Artykuły w czasopismach na temat „Streams”
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Reino, Stella, Robyn E. Sanderson, Nondh Panithanpaisal, Elena M. Rossi i Konrad Kuijken. "Orbital phase-driven biases in galactic mass constraints from stellar streams". Monthly Notices of the Royal Astronomical Society 509, nr 4 (3.11.2021): 5365–81. http://dx.doi.org/10.1093/mnras/stab3176.
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ABSTRACT One of the most promising tracers of the Galactic potential in the halo region is stellar streams. However, individual stream fits can be limited by systematic biases. To study these individual stream systematics, we fit streams in Milky Way-like galaxies from Feedback In Realistic Environments cosmological galaxy formation simulations with an analytical gravitational potential by maximizing the clustering of stream stars in action space. We show that for coherent streams the quality of the constraints depends on the orbital phase of the observed stream stars, despite the fact that the phase information is discarded in action-clustering methods. Streams on intermediate phases give the most accurate results, whereas pericentre streams can be highly biased. This behaviour is tied to the amount of correlation present between positions and momenta in each stream’s data: weak correlation in pericentre streams prohibits efficient differentiation between potentials, while strong correlation in intermediate streams promotes it. Although simultaneous fitting of multiple streams is generally prescribed as the remedy to combat individual stream biases, we find that combining multiple pericentric streams is not enough to yield a bias-free result. We finally show that adopting the two-component Stäckel model does not fundamentally induce a biased mass estimate. With our full data set of two multiwrap streams, we recovered the true rotation curve of the simulated galaxy within $12{{\ \rm per\ cent}}$ over the entire range of radii covered by our set of stars (10–176 kpc) and within $6.5{{\ \rm per\ cent}}$ between the 5 and 95 percentile distance range (23–109 kpc).
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Richmond, Ann D., i Kurt D. Fauseh. "Characteristics and function of large woody debris in subalpine Rocky Mountain streams in northern Colorado". Canadian Journal of Fisheries and Aquatic Sciences 52, nr 8 (1.08.1995): 1789–802. http://dx.doi.org/10.1139/f95-771.
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Large woody debris has been well studied in coastal forests of the Pacific Northwest, but little is known of its role in Rocky Mountain streams. Large woody debris was measured in 11 undisturbed streams draining subalpine old-growth forests in north central Colorado to assess abundance, characteristics, and function. Although large woody debris in Colorado had smaller diameter, length, and volume than in the Pacific Northwest, its abundance and function were similar. The majority of pools (76%) were plunge and dammed pools formed by large woody debris, most of which spanned the channels perpendicular to stream flow. Smaller streams had a greater proportion of such perpendicular pool-forming pieces than larger streams. Four disturbed streams had significantly less and smaller large woody debris than undisturbed streams. Flows in larger undisturbed streams were capable of moving large woody debris, so pieces were more often located at the stream margins, oriented diagonally, or distributed in clumps than in smaller streams. Individual pools were larger and deeper in larger streams, but their size was not related to the size of large woody debris pieces forming them. Therefore, the function of large woody debris in forming fish habitat in small Rocky Mountain streams is strongly influenced by the stream's location within the watershed.
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Licoppe, Christian, i Julien Morel. "Visuality, text and talk, and the systematic organization of interaction in Periscope live video streams". Discourse Studies 20, nr 5 (12.04.2018): 637–65. http://dx.doi.org/10.1177/1461445618760606.
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In this study, we use a conversation analysis framework to understand the systematic organization of interactions in Periscope live video streams, and its crucial features: (a) the talking heads orientation for the video stream, in common with video-mediated communication; (b) the expectation that the streamer should attend to all messages as much as possible; (c) the ‘loose’ organization of viewers’ responses to streamers’ turn-at-talk, as in multi-party chats. We also identify a distinctive design for streamers’ responses to messages, the ‘read-aloud and respond’ practice. These distinctive features are oriented to the highly asymmetrical communicative affordances of Periscope streams. Without precluding other forms of Periscope-based activities, this systematic organization of talk and messages, coupled with the affordances of the application, favors a basic mode of topic initiation resting on a typical and minimal adjacent pair: viewer’s noticing/streamers’ reading and responding. We argue that the particular salience of this organization of topic initiation may account for the emergence of the dominant kind of use for Periscope streams, that is, the online public exposure of youth to strangers in order to elicit some conversation.
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Penaluna, Brooke E., Steve F. Railsback, Jason B. Dunham, Sherri Johnson, Robert E. Bilby i Arne E. Skaugset. "The role of the geophysical template and environmental regimes in controlling stream-living trout populations". Canadian Journal of Fisheries and Aquatic Sciences 72, nr 6 (czerwiec 2015): 893–901. http://dx.doi.org/10.1139/cjfas-2014-0377.
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The importance of multiple processes and instream factors to aquatic biota has been explored extensively, but questions remain about how local spatiotemporal variability of aquatic biota is tied to environmental regimes and the geophysical template of streams. We used an individual-based trout model to explore the relative role of the geophysical template versus environmental regimes on biomass of trout (Oncorhynchus clarkii clarkii). We parameterized the model with observed data from each of the four headwater streams (their local geophysical template and environmental regime) and then ran 12 simulations where we replaced environmental regimes (stream temperature, flow, turbidity) of a given stream with values from each neighboring stream while keeping the geophysical template fixed. We also performed single-parameter sensitivity analyses on the model results from each of the four streams. Although our modeled findings show that trout biomass is most responsive to changes in the geophysical template of streams, they also reveal that biomass is restricted by available habitat during seasonal low flow, which is a product of both the stream’s geophysical template and flow regime. Our modeled results suggest that differences in the geophysical template among streams render trout more or less sensitive to environmental change, emphasizing the importance of local fish–habitat relationships in streams.
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Falke, Jeffrey A., i Keith B. Gido. "Effects of reservoir connectivity on stream fish assemblages in the Great Plains". Canadian Journal of Fisheries and Aquatic Sciences 63, nr 3 (1.03.2006): 480–93. http://dx.doi.org/10.1139/f05-233.
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The upstream effects of reservoirs on stream fish assemblages were highly localized in 3rd- through 5th-order streams in the Great Plains, USA. Streams that differed in connectivity to reservoirs were sampled at their confluences with a river or reservoir and between the confluence and the stream's origin. Sites at confluences had higher total, nonnative, and reservoir species richness than middle sites. Variability in fish assemblage structure upstream of reservoirs was influenced by catchment area, stream size, gradient, and reservoir connectivity. Confluence sites connected to reservoirs were correctly classified based on the presence of red shiners (Cyprinella lutrensis) and bluntnose minnows (Pimephales notatus) and the absence of sand shiners (Notropis stramineus); middle sites on connected streams were classified by the absence of redfin shiners (Lythrurus umbratilis). Intensive sampling across pool habitats within two streams isolated by a reservoir indicated that abundance of common reservoir species was related to pool size, turbidity, and canopy cover, but not proximity to the reservoir. These data suggest that streams connected to reservoirs can maintain diverse native fish communities with minimal invasions by reservoir-dwelling species, but a fraction of the community either has been lost or occurs at low abundance (e.g., sand shiners and redfin shiners).
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Sergeev, V. A., K. Liou, P. T. Newell, S. I. Ohtani, M. R. Hairston i F. Rich. "Auroral streamers: characteristics of associated precipitation,convection and field-aligned currents". Annales Geophysicae 22, nr 2 (1.01.2004): 537–48. http://dx.doi.org/10.5194/angeo-22-537-2004.
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Abstract. During the long-duration steady convection activity on 11 December 1998, the development of a few dozen auroral streamers was monitored by Polar UVI instrument in the dark northern nightside ionosphere. On many occasions the DMSP spacecraft crossed the streamer-conjugate regions over the sunlit southern auroral oval, permitting the investigation of the characteristics of ion and electron precipitation, ionospheric convection and field-aligned currents associated with the streamers. We confirm the conjugacy of streamer-associated precipitation, as well as their association with ionospheric plasma streams having a substantial equatorward convection component. The observations display two basic types of streamer-associated precipitation. In its polewardmost half, the streamer-associated (field-aligned) accelerated electron precipitation coincides with the strong (≥2–7μA/m2) upward field-aligned currents on the westward flank of the convection stream, sometimes accompanied by enhanced proton precipitation in the adjacent region. In the equatorward portion of the streamer, the enhanced precipitation includes both electrons and protons, often without indication of field-aligned acceleration. Most of these characteristics are consistent with the model describing the generation of the streamer by the narrow plasma bubbles (bursty bulk flows) which are contained on dipolarized field lines in the plasma sheet, although the mapping is strongly distorted which makes it difficult to quantitatively interprete the ionospheric image. The convective streams in the ionosphere, when well-resolved, had the maximal convection speeds ∼0.5–1km/s, total field-aligned currents of a few tenths of MA, thicknesses of a few hundreds km and a potential drop of a few kV across the stream. However, this might represent only a small part of the associated flux transport in the equatorial plasma sheet.Key words. Ionosphere (electric fiels and currents). Magnetospheric physics (aurroal phenomena; energetic particles, precipitating)
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He, Mingyang. "Analysis of the Policymaking Process of Undergraduate Tutorial System in China from the Perspective of Multiple Streams Theory". BCP Social Sciences & Humanities 19 (30.08.2022): 171–74. http://dx.doi.org/10.54691/bcpssh.v19i.1601.
