Pacific Northwest Streams Research Articles

Heterogeneity in post-fire thermal responses across Pacific Northwest streams: A multi-site study

Over the past century, water temperatures in many streams across the Pacific Northwest (PNW) have steadily risen, shrinking endangered salmonid habitats. The warming of PNW stream reaches can be further accelerated by wildfires burning forest stands that provide shade to streams. However, previous research on the effect of wildfires on stream water temperatures has focused on individual streams or burn events, limiting our understanding of the diversity in post-fire thermal responses across PNW streams. To bridge this knowledge gap, we assessed the impact of wildfires on daily summer water temperatures across 31 PNW stream sites, where 10–100% of their riparian area burned. To ensure robustness of our results, we employed multiple approaches to characterize and quantify fire effects on post-fire stream water temperature changes.Averaged across the 31 burned sites, wildfires corresponded to a 0.3 – 1°C increase in daily summer water temperatures over the subsequent three years. Nonetheless, post-fire summer thermal responses displayed extensive heterogeneity across burned sites where the likelihood and rate of a post-fire summer water temperature warming was higher for stream sites with greater proportion of their riparian area burned under high severity. Also, watershed features such as basin area, post-fire weather, bedrock permeability, pre-fire riparian forest cover, and winter snowpack depth were identified as strong predictors of the post-fire summer water temperature responses across burned sites. Our study offers a multi-site perspective on the effect of wildfires on summer stream temperatures in the PNW, providing insights that can inform freshwater management efforts beyond individual streams and basins.

A multidecadal oscillation in precipitation and temperature series is pronounced in low flow series from Puget Sound streams

AbstractIn Pacific Northwest streams, summer low flows limit water available to competing instream (salmon) and out‐of‐stream (human) uses, creating broad interest in how and why low flows are trending. Analyses that assumed linear (monotonic) change over the last ~60 years revealed declining low flow trends in minimally disturbed streams. Here, polynomials were used to model flow trends between 1929 and 2015. A multidecadal oscillation was observed in flows, which increased initially from the 1930s until the 1950s, declined until the 1990s, and then increased again. A similar oscillation was detected in precipitation series, and opposing oscillations in surface temperature, Pacific Decadal Oscillation, and Interdecadal Pacific Oscillation series. Multidecadal oscillations with similar periods to those described here are well known in climate indices. Fitted model terms were consistent with flow trends being influenced by at least two drivers, one oscillating and the other monotonic. Anthropogenic warming is a candidate driver for the monotonic decline, and variation in (internal) climatic circulation for the oscillating trend, but others were not ruled out. The recent upturn in streamflows suggests that anthropogenic warming has not been the dominant factor driving streamflow trends, at least until 2015. Climate projections based on simulations that omit drivers of multidecadal variation are likely to underestimate the range, and rate of change, of future climatic variation.

Hydroclimatic Conditions, Wildfire, and Species Assemblages Influence Co-Occurrence of Bull Trout and Tailed Frogs in Northern Rocky Mountain Streams

Although bull trout (Salvelinus confluentus) and tailed frogs (Ascaphus montanus) have co-existed in forested Pacific Northwest streams for millennia, these iconic cold-water specialists are experiencing rapid environmental change caused by a warming climate and enhanced wildfire activity. Our goal was to inform future conservation by examining the habitat associations of each species and conditions that facilitate co-occupancy. We repurposed data from previous studies in the northern Rocky Mountains to assess the efficacy of bull trout electrofishing surveys for determining the occurrence of tailed frogs and the predictive capacity of habitat covariates derived from in-stream measurements and geospatial sources to model distributions of both species. Electrofishing reliably detected frog presence (89.2% rate). Both species were strongly associated with stream temperature and flow regime characteristics, and less responsive to riparian canopy cover, slope, and other salmonids. Tailed frogs were also sensitive to wildfire, with occupancy probability peaking around 80 years after a fire. Co-occupancy was most probable in locations with low-to-moderate frequencies of high winter flow events, few other salmonids, a low base-flow index, and intermediate years since fire. The distributions of these species appear to be sensitive to environmental conditions that are changing this century in forests of the northern Rocky Mountains. The amplification of climate-driven effects after wildfire may prove to be particularly problematic in the future. Habitat differences between these two species, considered to be headwater specialists, suggest that conservation measures designed for one may not fully protect the other. Additional studies involving future climate and wildfire scenarios are needed to assess broader conservation strategies and the potential to identify refuge streams where both species are likely to persist, or complementary streams where each could exist separately into the future.

