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The River Continuum Concept (RCC) predicts that food webs (and, in particular, invertebrates) of rivers in temperate, forested drainages should exhibit a longitudinal gradient from reliance on terrestrially derived organic matter (e.g., seasonally shed leaves) in the headwaters to autochthonous sources (e.g., algae) in the mid-orders, to suspended material in larger rivers. This prediction has been evaluated by longitudinal comparisons of macroinvertebrate communities in terms of functional feeding groups (FFGs), but such an approach yields only indirect evidence regarding actual food use. To retest this prediction, we investigated invertebrate diets from the Salmon River, Idaho, by examining the gut contents of archived specimens from the longitudinal set of sites sampled in the original 1976 RCC study and by collecting invertebrates from these same sites in 2009. We detected no apparent shifts in diets over the ∼30-y time span. The importance of allochthonous materials in invertebrate diets diff...

Ecosystems are connected through fluxes of nutrients, organic matter, and organisms. Disturbances that alter structure and function of one ecosystem may have consequences for other linked ecosystems. We investigated how wildfire and subsequent debris flows altered fluxes of invertebrates from tributaries in the Salmon River Basin, Idaho, USA. We compared fluxes of invertebrates downstream through drift and laterally via insect emergence from streams with varying disturbance histories (unburned, burned, and burned + debris flow) during two summers (3–4 years post fire and 2–3 years post debris flow). We observed that the combination of wildfire and debris flow increased the biomass export of invertebrates from tributaries to main-stem ecosystems 2–3 × compared to other streams. In contrast, aquatic insect emergence did not differ in magnitude among streams of different disturbance histories, but instead diverged in timing. Underwater surveys indicated trout in the main-stem river selected confluence habitats, with a tendency for stronger selection of confluences with burned streams. In a behavioral comparison between confluence and non-confluence habitats, rates of agonistic behavior were 4–6 × higher in confluence areas, indicating that confluences may be worth defending. Abundances of web-spinning spiders that depend on emerging insects did not vary with disturbance history in early-mid summer, but tended to be highest in riparian areas along burned streams by August. Because wildfire and debris flows are predicted to increase, our results elucidate potential pathways by which altered disturbance regimes may affect coupled aquatic-terrestrial ecosystems.

Postfire disturbances, such as debris flows, may alter the recovery of stream ecosystems from wildfire. Furthermore, changes to productivity and the dynamics of nutrients and organic matter (OM) in tributaries may affect fluxes of materials and organisms to mainstem habitats. We investigated the consequences of watershed wildfire and debris flows for exports from tributaries to mainstem habitats in the South Fork Salmon River Basin of central Idaho, USA. We compared fluxes from 15 streams (n = 5 unaffected [UA], n = 5 fire-affected [FA], and n = 5 fire + debris flow-affected [FDA]) in summer 2011 (4 y postfire, 3 y postdebris flow). In early June, FDA streams exported 650% higher concentrations of sediment to downstream habitats than did UA streams (mean, FDA: 18.7 g/m3, UA: 1.9 g/m3). Overall, concentrations of dissolved organic C were 75% greater in FDA than in UA streams (FDA: 2.8, UA: 1.6 mg/L), and the quality of OM was higher (i.e., more chlorophyll a [chl a] and higher chl a:OM) in FDA than...

Droughts, fires, and floods are natural disturbances influencing aquatic ecosystems. If drought is accompanied by fires, and if fires are closely followed by floods, teasing apart their distinctive and potentially interactive responses can be difficult. We compared the responses of macroinvertebrate communities to fire via comparisons of streams in burned and unburned catchments in 3 fire-prone biomes that differ biogeographically and climatically (northwestern Mediterranean, southeastern Australia, and northwestern intermountain USA). The responses of macroinvertebrate communities in streams in burned catchments were similar in all biogeographic regions, but the magnitude of these responses varied. Fire combined with high seasonal stream flows, flooding, or drought was associated with reduced measures of taxonomic richness and increased abundance, especially of r-strategist taxa. Differences between sites in burned and unburned catchments were consistently stronger in southeastern Australia than ...

