Abstract Purpose Eutrophication and nuisance filamentous algal blooms (i.e. Cladophora ) are increasingly common occurrences throughout much of the western United States. Wildfire may be contributing to the frequency and magnitude of algal blooms through excess sediment and nutrient loading to streams and rivers. Our objective was to evaluate the effects the 2021 Woods Creek Fire had on sediment yields and phosphorus (total and bioavailable) partitioning in Camas Creek, a major tributary to the Smith River in Montana where Cladophora are now consistently reaching nuisance levels. Methods We collected water quality samples during snowmelt pulsing events as well as fixed interval sampling using an established U.S. Geological Survey stream gage instrumented with a continuous water quality sonde and an automatic peristaltic pump sampler. Water samples were processed for total phosphorus (TP), sediment-bound bioavailable phosphorus (S-BioP), soluble reactive phosphorus (SRP), and suspended sediment concentrations and were evaluated using linear regression and other nonparametric statistical tests. Continuous turbidity and streamflow were evaluated using hysteresis analysis to determine sediment sourcing and connectivity. Results We found that the Woods Creek Fire did not significantly influence TP and S-BioP in Camas Creek. However, there was a significant increase in SRP and turbidity in both postfire years (2022 and 2023). Hysteresis analysis of 91 delineated events indicated positive (clockwise) hysteresis was the dominant event pattern during the snowmelt period. This may indicate a lower hillslope to channel connectivity, with the major sediment supply originating from the channel and/or riparian areas. Conclusion Results from this study demonstrate the benefits of combining discrete water quality samples with high-frequency turbidity sensors to characterize postfire sediment and phosphorus dynamics. While a lack of postfire response in TP and S-BioP is contrary to many other studies, our findings highlight the role climate and catchment morphology play in attenuating a disturbance effect.

We determined the movement patterns of three abundant salmonids-Brown Trout (Salmo trutta), Mountain Whitefish (Prosopium williamsoni), and Rainbow Trout (Oncorhynchus mykiss)-in the Smith River watershed of Montana. We tagged 7,172 fish with passive integrated transponder (PIT) tags, monitored their movements past 15 stationary PIT arrays over four years, and located tagged fish between arrays by conducting mobile surveys. Movement patterns varied seasonally, among species, and among locations. Movement was greatest in the middle portion of the watershed, which included a pristine main-stem canyon and lower reaches of major tributaries. Fish rarely left the canyon, but movement into the canyon from other regions was common. Mountain Whitefish were most likely to move, and Brown Trout were least likely to move. Most fish travelled < 10 km, but some fish travelled over 100 km. Distinct movement patterns were not evident; rather, a continuous spectrum of movement behaviors was apparent. Movements by Mountain Whitefish and Rainbow Trout increased during their spawning periods. Movements peaked when mean daily water temperatures were between 11.3-17.1°C. Movements were diverse and probably contributed to metapopulation dynamics, population resiliency, and species diversity. Fish movements along stream networks connect populations across diverse landscapes, and therefore protecting and restoring stream connectivity along inland streams such as the Smith River is critical to maintaining productive fish assemblages.

