Clark Fork River Research Articles

Reducing Total Dissolved Gas and Gas Bubble Trauma in a Regulated River

When water is spilled over dams, atmospheric gases can become entrained, resulting in supersaturated water. Total dissolved gas (TDG) > 110% saturation can cause gas bubble trauma (GBT) in fish. The negative effects of GBT include increased buoyancy, decreased swimming performance, and possible mortality. The lower Clark Fork River (LCFR) in Idaho frequently has TDG > 110% saturation due to the spill at Cabinet Gorge Dam as well as from upstream facilities. Spillway crests on Cabinet Gorge Dam were modified to reduce TDG production and the potential harm from GBT. To evaluate the effectiveness of spillway crest modifications, relationships between river discharge and measured TDG were developed pre- and post-modification and used to calculate the predicted TDG in the LCFR pre- and post-modification under two spill season discharge scenarios. The predicted TDG for the scenarios was used with an established TDG-GBT relationship for the LCFR to estimate the expected GBT incidence. Generally, TDG was lower post-modification, and the discharge at which 110% and 120% saturation were exceeded increased by about 198 m3/s. Modification also reduced the number of days with elevated TDG. The lower TDG post-modification resulted in significant (p < 0.05) reductions in the probability of observing GBT. The modification of Cabinet Gorge Dam spillway crests reduced TDG production over a range of discharges and has resulted in improved conditions for fish downstream of the dam.

Divergent metabolism estimates from dissolved oxygen and inorganic carbon: Implications for river carbon cycling

AbstractRivers efficiently collect, process, and transport terrestrial‐derived carbon. River ecosystem metabolism is the primary mechanism for processing carbon. Diel cycles of dissolved oxygen (DO) have been used for decades to infer river ecosystem metabolic rates, which are routinely used to predict metabolism of carbon dioxide (CO2) with uncertainties of the assumed stoichiometry ranging by a factor of 4. Dissolved inorganic carbon (DIC) has been less used to directly infer metabolism because it is more difficult to quantify, involves the complexity of inorganic carbon speciation, and as shown in this study, likely requires a two‐station approach. Here, we developed DIC metabolism models using single‐ and two‐station approaches. We compared metabolism estimates based on simultaneous DO and DIC monitoring in the Upper Clark Fork River (USA), which also allowed us to estimate ecosystem‐level photosynthetic and respiratory quotients (PQE and RQE). We observed that metabolism estimates from DIC varied more between single‐ and two‐station approaches than estimates from DO. Due to carbonate buffering, CO2 is slower to equilibrate with the atmosphere compared to DO, likely incorporating a longer distance of upstream heterogeneity. Reach‐averaged PQE ranged from 1.5 to 2.0, while RQE ranged from 0.8 to 1.5. Gross primary production from DO was larger than that from DIC, as was net ecosystem production by . The river was autotrophic based on DO but heterotrophic based on DIC, complicating our understanding of how metabolism regulated CO2 production. We suggest future studies simultaneously model metabolism from DO and DIC to understand carbon processing in rivers.

Draft genome of co-cultured Melainabacteria sp. 17Bon1m.

We report the 7.6 Mb draft genome sequence of Melainabacteria sp. strain 17Bon1, which was sequenced from a co-culture with the diatom Rhopalodia gibba collected from the Clark Fork River in Bonita, MT.

Predicting the likelihood of gas bubble trauma in fishes exposed to elevated total dissolved gas in the lower Clark Fork River, Idaho

AbstractObjectiveGas bubble trauma (GBT) can occur in fish when water becomes supersaturated with gases, with effects ranging from minor tissue damage to death. Laboratory studies suggest that fish exposure to elevated total dissolved gas (TDG) at depths that compensate for gas supersaturation can result in reduced GBT incidence and that different fish species exhibit varying susceptibility to GBT. Elevated TDG levels associated with spill at Cabinet Gorge Dam in the lower Clark Fork River, Idaho, facilitated describing the incidence and severity of GBT, variables that affect GBT incidence, and the probability of observing GBT in different fish species.MethodsTotal dissolved gas and GBT data were collected during the typical spill period (i.e., April–July) in 2000, 2006, 2008, and 2017–2021.ResultA total of 6985 fish was examined for GBT at TDG of 101–137% saturation. Incidences of GBT varied with TDG levels, and the greatest incidence of GBT was typically observed near the date with peak daily mean TDG. Logistic regression models indicated that the probability of observing GBT was affected by TDG exposure and temperature but not length. The probability of observing GBT on fish was < 0.01 when 7‐day mean TDG was 110% saturation and < 0.04 when 7‐day mean TDG was 120% saturation. The models also indicated that the probability of observing GBT at a given TDG value differed between fish species.ConclusionWe suggest that species‐specific behavior and habitat composition in the sampled area (i.e., access to compensatory depths and locations with less TDG) were factors in our observations. We advocate that fisheries managers use a similar process to develop site‐ and species‐specific GBT probability curves where elevated TDG is an issue. These site‐specific curves can help managers evaluate the potential for population‐level effects to fisheries and need for TDG reduction or mitigation actions.

