Montana Stream Research Articles

Bull Trout Passage at Beaver Dams in Two Montana Streams

Bull Trout Passage at Beaver Dams in Two Montana Streams

Going with the flow - how a stream insect, Pteronarcys californica, exploits local flows to increase oxygen availability.

For insects, life in water is challenging because oxygen supply is typically low compared with in air. Oxygen limitation may occur when oxygen levels or water flows are low or when warm temperatures stimulate metabolic demand for oxygen. A potential mechanism for mitigating oxygen shortages is behavior - moving to cooler, more oxygenated or faster flowing microhabitats. Whether stream insects can make meaningful choices, however, depends on: (i) how temperature, oxygen and flow vary at microspatial scales and (ii) the ability of insects to sense and exploit that variation. To assess the extent of microspatial variation in conditions, we measured temperature, oxygen saturation and flow velocity within riffles of two streams in Montana, USA. In the lab, we then examined preferences of nymphs of the stonefly Pteronarcys californica to experimental gradients based on field-measured values. Temperature and oxygen level varied only slightly within stream riffles. By contrast, flow velocity was highly heterogeneous, often varying by more than 125 cm s-1 within riffles and 44 cm s-1 around individual cobbles. Exploiting micro-variation in flow may thus be the most reliable option for altering rates of oxygen transport. In support of this prediction, P. californica showed little ability to exploit gradients in temperature and oxygen but readily exploited micro-variation in flow - consistently choosing higher flows when conditions were warm or hypoxic. These behaviors may help stream insects mitigate low-oxygen stress from climate change and other anthropogenic disturbances.

Influence of biomimicry structures on ecosystem function in a Rocky Mountain incised stream

AbstractRising levels of stream degradation have motivated a boom in restoration projects across the globe. However, postrestoration monitoring is still frequently lacking and does not always incorporate biotic responses to changes in the physical template. Beaver mimicry structures (BMSs) are becoming a popular tool to restore degraded streams throughout the American West, but relatively little is known about how these installations influence both biotic and abiotic factors, with consequences for ecosystem functioning. We monitored basal resources, organic and inorganic material standing stocks, and macroinvertebrate density, biomass, and production to quantify functional responses to BMS installation. We compared conditions at BMS sites to naturally occurring beaver dam and reference riffle sites in a low‐gradient stream in southwest Montana. Thermal ranges were contracted, and daily maximum temperatures were higher, in the BMS treatment compared to the reference riffle treatment. Fine sediment standing stock and basal resources were similar in Beaver and BMS treatments, and both treatments were higher than reference riffles. All treatments differed in macroinvertebrate density, which was highest in the Beaver treatment, followed by Mimic and then Reference treatment. Biomass and secondary production were higher in Beaver and BMS treatments compared to the Reference treatment, but only Beaver and Reference treatments differed significantly, likely due to differences in physical habitat and basal resource availability. Consequently, production of collector–gatherers in the BMS treatment and shredders in the Beaver treatment was higher than in reference riffles. Changes to local hydrology and sediment dynamics resulting from BMS influence biotic functional responses like organic material standing stock and secondary production, creating habitat and ecosystem function distinct from riffles and similar to target conditions of natural beaver dams. To continue to improve BMS as a standard restoration practice, future research could consider the extent of degradation, increasing temporal scale of monitoring. Alterations to aquatic–terrestrial subsidies and impacts to fishes.

Evaluating Remote Site Incubators in Michigan Streams: Implications for Arctic Grayling Reintroduction