Assessment of multi-stressors on compositional turnover of diatom, invertebrate and fish assemblages along an urban gradient in Pacific Northwest streams (USA)

• Gradient forest (GF) models evaluate taxon specific responses to stressors. • GF diatom, invertebrate, fish models showed several consistent variables selected. • Variables included substrate size, dissolved oxygen, and various contaminant measures. • Nitrogen and phosphorus important in both diatom and invertebrate models but not fish. • Taxa responded to multiple stressors following patterns of sensitive versus tolerance. This study is part of the regional stream-quality assessment (RSQA) conducted by the U.S. Geological Survey (USGS) National Water Quality Assessment (NAWQA) project. The purpose of this study is to examine small streams along land-use and stressor gradients at the regional scale and to evaluate the relative importance of instream stressors on diatom, macroinvertebrate, and fish assemblages. In 2015, the RSQA project assessed stream quality in 82 wadeable streams that were selected along an urban land-use gradient in the Pacific Northwest Region (PNW) of the United States. This study evaluates the effects of four major categories of measured instream stressors – flow (i.e. alteration), water quality, habitat, and contaminants (in water and sediment) – on stream biota. We used gradient forest (GF) models to evaluate taxon specific responses to the various stressors for the three biotic assemblages. Results for diatom, invertebrate and fish assemblages showed that several environmental variables including substrate size, dissolved oxygen, and two or more different contaminants were selected in each of the GF models. In general, all three assemblages were negatively associated with any contaminant measures above zero, except the more tolerant taxa in each assemblage, which responded positively to contaminants. Total nitrogen (TN) and total phosphorus (TP) were important in both the diatom and invertebrate GF models but not in the fish models, which were related to temperature and stream flow. TP and TN were the top two variables for diatom GF models and various taxa responded at a range of nutrient concentrations; however, some taxa responded at low concentrations, for example around 0.02 for TP and 0.5 mg/L for TN. In general, the three biotic assemblages responded to multiple stressors following general patterns of known sensitive versus tolerant taxa for each of the biotic groups studied, yet the GF models allow us to explore taxon specific responses. For example, most of the sensitive Ephemeroptera, Plecoptera, Trichoptera invertebrate taxa (EPT) responded negatively when any contaminant increased above zero; yet some taxa such as the tolerant Trichoptera Cheumatopsyche responded positively to contaminants and many of the other stressors. The findings of this study demonstrate the value of using multiple assemblages to monitoring stressor gradients associated with urban stream systems and the importance of evaluating the responses of individual taxa to stressors.

A Non-Invasive Sampling Method for Detecting Non-Native Smallmouth Bass (Micropterus dolomieu)

The smallmouth bass (Micropterus dolomieu) is a cool-water fish species native to central North America. Widespread introductions and secondary spread outside of its historical range have led to new recreational fisheries and associated economic benefits in western United States, but have also resulted in a number of ecological impacts to recipient ecosystems, including threats to Pacific salmon. Management of introduced smallmouth bass populations, now and into the future, relies on accurate detection and monitoring of this species. To address this need, we developed an environmental DNA assay that can detect smallmouth bass DNA extracted from filtered water samples in concentrations as low as 2 mtDNA copies per reaction. Field testing demonstrated that eDNA sampling produced results largely consistent with snorkel surveys, a traditional visual assessment, and gained a few additional positive detections. While this assay is robust against non-target detection, including the only other Micropterus in Pacific Northwest streams, largemouth bass (M. salmoides), the high genetic similarity within the sunfish family Centrarchidae made it unable to distinguish smallmouth bass from spotted bass (M. punctulatus) and some Guadalupe bass (M. treculii). The high sensitivity of this method and assay will be particularly useful for identifying the location of non-native smallmouth bass in the Pacific Northwest, quantifying its rate of spread, and aiding management actions.