Summary Non-native species can affect food web and community structure, including the flow of resources from one habitat to another. In many streams of western North America, non-native brook trout (Salvelinus fontinalis) have replaced native cutthroat trout (Oncorhynchus clarkii). Because brook trout naturally occur at higher densities and exhibit different feeding habits, this replacement may have consequences for a range of organisms in stream-riparian food webs. We conducted a large-scale, 2-month field experiment to test whether, compared with cutthroat trout, brook trout reduce benthic insects, cause an increase in stream algae, and reduce emerging adult aquatic insects as well as riparian spiders that rely on emergence as prey. Twenty enclosed reaches from which trout were removed were treated by adding age-1 and older: (i) cutthroat trout at natural density (0.15 fish m−2); (ii) brook trout at a natural density (0.40 fish m−2); (iii) brook trout at a low density equal to the cutthroat trout treatment (0.15 fish m−2) or (iv) no trout added. Brook trout reduced the flux of emerging insects by 55% compared with cutthroat trout, but, surprisingly, only at the lower density. This reduction in emergent insects was predicted to reduce spider abundance by 20%, provided that sufficient branches were available to support riparian spider webs. We also detected an effect of trout on large-bodied benthic and emerging insects, but not on the entire assemblage of benthic insects, or periphyton. We hypothesise that our results were influenced by trout foraging behaviour mediated by their density and size structure. Regardless of the mechanisms responsible, our results indicate that non-native brook trout can reduce the flux of emerging insects, and further analysis showed that this could reduce riparian spiders and birds that prey on them. Similar effects of non-native fish are likely to occur in lotic and lentic waters beyond the western United States.

River regulation may mediate the interactions among native and nonnative species, potentially favoring nonnative species and contributing to the decline of native populations. We examined food resource use and diet overlap among small-bodied fishes in the Grand Canyon section of the Colorado River as a first step in evaluating potential resource competition. We compared the diets of the predominant small-bodied fishes (native Speckled Dace Rhinichthys osculus, juvenile Flannelmouth Sucker Catostomus latipinnis, and juvenile Bluehead Sucker C. discobolus, and nonnative Fathead Minnow Pimephales promelas) across seasons at four sites downstream of Glen Canyon Dam using nonmetric multidimensional scaling and Schoener's similarity index. The diets of these fishes included diatoms, amorphous detritus, aquatic invertebrates (especially simuliid and chironomid larvae), terrestrial invertebrates, and terrestrial vegetation. Diets varied with season and were affected by high turbidity. Fish consumed more amorphous detritus and terrestrial vegetation during the summer monsoon season (July–September), when turbidity was higher. The diets of all species overlapped, but there was large variation in the degree of overlap. The diets of juvenile suckers and Fathead Minnows were most similar, while Speckled Dace had relatively distinct diets. The differences took the form of higher proportions of diatoms and amorphous detritus in the diets of Bluehead Suckers and Fathead Minnows and higher proportions of simuliids and chironomids in those of Speckled Dace. If food resources are or become limiting, diet overlap suggests that competition may occur among native and nonnative species, which could have implications for the population dynamics of these fishes and for the management of the Colorado River ecosystem in Grand Canyon. Received September 4, 2013; accepted February 11, 2014

We examined the effect of agricultural land use on whole-stream nutrient availability, biofilm standing crop, and biofilm nutrient limitation and uptake in 21 stream locations in southeastern Idaho. Higher stream water concentrations of dissolved organic carbon (DOC), but not nitrate (NO3-N) or phosphate (PO4-P), were associated with % agriculture in the watershed. Streambed chlorophyll a (Chl a) and ash free dry weight (AF dry wt) also increased with agricultural land use. Nutrient diffusing substrate (NDS) bioassays, which determine biofilm nutrient limitation, showed that Chl a was NO3-N limited and suppressed by labile DOC, whereas AF dry wt did not respond to either NO3-N or labile DOC additions. Together, the different responses of Chl a and AF dry wt suggest potential competition between biofilm autotrophs and heterotrophs for nutrients or other resources. Nutrient uptake, determined with short-term releases of NO3-N, PO4-P, and DOC (as glucose) showed that NO3-N uptake velocity (Vf) increased with agricultural land use. Despite the N-limited status of biofilms indicated by the NDS results, uptake of NO3-N could not be consistently detected at all locations. The differences in response of biofilm to organic carbon enrichment suggests a difference in DOC quality, with labile DOC added with NDS compared to perhaps less-labile DOC found in-stream. Linking the interactive responses of biofilm communities to altered nutrient availability is an important step toward understanding whole ecosystem responses to land-use change.