AbstractThe successful use of remote site incubators (RSIs) to rear eggs of Arctic Grayling Thymallus arcticus along Montana streams has sparked interest in reestablishing the species in Michigan. As a preparatory step, we assessed the efficacy of RSIs by deploying them along three Michigan streams during 2 years using surrogate eggs from Rainbow Trout Oncorhynchus mykiss. Our objectives were to (1) compare hatching success between two different RSI designs (19‐L versus 265‐L RSIs), (2) test whether the removal of dead eggs (“picking”) from 19‐L RSIs affected hatching success, and (3) develop a simple model to predict fry yield and its uncertainty. Overall survival was 41.3% in 2018 and 52.4% in 2019. Differences in survival between unpicked 19‐L and 265‐L RSIs tended to be small, with mean differences from 4.82% (95% CI = –0.60 to +10.25) in 2018 to 0.08% (95% CI = –0.14 to +0.30) in 2019. On average, picked 19‐L RSIs had greater, although not always statistically significant, survival than unpicked 19‐L RSIs during both years (mean difference = 1.6% [2018] and 10.4% [2019]). We documented a significant positive correlation between survival and RSI flow rate. Survival abruptly declined in unpicked 19‐L RSIs when RSI flow rates dropped below ~0.3 L/min, suggesting that removing dead eggs from 19‐L RSIs likely increased survival when RSI flow rates were <0.3 L/min. The most notable result from our fry yield model was that increasing the number of RSIs reduced the coefficient of variation in fry yield following a pattern of diminishing returns, suggesting two or three RSIs usually will be a good choice. We showed that 19‐L and 265‐L RSIs can be used successfully in Michigan streams, with our model providing a tool for managers to explore the relative importance of several properties of RSI design and operation on fry yield and uncertainty.

Adapting Inland Fisheries Management to a Changing Climate

Natural resource decision makers are challenged to adapt management to a changing climate while balancing short‐term management goals with long‐term changes in aquatic systems. Adaptation will require developing resilient ecosystems and resilient management systems. Decision makers already have tools to develop or ensure resilient aquatic systems and fisheries such as managing harvest and riparian zones. Because fisheries management often interacts with multiple stakeholders, adaptation strategies involving fisheries managers and other partners focused on land use, policy, and human systems, coupled with long‐term monitoring, are necessary for resilient systems. We show how agencies and organizations are adapting to a changing climate in Minnesota and Ontario lakes and Montana streams. We also present how the Florida Fish and Wildlife Commission created a management structure to develop adaptation strategies. These examples demonstrate how organizations and agencies can cope with climate change effects on fishes and fisheries through creating resilient management and ecological systems.

Factors Influencing Successful Eradication of Nonnative Brook Trout from Four Small Rocky Mountain Streams Using Electrofishing

AbstractWe successfully eradicated nonnative Brook Trout Salvelinus fontinalis by electrofishing from 2.4‐ to 3.0‐km treatment reaches of four Rocky Mountain streams in Montana to conserve sympatric populations of native Westslope Cutthroat Trout Oncorhynchus clarkii lewisi. At least 6, and as many as 14, removal treatments of two to four electrofishing passes per treatment were required to successfully eradicate Brook Trout from these treatment reaches. We increased success by modifying our treatment efforts during this study from single annual treatments to several treatments a year to take advantage of autumn spawning and winter aggregating behavior. Eradication by electrofishing cost US$3,500 to $5,500 per kilometer where no riparian vegetation or woody debris clearing was necessary, increasing to $8,000 to $9,000 per kilometer where clearing was needed. Treatment costs without stream clearing were similar to costs of eradication using piscicides. Eradication by electrofishing may be preferable where native fish occur in sympatry with nonnative fish in smaller streams (base flow wetted widths <3.0 m) because native fish can be salvaged during removal efforts and because electrofishing may be more acceptable to the public than use of piscicides.Received December 16,2013; accepted June 9,2014

Whirling disease dynamics: An analysis of intervention strategies

Whirling disease (WD), a severe and widespread disease of salmonids, is caused by the myxosporean parasite Myxobolus cerebralis. It is further characterized by a unique two-host life cycle, utilizing the oligochaete Tubifex tubifex as an intermediate host. M. cerebralis is an invasive species that has been affecting populations in the United States including epidemics that killed in excess of 90% of populations in Colorado and Montana streams within the past 20 years. Currently, there is no known cure for WD, and the accepted method of control is removal of infected fish from the population. We have created a compartmental model of the WD system in order to assess more efficient means of control and management of the disease. Using data gathered from the literature, we used Bayesian model fitting to estimate model parameters and estimated that R0≈1.51 (95% CI: 1.39, 1.72), a value which implies that WD can be controlled using available strategies. To this end, we posit several parameters that we expect to be most influential to WD propagation, namely: release of triactinomyxons by T. tubifex, release of spores by salmonids, and infectious particle loads in each respective host. Based on currently available control strategies, approaches targeting the infectious particles and the oligochaete host appear the most effective alternative strategies for management and control of WD.