A water treatment method utilizing a continuous flow material recovery system to facilitate removal of contaminant ions

A continuous flow material recovery (CFMR) system was investigated for use in tandem with a magnetite (Fe3O4) adsorbent for the removal of contaminant ions from waters. The CFMR was assessed by examining the effects of flow rate, Cu(II) concentration, and Fe3O4 dose. Experiments indicated that low flow rates, under 3 Lpm, were ideal for minimizing release of Fe3O4 and maximizing saturation time of the Fe3O4 capture system. Over 98 % Fe3O4 recovery was observed near ideal conditions. Further experimentation revealed Fe3O4 capture efficiencies between 38 and 93 %, Cu(II) removal between 80 and 99 %, and loading up to 20 mg Cu(II)/g Fe3O4. Additionally, magnetite adsorption was evaluated by treating water samples from the Clark Fork River, located in southwestern Montana. Many contaminants tested were removed to below water quality criteria or instrument detection limits. This study poses a potential solution for water pollution, with the ability to be modified for applications such as environmental remediation and wastewater treatment, and demonstrates an efficient water treatment process for real-world applications. Ultimately, the study aims to establish CFMR operating conditions that minimize Fe3O4 loss to the environment and assess Fe3O4 adsorption capabilities on real water samples.

UAV-Based Hyperspectral Imaging for River Algae Pigment Estimation

Harmful and nuisance algal blooms are becoming a greater concern to public health, riverine ecosystems, and recreational uses of inland waterways. Algal bloom proliferation has increased in the Upper Clark Fork River due to a combination of warming water temperatures, naturally high phosphorus levels, and an influx of nitrogen from various sources. To improve understanding of bloom dynamics and how they affect water quality, often measured as algal biomass measured through pigment standing crops, a UAV-based hyperspectral imaging system was deployed to monitor several locations along the Upper Clark Fork River in western Montana. Image data were collected across the spectral range of 400–1000 nm with 2.1 nm spectral resolution during two field sampling campaigns in 2021. Included are methods to estimate chl a and phycocyanin standing crops using regression analysis of salient wavelength bands, before and after separating the pigments according to their growth form. Estimates of chl a and phycocyanin standing crops generated through a linear regression analysis are compared to in situ data, resulting in a maximum R2 of 0.96 for estimating fila/epip chl-a and 0.94 when estimating epiphytic phycocyanin. Estimates of pigment standing crops from total abundance, epiphytic, and the sum of filamentous and epiphytic sources are also included, resulting in a promising method for remotely estimating algal standing crops. This method addresses the shortcomings of current monitoring techniques, which are limited in spatial and temporal scale, by proposing a method for rapid collection of high-spatial-resolution pigment abundance estimates.

Exploring the mismatch between the theory and application of photosynthetic quotients in aquatic ecosystems

AbstractEstimates of primary productivity in aquatic ecosystems are commonly based on variation in , rather than . The photosynthetic quotient (PQ) is used to convert primary production estimates from units of to C. However, there is a mismatch between the theory and application of the PQ. Aquatic ecologists use PQ = 1–1.4. Meanwhile, PQ estimates from the literature support PQ = 0.1–4.2. Here, we describe the theory on why PQ may vary in aquatic ecosystems. We synthesize the current understanding of how processes such as assimilation and photorespiration can affect the PQ. We test these ideas with a case study of the Clark Fork River, Montana, where theory predicts that PQ could vary in space and time due to variation in environmental conditions. Finally, we highlight research needs to improve our understanding of the PQ. We suggest departing from fixed PQ values and instead use literature‐based sensitivity analyses to infer C dynamics from primary production estimated using .