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The formulation process of China's undergraduate tutor system involves many factors. Based on the perspective of multiple streams theory, this paper analyzes and discusses the driving factors for the establishment of China's undergraduate tutorial system policy agenda. Policy makers form the problem stream through surveys of students and teachers; the government and colleges, as policy entrepreneurs, shape the policy stream; under the China’s unique conditions, the educational philosophy of the Communist Party of China and the popularization of higher education develops into the politics stream. At a critical point, the three streams are coupled and the policy window opens, which eventually leads to the introduction of the undergraduate tutorial system. Additionally, this paper also analyzes the defects of the multiple stream’s theory, and puts forward suggestions for the revision of the theoretical model.
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Jennings, Jean-Jacques, i Avital Gasith. "Spatial and Temporal Changes in Habitat Conditions in the Na'aman Stream Ecosystem, Israel". Water Science and Technology 27, nr 7-8 (1.04.1993): 387–95. http://dx.doi.org/10.2166/wst.1993.0574.
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Nahal Na'aman is a small, shallow coastal stream in northern Israel. A three year study was conducted to examine the effect of habitat conditions on the biological structure and function of the stream ecosystem. Here we describe temporal and spatial changes in the water regime and water quality as measures of the stream's habitat conditions. Habitat condition is strongly influenced by the hydrological regime and the water quality. In dry years the water level drops and the upper section of the stream may dry up completely. Inflow of polluted water from various sources increasingly reduces water quality downstream. In general, the Na'aman may be categorized as oligo- to mesohaline stream, highly enriched with organic matter and nutrients. Sporadic pollution events markedly affect the water quality resulting in hypertrophic conditions, particularly at times of low stream levels. Low water quality was detected also in association with the drying and refilling of the stream's sections in late summer and in fall, respectively, and following runoff in winter. The oligohaine nature of the stream a priori reduces species diversity relative to other freshwater, lowland streams/Based on water quality conditions, highest species diversity may be expected in the spring area and the upper section of the stream. However, habitat conditions in this section are most unstable due to changes of the hydrological regime. This, in turn, is expected to further reduce species richness and diversity. The extreme conditions are expected to determine the limit for the development of plant and animal life in the stream. This study illustrates the inherent problems of the coastal streams of Israel, namely, diminishing natural flow which is often replaced by discharge of effluent or sewage. Rehabilitation of the Na'aman and other coastal streams demands a radical solution for these problems.
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Lessel, Pascal, Maximilian Altmeyer, Julian Sahner i Antonio Krüger. "Streamer's Hell - Investigating Audience Influence in Live-Streams Beyond the Game". Proceedings of the ACM on Human-Computer Interaction 6, CHI PLAY (25.10.2022): 1–27. http://dx.doi.org/10.1145/3549515.
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In the context of game live-streams, we focus on whether audience influence options can be extended beyond the game, e.g., to the streamers' environment (e.g., controlling their room lighting), the streamers themselves (e.g., activating vibration feedback on their forearms) and the streamers' hardware and peripheral devices (e.g., switching key bindings). An online study (n=81) showed that viewers have mixed feelings and that the context matters, as only a few game genres are assessed as suitable for such an experience. In a lab-study six streamers experienced the idea while playing a horror game. They saw appeal in extending the influence space, but also again highlighted that context matters and customization options are necessary. The studies hint that although this interactivity is from a technical perspective independent of the content streamed, in practice it is not, as the perception is moderated by e.g., the game and why the streamer is playing it.
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Kwon, Youngsang, Youkang Seo i Jihyun Hwang. "Is the High-Density Housing Layout Affected by River Direction? Lessons from Seoul, South Korea". Sustainability 11, nr 11 (28.05.2019): 3013. http://dx.doi.org/10.3390/su11113013.
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This study analyzes apartment building configurations in waterfront residential areas relative to water flow direction and assesses the waterfront impact on apartment construction planning. It surveyed 197 apartment buildings around Yangjaecheon, Gulpocheon, and Anyangcheon, three branches of the Han River, a major South Korean river, to ascertain the correlation between stream flows and apartment building configurations. The apartments were classified into four spatial-configuration categories relative to the adjacent stream’s flow axis—perpendicular, parallel, diagonal, and other—and three orientation categories—east- and/or west-facing, south-facing, and other. South-facing apartments were predominant around west- and north-flowing streams. The proportion of east- and/or west-facing apartments built and the percentage of south-facing apartments were relatively low, indicating that apartment building layouts are more diverse around north-flowing streams than around west-flowing streams. A t-test analysis of east- and south-facing apartments’ proportions relative to stream flow direction was statistically significant, and there were relatively higher percentages of east- and west-facing apartments near north-flowing streams than west-flowing ones. This suggests that the relationship with rivers is still important in urban housing in South Korea, and the importance of landscapes over the river is of increasing significance for planning urban settlements.
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Udy, James White, i Stuart Edward Bunn. "Short Communication: Elevated δ15N values in aquatic plants from cleared catchments: why?" Marine and Freshwater Research 52, nr 3 (2001): 347. http://dx.doi.org/10.1071/mf00002.
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δ15N values of plants and animals are being increasingly used to identify the flow of nitrogen through aquatic ecosystems. The δ15N values of crops, riparian trees, emergent and submerged aquatic vegetation in streams from both cleared (agricultural) and forested (rainforest) catchments were sampled. Riparian and aquatic plants had similar δ15N values in forested streams,suggesting a similar source of inorganic nitrogen.In cleared catchments, however, aquatic plants had δ15N values 4–8‰ higher than adjacent riparian vegetation and aquatic plants from streams in forested catchments. The elevated δ15N values of aquatic vegetation in streams with cleared catchments suggest that these plants either have access to a different source of N than those in undisturbed catchments or that high rates of microbial decomposition and nutrient cycling in the cleared catchments influence the δ15N value of available N. This also suggests that the aquatic plants in disturbed catchments are incorporating a different source of nitrogen than the adjacent riparian vegetation. This supports the proposal that in-stream processing of N affects the δ15N value of available N in streams with cleared catchments. These results begin to identify potential pathways for nitrogen transport to streams and the effect that internal cycling may have on a stream’s nitrogen load.
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Smiley, Peter C., Kevin W. King i Norman R. Fausey. "Public health perspectives of channelized and unchannelized headwater streams in central Ohio: a case study". Journal of Water and Health 8, nr 3 (9.03.2010): 577–92. http://dx.doi.org/10.2166/wh.2010.160.
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Headwater streams constitute the majority of watersheds in the United States and many in the midwest have been channelized for agricultural drainage. Public health implications of water chemistry and aquatic insects within channelized and unchannelized headwater streams have not been explored. We sampled water chemistry and aquatic insects in two channelized and two unchannelized headwater streams in central Ohio from December 2005 until November 2008. Maximum concentrations of ammonium, nitrate plus nitrite, and chlorothalonil were greater in channelized streams. Nitrate plus nitrite and atrazine also exceeded drinking water standards more often in channelized streams. Maximum concentrations of simazine and the percentage of times it exceeded the drinking water standards were greater in unchannelized streams. The predicted hazard potential of nutrient and pesticide mixtures was greater in channelized streams. Mosquito abundance did not differ between stream types. Chironomid abundance was greater in channelized streams. Biting dipterans did not exhibit consistent abundance trends and only differed between stream types in the summer and fall. Our results suggest that if whole stream uptake of nutrients and pesticides is minimal in channelized headwater streams then nutrient and pesticide inputs from these streams may impact downstream drinking water sources. Our results also suggest channelized and unchannelized headwater streams are not serving as a significant source of mosquitoes.
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Pearson, Sarah, Susan E. Clark, Alexis J. Demirjian, Kathryn V. Johnston, Melissa K. Ness, Tjitske K. Starkenburg, Benjamin F. Williams i Rodrigo A. Ibata. "The Hough Stream Spotter: A New Method for Detecting Linear Structure in Resolved Stars and Application to the Stellar Halo of M31". Astrophysical Journal 926, nr 2 (1.02.2022): 166. http://dx.doi.org/10.3847/1538-4357/ac4496.