Juvenile coho salmon growth and health in streams across an urbanization gradient

Expanding human population and urbanization alters freshwater systems through structural changes to habitat, temperature effects from increased runoff and reduced canopy cover, altered flows, and increased toxicants. Current stream assessments stop short of measuring health or condition of species utilizing these freshwater habitats and fail to link specific stressors mechanistically to the health of organisms in the stream. Juvenile fish growth integrates both external and internal conditions providing a useful indicator of habitat quality and ecosystem health. Thus, there is a need to account for ecological and environmental influences on fish growth accurately. Bioenergetics models can simulate changes in growth and consumption in response to environmental conditions and food availability to account for interactions between an organism's environmental experience and utilization of available resources. The bioenergetics approach accounts for how thermal regime, food supply, and food quality affect fish growth. This study used a bioenergetics modeling approach to evaluate the environmental factors influencing juvenile coho salmon growth among ten Pacific Northwest streams spanning an urban gradient. Urban streams tended to be warmer, have earlier emergence dates and stronger early season growth. However, fish in urban streams experienced increased stress through lower growth efficiencies, especially later in the summer as temperatures warmed, with as much as a 16.6% reduction when compared to fish from other streams. Bioenergetics modeling successfully characterized salmonid growth in small perennial streams as part of a more extensive monitoring program and provides a powerful assessment tool for characterizing mixed life-stage specific responses in urban streams.

Large Wood and Instream Habitat for Juvenile Coho Salmon and Larval Lampreys in a Pacific Northwest Stream

AbstractThe influences of large wood on Pacific salmon are well‐studied, but such studies on nonsalmonid species such as lampreys are uncommon. To address this need, we evaluated the potential effects of large wood on larval lampreys (Pacific Lamprey Entosphenus tridentatus and potentially Western Brook Lamprey Lampetra richardsoni) as well as on juvenile Coho Salmon Oncorhynchus kisutch in a small, coastal, Oregon stream. Our objectives were to (1) identify instream habitat characteristics associated with the presence of larval lampreys and abundance of juvenile Coho Salmon and (2) evaluate how these characteristics were associated with instream wood. To address habitat use, we quantified presence of larval lampreys in 92 pools and abundance of juvenile Coho Salmon in 44 pools during summer low flows. We focused on a study reach where large wood was introduced into the stream between 2008 and 2009. Results indicated that presence of larval lampreys was significantly associated with the availability of fine sediment and deeper substrate. The abundance of juvenile Coho Salmon (fish per pool) was strongly associated with pool surface area and to a weaker extent with the proportion of cobble and boulder substrates in pools. Pools with wood, regardless of whether they were formed by wood, had significantly greater coverage of fine sediment, deeper substrate, and greater pool surface area. Taken together, these results suggest that instream wood can provide habitat associated with the presence of larval lampreys and greater abundance of juvenile Coho Salmon.Received September 11, 2016; accepted March 25, 2017 Published online May 31, 2017

Long-term effects of riparian forest harvest on light in Pacific Northwest (USA) streams

AbstractRiparian forests exert strong influence on abiotic and biotic processes in adjacent streams by regulating light. Harvesting of riparian forests was once common practice, and consequently, many streamside forests across North America are in varying stages of development as they regenerate, thereby affecting stream light regimes. We used 2 approaches to evaluate the influence of riparian forest harvest and stand recovery on light availability in small mountain streams. We estimated light and canopy cover every 25 m along 11.5 km of a 4th-order stream network dominated by late-successional riparian forests that included 7 streamside harvest units 50 to 60 y old. Estimates of stream light fluxes were lower in harvest units than in up- and downstream sections bordered by old-growth forests even though only 1 stream bank was harvested in 5 of 7 units. Differences in stream light between harvested reaches and adjacent old-growth sections were greater when both banks had been logged. We also conducted a s...

Observations of Channel Change from Constructed Wood Jams on a Forested Gravel-Bed Stream

AbstractSalmonids in the Pacific Northwest face a number of threats: habit degradation, loss of habitat, overharvest, competition from hatchery fish, dams, and climate change. Wood has been shown to play a key role in many aspects of stream habitat quality; however, it is in low supply in many Pacific Northwest streams because of wood removal and timber harvest practices in riparian zones. Wood placement for restoration has the potential to benefit salmonid populations. However, common applications often fall short of producing the physical changes necessary to achieve the objectives, such as the formation of deep pools and cover. This study evaluated the hypothesis that wood jams constructed with whole-tree materials, high wood piece counts, and high wood volumes would be effective at creating instream geomorphic complexity, function, and aquatic habitat quality. Results were based on an evaluation of changes to surface sediment textures and channel morphology at eight constructed wood jams built with va...

