Stream Width Research Articles

A 50 µm acoustic resonator microchannel enables focusing 100 nm polystyrene beads and sub-micron bioparticles

The manipulation and focusing of submicron/nanometre-scale objects are becoming increasingly important in the fields of biology, chemistry, and materials science. Acoustofluidics provides for the high throughput and precise manipulation of cells and particles with simple equipment. However, application to submicron/nanoparticles is challenging due to the particle volume dependence of the acoustic radiation force and the relatively larger effect of the viscous drag force on small objects. Here, we present an acoustofluidic device that can focus submicron/nanoparticles, bacterial cells, and extracellular vesicles (EVs) using a high-frequency two-dimensional acoustic standing wave. We fabricate 50 µm × 50 µm square cross-section channels as acoustic resonators and generate a two-dimensional acoustic standing wave at an actuation frequency of 14.9 MHz. This configuration enables a strong acoustic radiation force towards the centre of the microchannel and a cross-section-centred single-vortex stream that does not counteract the acoustic radiation force. Using this device, polystyrene beads ranging in diameter from 50 to 500 nm were focused toward the channel centre, where a focused bead stream width of less than 5 µm was achieved at a flow rate of 3 µL min−1 for 100 nm beads and 9 µL min−1 for 200 nm beads. Furthermore, bacterial cells were successfully focused at a flow rate of 40 µL min−1, and the focusing of EVs was also demonstrated. Our acoustofluidic device can become a promising tool for a wide range of biological analyses targeting submicron cells, viruses, and EVs.

Numerical and experimental investigation of aerosol jet printing

A two-dimensional computational fluid dynamics model is presented to elucidate the fundamental aerodynamic phenomena dictating the morphology of aerosol jet printed features. Under compressible and laminar flow assumptions, governing equations were numerically solved to calculate crucial flow variables at discrete points throughout the fluid domain. Randomized single-factor numerical experiments were performed to unravel the role of volumetric flow rates of sheath gas, carrier gas, flow focusing ratio, overall gas flow rate, and aerosol droplet diameter. A Lagrangian discrete phase model was implemented to predict the trajectories of aerosol streams through the fluid domain at several process conditions. A mathematical model for predicting the width of the aerosol stream at the nozzle exit is also presented. Additionally, polydispersity in the droplet diameter distribution was modeled using the Rosin-Rammler distribution, and the role of the minimum droplet diameter in a polydisperse stream of aerosols in causing overspray is discussed. Overall, the numerical results showed good agreement with experimental measurements from an ultrasonic aerosol jet printing (AJP) system, making the computational framework a valuable tool for optimizing the printing process and for predicting the occurrence of printing defects.

Distribution patterns at different spatial scales reveal reproductive isolation and frequent syntopy among divergent lineages of an amphipod species complex in Western Carpathian streams

AbstractRecent discoveries of vast cryptic diversity among various aquatic invertebrates pose a challenge for understanding their ecology and biodiversity patterns, as well as for conservation. We studied the distribution, potential hybridization and habitat preferences of divergent lineages of the hyperdiverse Gammarus fossarum species complex (Crustacea: Amphipoda) in their contact zone in the Western Carpathians (Central Europe), to obtain insights into processes that may influence lineage coexistence. We initially screened over 60 sites to assess the regional distribution, confirming the presence of four lineages in streams of the study area. Two to three lineages were found to be syntopic at almost half the sites. Subsequently, nine such localities were studied in detail for the mesohabitat distribution (fast vs. slow water flow), pairing preferences, and temporal stability of the Gammarus community. A significant fraction of regional spatial variation was explained by the position in the dendritic river network, altitude, stream width, and anthropogenic stress. At the local scale, however, we did not find differences in distribution between mesohabitats with contrasting flow rates. Mixed precopulatory pairs in syntopy were extremely rare, even under highly imbalanced lineage ratios, confirming a strong prezygotic reproductive barrier between the studied lineages. This was congruent with species delimitation analyses using molecular markers, which confirmed the absence of any recent gene flow. The frequent and apparently temporally stable syntopy of these reproductively isolated Gammarus lineages warrants further research on the processes that may facilitate this coexistence, focusing on potential finer differences in their ecology, functional morphology, or biotic interactions.