Abstract Objective This study compares the probability of detecting juvenile Coho Salmon Oncorhynchus kisutch using both environmental DNA (eDNA) techniques and underwater visual count (UVC) surveys in northern California rivers. Here, UVC surveys commonly have detection probabilities (p) surpassing 0.90, providing an ideal setting to examine the performance of newer eDNA methods. We also evaluate the potential for using eDNA concentrations to predict the count of Coho Salmon within pool habitats. Methods We conducted paired eDNA and UVC surveys in 96 pools across 25 stream reaches within the Smith River basin, California. Method-specific p and the effect of environmental covariates were estimated using multiscale occupancy modeling. We used generalized linear models to evaluate the relationship of fish counts to eDNA concentrations and habitat covariates. Result The eDNA and UVC methods showed a high degree of agreement in detecting the presence of Coho Salmon within a pool (93% agreement) and survey reach (80% agreement). Detection probabilities for eDNA (peDNA) and for UVC (pUVC) were similar and high at median levels of pool residual depth and contributing basin area (peDNA = 91%, pUVC = 89%). Contributing basin area (a proxy for discharge) had a strong, negative effect that was more pronounced for peDNA than for pUVC (e.g., in the largest basins, peDNA = 34% whereas pUVC = 77%). We did not find eDNA concentrations to be a good predictor of Coho Salmon counts in small pools. Conclusion This study demonstrates that eDNA methods yielded nearly identical results to UVC surveys in catchments &amp;lt;36 km2 and can provide a highly effective approach for determining the distribution of Coho Salmon. However, additional investigation is required before eDNA could be used to estimate relative abundance in small pools.

Western Pearlshell (Margaritifera falcata) Extirpation in the Smith River, Montana, with a Possible Link to Warming Water Temperatures

Hybridization between coastal cutthroat trout (Oncorhynchus clarkii clarkii) and steelhead (O. mykiss) was assessed in the Smith River, California. Individuals were categorized as pure or as 1 of 10 hybrid classes using 30 "diagnostic" single-nucleotide polymorphisms positioned on 26 separate chromosomes. Most of the individuals examined (n = 876), were pure coastal cutthroat trout (n = 634) or pure steelhead (n = 213), and 29 individuals were identified as having hybrid ancestry. Among hybrids, first generation hybrids (n = 15) and coastal cutthroat trout backcrosses (n = 12) were the most common. No individuals were identified as backcrosses to SH, suggesting the presence of genetic or behavioral mechanisms constraining such backcrosses, or the growth and survival of their progeny. Mitochondrial DNA of 14 of 15 F1 hybrids was of steelhead origin, suggesting that hybridization was driven primarily by sneak-mating of male coastal cutthroat trout with female steelhead. Evaluation of classical phenotypic characters for coastal cutthroat trout and steelhead (i.e. jaw slash, maxillary length, and hyoid teeth) were not reliable by themselves for identification of either pure parental fish or hybrids. In contrast, analysis with geometric morphometrics revealed distinctive body shapes for pure coastal cutthroat trout and steelhead, and the combination of classical traits and geometric morphology was mostly accurate in distinguishing them. However, first generation hybrids and backcrosses overlapped completely with parental types, highlighting challenges in hybrid identification using phenotypic traits.

Species assemblages composed of non-native and native fishes are found in freshwater systems throughout the world, and interactions such as interspecific competition that may negatively affect native species are expected when non-native species are present. In the Smith River watershed, Montana, rainbow trout were introduced by 1930. Native mountain whitefish and non-native rainbow trout have presumably occurred in sympatry since the introduction of rainbow trout; however, knowledge about how these two species compete with one another for food resources is sparse. We quantified diet compositions of rainbow trout and mountain whitefish in the mainstem Smith River and in a tributary to the Smith River—Sheep Creek—to determine the degree of overlap in the diets of mountain whitefish and rainbow trout in the Smith River and between the mainstem Smith River and a tributary stream. Rainbow trout and mountain whitefish had generalist feeding strategies, which probably contribute to the amicable coexistence of these species. Diet overlap between rainbow trout and mountain whitefish was high (Pianka’s index value = 0.85) in the Smith River and moderate in Sheep Creek (Pianka’s index value = 0.57). Despite overlap in diets, some resource partitioning may alleviate resource competition (e.g., rainbow trout consumed far more Oligochaeta than mountain whitefish but fewer Brachycentridae and Chironomidae). Diet composition of rainbow trout and mountain whitefish did not differ greatly between the Smith River and Sheep Creek. Prey categories most commonly used by mountain whitefish at the population and individual levels (i.e., Ephemeroptera and Trichoptera) are sensitive taxa and many species within these orders have experienced extinctions and population declines. Therefore, future changes in resource availability or competition could be of concern.