A Large-Scale, Multiagency Approach to Defining a Reference Network for Pacific Northwest Streams.

Aquatic monitoring programs vary widely in objectives and design. However, each program faces the unifying challenge of assessing conditions and quantifying reasonable expectations for measured indicators. A common approach for setting resource expectations is to define reference conditions that represent areas of least human disturbance or most natural state of a resource characterized by the range of natural variability across a region of interest. Identification of reference sites often relies heavily on professional judgment, resulting in varying and unrepeatable methods. Standardized methods for data collection, site characterization, and reference site selection facilitate greater cooperation among assessment programs and development of assessment tools that are readily shareable and comparable. We illustrate an example that can serve the broader global monitoring community on how to create a consistent and transparent reference network for multiple stream resource agencies. We provide a case study that offers a simple example of how reference sites can be used, at the landscape level, to link upslope management practices to a specific in-channel response. We found management practices, particularly areas with high road densities, have more fine sediments than areas with fewer roads. While this example uses data from only one of the partner agencies, if data were collected in a similar manner they can be combined and create a larger, more robust dataset. We hope that this starts a dialog regarding more standardized ways through inter-agency collaborations to evaluate data. Creating more consistency in physical and biological field protocols will increase the ability to share data.

Food Habits of Sculpin Spp. in Small Idaho Streams: No Evidence of Predation on Newly Emerged Steelhead Alevins

Abstract Recent declines of anadromous salmonids in the Pacific Northwest have prompted a need to understand the factors limiting populations across habitats and life stages. In the weeks following emergence from the spawning gravel, juvenile salmonids have limited swimming capacity and can be particularly vulnerable to predation by piscivores, such as sculpins (Cottus sp.) which are widespread in Pacific Northwest streams. The objective of this study was to investigate the extent to which sculpin prey on newly emerged steelhead (Oncorhynchus mykiss) in a threatened population in Idaho. Three species of sculpin were present in the watershed, including Paiute (C. beldingii), mottled (C. bairdii), and torrent (C. rhotheus) sculpin. Gut content analyses of 360 sculpin showed that invertebrates were the dominant food source (> 85% of all sculpin preyed mainly on invertebrates), and piscivory was rare (< 2%). None of the samples contained steelhead alevins. We conclude that there was no indication of predation...

Rapid ecosystem response to restoration in an urban stream

Stream restoration seeks to re-establish ecological structure and function of river systems, and understanding its ecological consequences is a current focus of stream ecology. To characterize the short-term ecosystem response to restoration in an urbanized Pacific Northwest stream, we measured whole-system ammonium and phosphorus uptake, benthic and drifting aquatic insects, and fish community composition before and after restoration. We predicted that (1) nutrient demand would temporarily decrease ammonium and phosphorus concentrations, (2) periphyton accrual would structure the insect consumer response, and (3) restoration would change the fish community. After restoration, nutrient demand for ammonium and phosphorus temporarily increased to levels that have rarely been reported, but demand for both recovered to background levels within 35 days. Aquatic insect density tracked rapid periphyton accrual after restoration, and benthic insect density stabilized in less than a month whereas composition continued changing for 10 weeks. Within 11 months, the fish community returned to its pre-restoration composition dominated by non-native eastern brook trout (Salvelinus fontinalis). Restoration did not alter the community and ecosystem metrics we studied, but this urban stream underwent rapid succession during restoration-induced disturbance, perhaps because urban streams have resilient communities well-suited to rapid recovery.