Non-native brook trout (Salvelinus fontinalis) have replaced native cutthroat trout (Oncorhynchus clarkii) in streams across the western USA. Brook trout have been assumed to be functionally equivalent to cutthroat trout, which could argue against extensive control of this species by government agencies. This assumption was assessed by comparing the diets of the two trout species and their effects on benthic invertebrates in a large-scale field experiment. Within a Rocky Mountain stream where brook trout had already become established, trout species and density were manipulated in 20 fenced sections to create four treatments: cutthroat trout at a density natural for un-invaded streams, brook trout at two densities, natural for invaded streams or reduced to match the natural density of cutthroat trout, and areas depleted of most trout. By the end of the experiment, populations of brook trout at natural density consumed seven times more benthic invertebrates than cutthroat trout. Brook trout also consumed more Apatania caddisflies and Heterlimnius riffle beetles per capita than cutthroat trout. However, the greater consumption did not cause detectable reductions in benthic invertebrate densities. A large-scale experiment of trout removal like this may be inherently limited in its ability to detect effects on benthic invertebrate densities. However, this and several companion studies indicate that stream ecosystems would not function in the same way if cutthroat trout are replaced by brook trout. Sustaining these functions, as well as biodiversity and socioeconomic values, are important reasons to conserve native cutthroat trout. Copyright © 2012 John Wiley & Sons, Ltd.

Introductions of nonnative salmonids, such as rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta, have affected native fishes worldwide in unforeseen and undesirable ways. Predation and other interactions with nonnative rainbow trout and brown trout have been hypothesized as contributing to the decline of native fishes (including the endangered humpback chub Gila cypha) in the Colorado River, Grand Canyon. A multiyear study was conducted to remove nonnative fish from a 15-km segment of the Colorado River near the Little Colorado River confluence. We evaluated how sediment, temperature, fish prey availability, and predator abundance influenced the incidence of piscivory (IP) by nonnative salmonids. Study objectives were addressed through spatial (upstream and downstream of the Little Colorado River confluence) and temporal (seasonal and annual) comparisons of prey availability and predator abundance. Data were then evaluated by modeling the quantity of fish prey ingested by trout durin...

The effects of wildfire can alter the structure of stream insect assemblages. Post-fire shifts to dominance by r-strategist taxa could drive increases in productivity of primary consumer and predatory insects, but this possibility has not been explicitly investigated. Likewise, the extent and duration of such effects might be mediated by fire severity, but this hypothesis also has not been evaluated. We report results from a comparative study that examined the mid-term (5–10 y post-fire) effects of wildfire of varying severity on stream insect assemblage composition and productivity measured in terms of benthic larval biomass and flux of emerging adults. We compared benthos and emergence in a suite of 2nd- to 3rd-order, unburned streams to those that had experienced low-severity and high-severity wildfire in wilderness watersheds of central Idaho. Reaches that experienced high-severity burn had the greatest biomass of r-strategist, generalist primary consumers that included Chironomidae, Baetis, a...

Physical characteristics of riverine habitats, such as large wood abundance, pool geometry and abundance, riparian vegetation cover, and surface flow conditions, have traditionally been thought to constrain fish production in these ecosystems. Conversely, the role of food resources (quantity and quality) in controlling fish production has received far less attention and consideration, though they can also be key productivity drivers. Traditional freshwater food web illustrations have typically conveyed the notion that most fish food is produced within the local aquatic habitat itself, but the concepts and model we synthesize in this article show that most fish food comes from external or very distant sources—including subsidies from marine systems borne from adult returns of anadromous fishes, from fishless headwater tributaries that transport prey to downstream fish, and from adjacent streamside vegetation and associated habitats. The model we propose further illustrates how key trophic pathways and food...