On the application of sound radiation force for focusing of powder stream in directed energy deposition

One of the challenges in directed energy deposition via powder feeding (DED-PF) is the powder stream divergence that results in low catchment efficiency (i.e., the fraction of particles added to the melt pool). This article introduces a new ultrasound-based powder focusing method referred to as ultrasound particle lensing (UPL), tailored for powder used in DED-PF. The method uses an ultrasound phased array to produce a small volume of high-intensity ultrasound with the required period averaged sound intensity profile. UPL was used to acoustically focus streams of Ti64 and SS 316L particles with an average size of 89μm and a particle speed of 0.6 m/s, exiting from a DED-PF nozzle analog. The e−1 powder stream widths downstream of the resulting force fields for both materials were reduced by 30%. The experimental results closely match Lagrangian and Eulerian simulations of the process. This novel setup offers the possibility of fast control of the powder stream divergence angle and effective diameter in the process zone during the DED-PF process. This will in turn improve the feature resolution and catchment efficiency of the process.

Effect of topographical features on hydrologically connected riparian landscapes across different land-use patterns in colossal dams and reservoirs

Topographic features impact the riparian landscape, which shapes reservoir ecosystems. We know little about ecological network parameter (ENP) responses to topographical features (riparian width, stream-channel width, slope, and elevation) from three land-use areas (rural, urban, and rural-urban transitional) in larger dams and reservoirs globally. This study used a field-based approach with 305 transects on an inundated area of 58,000 km2 inside the Three Gorges Dam Reservoir (TGDR) in China. We discovered that topographical features influenced ENPs differently, involving parameters of plant cover, regeneration, exotics, erosion, habitat, and stressors. As per the Pearson correlation (p < 0.05), riparian width had the most significant effect on transitional ENPs and the least impact on urban ENPs. Riparian width showed the most important influence on the parameters of exotics (with r ≤ −0.44) and erosion (r ≤ 0.56). In contrast, stream-channel widths had the greatest effect on rural ENPs and the least on urban and transitional ENPs. The erosion parameters were the most affected (r ≤ −0.26) by stream width. The slope showed relationships with the fewest ENPs in all three areas and influenced the stress (with a range of −0.51 <r < 0.85) and erosion (r ≤ −0.39) parameters. The impact of elevation was higher in urban areas and was positively correlated with the parameters of plant cover (r ≤ 0.70), erosion (r ≤ 0.58), and habitat (r ≤ 0.69). These results justify the policy emphasis on riparian areas that are managed using the same techniques, which generally ignores their topographical features.

Environmental thresholds of dragonflies and damselflies from a Cerrado-Caatinga ecotone.

Aquatic ecosystems are affected by different land uses that modify gradients of environmental conditions. These impacts act directly on the community structure, especially the most sensitive ones, such as aquatic insects. Thus, dragonflies have been used as good models to assess these changes, since their suborders Anisoptera and Zygoptera have different ecophysiological and behavioral requirements. This study aimed to evaluate the following hypotheses: (1) dragonfly species composition differs along the environmental gradients of streams; therefore, we expect a higher proportion of species of the suborder Anisoptera in environments with a higher degree of disturbance, since these environmental conditions select heliothermic species with exophytic oviposition; (2) the reduction of habitat integrity and canopy cover will lead to a lower richness of the Zygoptera suborder, due to the restrictions of its thermoregulation and oviposition behavior in relation to Anisoptera, since the higher light input would favor heliothermic and exophytic species; (3) alterations in habitat integrity create ecological thresholds and points of change in the abundance and frequency of Odonata species, generating gradients in the environmental integrity conditions. Specimens were collected from 24 streams (first to third order), in a gradient of land uses. Canopy cover and stream width were predictors of taxonomic richness and abundance of the suborders Anisoptera and Zygoptera, with greater coverage and smaller width, positively affecting Zygoptera and negatively Anisoptera. The turning points were determined by a habitat integrity index, where below 0.38 there is an increase in generalist taxa and a decline in sensitive taxa. On the other hand, above 0.79, there was a sensitive taxa increase in detriment of generalists. Four individual taxa indicators were selected, two of which associated with a negative response (Perithemis tenera and Acanthagrion aepiolum) and two with positive responses (Epipleoneura metallica and Zenithoptera lanei) for habitat integrity. Our results are important to guide management strategies, recovery, and protection policies for areas of permanent protection, aiming to conserving biodiversity and natural resources essential to life quality maintenance.