Rock surface luminescence dating of gravel determines the age of a glacial outburst megaflood, Glacial Lake Missoula, Montana, USA

AbstractGiant gravel bars are important archives of megafloods; however, determining their depositional ages requires reliable geochronometric methods. Five gravel bars, reaching heights of 150–170 m, formed in the bedrock-lined Alberton Gorge along the Clark Fork River, Montana (USA), during draining of Glacial Lake Missoula (GLM). We report the first numerical ages for megaflood deposits in the GLM basin by successfully applying the novel optically stimulated luminescence (OSL) rock surface dating technique to date cobbles collected from three locations along one bar’s transport direction. Depth-dependent infrared stimulated luminescence and post-infrared pulsed OSL signals showed that exteriors of only 3 out of the 38 collected cobble samples were well bleached by exposure to daylight before burial, and hence suitable for dating. The cobbles provided ages of 16.5 ± 0.9, 18.5 ± 1.4, and 21.7 ± 1.1 ka, all of which are indistinguishable from the average cosmogenic nuclide age of 18.2 ± 1.5 ka (n = 4) for a large megaflood in the Channeled Scabland, eastern Washington State. The average of the two younger ages, 17.5 ± 1.0 ka, is our best estimate of the deposit age. We interpret the older age to be from a cobble that was reworked by the flood. Our results show that these techniques have great potential for providing reliable chronologies for paleofloods and other high-energy depositional events.

Temporal Variation in Capture Efficiency Underrepresents Spring Out‐Migrating Bull Trout in a Trap‐and‐Haul Program

AbstractTrap‐and‐haul programs can maintain connection among habitats for migratory salmonids in fragmented systems. To conserve diversity within and among life history strategies, downstream trap and transport of juvenile salmonids could ideally mimic the natural, underlying out‐migration dynamics of the population. A two‐way trap‐and‐haul program is implemented in the lower Clark Fork River, Montana, to conserve adfluvial Bull Trout Salvelinus confluentus. We used PIT technology to assess whether downstream trapping efforts are effectively capturing variation in the out‐migration dynamics of juvenile Bull Trout in Graves Creek, a key spawning and rearing tributary in the system. We tagged 821 juvenile Bull Trout in Graves Creek and used these tagged Bull Trout in conjunction with stationary PIT antennas to monitor out‐migration and evaluate efficiency of the downstream trapping program. Capture efficiency in Graves Creek varied substantially from autumn to spring, with 89–96% of autumn out‐migrating Bull Trout captured and 5–10% of spring out‐migrating Bull Trout captured. Overall, we found that Bull Trout transported during the autumn out‐migration periods generally reflect the natural out‐migration dynamics of the population; however, Bull Trout that out‐migrate in the spring are currently underrepresented in the downstream transport program. By understanding the underlying out‐migration dynamics of the Bull Trout population in Graves Creek, management of the downstream trapping efforts can focus on minimizing potential selection for or against out‐migrants based on timing and age at out‐migration. Minimizing selection will conserve variation within the adfluvial life history strategy and therefore maximize resilience of the adfluvial Bull Trout populations.

Nutrient processing domains: Spatial and temporal patterns of material retention in running waters

Reaches are a fundamental unit for lotic biogeochemical characterization, yet a functional classification of nutrient processing at the reach scale is currently lacking. Here, we introduce nutrient processing domains (NPDs) to integrate routing (nutrient delivery) and local (benthic uptake and transformation) processes that dictate longitudinal patterns of lotic biogeochemical function. An NPD is defined as a realm in functional space occupied by reaches that share similar biogeochemical character. Occupation of a given NPD reflects characteristic net material balance (NMB), exchange potential, and availability, associated with changes in solute load, the extent of hydrologic gain or loss, and changes in concentration from the head to the base of a reach, respectively. Using a mass-balance approach, we represent NMB as the effective solute flux (Feff, M L−2 T−1, where M = mass, L = length, and T = time), designating reaches as sources (+Feff) or sinks (−Feff). Discharge change along a reach is measured as the change in hydraulic load (ΔHL, L/T), reflecting the potential for import and export to influence solute loads. Finally, the ratio of downstream-to-upstream concentration (Cdwn:up) represents the net effect that processes have on nutrient availability. Using a 20-y historical record for N and P in the Upper Clark Fork River, Montana, USA, we employed this approach to 3 consecutive reaches covering nearly 90 km of channel length to address spatial and temporal dynamics in NPD behavior in a nutrient-rich, productive river system. For total N and total P, reaches typically occupied compiler or enhancer NPDs, displaying load increases without or with concomitant increases in concentration, respectively. In contrast, reaches were NO3− consumers, acting as sinks for NO3-N during summer and autumn. NO3− load reductions were typically accompanied by striking declines in concentration, despite positive exchange potential (i.e., +ΔHL). Measured Feff magnitudes for NO3− (−1.2 to −60.0 mg N m−2 d−1) were similar to those reported in the literature associated with autotrophic N demand. Individual reaches occupied contrasting NPDs for NO3-N and soluble reactive P by simultaneously serving as a sink for one and a source for the other. Hence, alternating reaches acted as enhancers or consumers, sequentially along the river, reflecting geologic and biological influences with implications for whole river behavior. The NPD approach combines routing influences of material exchange and local biological stream processes to provide a biogeochemical taxonomy for stream reaches with application to theory and practice.