Increased need to quantify adult insects emerging from streams as a part of foodweb and ecosystem studies has placed new demands on techniques used to sample adults. The population sampled must be better understood to establish the scope of inferences that may be drawn from emergence data. We used data from 2 different studies to compare the structure of insect assemblages represented by benthic samples and emergence-trap samples and to compare adult insect assemblages collected in emergence traps placed at mid-channel vs streambank locations. Nonmetric multidimensional scaling (NMDS) ordination showed that some components of the benthic assemblage were underrepresented in the emergence-trap samples and others were underrepresented in benthic samples. These differences were mainly caused by taxa that emerged by crawling out on the stream bank (e.g., Plecoptera) or whose larvae reside in habitats, such as stream margins, that are underrepresented with traditional benthic sampling (e.g., Dixidae). The flux of insects into traps placed mid-channel did not differ significantly from the flux into traps placed along the stream bank. Taxa collected by mid-channel and streambank traps overlapped considerably, but midchannel traps tended to collect proportionally more Trichoptera, Ephemeroptera, and Diptera, whereas streambank traps collected proportionally more Plecoptera. Our results can be used to improve trapping designs for future assessments of aquatic insect emergence in studies of insect behavior and life histories and as part of foodweb and ecosystem research.

The replacement of native species by nonnative species has been widely documented. In aquatic ecosystems, nonnative trout often replace native trout species to which they are closely related. For example, nonnative brook trout Salvelinus fontinalis have replaced native cutthroat trout Oncorhynchus clarkii throughout western North America. We hypothesized that when brook trout replace cutthroat trout, they exhibit greater density, biomass, and annual production than were achieved by the cutthroat trout before replacement. We tested this hypothesis in five paired streams in the Teton River drainage, Idaho, over a 4-year period. Streams were paired based on similar habitat characteristics and the presence of brook trout or cutthroat trout as the dominant species. Fish were surveyed annually by means of multipass depletion along representative stream reaches. Consistent with our hypothesis, brook trout exhibited 2.4 times greater density, 1.7 times greater biomass, and 2.5 times higher annual product...

We investigated the midterm effects of wildfire (in this case, five years after the fire) of varying severity on periphyton, benthic invertebrates, emerging adult aquatic insects, spiders, and bats by comparing unburned sites with those exposed to low severity (riparian vegetation burned but canopy intact) and high severity (canopy completely removed) wildfire. We observed no difference in periphyton chlorophyll a or ash-free dry mass among different burn categories but did observe significantly greater biomass of benthic invertebrates in both high severity burned and unburned reaches versus low severity burned reaches. Moreover, a significantly greater flux of adult aquatic insect emergence occurred at sites that experienced high severity fire versus low severity burned and unburned sites. The greatest number of spiders and bat echolocation calls were also observed at sites of high severity fire. Our results suggest that fires of different severity may have very different affects on stream-riparian food webs and that high severity wildfire may lead to an extended “fire pulse” that stimulates aquatic productivity and flux of prey to terrestrial habitats, driving local increases in riparian consumers.