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Abstract Stellar streams from globular clusters (GCs) offer constraints on the nature of dark matter and have been used to explore the dark matter halo structure and substructure of our Galaxy. Detection of GC streams in other galaxies would broaden this endeavor to a cosmological context, yet no such streams have been detected to date. To enable such exploration, we develop the Hough Stream Spotter (HSS), and apply it to the Pan-Andromeda Archaeological Survey (PAndAS) photometric data of resolved stars in M31's stellar halo. We first demonstrate that our code can re-discover known dwarf streams in M31. We then use the HSS to blindly identify 27 linear GC stream-like structures in the PAndAS data. For each HSS GC stream candidate, we investigate the morphologies of the streams and the colors and magnitudes of all stars in the candidate streams. We find that the five most significant detections show a stronger signal along the red giant branch in color–magnitude diagrams than spurious non-stream detections. Lastly, we demonstrate that the HSS will easily detect globular cluster streams in future Nancy Grace Roman Space Telescope data of nearby galaxies. This has the potential to open up a new discovery space for GC stream studies, GC stream gap searches, and for GC stream-based constraints on the nature of dark matter.
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Pépino, Marc, Marco A. Rodríguez i Pierre Magnan. "Incorporating lakes in stream fish habitat models: are we missing a key landscape attribute?" Canadian Journal of Fisheries and Aquatic Sciences 74, nr 5 (maj 2017): 629–35. http://dx.doi.org/10.1139/cjfas-2016-0221.
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Although lakes and rivers are intimately connected, more effort is needed to develop conceptual approaches accounting for lake–stream interactions within the drainage network. Lakes can buffer the impacts of environmental variability in streams and facilitate stream fish recolonization processes. However, lakes have rarely been incorporated in habitat models for stream fish. We examine whether including the presence of lakes in habitat models can improve our understanding of brook trout (Salvelinus fontinalis) abundance in streams. We quantified brook trout relative abundance in 36 streams over 3 consecutive years by single-pass electrofishing. Relative abundance of brook trout in streams was greatest when lakes were present in the stream network. Lakes had greater influence on relative abundance in headwater streams than in larger streams. These results emphasize the importance of considering lakes as a critical attribute in landscape fish habitat models, many of which focus on terrestrial landscape variables. We discuss potential gains from incorporating the presence of lakes in (i) multiscale habitat models, (ii) analyses of spatiotemporal distribution of thermal refuges, and (iii) metrics of habitat connectivity in lake–stream networks.
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Wood, Petra B., Mack W. Frantz i Douglas A. Becker. "Louisiana Waterthrush and Benthic Macroinvertebrate Response to Shale Gas Development". Journal of Fish and Wildlife Management 7, nr 2 (1.05.2016): 423–33. http://dx.doi.org/10.3996/092015-jfwm-084.
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Abstract Because shale gas development is occurring over large landscapes and consequently is affecting many headwater streams, an understanding of its effects on headwater-stream faunal communities is needed. We examined effects of shale gas development (well pads and associated infrastructure) on Louisiana waterthrush Parkesia motacilla and benthic macroinvertebrate communities in 12 West Virginia headwater streams in 2011. Streams were classed as impacted (n = 6) or unimpacted (n = 6) by shale gas development. We quantified waterthrush demography (nest success, clutch size, number of fledglings, territory density), a waterthrush Habitat Suitability Index, a Rapid Bioassessment Protocol habitat index, and benthic macroinvertebrate metrics including a genus-level stream-quality index for each stream. We compared each benthic metric between impacted and unimpacted streams with a Student's t-test that incorporated adjustments for normalizing data. Impacted streams had lower genus-level stream-quality index scores; lower overall and Ephemeroptera, Plecoptera, and Trichoptera richness; fewer intolerant taxa, more tolerant taxa, and greater density of 0–3-mm individuals (P ≤ 0.10). We then used Pearson correlation to relate waterthrush metrics to benthic metrics across the 12 streams. Territory density (no. of territories/km of stream) was greater on streams with higher genus-level stream-quality index scores; greater density of all taxa and Ephemeroptera, Plecoptera, and Trichoptera taxa; and greater biomass. Clutch size was greater on streams with higher genus-level stream-quality index scores. Nest survival analyses (n = 43 nests) completed with Program MARK suggested minimal influence of benthic metrics compared with nest stage and Habitat Suitability Index score. Although our study spanned only one season, our results suggest that shale gas development affected waterthrush and benthic communities in the headwater streams we studied. Thus, these ecological effects of shale gas development warrant closer examination.
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Harvey, Bret C. "Benthic assemblages in Utah headwater streams with and without trout". Canadian Journal of Zoology 71, nr 5 (1.05.1993): 896–900. http://dx.doi.org/10.1139/z93-117.
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In a series of high-gradient streams along the Wasatch Front in northern Utah, perlid stoneflies were more abundant in benthic samples from 14 fishless streams than in 9 similar streams which contained trout. Smaller-bodied perlodid stoneflies were more abundant in samples from streams containing trout. Herbivorous insect abundances varied substantially within groups of streams containing and lacking trout; multivariate analysis of variance using the six most abundant herbivorous taxa indicated no significant difference between the two groups of streams. Similarly, total numbers of invertebrates did not differ between streams with and without fish. Sites above and below the upstream limit of trout in three streams showed patterns in invertebrate abundances similar to that seen at the whole-stream scale. Trout may have no effect on the overall density of stream benthos because of their negative direct effects on invertebrate predators.
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Dolinsek, Ivan J., Robert L. McLaughlin, James W. A. Grant, Lisa M. O’Connor i Thomas C. Pratt. "Do natural history data predict the movement ecology of fishes in Lake Ontario streams?" Canadian Journal of Fisheries and Aquatic Sciences 71, nr 8 (sierpień 2014): 1171–85. http://dx.doi.org/10.1139/cjfas-2013-0294.
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Little is known about the movements of most stream fishes, so fisheries managers often rely on natural history data from the literature to make management decisions. Observations of over 15 000 individuals from 37 species across 3 years were used to evaluate four aspects of the reliability of literature data for predicting the movement behaviour of stream fishes: (i) water temperature when fish enter streams; (ii) reasons for moving into the streams; (iii) stream residence times of migrants; and (iv) relative use of lake and stream habitats. Comparisons of our data for arrival times in the streams, water temperature at arrival, and time spent in the streams were highly correlated with literature data, whereas relative use of the lake was not. Further, our detailed data revealed two novel findings: (1) in many species juveniles were also moving into streams, even in those species where adults were clearly spawning in the streams; and (2) adult-sized individuals were moving into streams for nonreproductive purposes. Our results suggest that fishery managers can confidently use natural history information to gain general insights into the movement ecology of fishes, but should also recognize that this information remains incomplete in important ways.
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Ludlam, John P., i Allison H. Roy. "Understanding effects of small dams on benthic metabolism and primary production in temperate forested streams". Fundamental and Applied Limnology / Archiv für Hydrobiologie 193, nr 3 (21.04.2020): 227–37. http://dx.doi.org/10.1127/fal/2020/1260.
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Dams can alter the chemical and physical conditions of downstream environments by increasing stream temperatures, altering nutrient limitation, reducing flow variability, and reducing fine sediment deposition. However, little is known about how fundamental stream ecosystem processes like productivity and respiration respond to dams. Nutrient diffusing substrates were installed in three dam streams and three control streams to evaluate the effect of dams on benthic gross primary productivity (GPP), respiration (R), and chlorophyll α production. Dam streams were an average of 5.6 °C warmer than control streams but GPP, R and chlorophyll α were not different between control and dam streams. Phosphorus enrichment increased heterotrophic R relative to controls (~1.8×) but not autotrophic GPP, R or chlorophyll α. Stream nutrient concentrations and nutrient limitation of heterotrophic R were similar in dam and control streams, suggesting that the dams had limited effects on nutrient transport downstream. Autotrophic GPP, R and chlorophyll α were limited by light and varied within and across streams, potentially masking our ability to detect differences caused solely by dams. Dams may alter stream ecosystem func- tion but consideration of other factors associated with and independent of dams is critical for predicting ecosystem responses to dams.
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McNie, Pierce M., i Russell G. Death. "The effect of agriculture on cave-stream invertebrate communities". Marine and Freshwater Research 68, nr 11 (2017): 1999. http://dx.doi.org/10.1071/mf16112.
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The impacts that land-use changes have on cave-stream fauna have not been considered widely in the investigations of land-use impacts on stream ecology. The present study examines how above-ground agriculture may influence cave-stream invertebrate communities. The invertebrate communities in four cave streams and their surface counterparts were sampled in 2014–2015, including two drained predominantly agricultural catchments and two drained forested catchments. These communities were examined alongside habitat and GIS land-use data to determine the relationship between above-ground land use and the stream communities. Invertebrate community composition and ecological health for surface streams was different between the agricultural and forest catchments. These differences were less pronounced within the cave-stream communities. Sedimentation was the principal agricultural stressor in the cave streams. The overall effects of agriculture were lower within the cave streams than on the surface; this is likely to be due to the reduced number of potentially deleterious stressors on cave streams.
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Melody, K. Jill, i John S. Richardson. "Riparian forest harvesting and its influence on benthic communities of small streams of sub-boreal British Columbia". Canadian Journal of Forest Research 37, nr 5 (maj 2007): 907–18. http://dx.doi.org/10.1139/x06-286.
