the changing weather conditions have not yet been mechanistically explored. Thus, a fully distributed, process-based catchment Nitrate model (mHM-Nitrate) was used to reveal the causal relations in the Bode catchment, of which river nitrate concentrations have experienced contrasting trends from upstream to downstream reaches. The model was evaluated using data from six gauging stations, reflecting different levels of runoff components and their associated nitrate-mixing from upstream to downstream. Results indicated that the mHM-Nitrate model reproduced dynamics of daily discharge and nitrate concentration well, with Nash-Sutcliffe Efficiency ≥ 0.73 for discharge and Kling-Gupta Efficiency ≥0.50 for nitrate concentration at most stations. Particularly, the spatially contrasting trends of nitrate concentration were successfully captured by the model. The decrease of nitrate concentration in the lowland area in drought years (2015–2018) was presumably due to (1) limited terrestrial export loading (ca. 40 % lower than that of normal years 2004–2014), and (2) increased in-stream retention efficiency (20 % higher in summer within the whole river network). From a mechanistic modelling perspective, this study provided insights into spatially heterogeneous flow and nitrate dynamics and effects of sequential droughts, which shed light on water-quality responses to future climate change, as droughts are projected to be more frequent.

Geochemical and Advanced Electron Microscopical Characterisations of Artisanal Gold Mining Rejects in Colombia

Artisanal gold mining causes widespread health problems due to illegal exposure to hazardous inorganic compounds, such as arsenic (As) and mercury (Hg). The sources and prevalence of mining pollution are strongly influenced by topography, stream dynamics, soil type, and land use. In the present study, the potential hazardous elements (PHEs), absorption abilities of nanoparticles (NPs), and ultrafine particles (UFPs) were analysed from clandestine gold mining soils in Colombia. The proportions of PHEs including As, Hg, Cu, Cr, and Pb in carbonates, sulfides, clays, oxides, hydroxides, and sulfates were determined by field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and selected area electron diffraction (SAED)/micro-beam diffraction (MBD)/energy dispersive X-ray spectroscopy (EDS). The results revealed that the concentrations of As, Hg, and Zn were significantly higher in clay particles when compared to the other soil samples. Furthermore, Al and Fe manifested excellent PHEs sorption abilities in the artisanal gold mining soils. The results presented will be useful for future mitigation measures in the gold mining areas.

Onchorynchus mykiss alter nutrient dynamics in high-altitude headwater streams in Boyacá, Colombia through displacement of the native fish community

A primary global threat to aquatic ecosystem conservation and biodiversity is the introduction of fish species, both deliberate and unintentional. Much of the research conducted on large predatory fish introductions has focused primarily on top-down controls that regulate the abundance and composition of native species assemblages, yet exotic species that alter ecosystem structure and function may pose an even greater threat. The objective of this study was to examine whether an introduced piscivorous fish alters nitrogen cycles in high elevation freshwater streams in the tropics by displacing the native species community through predation. To test this, we measured biomass and ammonium (NH4+-N) remineralization rates for introduced Onchorynchus mykiss and the two native species found in the area; Trichomycterus bogotensis and Grundulus bogotensis in six study sites along an elevation gradient in the Pómeca River Basin in Boyacá, Colombia. Nonnative O. mykiss populations remineralized ammonium at a rate that was 20 times higher than native G. bogotensis and 47 times higher than T. bogotensis. Our results indicate that high biomass of an introduced predatory fish species can have important implications in nutrient dynamics in freshwater streams through reduction in native species biomass when combined with differential nutrient remineralization rates.

Dynamics of Large-Scale Solar-Wind Streams Obtained by the Double Superposed Epoch Analysis: 5. Influence of the Solar Activity Decrease

In solar cycles 23–24, solar activity noticeably decreased and, as a result, solar wind parameters decreased. Based on the measurements of the OMNI base for the period 1976–2019, the time profiles of the main solar wind parameters and magnetospheric indices for the main interplanetary drivers of magnetospheric disturbances (solar wind types CIR. Sheath, ejecta and MC) are studied using the double superposed epoch method. The main task of the research is to compare time profiles for the epoch of high solar activity at 21–22 SC and the epoch of low activity at 23–24 SC. The following results were obtained. (1) The analysis did not show a statistically significant change in driver durations during the epoch of minimum. (2) The time profiles of all parameters for all types of SW in the epoch of low activity have the same shape as in the epoch of high activity, but locate at lower values of the parameters. (3) In CIR events, the longitude angle of the solar wind flow has a characteristic S shape; but in the epoch of low activity, it varies in a larger range than in the previous epoch.