Fish Species Composition, Distribution and Community Structure in Relation to Environmental Variation in a Semi-Arid Mountainous River Basin, Iran.

We analyzed spatial variation in fish species richness and community composition in the Karun River basin, Iran. Knowledge about fish diversity in the basin is incomplete and varies widely along spatial and temporal scales: The Karun is the longest river in Iran (950 km) with the largest drainage area (about 67,000 km2). Fish samples were collected from 54 sites from July through August 2019 using a backpack electro-fisher. Physico-chemical and habitat parameter data collected at each site included pH, conductivity (μS/cm), dissolved oxygen (mg/L), water temperature (°C), turbidity (NTU), stream width (m), stream depth (m), water velocity (m/s) and elevation (m). In total, 37 species were collected (5241 individuals weighing 110.67 kg). The species collected represented 12 families and 27 genera. A total of 13 endemic species (35.14%), 16 native species (43.24%), and eight non-native species (21.62%) were recorded. Diversity indices were calculated and used to measure the spatial variation in community composition. Relationships between native and endemic species assemblage structure and environmental descriptors were assessed using canonical correspondence analysis (CCA). The first two axes of the canonical correspondence analysis explained 62.57% of the variation in the data. Of the nine environmental descriptors analyzed, eight significantly affected species distribution; however, electrical conductivity and elevation were most influential. Our study provides up-to-date status information on the distribution of freshwater fishes in the Karun River basin. This information is essential for developing conservation and management strategies to support the long-term sustainability of fish populations in the Karun River basin.

River sensing: the inclusion of red band in predicting reach-scale types using machine learning algorithms

ABSTRACT This study aims to predict channel unit types (CUTs) by combining remotely sensed data with morphological variables using machine learning algorithms (random forest, support vector machines, multiple adaptive regression splines, extreme gradient boosting and adaptive boosting) within the Upper Ogun River Basin, Southwestern Nigeria. In achieving the aim of this study, we identified the most important variable(s) in CUT discrimination using the random forest – recursive feature elimination (RF-RFE). A total of 249 cross-sections across 83 reaches were sampled during the fieldwork. Landsat 8 and Sentinel-1 bands were retrieved for days the fieldwork was carried and mosaiced using the Google Earth Engine platform. The RF-RFE identified five top variables (accuracy: 0.79 ± 0.14; kappa: 0.39) discriminating the CUT as dimensionless stream power, slope, width, wetted perimeter and Band 4. In essence, there is much hope in the use of remote sensing in CUT mapping at the reach scale.