Channel water balance and exchange with subsurface flow along a mountain headwater stream in Montana, United States

Channel water balances of contiguous reaches along streams represent a poorly understood scale of stream‐subsurface interaction. We measured reach water balances along a headwater stream in Montana, United States, during summer base flow recessions. Reach water balances were estimated from series of tracer tests in 13 consecutive reaches delineated evenly along a 2.6 km valley segment. For each reach, we estimated net change in discharge, gross hydrologic loss, and gross hydrologic gain from tracer dilution and mass recovery. Four series of tracer tests were performed during relatively high, intermediate, and low base flow conditions. The relative distribution of channel water along the stream was strongly related to a transition in valley structure, with a general increase in gross losses through the recession. During tracer tests at intermediate and low flows, there were frequent substantial losses of tracer mass (>10%) that could not be explained by net loss in flow over the reach, indicating that many of the study reaches were concurrently losing and gaining water. For example, one reach with little net change in discharge exchanged nearly 20% of upstream flow with gains and losses along the reach. These substantial bidirectional exchanges suggest that some channel interactions with subsurface flow paths were not measurable by net change in flow or transient storage of recovered tracer. Understanding bidirectional channel water balances in stream reaches along valleys is critical to an accurate assessment of stream solute fate and transport and to a full assessment of exchanges between the stream channel and surrounding subsurface.

Habitat Heterogeneity and Associated Microbial Community Structure in a Small-Scale Floodplain Hyporheic Flow Path

The Nyack floodplain is located on the Middle Fork of the Flathead River, an unregulated, pristine, fifth-order stream in Montana, USA, bordering Glacier National Park. The hyporheic zone is a nutritionally heterogeneous floodplain component harboring a diverse array of microbial assemblages essential in fluvial biogeochemical cycling, riverine ecosystem productivity, and trophic interactions. Despite these functions, microbial community structure in pristine hyporheic systems is not well characterized. The current study was designed to assess whether physical habitat heterogeneity within the hyporheic zone of the Nyack floodplain was sufficient to drive bacterial beta diversity between three different hyporheic flow path locations. Habitat heterogeneity was assessed by measuring soluble reactive phosphorous, nitrate, dissolved organic carbon, dissolved oxygen, and soluble total nitrogen levels seasonally at surface water infiltration, advection, and exfiltration zones. Significant spatial differences were detected in dissolved oxygen and nitrate levels, and seasonal differences were detected in dissolved oxygen, nitrate, and dissolved organic carbon levels. Denaturing gradient gel electrophoresis (DGGE) and cell counts indicated that bacterial diversity increased with abundance, and DGGE fingerprints covaried with nitrate levels where water infiltrated the hyporheic zone. The ribosomal gene phylogeny revealed that hyporheic habitat heterogeneity was sufficient to drive beta diversity between bacterial assemblages. Phylogenetic (P) tests detected sequence disparity between the flow path locations. Small distinct lineages of Firmicutes, Actinomycetes, Planctomycetes, and Acidobacteria defined the infiltration zone and alpha- and beta-proteobacterial lineages delineated the exfiltration and advection zone communities. These data suggest that spatial habitat heterogeneity drives hyporheic microbial community development and that attempts to understand functional differences between bacteria inhabiting nutritionally heterogeneous hyporheic environments might begin by focusing on the biology of these taxa.