TALES FROM INDIA. 1: METEOR SHOWERS IN CLASSICAL AND COLONIAL SOURCES

Meteor phenomena are always fascinating and capture popular attention. This paper reports results of a search for references to and records of meteor showers observed in the Indian region, until the close of the nineteenth century. The sources explored were the Indian classics and chronicles, institutional reports and accounts by individuals, including those published in professional journals. We found very few references to such events in the classical sources. The earliest datable references that we found were in Shuka's <italic>Rajatarangini</italic> (Perseids or Leonids, 1533), Abu'l Fazl's <italic>Akbarnama</italic> (Alpha Capricornids or Delta Aquarids, 1592) and in Krishnaji Sabhasad's account of the life of Chhatrapati Shivaji Maharaj (Leonids, 1680). The subsequent accounts belong to the nineteenth century. Some of these are about sporadic meteors, while others are about meteor showers. The earliest published report is of the November Leonid meteor shower of 1832. We also came across a strong meteor shower on 10 September 1841 reported in the 13 September issue of the <italic>Englishman</italic> newspaper. We believe this is the September Epsilon Perseids, a minor shower known to peak on 9/10 September. This 1841 observation is 37 years before the September Epsilon Perseids were first described by William Denning, in 1878. We believe that such records can be of great value in fine-tuning time-lines in Indian history and understanding the dynamics of meteoroid streams.

Interstitial fluid streaming in deep tissue induced by ultrasound momentum transfer for accelerating nanoagent transport and controlling its distribution

Objective. This study aims to theoretically investigate the dynamics of ultrasound-induced interstitial fluid streaming and tissue recovery after ultrasound exposure for potentially accelerating nanoagent transport and controlling its distribution in tissue. Approach. Starting from fundamental equations, the dynamics of ultrasound-induced interstitial fluid streaming and tissue relaxation after an ultrasound exposure were modeled, derived and simulated. Also, both ultrasound-induced mechanical and thermal effects were considered in the models. Main results. The proposed new mechanism was named squeezing interstitial fluid via transfer of ultrasound momentum (SIF-TUM). It means that an ultrasound beam can squeeze the tissue in a small focal volume from all the directions, and generate a macroscopic streaming of interstitial fluid and a compression of tissue solid matrix. After the ultrasound is turned off, the solid matrix will recover and can generate a backflow. Rather than the ultrasound pressure itself or intensity, the streaming velocity is determined by the dot product of the ultrasound pressure gradient and its conjugate. Tissue and nanoagent properties also affect the streaming and recovery velocities. Significance. The mobility of therapeutic or diagnostic agents, such as drugs, drug carriers, or imaging contrast agents, in the interstitial space of many diseased tissues, such as tumors, is usually extremely low because of the inefficiency of the natural transport mechanisms. Therefore, the interstitial space is one of the major barriers hindering agent deliveries. The ability to externally accelerate agent transport and control its distribution is highly desirable. Potentially, SIF-TUM can be a powerful technology to accelerate agent transport in deep tissue and control the distribution if appropriate parameters are selected.

Inter-individual variability in dorsal stream dynamics during word production.

The current standard model of language production involves a sensorimotor dorsal stream connecting areas in the temporo-parietal junction with those in the inferior frontal gyrus and lateral premotor cortex. These regions have been linked to various aspects of word production such as phonological processing or articulatory programming, primarily through neuropsychological and functional imaging group studies. Most if not all the theoretical descriptions of this model imply that the same network should be identifiable across individual speakers. We tested this hypothesis by quantifying the variability of activation observed across individuals within each dorsal stream anatomical region. This estimate was based on electrical activity recorded directly from the cerebral cortex with millisecond accuracy in awake epileptic patients clinically implanted with intracerebral depth electrodes for pre-surgical diagnosis. Each region's activity was quantified using two different metrics-intra-cerebral evoked related potentials and high gamma activity-at the level of the group, the individual and the recording contact. The two metrics show simultaneous activation of parietal and frontal regions during a picture naming task, in line with models that posit interactive processing during word retrieval. They also reveal different levels of between-patient variability across brain regions, except in core auditory and motor regions. The independence and non-uniformity of cortical activity estimated through the two metrics push the current model towards sub-second and sub-region explorations focused on individualized language speech production. Several hypotheses are considered for this within-region heterogeneity.