Basin‐scale estimates of greenhouse gas emissions from the Mara River, Kenya: Importance of discharge, stream size, and land use/land cover

AbstractGreenhouse gas fluxes (CO2, CH4, and N2O) from African streams and rivers are under‐represented in global datasets, resulting in uncertainties in their contributions to regional and global budgets. We conducted year‐long sampling of 59 sites in a nested‐catchment design in the Mara River, Kenya in which fluxes were quantified and their underlying controls assessed. We estimated annual basin‐scale greenhouse gas emissions from measured in‐stream gas concentrations, modeled gas transfer velocities, and determined the sensitivity of up‐scaling to discharge. Based on the total annual CO2‐equivalent emissions calculated from global warming potentials (GWP), the Mara basin was a net greenhouse gas source (294 ± 35 Gg CO2 eq yr−1). Lower‐order streams (1–3) contributed 81% of the total fluxes, and higher stream orders (4–8) contributed 19%. Cropland‐draining streams also exhibited higher fluxes compared to forested streams. Seasonality in stream discharge affected stream widths (and stream area) and gas exchange rates, strongly influencing the basin‐wide annual flux, which was 10 times higher during the high and medium discharge periods than the low discharge period. The basin‐wide estimate was underestimated by up to 36% if discharge was ignored, and up to 37% for lower stream orders. Future research should therefore include seasonality in stream surface areas in upscaling procedures to better constrain basin‐wide fluxes. Given that agricultural activities are a major factor increasing riverine greenhouse gas fluxes in the study region, increased conversion of forests and agricultural intensification has the possibility of increasing the contribution of the African continent to global greenhouse gas sources.

Using Automated Seepage Meters to Quantify the Spatial Variability and Net Flux of Groundwater to a Stream

AbstractWe utilized 251 measurements from a recently developed automated seepage meter (ASM) in streambeds in the Nebraska Sand Hills, USA to investigate the small‐scale spatial variability of groundwater seepage flux (q) and the ability of the ASM to estimate mean q at larger scales. Small‐scale spatial variability of q was analyzed in five dense arrays, each covering an area of 13.5–28.0 m2 (169 total point measurements). Streambed vertical hydraulic conductivity (K) was also measured. Results provided: (a) high‐resolution contour plots of q and K, (b) anisotropic semi‐variograms demonstrating greater correlation scales of q and K along the stream length than across the stream width, and (c) the number of rows of points (perpendicular to streamflow) needed to represent the groundwater flux of areas up to 28.0 m2. The findings suggest that representative streambed measurements are best conducted perpendicular to streamflow to accommodate larger seepage flux heterogeneity in this direction and minimize sampling redundancy. To investigate the ASM's ability to produce accurate mean q at larger scales, seepage meters were deployed in four stream reaches (170–890 m), arranged in three to six transects (three to eight points each) per reach across the channel. In each reach, the mean seepage flux from ASMs was compared to the seepage flux from bromide tracer dilution. Agreement between the two methods indicates the viability of a modest number of seepage meter measurements to determine the overall groundwater flux to the stream and can guide sampling for solutes and environmental tracers.

The Pristine survey – XVII. The C-19 stream is dynamically hot and more extended than previously thought

ABSTRACT The C-19 stream is the most metal-poor stellar system ever discovered, with a mean metallicity [Fe/H] = −3.38 ± 0.06. Its low metallicity dispersion (σ[Fe/H] &amp;lt; 0.18 at the 95 per cent confidence level) and variations in sodium abundances strongly suggest a globular cluster origin. In this work, we use Very Large Telescope (VLT)/UV–Visual Echelle Spectrograph (UVES) spectra of seven C-19 stars to derive more precise velocity measurements for member stars, and to identify two new members with radial velocities and metallicities consistent with the stream’s properties. One of these new member stars is located 30° away from the previously identified body of C-19, implying that the stream is significantly more extended than previously known and that more members likely await discovery. In the main part of C-19, we measure a radial velocity dispersion σv = 6.2$^{+2.0}_{-1.4}{\rm \, km\, s^{-1}}$ from nine members, and a stream width of 0.56° ± 0.08°, equivalent to ∼158 pc at a heliocentric distance of 18 kpc. These confirm that C-19 is comparatively hotter, dynamically, than other known globular cluster streams and shares the properties of faint dwarf galaxy streams. On the other hand, the variations in the Na abundances of the three newly observed bright member stars, the variations in Mg and Al for two of them, and the normal Ba abundance of the one star where it can be measured provide further evidence for a globular cluster origin. The tension between the dynamical and chemical properties of C-19 suggests that its progenitor experienced a complex birth environment or disruption history.