Abstract Adult salmonid migration to natal habitats and spawning are affected both by physiological factors and environmental conditions. While research has focused on physiological thresholds that influence the initiation of migration, few studies have investigated the relationship between both hydrological and thermal conditions and salmon spawning throughout the course of the reproductive period. We examined whether Oregon coastal coho salmon (Oncorhynchus kisutch) returning to three tributaries of the Smith River watershed (in the central Oregon Coast Range) responded to the stream hydroregime throughout their spawning period. Generalised linear mixed models were constructed to evaluate relationships between various stream discharge metrics, water temperature and redd count data collected between 2010 and 2016. Across the three sub‐basins we analysed, discharge and temperature metrics were important in explaining redd construction timing. However, the same parameters were not consistently important for every sub‐basin. Water temperature was important in explaining redd construction in the largest sub‐basin, North Sister Creek, and discharge metrics were consistently important in Beaver Creek, the smallest sub‐basin. At the sub‐basin scale, peak redd construction by coho salmon starts after increase in discharge (25th percentile) occurs but before the highest discharge events take place. However, synchrony among sub‐basins was evident in delayed redd construction during 2013 when the autumn rains were delayed. Understanding relationships between the timing of redd construction and characteristics of the hydrological regime are critical to analysis of potential future climate impacts on all life stages of Oregon Coastal coho salmon.

Identification of introduced species can be important to understanding ecological systems and meeting conservation and management goals, but the process can be surprisingly challenging. The Klamath smallscale sucker Catostomus rimiculus seems likely to be native to the Smith River because the drainage separates two basins believed to be within the fish's native range, the Rogue and Klamath rivers. Further, C. rimiculus is broadly distributed in the Smith River, and the indigenous Dee-ni' People of the Smith River have a unique word for sucker. Nonetheless, a historical survey of fishes that described C. rimiculus from the Rogue and Klamath rivers did not include C. rimiculus among the fishes of the Smith River. To determine whether the genetic structure of the Smith River C. rimiculus reflects expectations for a native sucker population, the authors of this study examined variation in microsatellite and mitochondrial genetic markers from the Smith River and surrounding drainages. The genetic analyses revealed a pattern consistent with extreme founder effects in Smith River C. rimiculus, as would be expected from a single introduction of six or fewer effective individuals. The sharing of a high-frequency haplotype between the Smith River and Klamath River that is not detected in the Rogue River suggests the Klamath River as the likely source for the introduction. The findings highlight that local-scale introductions can be easily overlooked because the newly established populations can appear to be parts of contiguous natural distributions.