Progress of cavitation and acoustic streaming dynamics of liquid materials within ultrasonic field

<p indent="0mm">Power ultrasound can effectively control the heat and mass transfer processes in liquids due to its cavitation and acoustic streaming effects, leading to a broad application prospect in the field of material preparation. Due to the opacity of alloy melt, it is impossible to observe the ultrasonic process directly in experiment, and numerical simulation becomes an important method to fully analyze the propagation characteristics of ultrasonic and its effect on alloy solidification. This overview firstly summarizes the evolution of sound propagation equation from linear model to non-linear model and the modification mechanisms of ultrasonic power, sonotrode size, container shape and ultrasonic dimension on sound pressure and acoustic streaming. Besides, the numerical simulation results of cavitation dynamics in single and multiple bubble systems is introduced, including bubble instability mechanism, bubbles interaction and the effect of cavitation on the liquid pressure and temperature. Furthermore, by combining ultrasonic cavitation and acoustic streaming dynamics with metal solidification process, several macro-models and micro-models to simulate ultrasonic solidification is presented, and the mechanisms of ultrasonic cavitation and acoustic streaming on crystal nucleation growth, heat transfer and liquid flow are systematically summarized. Finally, a concise perspective is provided for its future advances.

Probability Distribution of Extreme Events in a Baroclinic Wave Laboratory Experiment

Atmospheric westerly jet streams are driven by temperature differences between low and high latitudes and the rotation of the Earth. Meandering jet streams and propagating Rossby waves are responsible for the variable weather in the mid-latitudes. Moreover, extreme weather events such as heat waves and cold spells are part of the jet stream dynamics. For many years, a simple analog in the form of a simplified laboratory experiment, the differentially heated rotating annulus, has provided insight into the dynamics of the meandering jet stream. In the present study, probability density distributions of extreme events from a long-term laboratory experiment are studied and compared to the atmospheric probability density distributions. Empirical distributions of extreme value monthly block data are derived for the experimental and atmospheric cases. Generalized extreme value distributions are adjusted to the empirical distributions, and the distribution parameters are compared. Good agreement was found, but the distributions of the experimental data showed a shift toward larger extreme values, and some explanations for this shift are suggested. The results indicate that the laboratory model might be a useful tool for investigating changes in extreme event distributions due to climate change. In the laboratory context, the change can be modeled by an increase in total temperature accompanied by a reduction in the radial heat contrast.

Export and bioaccumulation of methylmercury in streams draining distinct soils in the Central Brazilian Amazon, 2012-2013

BackgroundUpland forest streams of the Central Amazon are unique aquatic systems.These small streams have short, unpredictable and multimodal flood-pulses that are influenced by local rainfall. The biogeochemical cycles in these systems are almost unknown. This study investigated the role of soil type on the export and bioaccumulation of methylmercury (MeHg) in upland forest streams of the Central Amazon during a complete annual cycle. Basic ProceduresLimnological measurements and water samples for MeHg analyses were collected monthly from October 2012 to October 2013 in two headwater streams drained by different soil types, spodzol (Campina Stream) and oxisol (Barro Branco Stream), in natural forest reserves. Shrimp and fish were collected for total mercury (THg) in April 2013 in both streams. Main findingsMeHg in water varied from 0.04 to 0.50 ng/L in the Campina Stream and between <detection limit and 0.04 ng/L in Barro Branco Stream. Physical characteristics of soils and the interaction between mercury and organic matter influenced the methylation of mercury and its export to the streams. In both streams, MeHg export was highest during the rainy season, probably due to soil leaching, lateral flooding and soil hydromorphism during this period, processes conducive to mercury methylation and export. THg in shrimps (omnivores) and carnivorous fish, which fed on aquatic food items, reflected the MeHg differences between streams while those in insectivorous fish, feeding on allochthonous food items, did not. Principal ConclusionsMeHg dynamics in streams were influenced by the physical characteristics of basin soils and by local seasonal rainfall.

On the Relation Between Active Network Length and Catchment Discharge.