Revealing early life history of brown trout in an impaired watershed through otolith geochemistry

Early life history data are critical for conservation and management of trout species in freshwater river networks and are imperative for planning habitat restoration in degraded watersheds. In this study, we use otolith geochemical signatures to assign natal provenance and determine age of tributary outmigration for fluvial brown trout ( Salmo trutta) in the Upper Clark Fork River watershed, a large impaired river network. Distinct spatial variations in chemical markers allowed for accurate assignment of fish to their stream of origin and often to specific natal sites. All 10 natal tributaries investigated in this study contributed brown trout to the mainstem and most fish migrated from tributaries to the mainstem during age 1. Mainstem natal habitats, previously thought to be limited by pollution, contributed 29% of the total natal production. Our results indicate that trout in the Upper Clark Fork River use spawning and rearing habitats that are spread throughout the basin. Thus, restoration strategies should focus on maintaining and enhancing a broad variety of habitats and life histories to be successful.

From fragments to connections to restoration: A case history of emergent sociocultural services in the Clark Fork River and Lake Pend Oreille fishery

Abstract Lake Pend Oreille and the Clark Fork River provide essential ecosystem services, including fisheries and hydroelectric power, to residents of Montana, Idaho, and Washington. Although conflicts exist, these services are maintained in concert by emergent sociocultural services created by a multi-institutional, transboundary collaboration. This has been enabled by an innovative Federal Energy Regulatory Commission license settlement agreement among a multitude of stakeholders. The consensus-based agreement promotes connections among people, projects, waterways, and fish populations. Collaborative management efforts allow stakeholders to address controversial issues, such as invasive fish suppression. We demonstrate how reciprocal cultural ecosystem services and services to ecosystems can enable ecosystem-scale restoration that addresses invasive species, habitat protection, and water quality management. Continued ecosystem management success relies on sustaining the relationship-building and shared knowledge services that have emerged over the past 25 years.

The identification of watermilfoil, discovery of hybrid watermilfoil, and their implications for aquatic plant management in the Clark Fork River, Western MT, USA

Eurasian watermilfoil (Myriophyllum spicatum) is an invasive submersed macrophyte that has infested many waters in North America since its introduction. Eurasian watermilfoil has the ability to alter the structure and function of the ecosystems that it invades. Eurasian watermilfoil was first surveyed in the Clark Fork River, MT in 2008, alongside the native northern watermilfoil (Myriophyllum sibiricum). Three reservoirs (Cabinet Gorge, Noxon Rapids and Thompson Falls) on the lower Clark Fork River had entire lake surveys conducted using the point intercept method. Morphological data from these surveys showed that only Eurasian watermilfoil and northern watermilfoil were present during the time of the surveys in 2008. The results of the morphological identification were supported by molecular identification at three different laboratories. In 2015, a genetic survey of watermilfoil species was conducted on the Noxon Rapids Reservoir and found that hybrid watermilfoil (Myriophyllum spicatum × sibiricum) was present. This hybridization event poses a number of issues for aquatic plant management. Hybrid watermilfoil is much more difficult to identify morphologically than its parent types. The hybrid is also more invasive and may be differentially susceptible to some herbicides than the parental type Eurasian watermilfoil.

Surrender: The Call of the American West by Joanna Pocock

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...