Reviewed by: Surrender: The Call of the American West by Joanna Pocock O. Alan Weltzien, emeritus Joanna Pocock, Surrender: The Call of the American West. Toronto: House of Anansi Press, 2019. 373 pp. Paper, $22.95 CAN; e-book, $18.95 CAN. Londoner Joanna Pocock’s journalistic memoir joins an increasingly rich genre of trans-Atlantic interpretations of whatever the American West is becoming in the early twenty-first century. Pocock announces straightaway, “The mid-life crisis package I was handed came in a box marked with one simple word: Montana” (2). Pocock, her husband Jason, and young daughter Eve quit the city and spent two years (2014–16) residing in Missoula. She confesses to nomadism though she’s called London home for a quarter century, and during this period (as well as at least one subsequent trip), she ranges into central Oregon and Washington backcountry, following a series of “rewilders.” Her love and longing for Big Sky Country feels as palpable as her growing disillusionment with London. Pocock’s voice joins an old international chorus, entranced by the monumentality of western [End Page 91] American landscapes: “The vastness, the inscrutability of so much space, performs an act of initiation. It does things to you that cannot be undone” (364). Hers is a Missoula-centric version of Montana, and her version of the American West tracks both familiar and obscure topics. She and her family witness wolves in Yellowstone’s Lamar Valley, and she spends time with the Buffalo Field Campaign (and “Buffalo Bridge Collective”) outside Gardner, Montana. The annual bison culling and annual conflict between the stockgrower-led state forces and the federal agencies is old news. She reviews the Tintina Corporation’s proposed copper mine (the “Black Butte Project”) near Montana’s beloved Smith River as well as restoration efforts by Trout Unlimited upstream and downstream from Missoula. Oddly, Pocock doesn’t cover the removal of the Milltown Union Dam (2008) and subsequent Clark Fork River restoration projects. Farther afield, she glances at North Dakota’s Standing Rock protests (342–26) and the notorious Rajneesh community near Antelope, Oregon, in the early 1980s (309–11). Pocock unduly focuses upon certain fringe groups who might be lumped under the umbrella notion of survivalists. But most of her survivalists are not white supremacist groups whose loud online noise masks their tiny numbers: the sort of fringes tracked by organizations such as the Montana Human Rights Network. The 3 Percenters, or “Threepers,” fall under this category, and her closing scene of the Boundary County (Idaho) Fair highlights the booths of the NRA, tragically mainstream, as well as the “Oath Keepers” (359–62). It’s no surprise that Pocock surveys the annual Rainbow Gathering. She’s much more intrigued by a few rewilders who have adopted, in sundry ways, a hunter-gatherer ethos and not only live off the grid but forage for their “Paleo diet.” She profiles, for example, Peter Michael Brown, part of “Rewild Portland,” who leads a basket weaving workshop, and spends much more time with Finisia Medrano, a sixty-one-year-old rewilder who, over years and decades, lives “on the hoop.” It’s hard to see Medrano, a caustic, transgendered stoner specializing in digging biscuit root and planting seeds of edible wild plants, as the positive role model she becomes for Pocock. Despite Pocock’s admiring reference to [End Page 92] John Lanchester’s article about hunter gatherers (The New Yorker, 18 Sept. 2017), Medrano and her ilk lack the personal appeal let alone the audience Euell Gibbons commanded two generations ago. Lanchester’s claim— “‘It turns out that hunting and gathering is a good way to live. . . . The lives of most of our progenitors were better than we think’”— seems dubious at best. Pocock overstates the case when she claims, “So many of these fringe outliers are now having their cries taken up by academics and writers.” Here’s the issue, as she concedes: “We can’t all live as hunter-gatherers” (295). No kidding. Nor would most folks willingly adopt the tribal style “fringe outliers” and “hunter-gatherers” depend upon. That said, there is much to admire about widely disseminated knowledge of edible plants— what...

Abstract The movement patterns of native migratory fishes may reflect different selection pressures in different environments that are associated with predictable patterns of temperature and discharge. Spatial and temporal variability in the movement patterns of adult Coho Salmon Oncorhynchus kisutch were explored with data that were collected from the Umpqua River basin, Oregon, focusing on two points in their return migration: (1) main‐stem midriver migration timing of adult Coho Salmon as they pass Winchester Dam, Oregon, and (2) adult spawn timing in tributary streams of the Smith River. Main‐stem migration of Coho Salmon as they pass Winchester Dam began 7 to 15 d after peak annual water temperature, when mean daily temperatures cooled to 18°C, but before the increases in discharge that are associated with autumn rains. Although migration timing appeared to be strongly related to river temperature, spawn timing of Coho Salmon in tributaries of the Smith River subbasin appeared to respond to a combination of both discharge and temperature thresholds. Spawning occurred after initial annual peak discharge events and when stream temperatures fell below a threshold of 12°C. These results directly inform water conservation and protection planning for environmental flow criteria and thermal ranges during migration and spawn timing of imperiled Coho Salmon in the Oregon Coast Range.