The ever‐changing hydroclimatic conditions of the landscape induce ceaseless variations in the wet channel length (L) and the streamflow (Q) of a catchment. Here we use a perceptual model to analyze the links among (and the drivers of) four descriptors commonly used to characterize discharge and active length dynamics in streams, namely the L(Q) relationship and the cumulative distributions of local persistency, flowrate and active length. The model demonstrates that the shape of the L(Q) law is defined by the cumulative distribution of the specific subsurface discharge capacity along the network, a finding which provides a clue for the parametrization of L(Q) relations in dynamic streams. Furthermore, we show that L(Q) laws can be constructed combining the streamflow distribution with disjoint active length data. Our framework links previously unconnected formulations for characterizing stream network dynamics, and offers a novel perspective to describe the scaling between wet length and discharge in rivers.

Abundance, Restoration, and Transport of Unanchored Large Wood in a Small River in Central Idaho

AbstractRemoval of large wood along and within streams has disrupted processes that are essential for the establishment of important habitat for fish in many areas. Therefore, habitat improvement activities often include addition of large wood to streams. Historical timber harvests in portions of the Yankee Fork drainage reduced the abundance of large wood in these areas compared to areas that have not experienced harvest. In this study, large wood was added to the Yankee Fork to simulate wood recruitment to the stream by natural processes, including streamside trees falling into the stream, avalanches, and debris flows. The added wood was not buried, anchored, or purposefully wedged to prevent movement. Therefore, natural stream dynamics could reposition the wood, resulting in natural fish habitat. The abundance of large wood in the treatment reaches, although not static, was maintained over multiple years despite the occurrence of a near 25‐year high‐flow event. Tracking of 20 radio‐tagged pieces of added large wood over 5 years revealed a maximum transport distance of 940 m, with most pieces moving &lt;28 m in any given year. The results of the present study demonstrate that large‐wood abundance in a small river, increased by simulating natural processes, can be maintained at levels observed in similar reference areas despite high flows and some wood transport. The restoration approach proposed in this study is appropriate for small rivers on public or undeveloped private land; however, caution should be exercised in rivers where man‐made infrastructure could be damaged by unanchored large wood.

Organic matter seasonality and ecosystem metabolism in two tropical first-order streams

Dissolved and particulate organic matter are the energy source for secondary production in forested streams. Cycling of or¬ganic matter and stream ecosystem functioning are linked to organic matter input and storage capacity and timing. This study assessed the seasonal variation (dry and rainy seasons) of environmental parameters, organic matter stock and input, and stream metabolism in two first-order tropical streams in the Selva Lacandona, Mexico. We also aimed to identify the drivers of organic matter and stream metabolism seasonality. We found seasonal variation in organic matter stock and input correlated with trop¬ical seasonality. Dissolved organic matter and seston increased in the rainy season, while benthic primary producers and leaf litter stock and input increased in the dry season correlated with lower water discharge. Gross primary production increased in the dry season, while ecosystem respiration did not differ between seasons. Seasonality defined by the rainfall pattern and its effect on stream hydrology is the main driver of organic matter dynamics in tropical streams. However, environmental parameters and organic matter stock and input were not good predictors of stream metabolism.

Spatial and Seasonal Variations in the Bacterial Community of an Anthropogenic Impacted Urban Stream.

Environmental changes and human activities can alter the structure and diversity of aquatic microbial communities. In this work, we analyzed the bacterial community dynamics of an urban stream to understand how these factors affect the composition of river microbial communities. Samples were taken from a stream situated in Buenos Aires, Argentina, which flows through residential, peri-urban horticultural, and industrial areas. For sampling, two stations were selected: one influenced by a series of industrial waste treatment plants and horticultural farms (PL), and the other influenced by residential areas (R). Microbial communities were analyzed by sequence analysis of 16S rRNA gene amplicons along an annual cycle. PL samples showed high nutrient content compared with R samples. The diversity and richness of the R site were more affected by seasonality than those of the PL site. At the amplicon sequence variants level, beta diversity analysis showed a differentiation between cool-season (fall and winter) and warm-season (spring and summer) samples, as well as between PL and R sites. This demonstrated that there is spatial and temporal heterogeneity in the composition of the bacterial community, which should be considered if a bioremediation strategy is applied. The taxonomic composition analysis also revealed a differential seasonal cycle of phototrophs and chemoheterotrophs between the sampling sites, as well as different taxa associated with each sampling site. This analysis, combined with a comparative analysis of global rivers, allowed us to determine the genera Arcobacter, Simplicispira, Vogesella, and Sphingomonas as potential bioindicators of anthropogenic disturbance.