Biofilm nutrient limitation, metabolism, and standing crop responses to experimental application of salmon carcass analog in Idaho streams

Dramatic declines of Pacific salmon (Oncorhynchus spp.) populations have decreased delivery of marine-derived material to Pacific Northwest streams where juvenile salmon reside. Managers use artificial nutrient additions to increase juvenile salmon growth and survival and typically assume nutrient-driven increases in biofilm production are an important pathway by which nutrients become available to higher trophic levels. To evaluate how biofilms respond to additions of salmon carcass analog, a pasteurized, processed form of nutrient mitigation materials, we quantified biofilm nutrient limitation, benthic and whole-stream metabolism, and biofilm standing crops before and following experimental additions in tributaries of the Salmon River, Idaho, USA. Biofilm nutrient limitation did not change and standing crop did not increase in response to analog additions at two different levels (low, 30 g·m−2; or high, 150 g·m−2) within 1 month of addition. In contrast, whole-stream and benthic primary productivity and respiration increased in a high-analog treated segment, but did not increase in a low-analog treated segment. Together, our results suggest that metabolism may be a more appropriate tool for assessing the ecosystem effects of nutrient additions than biofilm standing crop or nutrient limitation, which are constrained by a variety of abiotic and biotic factors like hydrology and grazing.

Correlates and consequences of injury in a large, predatory stream salamander (Dicamptodon tenebrosus)

Conspecific aggression is an important factor structuring population dynamics through intra- and interspecific interactions, but is rarely studied in un-manipulated populations. In this study, we evaluated rates of injury as a proxy for conspecific aggression using a depletion survey of predatory coastal giant salamanders (Dicamptodon tenebrosus) in a tributary of the South Fork Eel River, California. We tested a range of hypotheses including a suite of environmental and biotic factors for the rate of injury in a population by using an AIC model-selection approach that examined the weight of evidence for individual models. We examined both the probability of a given individual being injured, and the proportion of individuals within a given study pool being injured. We found strong support for models including salamander size, density of young-of-the-year steelhead, and density of the largest size-class of salamander as factors positively influencing the rate of injury at both the individual and habitat levels. We also found that density of older steelhead (1+ steelhead) had a strong, but highly variable positive impact on frequency of injury. This study shows that both conspecific and heterospecific factors influence intraspecific aggression for the dominant salamander throughout coastal Pacific Northwest streams. Our methodology demonstrates a non-manipulative approach to identifying correlates of natural injury in a cryptic species of amphibian. More work is needed to determine how these factors directly and indirectly influence the spatial distribution, individual fitness, and dynamics of salamander populations within streams.

Macroinvertebrate response to salmon carcass analogue treatments: exploring the relative influence of nutrient enrichment, stream foodweb, and environmental variables

AbstractIn Pacific Northwest (USA) streams, historical levels of marine-derived subsidies of C, N, and P from spawning salmon and steelhead are either greatly diminished or no longer present. A novel nutrient enrichment form, pasteurized salmon carcass analogue (SCA), has been developed as a management tool to increase freshwater productivity. We analyzed macroinvertebrate assemblages in 4 central Idaho (USA) streams to explore the relative influence of reach-scale SCA treatments on macroinvertebrate assemblages. We stratified study streams into upstream (control) and downstream (treatment) reaches and applied a single SCA treatment in mid-September to the downstream reaches of 2 treatment streams. We measured chemical, physical, and biological variables in all study streams and used nonmetric multidimensional scaling (NMDS) ordination of macroinvertebrate communities to illustrate relationships to foodweb and environmental variables. Macroinvertebrate assemblages differed significantly among streams (p <...

Juvenile Chinook Salmon Summer Microhabitat Availability, Use, and Selection in a Central Idaho Wilderness Stream