Abstract The Smith River is a popular recreational sport fishery in western Montana, but salmonid abundances there are thought to be artificially limited by riparian land‐use alterations, irrigation water withdrawals, and high summer water temperatures. We used integrated networks of temperature loggers, PIT tag antenna stations, and in situ temperature mapping to investigate the thermal hydrodynamics and associated movements of PIT‐tagged salmonids at the confluence of Tenderfoot Creek, a major, unaltered coldwater tributary of the Smith River. Contrary to expectations, Tenderfoot Creek itself was not used as a thermal refuge by salmonids during periods of high water temperatures in Smith River; rather, its cool outflow plume into the main stem was used instead. Mean daily outflow water temperatures averaged 2.9°C lower than those of the Smith River during summer and ranged from 0.5°C to 6.1°C lower. Moreover, measured and estimated temperatures in the outflow were cooler (by up to 2.8°C) than in Tenderfoot Creek itself at times as a result of groundwater upwelling at the confluence. Detections of PIT‐tagged fish in the thermal plume increased, especially at night, when daily mean water temperatures exceeded 20°C in the main‐stem Smith River; more than four times as many PIT‐tagged fish were detected in the plume (N = 52) than along the opposite bank (N = 12), which ostensibly afforded better cover. Coldwater tributary confluences may provide superior thermal refuges for salmonids—cooler than the tributaries themselves—when water temperatures in river main stems are stressful.

Abstract Contact metamorphism associated with mafic intrusives is one of several mechanisms that has been invoked to produce extensive high‐temperature (HT) metamorphism and associated partial melting of the crust. Indisputable evidence for polymetamorphism in these settings can be difficult to decipher because both melt loss and retrogression (i.e. rehydration) can erase or obscure the records of earlier HT metamorphism by modifying HT mineral parageneses and compositions. Here, a combination of detailed field and petrographical observations, inverse mineral thermometry, and thermodynamic forward modelling is used to delineate the polymetamorphic history of migmatites from the Smith River Allochthon (SRA) in the central Appalachians. Bulk rock geochemical data suggest that some metapelitic samples lost a significant amount of melt during interpreted contact metamorphism with the Rich Acres gabbro, resulting in a residual bulk composition (&lt;50 wt% SiO2, ~30 wt% Al2O3). Garnet cores (Grt1) in SiO2‐depleted samples are interpreted to grow during this HT contact metamorphism, with Fe‐Ti oxide thermometry on spinel inclusions in Grt1, cordierite–garnet thermometry, and thermodynamic forward modelling constraining peak P–T conditions during contact heating of the migmatites to ~800ºC and ∼0.5 GPa. This is associated with an inferred peak assemblage prior to melt loss of crd+kfs+pl+grt+bt+spl (mag+usp+hc)+ilm+sil+qtz+melt. Garnet in SiO2‐depleted samples has a distinct high‐Ca rim (Grt2), which appears to record a younger metamorphic event. A combination of substantial melt loss and later rehydration appears to be a major control on the ability of SiO2‐depleted samples to faithfully record evidence for this polymetamorphism. The tectonic implications of this younger metamorphic event are not entirely clear, but it appears to record renewed burial and heating of the SRA sometime after the Taconic orogeny, which may be related to either the neo‐Acadian or Alleghanian orogenies.

We present a taxonomic revision of the black salamander (Aneides flavipunctatus) complex of northwestern California and extreme southeastern Oregon. The revision is based on a number of published works as well as new molecular and morphological data presented herein. The subspecies Aneides flavipunctatus niger Myers & Maslin 1948 is raised in rank to a full species. It is isolated far to the south of the main range on the San Francisco Peninsula, south and west of San Francisco Bay. Another geographically isolated set of populations occurs well inland in Shasta County, northern CA, mainly in the vicinity of Shasta Lake. It is raised from synonymy and recognized as Aneides iecanus (Cope 1883). The remaining taxa occur mainly along and inland from the coast from the vicinity of the Russian River and Lake Berryessa/Putah Creek, north to the vicinity of the Smith River near the Oregon border and more inland along the Klamath and Trinity Rivers and tributaries into Oregon. The northern segment of this nearly continuous range is named Aneides klamathensis Reilly and Wake 2019. We use molecular data to provide a detailed examination of a narrow contact zone between the northern A. klamathensis and the more southern A. flavipunctatus in southern Humboldt County in the vicinity of the Van Duzen and main fork of the Eel rivers. To the south is the remnant of the former species and it takes the name Aneides flavipunctatus (Strauch 1870). It is highly diversified morphologically and genetically and requires additional study.