An empirical method for estimating instream pre-mining pH and dissolved Cu concentration in catchments with acidic drainage and ferricrete

Methods for assessing natural background water quality of streams affected by historical mining are vigorously debated. An empirical method is proposed in which stream-specific estimation equations are generated from relationships between either pH or dissolved Cu concentration in stream water and the Fe/Cu concentration ratio in Fe-precipitates presently forming in the stream. The equations and Fe/Cu ratios for pre-mining deposits of alluvial ferricrete then were used to reconstruct estimated pre-mining longitudinal profiles for pH and dissolved Cu in three acidic streams in Montana, USA. Primary assumptions underlying the proposed method are that alluvial ferricretes and modern Fe-precipitates share a common origin, that the Cu content of Fe-precipitates remains constant during and after conversion to ferricrete, and that geochemical factors other than pH and dissolved Cu concentration play a lesser role in determining Fe/Cu ratios in Fe-precipitates. The method was evaluated by applying it in a fourth, naturally acidic stream unaffected by mining, where estimated pre-mining pH and Cu concentrations were similar to present-day values, and by demonstrating that inflows, particularly from unmined areas, had consistent effects on both the pre-mining and measured profiles of pH and Cu concentration. Using this method, it was estimated that mining has affected about 480 m of Daisy Creek, 1.8 km of Fisher Creek, and at least 1 km of Swift Gulch. Mean values of pH decreased by about 0.6 pH units to about 3.2 in Daisy Creek and by 1–1.5 pH units to about 3.5 in Fisher Creek. In Swift Gulch, mining appears to have decreased pH from about 5.5 to as low as 3.6. Dissolved Cu concentrations increased due to mining almost 40% in Daisy Creek to a mean of 11.7 mg/L and as much as 230% in Fisher Creek to 0.690 mg/L. Uncertainty in the fate of Cu during the conversion of Fe-precipitates to ferricrete translates to potential errors in pre-mining estimates of as much as 0.25 units for pH and 22% for dissolved Cu concentration. The method warrants further testing in other mined and unmined watersheds. Comparison of pre-mining water-quality estimates derived from the ferricrete and other methods in single watersheds would be particularly valuable. The method has potential for use in monitoring remedial efforts at mine sites with ferricrete deposits. A reasonable remediation objective might be realized when the downstream pattern of Fe/Cu ratios in modern streambed Fe-precipitates corresponds to the pattern in pre-mining alluvial ferricrete deposits along a stream valley.

Susceptibility of Tubifex tubifex (Annelida: Oligochaeta: Tubificidae) from the Rock Creek Drainage of West Central Montana, U.S.A., to Myxobolus cerebralis (Myxozoa: Myxosporea: Myxobolidae), the Causative Agent of Salmonid Whirling Disease

The objective of this study was to determine whether the low prevalence of Tubifex tubifex infected with Myxobolus cerebralis in a Montana stream was due to a large percentage of worms being resistant to the parasite or whether other factors were involved. For this, specimens of T. tubifex were collected from various localities throughout the Rock Creek drainage of west central Montana, U.S.A., a stream known to be heavily contaminated with M. cerebralis, the causative agent of salmonid whirling disease. The natural occurring prevalence of infection was determined, and then noninfected worms were exposed to myxospores of M. cerebralis under controlled, laboratory conditions. Results showed that the percentage of noninfected T. tubifex that became infected with M. cerebralis was always greater than the percentage of naturally infected worms found at the same locality. Further, T. tubifex susceptible to infection were found at localities where no naturally infected worms were recovered. However, the prevalence of infection was low in both groups and did not exceed 4.1% for naturally infected T. tubifex or 19.0% for experimentally infected worms. In comparison, a control group of highly susceptible T. tubifex from California, U.S.A., had a 72–88% prevalence of infection after laboratory exposures to myxospores of M. cerebralis. Therefore, it appears that a large percentage of T. tubifex in Rock Creek are resistant to infection, although the mechanism of resistance is not known.