AbstractWe measured summer microhabitat use, availability, and selection by age‐0 Chinook salmon Oncorhynchus tshawytscha in the Big Creek drainage, Idaho. Age‐0 fish selected for low‐velocity (0‐25 cm/s), moderate‐depth (40‐80 cm) habitats that were located within 80 cm of cover. Pools (52%) and runs (38.5%) were the most commonly used habitat types, while pebbles (33.7%) and sand (23%) were the most often used substrates. Cover type use was predominated by woody debris (54.8%) and rock outcrops (23.7%). Run (38.5%) and riffle (32.9%) were the most available habitats in Big Creek, while pebble (38.4%) and cobble (28.2%) were the most available substrates. Mean water velocity (47 cm/s) availability and distance to cover (108 cm) availability were greater than those selected by age‐0 Chinook salmon, while mean total water depth (30 cm) availability was lower than that selected by the fish. Linear regression was used to show that an increase in juvenile Chinook salmon total length was significantly (P &lt; 0.05) related to increased total water depth (r2 = 0.68), focal water depth (r2 = 0.73), and focal water velocity (r2 = 0.49) use. The relationship of habitat use and fish total lengths indicate that even within a short temporal period, juvenile Chinook salmon will select for different habitats as they grow. Upper and lower Big Creek microhabitat availability characteristics differed significantly (P &lt; 0.05). Upper Big Creek had more fish per unit of preferred rearing habitat than lower Big Creek, which suggests that either summer microhabitat availability or redd density partially explain the density differences observed in Big Creek. Microhabitat use and availability data were useful for identifying habitat selection of age‐0 Chinook salmon in Big Creek. The data from this study can be used for future identification, quantification, and restoration of suitable Chinook salmon rearing habitat in other Pacific Northwest streams.

Bed Stability and Sedimentation Associated With Human Disturbances in Pacific Northwest Streams1

Abstract: To evaluate anthropogenic sedimentation in United States (U.S.) Pacific Northwest coastal streams, we applied an index of relative bed stability (LRBS*) to summer low flow survey data collected using the U.S. Environmental Protection Agency’s Environmental Monitoring and Assessment Program field methods in a probability sample of 101 wadeable stream reaches. LRBS* is the log of the ratio of bed surface geometric mean particle diameter (Dgm) to critical diameter (D*cbf) at bankfull flow, based on a modified Shield’s criterion for incipient motion. We used a formulation of LRBS* that explicitly accounts for reductions in bed shear stress that result from channel form roughness due to pools and wood. LRBS* ranged from −1.9 to +0.5 in streams within the lower quartile of human riparian and basin disturbance, and was substantially lower (−4.2 to −1.1) in streams within the upper quartile of human disturbance. Modeling results suggest that the expected range of LRBS* in streams without human disturbances in this region might be generally between −0.7 and +0.5 in either sedimentary or volcanic lithology. However, streams draining relatively soft, erodible sedimentary lithology showed greater reductions in LRBS* associated with disturbance than did those having harder, more resistant volcanic (basalt) lithology with similar levels of basin and riparian disturbance. At any given level of disturbance, smaller streams had lower LRBS* than those with larger drainages. In sedimentary lithology (sandstone and siltstone), high‐gradient streams had higher LRBS* than did low‐gradient streams of the same size and level of human disturbance. High gradient streams in volcanic lithology, in contrast, had lower LRBS* than low‐gradient streams of similar size and disturbance. Correlations between Dgm and land disturbance were stronger than those observed between D*cbf and land disturbance. This pattern suggests that land use has augmented sediment supplies and increased streambed fine sediments in the most disturbed streams. However, we also show evidence that some of the apparent reductions in LRBS*, particularly in steep streams draining small volcanic drainages, may have resulted in part from anthropogenic increases in bed shear stress. The synoptic survey methods and designs we use appear adequate to evaluate regional patterns in bed stability and sedimentation and their general relationship to human disturbances. More precise field measurements of channel slope, cross‐section geometry, and bed surface particle size would be required to use LRBS* in applications requiring a higher degree of accuracy and precision, such as site‐specific assessments at individual streams.