Two formerly monotypic lumbriculid genera, Guestphalinus Michaelsen, 1933 and Kincaidiana Altman, 1936, are reviewed using morphological and molecular data, following the discovery of new northwestern, Nearctic species. Several populations of Kincaidiana hexatheca Altman, 1936 were examined, and both morphology and DNA data suggest a single, variable species in Pacific drainages extending from northern California through Washington, USA. Specimens of Kincaidiana from the Smith River drainage with a single, median atrium and differing genetically from K. hexatheca are assigned to K. smithi sp. nov. The chaetal morphology of North American Guestphalinus populations is variable, and two basic morphotypes are assigned to G. elephantinus sp. nov. and G. exilis sp. nov. This decision is supported by molecular data. The tree topology, based on the mitochondrial 16S rRNA and Cytochrome Oxidase I (COI), and the nuclear 28S rRNA gene sequences, confirmed the close phylogenetic relationships among the Nearctic Guestphalinus, Kincaidiana and Uktena Fend, Rodriguez &amp; Lenat, 2015. Probable synapomorphies associating these genera include a filiform, ringed proboscis, a forward shift of reproductive organs relative to the usual position in the family, and spermathecae in the atrial segment.

Evaluating the impact of irrigation on surface water – groundwater interaction and stream temperature in an agricultural watershed

According to the 2005 U.S. Geological Survey national water use compilation, irrigation is the second largest use of fresh water in the United States, accounting for 37%, or 484.48 million cubic meters per day, of total freshwater withdrawal. Accurately estimating the amount of water withdrawals and actual consumptive water use (the difference between water withdrawals and return flow) for irrigation at a regional scale is difficult. Remote sensing methods make it possible to compare actual ET (ETa) rates which can serve as a proxy for consumptive water use from different irrigation regimes at a regional scale in a systematic manner. This study investigates crucial components of water use from irrigation such as the difference of ETa rates from flood- and sprinkler-irrigated fields, spatial variability of ETa within a watershed, and the effect of sprinkler irrigation on the water budget of the study area. The mean accumulated ETa depth for the 1,051 square kilometer study area within the upper Smith River watershed was about 467 mm 30-meter per pixel for the 2007 growing season (April through mid-October). The total accumulated volume of ETa for the study area was about 474.705 million cubic meters. The mean accumulated ETa depth from sprinkler-irrigated land was about 687 mm and from flood-irrigated land was about 621 mm from flood-irrigated land. On average, the ETa rate from sprinkler-irrigated fields was 0.25 mm per day higher than flood-irrigated fields over the growing season. Spatial analysis showed that ETa rates within individual fields of a single crop type that are irrigated with a single method (sprinkler or flood) can vary up to about 8 mm per day. It was estimated that the amount of sprinkler irrigation in 2007 accounted for approximately 3% of the total volume of ETa in the study area. When compared to non-irrigated dryland, sprinkler irrigation increases ETa by about 59 to 82% per unit area.

In this research files article, Shannon Tushingham and Richard Brooks discuss collaborative research on the history of human use of the Hiouchi Flat area near the north bank of the Smith River in California. The authors met in 2003 when Tushingham was conducting archaeological research as a graduate student. Through her research and archaeological work, Tushingham became interested in how the Native community living in the area persisted after Euro-American contact in ways that melded and introduced cultural elements within a traditional Tolowa way of life. The authors document the remembrances and stories of two families — the Cookes and the Catchings — who are examples “of how Tolowa people persisted in the aftermath of the Gold Rush at Hiouchi Flat,” and how “many Indian traditions were passed on because of this persistence.”