Interaction between droplets and co-flow interface in a microchannel: Droplet migration and interfacial deformation

We investigate hydrodynamic interactions between droplets and the interface of two co-flowing immiscible streams in a microchannel. We find that small droplets of confinement ratio (drop size to suspending stream width), $\ensuremath{\beta}&lt;0.5$ migrate towards the co-flow interface while larger droplets of $0.5&lt;\ensuremath{\beta}&lt;1$ unexpectedly drift away from the interface. Large droplets with $\ensuremath{\beta}&gt;1$ cause deformation waves in an initially stable and flat interface that propagate downstream akin to traveling peristaltic waves. The deformation wave amplitude associated with a droplet grows spatially downstream but remains the same for a train of droplets crossing a fixed location, indicating convective instability.

Gulf Stream Position, Width, and Orientation Estimated from HF Radar Radial Velocity Maps off Cape Hatteras, North Carolina

Abstract A method to extract characteristics of the Gulf Stream (GS) surface flow field using high-frequency radar (HFR)–derived currents is described. Radial velocity measurements, from radar installations near Cape Hatteras, North Carolina, serve as input, chosen because of the greater spatial and temporal coverage provided compared to total velocity fields. The landward GS edge, jet axis, orientation, and cyclonic shear zone (CSZ) width are identified along bearings within the radar footprint. The method is applied to observations from two radar installations from November 2014 and provides GS estimates with daily temporal resolution. Results along eight bearings provide a consistent representation of GS variability dominated by the passage of meanders. Average distance to the GS edge along bearings varies from 50 to 100 km; distance estimate quality degrades with range from the radars. Monthly mean GS jet axis locations from satellite sea surface height (SSH) and the algorithm are consistent. Cross correlations between estimates of GS characteristics in the same region vary from 0.37 to 0.73 for the GS edge. Estimates of radar distance to the GS edge are negatively correlated with current velocity measurements nearest the surface from a moored 150-kHz acoustic Doppler current profiler and vary between −0.58 and −0.71. GS CSZ width metrics range from mean values of 29–31 km. Daily GS orientation estimates are affected by the crossing angle of the radial bearing relative to the GS. Lags from the cross correlations of monthly mean properties suggest meander propagation speed estimates increase from 43.2 km day−1 south of the cape, to 136.8 km day−1 just east of it.

Stream broadening in free flow affinity electrophoresis

Complexation plays a vital role in a variety of chemical and biological systems. Thus, our ability to reliably measure the equilibrium and kinetic parameters governing complexation reactions is crucial to comprehending important natural and artificial processes. Free-Flow Affinity Electrophoresis or FFAE offers a simple and powerful approach to measuring complexation parameters at high throughputs over a wide range of experimental conditions. However, the range and accuracy of analytical information that can be extracted from these affinity measurements remains limited due to significant knowledge gaps in our understanding of analyte transport in FFAE systems. To fill this gap in knowledge, the current article describes a mathematical formulation for quantitating stream broadening in FFAE assays. A closed-form expression has been derived for the stream width based on this formulation in the Taylor-Aris dispersion limit assuming fast analyte-ligand binding kinetics. It has been shown that the effects of affinity interactions on the stream dispersion in FFAE devices can be described using four terms that are additive to the contributions observed in conventional free-flow electrophoresis. Notably, all these additional terms were determined to scale with the square of the distance migrated by the analyte stream in the lateral direction. Moreover, they were shown to vary inversely with the Damköhler number in the system computed as the ratio of the rate of reaction over that of diffusive mass transfer.