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Forest harvesting in riparian areas can alter the leaf-litter inputs, shading, and stability of small streams, and many of the details of these impacts are known for coastal streams of the Pacific Northwest. However, little is known about how small streams in the drier, continental areas of western North America respond to logging. We conducted a study of paired stream reaches (comparing one recently harvested (≤3 years) reach and two upstream, forested reaches in each of five streams) in which periphyton, detritus, macroinvertebrate abundance and biomass, and physical features were measured in summer and autumn. In general, recently harvested stream sections tended to be wider and contained more riffle areas than the upstream forested sections. The amounts of leaf litter and algae varied among streams and were not consistently greater or lesser in the forested sections than in the harvested sections. Though the variation in amounts within streams was mainly seasonal, amounts differed more among streams than between pairs of harvested and forested reaches. The communities of benthic invertebrates differed significantly between forested and harvested reaches, but often in opposite directions between streams. The magnitude and direction of differences observed between treatments, streams, or seasons were associated with the specific stream and the method of riparian harvesting used.
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HINZE, RALF. "Concrete stream calculus: An extended study". Journal of Functional Programming 20, nr 5-6 (listopad 2010): 463–535. http://dx.doi.org/10.1017/s0956796810000213.
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AbstractThis paper shows how to reason about streams concisely and precisely. Streams, infinite sequences of elements, live in a coworld: they are given by a coinductive datatype, operations on streams are implemented by corecursive programs, and proofs are typically concocted using coinduction. This paper offers an alternative to coinduction. Suitably restricted, stream equations possessunique solutions. This property gives rise to a simple and attractive proof technique, essentially bringing equational reasoning to the coworld. We redevelop the theory of recurrences, finite calculus and generating functions using streams and stream operators, building on the cornerstone of unique solutions. The paper contains a smörgåsbord of examples: we study recursion elimination, investigate the binary carry sequence, explore Sprague-Grundy numbers and present two proofs of Moessner's Theorem. The calculations benefit from the rich structure of streams. As the type of streams is an applicative functor we can effortlessly lift operations and their properties to streams. In combination with Haskell's facilities for overloading, this greatly contributes to conciseness of notation. The development is indeed constructive: streams and stream operators are implemented in Haskell, usually by one-liners. The resulting calculus or library, if you wish, is elegant and fun to use.
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Silva, Daniela M. L., Plínio B. Camargo, William H. Mcdowell, Ivan Vieira, Marcos S. M. B. Salomão i Luiz A. Martinelli. "Influence of land use changes on water chemistry in streams in the State of São Paulo, southeast Brazil". Anais da Academia Brasileira de Ciências 84, nr 4 (grudzień 2012): 919–30. http://dx.doi.org/10.1590/s0001-37652012000400007.
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Streamwater is affected by several processes in the watershed including anthropogenic activities that result in changes in water quality as well as in the functioning of these stream ecosystems. Therefore, this work aims to evaluate the concentration of major ions (Ca2+, Mg2+, Na+, K+, NH4+, NO3-, NO2-, Cl-, SO4(2-), PO4(3-), HCO3-) in streams in the state of São Paulo (southeast Brazil). The sampling sites are located at undisturbed (ombrophilus dense forest, semideciduous forest and savanna - cerrado) and disturbed areas (pasture, urbanization and sugar cane crops). Streamwater chemistry varied according to land use change and, in general, was higher in disturbed sites. Streams located in undisturbed sites at Ribeira de Iguape/Alto Paranapanema watershed (streams 1, 2 and 3) seem to be regulated by soil characteristics, as the disturbed streams located at the same watershed covered by pasture (stream 7) showed high concentration for the most of the variables. Exception to streams located at Pontal do Paranapanema watershed where both disturbed (stream 8) and undisturbed streams (stream 4 and 5) presented similar patterns for almost all variables measured.
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Li, Ting S., Alexander P. Ji, Andrew B. Pace, Denis Erkal, Sergey E. Koposov, Nora Shipp, Gary S. Da Costa i in. "S 5: The Orbital and Chemical Properties of One Dozen Stellar Streams". Astrophysical Journal 928, nr 1 (1.03.2022): 30. http://dx.doi.org/10.3847/1538-4357/ac46d3.
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Abstract We report the kinematic, orbital, and chemical properties of 12 stellar streams with no evident progenitors using line-of-sight velocities and metallicities from the Southern Stellar Stream Spectroscopic Survey (S 5), proper motions from Gaia EDR3, and distances derived from distance tracers or the literature. This data set provides the largest homogeneously analyzed set of streams with full 6D kinematics and metallicities. All streams have heliocentric distances between ∼10 and 50 kpc. The velocity and metallicity dispersions show that half of the stream progenitors were disrupted dwarf galaxies (DGs), while the other half originated from disrupted globular clusters (GCs), hereafter referred to as DG and GC streams. Based on the mean metallicities of the streams and the mass–metallicity relation, the luminosities of the progenitors of the DG streams range between those of Carina and Ursa Major I (−9.5 ≲ M V ≲ −5.5). Four of the six GC streams have mean metallicities of [Fe/H] < −2, more metal poor than typical Milky Way (MW) GCs at similar distances. Interestingly, the 300S and Jet GC streams are the only streams on retrograde orbits in our dozen-stream sample. Finally, we compare the orbital properties of the streams with known DGs and GCs in the MW, finding several possible associations. Some streams appear to have been accreted with the recently discovered Gaia–Enceladus–Sausage system, and others suggest that GCs were formed in and accreted together with the progenitors of DG streams whose stellar masses are similar to those of Draco to Carina (∼105–106 M ⊙).
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Jankowski, Kathi Jo, Linda A. Deegan, Christopher Neill, Hillary L. Sullivan, Paulo Ilha, Leonardo Maracahipes-Santos, Nubia Marques i Marcia N. Macedo. "Land Use Change Influences Ecosystem Function in Headwater Streams of the Lowland Amazon Basin". Water 13, nr 12 (15.06.2021): 1667. http://dx.doi.org/10.3390/w13121667.
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Intensive agriculture alters headwater streams, but our understanding of its effects is limited in tropical regions where rates of agricultural expansion and intensification are currently greatest. Riparian forest protections are an important conservation tool, but whether they provide adequate protection of stream function in these areas of rapid tropical agricultural development has not been well studied. To address these gaps, we conducted a study in the lowland Brazilian Amazon, an area undergoing rapid cropland expansion, to assess the effects of land use change on organic matter dynamics (OM), ecosystem metabolism, and nutrient concentrations and uptake (nitrate and phosphate) in 11 first order streams draining forested (n = 4) or cropland (n = 7) watersheds with intact riparian forests. We found that streams had similar terrestrial litter inputs, but OM biomass was lower in cropland streams. Gross primary productivity was low and not different between land uses, but ecosystem respiration and net ecosystem production showed greater seasonality in cropland streams. Although we found no difference in stream concentrations of dissolved nutrients, phosphate uptake exceeded nitrate uptake in all streams and was higher in cropland than forested streams. This indicates that streams will be more retentive of phosphorus than nitrogen and that if fertilizer nitrogen reaches streams, it will be exported in stream networks. Overall, we found relatively subtle differences in stream function, indicating that riparian buffers have thus far provided protection against major functional shifts seen in other systems. However, the changes we did observe were linked to watershed scale shifts in hydrology, water temperature, and light availability resulting from watershed deforestation. This has implications for the conservation of tens of thousands of stream kilometers across the expanding Amazon cropland region.
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Lapides, Dana Ariel, i Michael Manga. "Large wood as a confounding factor in interpreting the width of spring-fed streams". Earth Surface Dynamics 8, nr 1 (19.03.2020): 195–210. http://dx.doi.org/10.5194/esurf-8-195-2020.
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Abstract. Spring-fed streams throughout volcanic regions of the western United States exhibit larger widths than runoff-fed streams with similar discharge. Due to the distinctive damped hydrograph of spring-fed streams (as compared to large peaks visible in the hydrographs of runoff-fed streams), large wood is less mobile in spring-fed than runoff-fed stream channels, so wood is more likely to remain in place than form logjams as in runoff-fed streams. The consequent long residence time of wood in spring-fed streams allows wood to potentially have long-term impacts on channel morphology. We used high-resolution satellite imagery in combination with discharge and climate data from published reports and publicly available databases to investigate the relationship between discharge, wood length, and channel width in 38 spring-fed and 20 runoff-fed streams, additionally responding to a call for increased use of remote sensing to study wood dynamics and daylighting previously unpublished data. We identified an order of magnitude more logjams than single logs per unit length present in runoff-fed streams as compared to spring-fed streams. Histograms of log orientation in spring-fed streams additionally confirmed that single logs are immobile in the channel so that the impact of single logs on channel morphology could be pronounced in spring-fed streams. Based on these observed differences, we hypothesized that there should be a difference in channel morphology. A model for stream width in spring-fed streams based solely on length of wood is a better model than one derived from discharge or including both discharge and wood length. This study provides insights into controls on stream width in spring-fed streams.