Abstract For several species of salmonids, Oncorhynchus and Salvelinus spp., inhabiting Pacific coastal temperate streams, juvenile fish have been recorded moving between main‐stem and tributary habitats during the transition from the summer dry season to the winter wet season. Movement connecting summer and winter habitats may be particularly important for Coho Salmon O. kisutch because availability of overwintering habitat can limit freshwater survival for this species. Here, we describe basin‐scale variability in movement between main‐stem and tributary habitat for juvenile Coho Salmon tagged in the summer with PIT tags and detected in the fall at four stationary detection sites at tributary–main‐stem confluences of the West Fork Smith River, Oregon. We used odds ratios to evaluate spatial patterns in tributary–main‐stem movement across tributary junctions at upper‐river, midriver, and lower‐river locations. Three types of movement were assessed: (1) emigration out of tributaries into the main stem, (2) immigration into a tributary from the main stem downstream from the tributary junction, and (3) immigration from the main stem upstream from the tributary junction. The likelihood of emigration had a distinct spatial pattern. Only at the two upper‐river detection sites were juvenile Coho Salmon more likely to emigrate than immigrate. Fish immigrating into a midriver tributary were more likely to originate from the main stem downstream from the confluence, whereas fish immigrating into two lower‐river tributaries were more likely to originate from the main stem upstream from the confluence. This basin‐scale variation in patterns of immigration and emigration demonstrates complexity in the connectivity of juvenile Coho Salmon seasonal habitats within a stream network. We conclude that effective restoration planning and watershed management should account for the spatial pattern of connectivity of summer‐rearing and overwintering habitat throughout a stream network and consider the full diversity of movement patterns that may be required for fish to access seasonal habitats.Received December 30, 2015; accepted May 4, 2016 Published online August 5, 2016

The hydrologic and physical structure of streams strongly influences the biological composition of benthic macroinvertebrate communities. Research on step–pool systems in high-gradient streams has focused primarily on physical processes rather than on ecological characteristics. This study examined both the biological and physical attributes of 27 step–pool sequences in three steep mountain streams of the Smith River Basin in northern California, USA. Multivariate analysis using non-metric multidimensional scaling (NMS) found a biological separation of step and pool sites (based on benthic macroinvertebrate data) in all three study watersheds. Step habitats had greater taxa richness, diversity, %Plecoptera, %Heptageniidae, %Nemouridae, and %clingers compared to pools. Steps also differed from pools in physical characteristics such as grain size distribution, whereby steps were dominated by boulders compared to pools characterized by gravel and cobbles. Moreover, steps had higher dissolved oxygen, greater water velocity, and shallower water depths compared to pools. NMS ordinations showed a correlation between physical factors and biological communities. These results suggest the ecological importance of step–pools streams, in that the development of step sequences creates and maintains a repetitive pattern of high-quality ecological environments.

Abstract Potholes (circular depressions carved into bedrock) are the dominant roughness elements in many bedrock channels. Here we show, using data from previous studies and new data from the Smith River, Oregon, that pothole depths increase in proportion to both the mean pothole radius (such that the most common pothole depth‐to‐radius ratio is 2) and the diameter of the largest clasts episodically stored in potholes. We present a theory for these observations based on computational fluid dynamics and sediment transport modeling of vortices in cylindrical cavities of different shapes and sizes. We show that the shear stress at the bottom of a pothole (which controls the rate of pothole growth) is maximized for potholes with a depth‐to‐radius ratio of approximately 1 and decreases nonlinearly with increasing depth‐to‐radius ratio such that potholes with depth‐to‐radius ratios larger than 3 are uncommon. Our model provides a mechanistic explanation for pothole shapes and sizes.