Evaluation of sunlight penetration through riparian forest and its effects on stream biota

Riparian streams contain various types of terrestrial organic and inorganic matter that are continuously transported from hillsides. Riparian forest forms alongside streams and blocks direct sunlight. It also supports the formation of various in-stream habitats, leading to the diversification of in-stream benthic invertebrates. In this study, sunlight passing through riparian forest canopy was measured and its relationship with the biota in the stream was analysed. Then, the light conditions favourable to stream biota were clarified for the purpose of riparian forest management. Differences in light conditions, chlorophyll a levels, and the richness of benthic invertebrates were observed, even in areas with stream widths of less than 5 m. As the canopy was closed in the upper stream area, intense sunlight was required to increase the solar radiation and chlorophyll a levels. Family richness was related to amounts of chlorophyll a. In contrast, in lower stream areas, because of the many gaps in the forest canopy, intense light was not necessary to increase the solar radiation, amounts of chlorophyll a, or family richness. Afternoon sunlight led to greater illuminance and higher chlorophyll a levels than did morning sunlight. The riparian forest on the west side of the stream was essential, as it blocked strong direct afternoon sunlight in summer. In riparian forest management, sunlight direction should be considered while paying attention to the composition of riparian forest. • Chlorophyll a levels differed even in areas with stream widths of less than 5 m. • Benthic invertebrates also differed even in areas with stream widths of less than 5 m. • Intense sunlight was required to increase solar radiation and chlorophyll a levels. • Afternoon sunlight led to greater illuminance and higher chlorophyll a levels. • For the riparian forest management, sunlight direction should be considered.

Evaluation of the prediction capability of AHP and F-AHP methods in flood susceptibility mapping of Ernakulam district (India)

Floods are one of the frequent natural hazards occurring in Kerala because of the remarkably high annual rate of rainfall. The objective of this study is to prepare the flood susceptibility maps of Ernakulam district by integrating remote sensing data, GIS, analytical hierarchy process (AHP), and fuzzy-analytical hierarchy process methods. Ernakulam is one of Kerala's most flood-prone districts. The development of this map can help to raise awareness about the risks of flooding. Factors such as slope angle, soil types (texture), land use/land cover, stream density, water ratio index, normalized difference built-up index, topographic wetness index, stream power index, aspect, and sediment transport index have been selected. The area of the final maps is grouped into five flood susceptible zones, ranging from very low to very high. The major reasons for flood occurrence in Ernakulam district are the combined effect of multiple factors such as excess silting, reduction of stream width due to anthropogenic activities, and changes in land cover and land-use pattern, lower slope, higher soil moisture content, lower stream capacity, and poor infiltration capacity of soils. The prepared map was validated using the receiver operating characteristic (ROC) curve method. The area under the ROC curve (AUC) values of 0.75 and 0.81 estimated by the ROC curve method for the AHP and F-AHP methods are considered acceptable and excellent, which confirms the prediction capability of the prepared maps. The very high susceptible zone constitutes around 19% of the district. This map is useful for land-use planners and policymakers to adopt strategies that will reduce the impact of flood hazards and damage in the future.

The Effects of Livestock, Proximity to Trees, and Aquatic Characteristics on the Abundance of Ambystoma Altamirani within a Stream

The endangered, endemic salamander, Ambystoma altamirani, is distributed in streams in the Transvolcanic Belt around Mexico City. Like other Mexican ambystomatids, A. altamirani is threatened by several anthropogenic stressors, including land use changes. Here we examine how aspects of the terrestrial habitat, such as the distance to wooded habitats and the presence of livestock, as well as several aspects of the aquatic habitat, affect the abundance of adult and larval A. altamirani along the Arroyo los Axolotes. The presence of livestock and proximity to the nearest trees did not affect the abundance of adult or larval A. altamirani. The abundance of adult A. altamirani was positively associated to the proportion of visits with water, mean total dissolved solids, mean stream width, mean bank height, and mean water velocity, and negatively related to mean water temperature and mean water depth. The abundance of larvae was not related to any measured variables. In conclusion, the abundance of A. altamirani along the Arroyo los Axolotes is primarily associated with aquatic factors, with limited influence of terrestrial factors. From a conservation and management perspective it is imperative to conserve the aquatic characteristics of streams where A. altamirani is found.