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Shavers, E., i L. Stanislawski. "STREAMS DO WORK: MEASURING THE WORK OF LOW-ORDER STREAMS ON THE LANDSCAPE USING POINT CLOUDS". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-4 (19.09.2018): 573–78. http://dx.doi.org/10.5194/isprs-archives-xlii-4-573-2018.
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<p><strong>Abstract.</strong> The mutable nature of low-order streams makes regular updating of surface water maps necessary for accurate representation. Low-order streams make up roughly half the streams in the conterminous United States by length, and small inaccuracies in stream head location can result in significant error in stream reach, order, and density. Reliable maps of stream features are vital for hydrologic modeling, ecosystem research, and boundary monitoring. High resolution digital elevation models derived from lidar data have shown promise in low order stream modeling yet forested high relief landscapes and low relief agricultural areas remain challenging. Here we present early results from research analyzing lidar point clouds to identify features and patterns that may be used in low-order stream identification and classification in challenging geographic conditions. This work has identified characteristics derived from point clouds that correlate with the presence of streams and stream heads and show promise for mapping small streams. In low topographic relief agricultural areas, cross sections collected at regular intervals along drainage channels extracted as 3D lines show a significant jump in value and variance of profile curvature standard deviation at stream heads. In high relief areas, observations show potential for stream mapping by identifying trends in riparian zone structure. Lidar return point density from riparian vegetation under 30 feet tall dips in the vicinity of intermittent stream heads. Also seen is an increase in point density above 60 feet downstream of stream heads. The trends found here likely reflect a change in vegetation structure relative to the presence of streams.</p>
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Qian, Yansong, Yumna Arshad i Jo Bovy. "The structure of accreted stellar streams". Monthly Notices of the Royal Astronomical Society 511, nr 2 (29.01.2022): 2339–48. http://dx.doi.org/10.1093/mnras/stac238.
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ABSTRACT Many of the Milky Way’s globular clusters are likely accreted from satellite galaxies that have long since merged with the Milky Way. When these globular clusters are susceptible to tidal disruption, this process likely starts already inside the parent satellite leading to an early stellar stream within the satellite. When the parent satellite merges with the Milky Way, the globular cluster and its pre-merger stellar stream are accreted in a somewhat chaotic process. Here, we investigate the properties of the accreted stream after the merger as we would see it today using a suite of simulations of accretion events. We find that the accretion process leads to a wide range of behaviours, but generally scatters the accreted stream over a wide, 2D area of the sky. The behaviour ranges from a set of a few or more well-defined ‘sub-streams’ extending out from the post-merger thin stream by tens of degrees to more widely dispersed debris over much of the sky, depending on how close to the centre of the Milky Way the merger happened. Using mock Gaia-like observations of the simulated streams, we demonstrate that an accreted-stream component can explain the off-track features observed in the GD-1 stream. Sub-streams can appear like thin tidal streams themselves that are seemingly unassociated with the post-merger stream, raising the possibility that some of the progenitor-less streams observed in the Milky Way are part of a single or a few accreted streams created in an ancient merger event.
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Vidotto-Magnoni, Ana Paula, Diego Azevedo Zoccal Garcia, Alexandro Derly Augusto Costa, Jaqueline Garcia de Souza, Marcelo Hideki Shigaki Yabu, Fernanda Simões de Almeida i Mário Luís Orsi. "Ichthyofauna of streams of the Lower Paranapanema River basin, state of Paraná, Brazil". Check List 11, nr 5 (2.10.2015): 1756. http://dx.doi.org/10.15560/11.5.1756.
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Several studies of small watersheds of in the Upper Paraná River basin are currently available. Howev-er, the number and extent of its tributary streams still pose a challenge to enhancing current knowledge of their ichthyofauna. This study aimed to survey the fish fauna of three streams of the Lower Paranapanema River basin, state of Paraná, Brazil (Capim, Tenente and Centenário streams). The sampling included 3,167 specimens belonging to five orders, 17 families and 56 species. The streams presented differences in species richness (Centenário Stream: 41 species; Tenente Stream: 33 species; Capim Stream: 30 species). Two species occurred at all collection sites (Astyanax bockmanni and Hypostomus ancistroides). Nine non-native species were recorded, four of them found exclusive-ly in the Centenário Stream.
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Price, Karen, Arlene Suski, Joanna McGarvie, Barbara Beasley i John S. Richardson. "Communities of aquatic insects of old-growth and clearcut coastal headwater streams of varying flow persistence". Canadian Journal of Forest Research 33, nr 8 (1.08.2003): 1416–32. http://dx.doi.org/10.1139/x03-089.
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Headwater streams, varying in flow persistence from ephemeral to intermittent to perennial, provide the tightest coupling between water and land, yet they often receive the least protection during forest management. We described communities of aquatic insects in perennial, intermittent, and ephemeral channels surrounded by old-growth forest and 4- to 8-year-old clearcuts in Clayoquot Sound, British Columbia, to determine whether temporary streams have unique aquatic communities and to examine the short-term impacts of harvesting. We measured flow persistence, stream size, canopy cover, organic detritus, and algal biomass in 19 streams. We sampled aquatic invertebrates with a combination of emergence cages and kicknet samples. Temporary and old-growth streams had more organic detritus and a higher abundance of shredders. Perennial and clearcut streams had a higher abundance of some algal grazers, but not higher algal biomass. Insect richness was similar in intermittent and perennial streams of each seral stage but lower in ephemeral streams. Intermittent streams contained four taxa not found in the other stream classes; perennial and ephemeral streams had none. Communities of aquatic insects differed between streams surrounded by clearcuts and old growth, and varied with continuity of flow.
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Kraft, Clifford E., Rebecca L. Schneider i Dana R. Warren. "Ice storm impacts on woody debris and debris dam formation in northeastern U.S. streams". Canadian Journal of Fisheries and Aquatic Sciences 59, nr 10 (1.10.2002): 1677–84. http://dx.doi.org/10.1139/f02-129.
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In January 1998, an ice storm damaged forests in northeastern United States and eastern Canada, causing coarse woody debris (CWD) deposition in riparian areas and associated streams. During 1999 and 2000, tree canopy damage, stream physical habitat, and wood deposition were evaluated within 51 first-, second-, and third-order streams located within five eastern Adirondack Mountain watersheds (New York, U.S.A.). In first- through third-order streams, the number and volume of stream debris dams increased in response to streamside trees with canopy damage. Tree canopy damage was not a significant predictor for individual pieces of stream CWD but was correlated with CWD >10 cm in diameter in third-order, but not first-order, streams. At debris dam locations, bankfull width was greater and stream substrates consisted of increased fines. Woody debris resulting from the 1998 ice storm was not associated with increased pool formation; instead, boulders and rocky substrate were the dominant pool-forming elements. CWD length in first-order streams generally exceeded bankfull width, but in third-order streams, CWD length was shorter than bankfull width and therefore was subject to greater transport and accumulation into debris dams. Our results indicate that ice storm disturbances can increase wood inputs to first- through third-order forested stream ecosystems.
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Bulger, Arthur J., Bernard J. Cosby i James R. Webb. "Current, reconstructed past, and projected future status of brook trout (Salvelinus fontinalis) streams in Virginia". Canadian Journal of Fisheries and Aquatic Sciences 57, nr 7 (1.07.2000): 1515–23. http://dx.doi.org/10.1139/f00-086.
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Southern Appalachian streams host a rich diversity of fishes, but the Southern Appalachian Assessment concluded that 70% of stream locations showed significant fish community degradation, partly due to acid deposition. About 40% of total Southern Appalachian trout stream length occurs in Virginia. Our research in Shenandoah National Park, Virginia, has documented both chronic and episodic acidification in streams and brook trout (Salvelinus fontinalis) mortality during acid episodes. Here, we analyze a representative sample of 60 Virginia brook trout streams on noncarbonate bedrock with minimal human disturbance in their watersheds. Of more than 300 such streams in Virginia, only about 50% are currently suitable for brook trout, based on their acidification status. For the population of brook trout streams to which this analysis applies, model-based projections indicate that continued sulfate deposition at 1991 levels will result in about 70 additional streams becoming chronically acidic and unsuitable for brook trout. A 40% reduction will result in about 48 additional chronically acidic streams. Even a 70% reduction will likely result in about 15 additional streams becoming acidified. We conclude that reductions in sulfate deposition greater than 70% (relative to 1991 levels) are needed to prevent more brook trout stream losses in Virginia.
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Zook, H. A., E. Grün, M. Baguhl, D. Hamilton, G. Linkert, J. C. Liou, R. Forsyth i J. L. Phillips. "Jovian Dust Bursts". International Astronomical Union Colloquium 150 (1996): 23–25. http://dx.doi.org/10.1017/s0252921100501201.