Downstream hydrologic and geomorphic effects of large dams on American rivers

The hydrology and geomorphology of large rivers in America reflect the pervasive influence of an extensive water control infrastructure including more than 75,000 dams. One hundred thirty-seven of the very large dams, each storing 1.2 km 3 (10 6 acre feet) of water or more, alter the flows of every large river in the country. The hydrologic effects of these very large dams emerge from an analysis of the stream gage records of 72 river reaches organized into 36 pairs. One member of each pair is an unregulated reach above a dam, whereas the other is a regulated reach downstream from the same structure. Comparison of the regulated and unregulated reaches shows that very large dams, on average, reduce annual peak discharges 67% (in some individual cases up to 90%), decrease the ratio of annual maximum/mean flow 60%, decrease the range of daily discharges 64%, increase the number of reversals in discharge by 34%, and reduce the daily rates of ramping as much as 60%. Dams alter the timing of high and low flows and change the timing of the yearly maximum and minimum flows, in some cases by as much as half a year. Regional variation in rivers, dams, and responses are substantial: rivers in the Great Plains and Ozark/Ouachita regions have annual maximum/mean flow ratios that are 7 times greater than ratios for rivers in the Pacific Northwest. At the same time, the ratio of storage capacity/mean annual water yield for dams is greatest for Interior Western, Ozark/Ouachita and Great Plains rivers and least for Pacific Northwest streams. Thus, in many cases those rivers with the highest annual variability have the greatest potential impact from dams because structures can exert substantial control over downstream hydrology. The hydrologic changes by dams have fostered dramatic geomorphic differences between regulated and unregulated reaches. When compared to similar unregulated reaches, regulated reaches have 32% larger low flow channels, 50% smaller high flow channels, 79% less active flood plain area, and 3.6 times more inactive flood plain area. Dams also affect the area of active areas, the functional surfaces that are functionally connected to the present regime of the river. Regulated reaches have active areas that are 72 smaller than the active areas of similar unregulated reaches. The geomorphic complexity (number of separate functional surfaces per unit of channel length) is 37% less in regulated reaches. Reductions in the size of hydrologically active functional surfaces are greatest in rivers in the Great Plains and least in Eastern streams. The largest differences in geomorphic complexity are in interior western rivers. The shrunken, simplified geomorphology of regulated large rivers has had direct effects on riparian ecology, producing spatially smaller, less diverse riparian ecosystems compared to the larger, more complex ecosystems along unregulated reaches of rivers.

Influence of Salmon Carcass Placement in Red Alder Riparian Areas on Stream Chemistry in Lowland Western Washington

AbstractPopulations of Pacific salmon Oncorhynchus spp., which historically returned large quantities of marine‐derived nutrients (MDN) to Pacific Northwest streams and riparian areas, are now much lower. In response, salmon carcasses are now being placed in streams and riparian areas to compensate for the loss of MDN, particularly organic N and P. Our objectives were to determine (1) whether placement of chum salmon O. keta carcasses in riparian areas dominated by red alder Alnus rubra, an N‐fixing tree, changed stream chemistry and (2) whether carcass placement affected water quality. Study sites were Brown and Le Bar creeks, two small streams in the Skokomish River valley in western Washington. The amount of N in carcasses placed in riparian areas in Brown and Le Bar creeks in November 1999 was estimated to be 22.4 and 59.8 kg/ha, respectively, while the amount of P was 2.7 and 7.2 kg/ha. Monthly stream grab samples were taken between September 1999 and October 2000 upstream and downstream of salmon carcass placement areas and analyzed for NO3‐N, NH4‐N, PO4‐P, pH, electrical conductivity, and alkalinity. The maximum concentration was low for NO3‐N (0.32 mg/L), NH4‐N (0.10 mg/L), and PO4‐P (0.026 mg/L). Salmon carcass placement did not significantly change stream chemistry. This could have been because of the particular amounts of N and P added or uptake by soil organisms, riparian vegetation, and stream processes. Substantial amounts of nutrients in salmon carcasses can be added to the system with little influence on stream water quality. Red alder in the riparian areas did not strongly influence the stream concentration of NO3‐N.

Responses of Benthic Fishes and Giant Salamanders to Placement of Large Woody Debris in Small Pacific Northwest Streams

Abstract The placement of large woody debris (LWD) to improve or restore habitat for fishes is a common practice in North American streams, and the responses of salmonids to this practice have frequently been examined. In contrast, little information exists on the effects of LWD placement on nonsalmonid fishes and amphibians. In this study, I examined the responses of giant salamanders Dicamptodon spp., juvenile lampreyss Entosphenus tridentatus and Lampetra spp., reticulate sculpins Cottus perplexus, and torrent sculpins C. rhotheus to artificially placed LWD by sampling 29 small streams with paired treatment and reference reaches. Densities and mean lengths of giant salamanders, reticulate sculpins, torrent sculpins, and lampreyss did not differ significantly between treatment and references reaches. I also examined whether the observed responses were correlated with differences in physical habitat between reference and treatment reaches. Lampreys densities (log10(treatment) − log10(reference)) and leng...