Effect of native and exotic leaf litter on macroinvertebrate communities and decomposition in a western Montana stream

ABSTRACTInvasion by exotic trees into riparian areas has the potential to impact terrestrial and aquatic systems. To test the effect of different streamside tree species on the aquatic food web in a stream in Montana, we compared decomposition rates of leaf litter and invertebrate assemblages associated with the leaf litter of the exotic Acer platanoides and the dominant native Populus trichocarpa trees. Macroinvertebrate family richness, evenness, and diversity increased with days of aquatic processing; however, there was no effect of leaf species. Leaves of the A. platanoides were associated with 70% greater density of macroinvertebrates of the family Nemouridae. This family consists primarily of detritivores and had the greatest overall density and frequency of occurrence relative to other macroinvertebrate families. The density of a family of predatory macroinvertebrates (Rhyacophilidae) was also generally (73%) greater in association with A. platanoides than P. trichocarpa leaves. The density of Ephemerellidae and Rhyacophilidae increased over time. In contrast to studies comparing leaves of exotic vs. native trees, we observed no difference in leaf decomposition rates; however, the amount of leaf inputs are likely to differ between native and invaded forests. The results indicate that replacement of native riparian trees with exotics affected the most common family of macroinvertebrates and possibly a common family of predatory macroinvertebrates (Rhyacophilidae), which may affect the detrital food web.

Divergent patterns of abundance and age-class structure of headwater stream tadpoles in burned and unburned watersheds

Wildfire is a potential threat to many species with narrow environmental tolerances like the Rocky Mountain tailed frog ( Ascaphus montanus Mittleman and Myers, 1949), which inhabits a region where the frequency and intensity of wildfires are expected to increase. We compared pre- and post-fire counts of tadpoles in eight streams in northwestern Montana to determine the effects of wildfire on A. montanus. All streams were initially sampled in 2001, 2 years before four of them burned in a large wildfire, and were resampled during the 2 years following the fire. Counts of tadpoles were similar in the two groups of streams before the fire. After the fire, tadpoles were almost twice as abundant in unburned streams than in burned streams. The fire seemed to have the greatest negative effect on abundance of age-1 tadpoles, which was reflected in the greater variation in same-stream age-class structure compared with those in unburned streams. Despite the apparent effect on tadpoles, we do not expect the wildfire to be an extirpation threat to populations in the streams that we sampled. Studies spanning a chronosequence of fires, as well as in other areas, are needed to assess the effects of fires on streams with A. montanus and to determine the severity and persistence of these effects.

Light-mediated Zn uptake in photosynthetic biofilm

Our experiments conducted under controlled laboratory conditions demonstrate diel uptake and release of zinc (Zn) in lab-cultured biofilm exposed to Zn concentrations that are present in some mining-impacted streams (1–2 mg Zn/l). Specifically, at constant pH, temperature, and aqueous Zn concentrations in the exposure water, biofilm accumulated Zn during the light periods of the photocycle and released Zn during the dark periods of the photocycle. The range of Zn uptake measured in biofilm during one light period in these laboratory experiments (0.6–8.3 mg Zn/g dw biofilm) encompassed the estimated Zn uptake (1.5–3.7 mg Zn/g dw biofilm) necessary to attribute aqueous diel Zn cycling in a mining-impacted stream in Montana (High Ore Creek) to uptake in biofilm. This is relevant to in situ studies of diel Zn cycling because we controlled three important parameters that naturally fluctuate daily in the field, thus demonstrating the potential for biofilm to remove large percentages of Zn from some mining-impacted streams. Researchers, modelers, regulators, and reclamation teams working in metals-contaminated streams should be aware of diel metal cycling, because the highest Zn concentrations (and therefore, perhaps the most toxic conditions) in the water column might occur at night, and the greatest exposure of grazers of phototrophs to dietborne Zn might occur during daylight hours.

Effect of native and exotic leaf litter on macroinvertebrate communities and decomposition in a western Montana stream

Effect of native and exotic leaf litter on macroinvertebrate communities and decomposition in a western Montana stream

Observer Error Structure in Bull Trout Redd Counts in Montana Streams: Implications for Inference on True Redd Numbers