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Six streams of dust were unexpectedly detected by the Ulysses dust detector while this spacecraft was approximately within one AU distance from Jupiter (Grün et al., 1993). Stream durations ranged from hours to days for individual streams. It was clear that the dust in these streams (or bursts), from their directionality of approach to the spacecraft and from the nearness of stream occurrences to Jupiter, emanated from the Jovian system.Following the original report, Baguhl et al. (1994) later relaxed the criteria for differentiating true dust impacts from “noise pulses” and found almost triple the number of dust impacts in the six streams already found. They also found 5 more streams that, except for one stream, clearly emanated from the Jovian system. The criteria were relaxed in such a way as to not introduce “noise events” into the data.
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Stenroth, Karolina, Trent M. Hoover, Jan Herrmann, Irene Bohman i John S. Richardson. "A model-based comparison of organic matter dynamics between riparian-forested and open-canopy streams". Riparian Ecology and Conservation 2, nr 1 (3.01.2014): 1–13. http://dx.doi.org/10.2478/remc-2014-0001.
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AbstractThe food webs of forest streams are primarily based upon inputs of organic matter from adjacent terrestrial ecosystems. However, streams that run through open landscapes generally lack closed riparian canopies, and an increasing number of studies indicate that terrestrial organic matter may be an important resource in these systems as well. Combining key abiotically-controlled factors (stream discharge, water temperature, and litter input rate) with relevant biotic processes (e.g. macroinvertebrate CPOM consumption, microbial processing), we constructed a model to predict and contrast organic matter dynamics (including temporal variation in CPOM standing crop, CPOM processing rate, FPOM production, and detritivore biomass) in small riparian-forested and open-canopy streams. Our modeled results showed that the standing crop of CPOM was similar between riparian-forested and open-canopy streams, despite considerable differences in litter input rate. This unexpected result was partly due to linkages between CPOM supply and consumer abundance that produced higher detritivore biomass in the forest stream than the open-canopy stream. CPOM standing crop in the forest stream was mainly regulated by top-down consumer control, depressing it to a level similar to that of the open-canopy stream. In contrast, CPOM standing crop in the open-canopy stream was primarily controlled by physical factors (litter input rates and discharge), not consumption. This suggests that abiotic processes (e.g. discharge) may play a greater role in limiting detrital resource availability and consumer biomass in open-canopy streams than in forest streams. These model results give insight on functional differences that exists among streams and they can be used to predict effects of anthropogenic influences such as forestry, agriculture, urbanization, and climate change on streams and how riparian management and conservation tools can be employed to mitigate undesirable effects.
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Cai, Walter, Philip A. Bernstein, Wentao Wu i Badrish Chandramouli. "Optimization of threshold functions over streams". Proceedings of the VLDB Endowment 14, nr 6 (luty 2021): 878–89. http://dx.doi.org/10.14778/3447689.3447693.
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A common stream processing application is alerting, where the data stream management system (DSMS) continuously evaluates a threshold function over incoming streams. If the threshold is crossed, the DSMS raises an alarm. The threshold function is often calculated over two or more streams, such as combining temperature and humidity readings to determine if moisture will form on a machine and therefore cause it to malfunction. This requires taking a temporal join across the input streams. We show that for the broad class of functions called quasiconvex functions, the DSMS needs to retain very few tuples per-data-stream for any given time interval and still never miss an alarm. This surprising result yields a large memory savings during normal operation. That savings is also important if one stream fails, since the DSMS would otherwise have to cache all tuples in other streams until the failed stream recovers. We prove our algorithm is optimal and provide experimental evidence that validates its substantial memory savings.
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Ice, George G., Jeff Light i Maryanne Reiter. "Use of Natural Temperature Patterns to Identify Achievable Stream Temperature Criteria for Forest Streams". Western Journal of Applied Forestry 19, nr 4 (1.10.2004): 252–59. http://dx.doi.org/10.1093/wjaf/19.4.252.
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Abstract Almost 90% of the streams listed on the EPA's nationwide database as water-quality impaired for temperature are in the Northwest. Historic records, monitoring of streams in federal wilderness areas in Oregon, and available data for least-impaired streams in Oregon, Washington, and Idaho show that many of these streams cannot achieve state temperature criteria. Forest management often is cited as a cause for increased stream temperature above state standards. The expectation that all forested streams should be below state targets has led to unnecessary listing of streams as impaired, wasting limited watershed protection resources. State water-quality programs should base water temperature criteria on natural patterns of stream temperature and on factors that have biological relevance to beneficial uses. West. J. Appl. For. 19(4):252–259.
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DeWalle, David R., Bryan R. Swistock i William E. Sharpe. "Episodic flow–duration analysis: a method of assessing toxic exposure of brook trout (Salvelinus fontinalis) to episodic increases in aluminum". Canadian Journal of Fisheries and Aquatic Sciences 52, nr 4 (1.04.1995): 816–27. http://dx.doi.org/10.1139/f95-081.
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Episodic flow–duration curves were developed that summarize stream flow data by considering the duration of sustained flows at or above specified levels. These curves and relationships between dissolved aluminum concentrations and stream flow were combined for five Appalachian (Pennsylvania) streams to determine the frequency of occurrence of acutely toxic aluminum conditions for brook trout (Salvelinus fontinalis). Concentrations of total dissolved aluminum (AlTD) increased with stream flow in all streams, but reached a plateau or decreased during extreme high flows in some streams. AlTD was dominated by inorganic monomeric species in all streams except Benner Run and Baldwin Creek. Episodic AlTD concentrations and durations were compared with a toxicity curve developed using caged wild and hatchery-reared brook trout. Results predicted that lethal episodes occurred on Linn, Stone, and Roberts runs, but not on Benner Run and Baldwin Creek. With the exception of Stone Run, brook trout populations were largest in streams without predicted lethal episodes (Benner Run and Baldwin Creek) and were smallest in streams with predicted lethal episodes (Linn and Roberts runs). This analysis could be adapted for prediction of toxic conditions in streams for other pollutants where toxicity varies with both concentration and duration of exposure.
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Growns, IO, i JA Davis. "Comparison of the macroinvertebrate communities in streams in logged and undisturbed catchments 8 years after harvesting". Marine and Freshwater Research 42, nr 6 (1991): 689. http://dx.doi.org/10.1071/mf9910689.
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Changes in lotic macroinvertebrate communities 8 years after logging were examined in two sets of paired catchments (Sutton and Lewin) in south-western Western Australia by using analysis of variance, classification (TWINSPAN), and ordination (semi-strong hybrid multidimensional scaling). Both paired catchments contained an undisturbed stream and a stream where clearfelling had been taken to the stream edges. The Sutton catchment also contained a stream where clearfelling had occurred but a 100 m-wide strip of vegetation had been retained as a buffer zone. Differences in richness and abundance of animals between the undisturbed and clearfelled streams in the two catchments were obscured by differences between the sites within each stream. However, ordination of the samples revealed differences in the composition of the macroinvertebrate communities between the clearfelled and undisturbed streams in both catchments. Underlying environmental gradients that separated the invertebrate communities in the clearfelled streams from those in the undisturbed streams, in ordination space, were conductivity, the amount of coarse and fine particulate organic matter, and a reduction in total nitrogen. In all, 11 macroinvertebrate taxa were found to be associated with the separation of samples from the undisturbed and clearfelled streams, this response probably being due to increases in conductivity within the clearfelled streams. Macroinvertebrate community structure in the buffered stream was different from that in the undisturbed stream but was more similar to the latter than to that in the clearfelled stream. Physical and chemical parameters of the buffered stream were also more similar to those of the undisturbed stream. These results indicated that the 100 m-wide buffer zone appeared to be effective in ameliorating any disturbance due to clearfelling.
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Jones, Jeremy B., i Amanda J. Rinehart. "The long-term response of stream flow to climatic warming in headwater streams of interior AlaskaThis article is one of a selection of papers from The Dynamics of Change in Alaska’s Boreal Forests: Resilience and Vulnerability in Response to Climate Warming." Canadian Journal of Forest Research 40, nr 7 (lipiec 2010): 1210–18. http://dx.doi.org/10.1139/x10-047.
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Warming in the boreal forest of interior Alaska will have fundamental impacts on stream ecosystems through changes in stream hydrology resulting from upslope loss of permafrost, alteration of availability of soil moisture, and the distribution of vegetation. We examined stream flow in three headwater streams of the Caribou–Poker Creeks Research Watershed (CPCRW) in interior Alaska over a 30-year period to determine (i) how stream flow varied among streams draining watersheds with varying extents of permafrost and (ii) evaluate if stream hydrology is changing with loss of permafrost. The three streams drained subcatchments with permafrost extents ranging from 4% to 53%. For each stream, runoff data were analyzed by separating base and storm flow contributions using a local-minimum method and with analysis of flood recession curves. Mean daily runoff during the ice-free season did not significantly vary among streams (mean = 0.57 mm·d–1), although the watersheds with lower permafrost had a greater contribution of base flow. Across years, flow was variable and was related with summer temperature in the watershed with low permafrost and with precipitation in the watershed with high permafrost. With climate warming and loss of permafrost, stream flows will become less responsive to precipitation and headwater streams may become ephemeral.