Conditions to Preserve the Sedimentary Record of Channel Planforms in Temperate Rivers of the Northern Hemisphere

AbstractWe aim to identify conditions that influence the preservation of a complete record of channel planforms in the topmost layer of floodplains, prior to the maintenance in the rock record. We have tested a hypothesis that a successive decrease of stream power and channel belt width are necessary to preserve the record of channel planforms in the topmost floodplain layer over 103 to 104‐year time scales. A literature review was conducted for rivers of the temperate zone of the Northern Hemisphere. Stream power, valley, and channel belt widths, paleodischarges, sediment grain‐size, and age of paleochannels were used to identify four groups of rivers with preservation potential ranging from tens of thousands years to annual time scales. The decrease in stream power followed by sustained low stream power, and successive decrease of channel belt width were identified in rivers preserving a 103 to 104‐year record of channel planforms. River valleys with the record of at least two generations of paleochannels, and valley width/channel belt width ratios between 6 and 12, potentially preserve fluvial records over 103 to 104‐year time scales. We analyzed unusually well‐preserved records of channel planforms from the Obra and Sió Rivers (central Europe). A determination of trends in changes of stream power and channel belt widths based on an extensive set of geophysical, geological data, and sediment dating from earlier studies, confirmed the tested hypothesis. The proposed framework can be extended by fluvial records preserved by large, and coastal rivers, with the potential to include ancient fluvial records.

Joint-species analysis reveals potential displacement of native fishes by non-native fishes within the Santa Ana River, California

Accurate estimates of abundance are a cornerstone for resource managers to make effective decisions for fish conservation. However, multiple sampling methods often are required to sample fish communities and ignoring the detection process can create substantial bias in latent state parameter estimation (e.g., abundance, survival). We developed a joint-species N-mixture model that integrated snorkel, seining, and electrofishing surveys to estimate factors affecting native and non-native fish distributions in the Santa Ana River, California. We found through data integration that native Santa Ana sucker (Catostomus santaanae) and arroyo chub (Gila orcuttii) were most abundant in wide stream channels, and the abundance of both native fishes were negatively correlated with non-native largemouth bass (Micropterus salmoides). Our results highlight the power of integrating multiple data sets into a single analysis and incorporating among-species correlation into abundance modeling. Our results also highlight a pattern of native fish declines that coincide with an expanding largemouth bass population, a concern for the management of native aquatic communities within the Santa Ana River.

From the Fire: A Deeper Look at the Phoenix Stream

Abstract We use 6 yr of data from the Dark Energy Survey to perform a detailed photometric characterization of the Phoenix stellar stream, a 15° long, thin, dynamically cold, low-metallicity stellar system in the Southern Hemisphere. We use natural splines, a nonparametric modeling technique, to simultaneously fit the stream track, width, and linear density. This updated stream model allows us to improve measurements of the heliocentric distance (17.4 ± 0.1 (stat.) ±0.8 (sys.) kpc) and distance gradient (−0.009 ± 0.006 kpc deg−1) of Phoenix, which corresponds to a small change of 0.13 ± 0.09 kpc in heliocentric distance along the length of the stream. We measure linear intensity variations on degree scales, as well as deviations in the stream track on ∼2° scales, suggesting that the stream may have been disturbed during its formation and/or evolution. We recover three peaks and one gap in linear intensity along with fluctuations in the stream track. Compared to other thin streams, the Phoenix stream shows more fluctuations and, consequently, the study of Phoenix offers a unique perspective on gravitational perturbations of stellar streams. We discuss possible sources of perturbations to Phoenix, including baryonic structures in the Galaxy and dark matter subhalos.