AbstractDespite the widespread use of redd counts to monitor trends in salmonid populations, few studies have evaluated the uncertainties in observed counts. We assessed the variability in redd counts for migratory bull trout Salvelinus confluentus among experienced observers in Lion and Goat creeks, which are tributaries to the Swan River, Montana. We documented substantially lower observer variability in bull trout redd counts than did previous studies. Observer counts ranged from 78% to 107% of our best estimates of true redd numbers in Lion Creek and from 90% to 130% of our best estimates in Goat Creek. Observers made both errors of omission and errors of false identification, and we modeled this combination by use of a binomial probability of detection and a Poisson count distribution of false identifications. Redd detection probabilities were high (mean = 83%) and exhibited no significant variation among observers (SD = 8%). We applied this error structure to annual redd counts in the Swan River basin (1982–2004) to correct for observer error and thus derived more accurate estimates of redd numbers and associated confidence intervals. Our results indicate that bias in redd counts can be reduced if experienced observers are used to conduct annual redd counts. Future studies should assess both sources of observer error to increase the validity of using redd counts for inferring true redd numbers in different basins. This information will help fisheries biologists to more precisely monitor population trends, identify recovery and extinction thresholds for conservation and recovery programs, ascertain and predict how management actions influence distribution and abundance, and examine effects of recovery and restoration activities.

The influence of hydrous Mn–Zn oxides on diel cycling of Zn in an alkaline stream draining abandoned mine lands

Many mining-impacted streams in western Montana with pH near or above neutrality display large (up to 500%) diel cycles in dissolved Zn concentrations. The streams in question typically contain boulders coated with a thin biofilm, as well as black mineral crusts composed of hydrous Mn–Zn oxides. Laboratory mesocosm experiments simulating diel behavior in High Ore Creek (one of the Montana streams with particularly high Zn concentrations) show that the Zn cycles are not caused by 24-h changes in streamflow or hyporheic exchange, but rather to reversible in-stream processes that are driven by the solar cycle and its attendant influence on pH and water temperature ( T). Laboratory experiments using natural Mn–Zn precipitates from the creek show that the mobilities of Zn and Mn increase nearly an order of magnitude for each unit decrease in pH, and decrease 2.4-fold for an increase in T from 5 to 20 °C. The response of dissolved metal concentration to small changes in either pH or T was rapid and reversible, and dissolved Zn concentrations were roughly an order of magnitude higher than Mn. These observations are best explained by sorption of Zn 2+ and Mn 2+ onto the secondary Mn–Zn oxide surfaces. From the T-dependence of residual metal concentrations in solution, approximate adsorption enthalpies of +50 kJ/mol (Zn) and +46 kJ/mol (Mn) were obtained, which are within the range of enthalpy values reported in the literature for sorption of divalent metal cations onto hydrous metal oxides. Using the derived pH- and T-dependencies from the experiments, good agreement is shown between predicted and observed diel Zn cycles for several historical data sets collected from High Ore Creek.

Diel behavior of rare earth elements in a mountain stream with acidic to neutral pH

Diel (24-h) changes in concentrations of rare earth elements (REE) were investigated in Fisher Creek, a mountain stream in Montana that receives acid mine drainage in its headwaters. Three simultaneous 24-h samplings were conducted at an upstream station (pH = 3.3), an intermediate station (pH = 5.5), and a downstream station (pH = 6.8). The REE were found to behave conservatively at the two upstream stations. At the downstream station, REE partitioned into suspended particles to a degree that varied with the time of day, and concentrations of dissolved REE were 2.9- to 9.4-fold (190% to 830%) higher in the early morning vs. the late afternoon. The decrease in dissolved REE concentrations during the day coincided with a corresponding increase in the concentration of REE in suspended particles, such that diel changes in the total REE concentrations were relatively minor (27% to 55% increase at night). Across the lanthanide series, the heavy REE partitioned into the suspended solid phase to a greater extent than the light REE. Filtered samples from the downstream station showed a decrease in shale-normalized REE concentration across the lanthanide series, with positive anomalies at La and Gd, and a negative Eu anomaly. As the temperature of the creek increased in the afternoon, the slope of the REE profile steepened and the magnitude of the anomalies increased. The above observations are explained by cyclic adsorption of REE onto suspended particles of hydrous ferric and aluminum oxides (HFO, HAO). Conditional partition coefficients for each REE between the suspended solids and the aqueous phase reached a maximum at 1700 hours and a minimum at 0700 hours. This pattern is attributed to diel variations in stream temperature, possibly reinforced by kinetic factors (i.e., slower rates of reaction at night than during the day). Estimates of the enthalpy of adsorption of each REE onto suspended particles based on the field results averaged +82 kJ/mol and are similar in magnitude to estimates in the literature for adsorption of divalent metal cations onto clays and hydrous metal oxides. The results of this study have important implications to the use of REE as hydrogeochemical tracers in streams.