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Tronstad, Lusha, Scott Hotaling, J. Giersch, Debra Finn, Oliver Wilmot i Mark Anderson. "Characterizing Biodiversity of Alpine Streams in Grand Teton National Park, Wyoming". UW National Parks Service Research Station Annual Reports 38 (1.01.2015): 89–98. http://dx.doi.org/10.13001/uwnpsrc.2015.4103.
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The highest rate of climate change is occurring in alpine areas above permanent treeline. The Teton Mountains in northwestern Wyoming are one of these ecosystem and little work has been done on alpine streams in the area. We sampled 6 streams in the Teton Mountains in 2015 at both upper and lower sites. We measured environmental variables (e.g., glacierality index, basic water quality, and temperature), aquatic invertebrate assemblages and microbial diversity. The water sources for sampled streams were glacier-fed, snowmelt and icy-seep. Aquatic invertebrate density (116-11,523 ind/m2) and biomass (31-21,704 mg/m2) varied greatly among streams. Snowmelt streams had the highest biomass of invertebrates, but the density and richness did not differ among stream types. Micrbial diversity in groundwater-fed springs harbored higher diversity than glacier-fed streams. The discovery of an icy-seep stream type lead us to sample rock glacier in the Teton Mountains during 2016. We hope to continue to sample alpine streams in the Teton Mountains to understand how climate change will alter streams of different types.
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Giberson, Donna J., i Rosemary J. Mackay. "Life history and distribution of mayflies (Ephemeroptera) in some acid streams in south central Ontario, Canada". Canadian Journal of Zoology 69, nr 4 (1.04.1991): 899–910. http://dx.doi.org/10.1139/z91-135.
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Life histories and distribution of mayflies (Insecta: Ephemeroptera) were investigated in 11 streams in south central Ontario that ranged from highly acidic to circumneutral. At least 29 mayfly species were recorded from the streams, with 16 common enough for life history analysis. Mayfly distribution and diversity were correlated with pH regime and stream size. No mayflies were found in the smallest, most acid stream, and numbers of mayfly species and their relative abundances generally increased with both increasing stream size and stream pH. Incorporation of life cycle information with distributional data enabled us to determine the precise stream-water pH range encountered by different mayfly life stages in the study streams. Generally, during the period of greatest acid stress in the streams (pH depressions associated with spring snowmelt) the mayflies were present in large or dormant stages, which are believed to be more tolerant of lowered pH.
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Wiliams, I. P. "The Dynamics of Meteoroid Streams". Symposium - International Astronomical Union 152 (1992): 299–313. http://dx.doi.org/10.1017/s0074180900091312.
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Meteor showers are seen at regular and frequent intervals on Earth. They are caused by meteoroids (that is small dust grains) in a coherent stream, all moving on similar heliocentric orbits, burning up on encountering the atmosphere of the Earth. Such streams contain 1012 or more meteoroids, with the mass of the visible meteoroids ranging up to about 1 g. The main evolutionary effect on such streams is gravitational perturbations by the planets. Though grain-grain collision may be catastrophic for the two grains involved, it has no effect on the remainder of the stream, other than the fact that there are now two less grains in it. Solar radiation has some effect, but this can be included in the equations of motion. Because of the large numbers of particles involved, meteoroid streams represent a laboratory where many of our dynamical concepts can be tested.At a basic level, meteoroid streams represent a collective dynamical phenomenon in which all members display roughly the same behavior. One of the fundamental questions which can be investigated is whether the behavior of the mean orbit of the whole stream represents the mean behavior of the stream members. Within the boundaries of some meteor streams lie regions where the orbits are in high order resonance with Jupiter. This also represents a phenomenon of interest. Finally, the possibility exists that some streams are in chaotic regions and it is interesting to investigate whether or not meteoroids in such regions do display chaotic behavior.
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Altuna, Maddi, Eugènia Martí, Francesc Sabater, José Ramón Díez, Joan Lluís Riera, Félix Izco i Arturo Elosegi. "Incorporating In-Stream Nutrient Uptake into River Management: Gipuzkoa Rivers (Basque Country, North Spain) as a Case Study". Sustainability 11, nr 9 (11.05.2019): 2692. http://dx.doi.org/10.3390/su11092692.
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Gipuzkoa (Basque Country, North Spain) is an industrial region where investments in sanitation and wastewater treatment have improved water quality and partially recovered river biological communities. However, further technological improvements are unlikely. Our objective was to assess whether in-stream self-purification may contribute to improvement of the trophic state of rivers. We propose an integrative approach to assessing river water quality, which diagnoses problems, identifies likely causes and prescribes solutions. We first analysed the loads of nutrients transported by Gipuzkoa rivers and compared them with the potential nutrient uptake rates (estimated from published empirical regressions). In reaches where both of them were within one order of magnitude, we considered that the self-purification capacity of river channels may influence nutrient concentrations. Then, we selected some river reaches where no other water quality problems beyond nutrient concentrations occurred and ran the expert system STREAMES 1.0 to diagnose the problems and detect their causes. The studied reaches differed in their problems and in their potential solutions. We empirically determined nutrient retention in two streams by means of mass balances and slug nutrient additions. We detected large differences in retention capacity between reaches and siltation as one of the main problems affecting the self-purification capacity of the study streams. Finally, we used STREAMES 1.0 to identify potential solutions to specific river sections. The results obtained so far point towards an important potential of in-stream bioreactive capacity to reduce nutrient loads and to specific restoration activities that may improve the functionality and trophic status of the streams in Gipuzkoa.
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Lester, Rebecca E., Wendy Wright i Michelle Jones-Lennon. "Does adding wood to agricultural streams enhance biodiversity? An experimental approach". Marine and Freshwater Research 58, nr 8 (2007): 687. http://dx.doi.org/10.1071/mf06198.
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Riparian clearing and the removal of wood from channels have affected many streams in agricultural landscapes. As a result, these streams often have depauperate in-stream wood loads, and therefore decreased habitat complexity and lower levels of in-stream biodiversity. The introduction of wood was investigated as a possible rehabilitation technique for agricultural streams. Wood was re-introduced to eight streams in two separate high-rainfall, intensively grazed regions of Victoria, Australia and the effect on aquatic macroinvertebrate communities was measured. The addition of wood increased overall family richness and the richness of most functional feeding groups occupying edge and benthic habitats within the stream. Wood addition led to less overlap between benthic and edge macroinvertebrate communities, suggesting increased habitat heterogeneity within the stream ecosystem. Of all sampled habitats, wood supported the greatest density of families and was colonised by all functional feeding groups. Wood habitats also had the highest overall richness and supported the most taxa that were sensitive to disturbance. These findings suggest that re-introducing wood to agricultural streams is an appropriate rehabilitation technique where those streams are affected by reduced habitat complexity. Additional work is needed to confirm these findings over larger spatial and temporal scales.
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Sasongko, Arif, I. M. Narendra Kumara, Arief Wicaksana, Frédéric Rousseau i Olivier Muller. "Hardware Context Switch-based Cryptographic Accelerator for Handling Multiple Streams". ACM Transactions on Reconfigurable Technology and Systems 14, nr 3 (30.09.2021): 1–25. http://dx.doi.org/10.1145/3460941.
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The confidentiality and integrity of a stream has become one of the biggest issues in telecommunication. The best available algorithm handling the confidentiality of a data stream is the symmetric key block cipher combined with a chaining mode of operation such as cipher block chaining (CBC) or counter mode (CTR). This scheme is difficult to accelerate using hardware when multiple streams coexist. This is caused by the computation time requirement and mainly by management of the streams. In most accelerators, computation is treated at the block-level rather than as a stream, making the management of multiple streams complex. This article presents a solution combining CBC and CTR modes of operation with a hardware context switching. The hardware context switching allows the accelerator to treat the data as a stream. Each stream can have different parameters: key, initialization value, state of counter. Stream switching was managed by the hardware context switching mechanism. A high-level synthesis tool was used to generate the context switching circuit. The scheme was tested on three cryptographic algorithms: AES, DES, and BC3. The hardware context switching allowed the software to manage multiple streams easily, efficiently, and rapidly. The software was freed of the task of managing the stream state. Compared to the original algorithm, about 18%–38% additional logic elements were required to implement the CBC or CTR mode and the additional circuits to support context switching. Using this method, the performance overhead when treating multiple streams was low, and the performance was comparable to that of existing hardware accelerators not supporting multiple streams.
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Whittier, J. C., S. Nittel i I. Subasinghe. "REAL-TIME EARTHQUAKE MONITORING WITH SPATIO-TEMPORAL FIELDS". ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences IV-4/W2 (20.10.2017): 215–22. http://dx.doi.org/10.5194/isprs-annals-iv-4-w2-215-2017.