Autonomous in situ measurements of freshwater alkalinity

AbstractTotal alkalinity (AT) is an important parameter in the study of aquatic biogeochemical cycles, chemical speciation modeling, and many other important fundamental and anthropogenic (e.g., industrial) processes. We know little about its short‐term variability, however, because studies are based on traditional bottle sampling typically with coarse temporal resolution. In this work, an autonomous AT sensor, named the Submersible Autonomous Moored Instrument for Alkalinity (SAMI‐alk), was tested for freshwater applications. A comprehensive evaluation was conducted in the laboratory using freshwater standards. The results demonstrated excellent precision and accuracy (± 0.1%–0.4%) over the AT range from 800 to 3000 μmol L−1. The system had no drift over an 8 d test and also demonstrated limited sensitivity to variations in temperature and ionic strength. Three SAMI‐alks were deployed for 23 d in the Clark Fork River, Montana, with a suite of other sensors. Compared to discrete samples, in situ accuracy for the three instruments were within 10–20 μmol L−1 (0.3–0.6%), indicating good performance considering the challenges of in situ measurements in a high sediment, high biofouling riverine environment with large and rapid changes in temperature. These data reveal the complex AT dynamics that are typically missed by coarse sampling. We observed AT diel cycles as large as 60–80 μmol L−1, as well as a rapid change caused by a runoff event. Significant errors in inorganic carbon system modeling result if these short‐term variations are not considered. This study demonstrates both the feasibility of the technology and importance of high‐resolution AT measurements.

Trophic interactions among algal blooms, macroinvertebrates, and brown trout: Implications for trout recovery in a restored river

AbstractPositive correlation between trout abundance and dissolved metal concentrations along the Upper Clark Fork River (UCFR; Montana, USA) have forced restoration practitioners to seek underlying causes of reduced fish density beyond heavy metal contamination. Throughout the river, nutrient enrichment and summer algal blooms may be hindering full recovery of trout populations. In this study, we evaluated the community structure and metal body burdens of benthic invertebrates and characterized existing trophic linkages between brown trout and dominant invertebrate taxa before and during summer algal blooms in a downstream reach of the UCFR where fish densities are low (20–30 trout/km), and where metal contamination is relevant but minimal compared with upstream. In spring, estimated invertebrate abundance was 1,727 ± 217 individuals/m2 and dominated by Ephemerellidae and Baetidae families. During summer algal bloom, invertebrate abundance increased 15‐fold (20,580 ± 3,510 individuals/m2) mostly due to greater abundance of Chironomidae, Hydropsychidae, and Simulidae. Copper body burdens (130 ± 42 ppm) were higher than any other heavy metal regardless of season, but detectable concentrations of arsenic, cadmium, and lead were also found. A Bayesian mixing model combining metal burdens and stable isotopes showed that in the spring, trout of average size (355 ± 65 g) relied mostly on epibenthic taxa (Ephemerellidae and Hydropsychidae), contrasting with small (<100 g) and large (>400 g) trout relying heavily on Baetidae, a major component of invertebrate drift. Foraging segregation related to trout size did not occur during summer algal blooms, which may reflect increasing influence of benthic algal proliferation or indicate the indiscriminate use of pool habitats as thermal refugia over summer conditions by trout of different ages.

Application of multistate modeling to estimate salmonid survival and movement in relation to spatial and temporal variation in metal exposure in a mining-impacted river

Multistate modeling was used to estimate survival and movement of brown trout (Salmo trutta) and westslope cutthroat trout (Oncorhynchus clarkii lewisi) in relation to copper concentrations in the mining-impacted Clark Fork River, Montana. Survival probability in the uppermost river segment, where dissolved copper concentrations frequently exceeded acute criteria for aquatic life (range: 31–60 days > 13.4 μg·L–1), was 2.1 times lower for brown trout and 122 times lower for westslope cutthroat trout compared with survival rates in the lowermost segment that had relatively low dissolved copper (0 days exceedance of acute concentration). Lowest survival for both species occurred in the spring–summer period when dissolved copper concentrations were elevated coincident with higher discharge. Movement among study segments was generally low, and cutthroat trout showed low movement into the uppermost river segment with the most elevated copper levels. Both species showed high rates of movement into tributaries, which coincided with their respective spawning migrations rather than as an apparent avoidance of elevated copper levels. The linkage between survival rate and level of copper exposure for both trout species suggests that additional removal of tailings deposits could improve survival rates.