Simulation of Metals Total Maximum Daily Loads and Remediation in a Mining-Impacted Stream

Simulation of metals transport was performed to help develop metals total maximum daily loads ~TMDLs! and evaluate remediation alternatives in a mountain stream in Montana impacted by hundreds of abandoned hardrock metal mines. These types of watersheds are widespread in Montana and many other areas of the western United States. Impacts from abandoned hardrock or metal mines include loadings of sediment, metals, and other pollutants causing impairment of multiple beneficial uses and exceedances of water quality standards. The United States Environmental Protection Agency ~EPA! Water Quality Analysis Simulation Program (WASP)was used to model and evaluate TMDLs for several heavy metals in Tenmile Creek, a mountain stream supplying drinking water to the City of Helena, Mont. The model was calibrated for baseflow conditions and validated using data collected by the EPA and the United States Geological Survey, and used to assess existing metals loadings and losses, including interactions between metals in water and bed sediment, uncertainty, water quality standard exceedances, TMDLs, potential source areas, and required reductions in loadings. During baseflow conditions, adits and point sources contribute significant metals loadings to Tenmile Creek. Exceedances of standards are widespread throughout the stream under both baseflow and higher flow conditions. Adsorption and precipitation onto bed sediments play a primary role in losses from the water column in some areas. Modeling results indicate that some uncertainty exists in the metal partition coefficients associated with sediment, significance of precipitation reactions, and in locations of unidentified sources and losses of metals. TMDLs and loading reductions were calculated based on variations in flow, concentrations, loadings, and standards ~which vary with hardness! along the mainstem. In most cases, considerable reductions in loadings are required to achieve TMDLs and water quality standards. Reductions in loadings from point sources, mine waste near watercourses, and streambed sediment can help improve water quality, but alteration of the water supply scheme and increasing baseflow will also be needed.

Factors That May Be Influencing Nonnative Brook Trout Invasion and Their Displacement of Native Westslope Cutthroat Trout in Three Adjacent Southwestern Montana Streams

AbstractI examined trends in community structure and abundance in populations of native westslope cutthroat trout (WCT) Oncorhynchus clarki lewisi and nonnative brook trout Salvelinus fontinalis and fish habitat characteristics in three adjacent southwestern Montana streams during 1988, 1993–1995, and 1997–1999. Delano and upper Jerry creeks had relatively undisturbed riparian forests, whereas Libby Creek's riparian forest was harvested along much (0.9 km) of the stream during 1971. Libby Creek had higher summer water temperatures (average daily temperatures were 1–2°C higher) than Delano Creek. Libby Creek also contained more woody debris, a higher percentage of fine sediments within the streambed, and a higher proportion of pool habitats than Delano and upper Jerry creeks. Brook trout dominated the trout community in Libby Creek (78– 91%), whereas WCT dominated in Delano and upper Jerry creeks (77–100%). Similarly, brook trout densities were significantly higher in Libby Creek, and WCT densities were significantly greater in Delano and upper Jerry creeks. These data suggest that brook trout invasion and the displacement of WCT in these streams may have been influenced by water temperature, debris and pool frequencies, erosion and deposition of fine sediments on the streambed, or some combination of these factors. Past research has linked changes in these physical parameters to riparian timber harvest activities. More research is needed to better quantify potential influences of abiotic factors on brook trout invasion and the subsequent displacement of WCT. Until such research is completed, resource managers who wish to protect and conserve stream populations of native WCT should consider the effects of land management and fish restoration activities on the aforementioned stream habitat conditions, especially in systems that contain or could potentially be invaded by nonnative brook trout.