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With live streaming sensors and sensor networks, increasingly large numbers of individual sensors are deployed in physical space. Sensor data streams are a fundamentally novel mechanism to deliver observations to information systems. They enable us to represent spatio-temporal continuous phenomena such as radiation accidents, toxic plumes, or earthquakes almost as instantaneously as they happen in the real world. Sensor data streams discretely sample an earthquake, while the earthquake is continuous over space and time. Programmers attempting to integrate many streams to analyze earthquake activity and scope need to write code to integrate potentially very large sets of asynchronously sampled, concurrent streams in tedious application code. In previous work, we proposed the field stream data model (Liang et al., 2016) for data stream engines. Abstracting the stream of an individual sensor as a temporal field, the field represents the Earth’s movement at the sensor position as continuous. This simplifies analysis across many sensors significantly. In this paper, we undertake a feasibility study of using the field stream model and the open source Data Stream Engine (DSE) Apache Spark(Apache Spark, 2017) to implement a real-time earthquake event detection with a subset of the 250 GPS sensor data streams of the Southern California Integrated GPS Network (SCIGN). The field-based real-time stream queries compute maximum displacement values over the latest query window of each stream, and related spatially neighboring streams to identify earthquake events and their extent. Further, we correlated the detected events with an USGS earthquake event feed. The query results are visualized in real-time.
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Scrimgeour, Garry J., William M. Tonn i Nicholas E. Jones. "Quantifying effective restoration: reassessing the productive capacity of a constructed stream 14 years after construction". Canadian Journal of Fisheries and Aquatic Sciences 71, nr 4 (kwiecień 2014): 589–601. http://dx.doi.org/10.1139/cjfas-2013-0354.
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Using natural streams as references against which ecosystem structure and function could be compared, we examined the short-term (1–3 years) and long-term (14 years) effectiveness of a 3.4 km constructed stream in the Northwest Territories, Canada. The constructed stream variously showed little to marked improvements 14 years after construction (2011), relative to 1998–2000 and to reference streams, depending on the stream attribute. Many attributes related to stocks of organic matter remained well below reference levels in the constructed stream after 14 years. Leaf matter processing rates increased in the constructed stream to the point of convergence with reference streams in 2011, but the latter still had superior leaf retention abilities. By Year 14, benthic invertebrate composition in the constructed stream showed some convergence with reference streams, although densities generally lagged, especially in riffles. In 2011, growth of young-of-the-year Arctic grayling (Thymallus arcticus) from the constructed stream was substantially greater relative to 1998–2001, but remained well below contemporary reference levels. Our mixed results raise questions about the definition and time scale of successful restoration.
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Mcintosh, Bruce A. "Debris from Comets: The Evolution of Meteor Streams". International Astronomical Union Colloquium 116, nr 1 (1989): 557–91. http://dx.doi.org/10.1017/s0252921100109832.
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AbstractThe evolution of meteor streams is controlled basically by: (a) the initial velocities with which the particles were ejected from the parent body; (b) gravitational perturbations by the planets; (c) radiation forces; and (d) collisions. This review focuses mainly on recent numerical modelling dealing with (b) and (a).Ejection velocities spread the particles around the orbit, closing the ring in a few tens of revolutions. The greater ejection velocities of smaller particles cause more rapid dispersion both around the orbit and in the cross section.A determination of the effects of gravitational perturbations must take into account the distributed properties of the stream. The stream’s evolution is dependent on the short-term impulse nature of planetary perturbations, as well as on long-term secular effects. The combined effects produce complex stream cross-sections as in the ribbon-like form of the Halley stream (Orionid and η Aquarid showers) or as in the changes in the annual position of peak shower activity shown by the Quadrantids. Perturbations may cause the orbit of a parent body to sweep rapidly across the orbit of the Earth. But the associated particle stream may not be lost as a meteor shower because it tends to become dispersed in a manner that ensures a continuing supply of particles in Earth-crossing orbits. The nodes of the observed meteoroid orbits may show very little motion compared with the rapid motion of the nodes of the orbit of the parent object.Radiation effects contribute to size separation of particles. Very small particles are blown out of the stream or spiral in toward the sun because of Poynting–Robertson drag. Older meteor streams usually show a predominance of large particles.
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Arbaugh, J. Ben, Alvin Hwang, Jeffrey J. McNally, Charles J. Fornaciari i Lisa A. Burke-Smalley. "Discerning citation patterns in dominant BME literature streams: lessons for BME scholars". Organization Management Journal 18, nr 3/4 (6.04.2021): 145–72. http://dx.doi.org/10.1108/omj-06-2020-0967.
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Purpose This paper aims to compare the nature of three different business and management education (BME) research streams (online/blended learning, entrepreneurship education and experiential learning), along with their citation sources to draw insights on their support and legitimacy bases, with lessons on improving such support and legitimacy for the streams and the wider BME research field. Design/methodology/approach The authors analyze the nature of three BME research streams and their citation sources through tests of differences across streams. Findings The three streams differ in research foci and approaches such as the use of managerial samples in experiential learning, quantitative studies in online/blended education and literature reviews in entrepreneurship education. They also differ in sources of legitimacy recognition and avenues for mobilization of support. The underlying literature development pattern of the experiential learning stream indicates a need for BME scholars to identify and build on each other’s work. Research limitations/implications Identification of different research bases and key supporting literature in the different streams shows important core articles that are useful to build research in each stream. Practical implications Readers will understand the different research bases supporting the three research streams, along with their targeted audience and practice implications. Social implications The discovery of different support bases for the three different streams helps identify the network of authors and relationships that have been built in each stream. Originality/value According to the authors’ knowledge, this paper is the first to uncover differences in nature and citation sources of the three continuously growing BME research streams with recommendations on ways to improve the support of the three streams.
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Cecala, Kristen, Michael Dorcas i Steven Price. "Ecology of juvenile Northern watersnakes (Nerodia sipedon) inhabiting low-order streams". Amphibia-Reptilia 31, nr 2 (2010): 169–74. http://dx.doi.org/10.1163/156853810791069029.
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AbstractThe juvenile stage for many reptiles is considered “the lost years” because of low capture probabilities, however understanding factors impacting juvenile survivorship and recruitment is critical for conservation of populations. We studied the ecology of juvenile Northern watersnakes, Nerodia sipedon, by intensively sampling a first-order stream and determined the occupancy of juveniles in 30 low-order streams in the Piedmont of North Carolina. Juveniles were relatively abundant within a single stream (n = 62 ± 9), and their capture probabilities were positively related to increasing stream-water temperatures. We also found that juveniles had high survivorship (ϕ = 0.87 ± 0.017). Occupancy of juvenile N. sipedon in low-order, Piedmont streams may be greater at streams that have confluences with high order streams or lakes, which potentially support adult N. sipedon populations. This study provides important information regarding the natural history of juvenile reptiles and indicates the importance of low order streams as habitat for N. sipedon populations.
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Truffer, Martin, i Keith A. Echelmeyer. "Of isbræ and ice streams". Annals of Glaciology 36 (2003): 66–72. http://dx.doi.org/10.3189/172756403781816347.
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AbstractFast-flowing ice streams and outlet glaciers provide the major avenues for ice flow from past and present ice sheets. These ice streams move faster than the surrounding ice sheet by a factor of 100 or more. Several mechanisms for fast ice-stream flow have been identified, leading to a spectrum of different ice-stream types. In this paper we discuss the two end members of this spectrum, which we term the “ice-stream” type (represented by the Siple Coast ice streams in West Antarctica) and the “isbræ” type (represented by Jakobshavn Isbræ in Greenland). The typical ice stream is wide, relatively shallow (∼1000 m), has a low surface slope and driving stress (∼10 kPa), and ice-stream location is not strongly controlled by bed topography. Fast flow is possible because the ice stream has a slippery bed, possibly underlain by weak, actively deforming sediments. The marginal shear zones are narrow and support most of the driving stress, and the ice deforms almost exclusively by transverse shear. The margins seem to be inherently unstable; they migrate, and there are plausible mechanisms for such ice streams to shut down. The isbræ type of ice stream is characterized by very high driving stresses, often exceeding 200 kPa. They flow through deep bedrock channels that are significantly deeper than the surrounding ice, and have steep surface slopes. Ice deformation includes vertical as well as lateral shear, and basal motion need not contribute significantly to the overall motion. The marginal shear zone stend to be wide relative to the isbræ width, and the location of isbræ and its margins is strongly controlled by bedrock topography. They are stable features, and can only shut down if the high ice flux cannot be supplied from the adjacent ice sheet. Isbræs occur in Greenland and East Antarctica, and possibly parts of Pine Island and Thwaites Glaciers, West Antarctica. In this paper, we compare and contrast the two types of ice streams, addressing questions such as ice deformation, basal motion, subglacial hydrology, seasonality of ice flow, and stability of the ice streams.