Timing of lake-level changes for a deep last-glacial Lake Missoula: optical dating of the Garden Gulch area, Montana, USA

Glaciolacustrine sediments in the Clark Fork River valley at Garden Gulch, near Drummond, Montana, USA record highstand positions of the ice-dammed glacial Lake Missoula and repeated subaerial exposure. During these highstands the lake was at greater than 65% of its recognized maximum capacity. The initial lake transgression deposited a basal sand unit. Subsequent cycles of lake-level fluctuations are recorded by sequences of laminated and cross laminated silt, sand, and clay deformed by periglacial processes during intervening periods of lower lake levels.Optically stimulated luminescence (OSL) dating of quartz sand grains, using single-aliquot regenerative-dose procedures, was carried out on 17 samples. Comparison of infrared stimulated luminescence (IRSL) from K-rich feldspar to OSL from quartz for all the samples suggests that they were well bleached prior to deposition and burial. Ages for the basal sand and overlying glaciolacustrine exposure surfaces are indistinguishable within one standard deviation, and give a weighted mean age of 20.9 ± 1.3 ka (n = 11). Based on sedimentological and stratigraphic analysis we infer that the initial transgression, and at least six cycles of lake-level fluctuation, occurred over time scales of decades to ∼2 ka. Bioturbated sandy slopewash dated at 10.6 ± 0.9 ka and 11.9 ± 1.2 ka unconformably overlies the upper glaciolacustrine deposits. The uppermost sediments, above the glaciolacustrine section, are younger than the Glacier Peak tephra (13.7–13.4 cal ka B.P.), which was deposited across parts of the drained lake basin, but has not been found at Garden Gulch.Our study indicates that glacial Lake Missoula reached >65 percent of maximum capacity by about 20.9 ± 1.3 ka and either partially or completely drained twelve times from this position. Rapid lowering from the lake's highstand position due to ice-dam failure likely led to scour in the downstream portions of the glacial Lake Missoula basin and megafloods in the Channeled Scabland.

Repeated sedimentation and exposure of glacial Lake Missoula sediments: A lake-level history at Garden Gulch, Montana, USA

Abstract Glaciolacustrine sediments record lake transgression, regression, and subaerial modification of the silty lake-bottom of glacial Lake Missoula in the Clark Fork River valley. The sequence preserved at Garden Gulch, MT documents lake-level fluctuations at >65% of its full-pool volume. Twelve sedimentary cycles fine upwards from (1) very fine-grained sandy silt to (2) silt with climbing ripples to (3) rhythmically laminated silt and some clay. The cycles are fine-grained turbidites capped locally by thin layers of angular gravel derived from local bedrock outcrops. The gravels appear to be the toes of mass wasting lobes carried onto the exposed lakebed surface during repeated lake-level lowerings. Periglacial wedges, small rotational faults, involutions, and clastic dikes deform the tops of eleven cycles. The wedges are 10–30 cm wide, penetrate 30–70 cm deep, are spaced The lowest five cycles are thicker and display more periglacial modification at their tops than the upper seven cycles. The Garden Gulch section may represent as few as seven and as many as twelve substantial fillings and partial to complete drainings of glacial Lake Missoula.

Dams impact westslope cutthroat trout metapopulation structure and hybridization dynamics

Dams fragment aquatic networks and impact the evolutionary dynamics of migratory fish populations. Historically, the Lake Pend Oreille–lower Clark Fork River system in Idaho and Montana supported a large metapopulation of adfluvial westslope cutthroat trout (westslope). These fish matured in the lake and made upstream spawning migrations to their natal tributaries in the river. Currently, dams allow downstream passage for juvenile fish to the lake, but no upstream passage for adults. We examined 19 microsatellite and anonymous nuclear loci to characterize spatial patterns of non-native rainbow trout (rainbow) genetic introgression in westslope populations upstream and downstream of these dams. We detected hybridization at 20 of 42 sites sampled throughout the system, with rainbow introgression ranging from 1.1 to 99.8%. Rainbow introgression was higher in tributaries downstream of both dams (12 of 18 sites downstream vs 6 of 22 sites upstream). Within tributaries, hybrids were more common in lower sections and only one sampled site contained a hybrid swarm. Fish collected below both dams during the spawning migration were admixtures of westslope, rainbows and hybrids with an average rainbow introgression of 48%. Phenotypic criteria reduced rainbow introgression to less than 1% for putative westslope identified for selective upstream transport at both dams. Lack of upstream fish passage at these dams has likely constrained spread of hybridization and increased isolation among non-hybridized westslope populations by reducing the abundance of the migratory life history form in areas upstream of these dams.