SUMMARY 1. Streams are highly connected to their landscapes and so are easily altered by multiple stressors that affect both uplands and riparian zones, and the streams themselves. These include dams and diversions, channelisation, deforestation, water pollution, biological invasions and climate change. 2. We review research conducted in Hokkaido Island, northern Japan, which measured the effects of many of these stressors on both stream food webs and fluxes of invertebrates to and from the riparian zone that feed aquatic and terrestrial consumers. About half the energy that sustains fish falls directly into streams as terrestrial invertebrates, and a quarter of the energy needs for riparian birds is supplied by adult aquatic insects emerging from the stream. 3. Single stressors in these Hokkaido streams, including deforestation, channelisation, erosion-control dams, biological invasions and climate change, have drastic effects on stream food webs, the fishes they support and riparian predators (spiders, birds, and bats). Most stressors caused 30–90% declines in foraging, growth, or abundance of aquatic or terrestrial predators. Indirect effects of stressors also cascaded throughout stream food webs and across the aquatic–terrestrial boundary. 4. Effects of individual stressors were largely concordant across spatial scale, through time during years of different productivity and among different food web components. 5. Two studies of multiple stressors revealed that each stressor alone reduced food web components like abundance of stream benthos or riparian spiders to low levels (35–83% reduction; mean 59%), beyond which an additional stressor had little effect. Synergism and antagonism are less relevant when individual stressors have such large effects. 6. Thematic implications: small streams in Hokkaido are highly sensitive to many individual stressors and have little resistance or resilience to their effects. Moreover, each stressor alone can reduce biota strongly, indicating that restoration will need to consider all simultaneously to protect biotic diversity.

Our ability to perceive quality in nature begins, as in art, with the pretty. It expands through successive stages of the beautiful to values as yet uncaptured by language.

We review the ecology and conservation of three lesser-known chars (genus Salvelinus): Dolly Varden (S. malma), white-spotted char (S. leucomaenis), and bull trout (S. confluentus). Dolly Varden is distributed across the northern Pacific Rim and co-occurs with bull trout and white-spotted char at the southern extremes of its range. In contrast, bull trout and white-spotted char are naturally isolated, with the former restricted to North America and the latter distributed in northeastern Asia. Though the range of Dolly Varden overlaps with the two other chars, it is most closely related to Arctic char (S. alpinus), whereas bull trout and white-spotted char are sister taxa. Each species exhibits diverse life histories with respect to demographic characteristics, trophic ecology, and movement. This diversity appears to be tied to environmental variability (e.g., temperature, habitat connectivity), resource availability (e.g., food), and species interactions. Increasingly, these interactions involve ...

Large-scale patterns of hyporheic exchange are predictable within some river systems, but our understanding of the factors driving hyporheic processes and the magnitude of hyporheic exchange needed to influence biophysical patterns at larger scales remains limited. We investigated the patterns, magnitude, and potential effects on biota of reach-scale hyporheic exchange in an alluvial river of the Pacific Northwest. The river was topographically similar to and in the same geographic region as other systems where large-scale hyporheic exchange and associated biological responses have been observed. We hypothesized that predictable reach-scale patterns of hyporheic exchange would occur in alluvial valley segments of the river and that hyporheic upwelling would be associated with reach-scale patterns of physical and biological characteristics. We used in-channel piezometers and synoptic stream flow measurements to quantify hyporheic exchange. We measured temperature, dissolved O2, pH, specific conduct...

SUMMARY 1. Streams and their adjacent riparian zones are closely linked by reciprocal flows of invertebrate prey. We review characteristics of these prey subsidies and their strong direct and indirect effects on consumers and recipient food webs. 2. Fluxes of terrestrial invertebrates to streams can provide up to half the annual energy budget for drift-feeding fishes such as salmonids, despite the fact that input occurs principally in summer. Inputs appear highest from closed-canopy riparian zones with deciduous vegetation and vary markedly with invertebrate phenology and weather. Two field experiments that manipulated this prey subsidy showed that it affected both foraging and local abundance of stream fishes. 3. Emergence of adult insects from streams can constitute a substantial export of benthic production to riparian consumers such as birds, bats, lizards, and spiders, and contributes 25–100% of the energy or carbon to such species. Emergence typically peaks in early summer in the temperate zone, but also provides a low-level flux from autumn to spring in ice-free streams. This flux varies with in-stream productivity, and declines exponentially with distance from the stream edge. Some predators aggregate near streams and forage on these prey during periods of peak emergence, whereas others rely on the lower subsidy from autumn through spring when terrestrial prey are scarce. Several field experiments that manipulated this subsidy showed that it affected the short-term behaviour, growth, and abundance of terrestrial consumers. 4. Reciprocal prey subsidies also have important indirect effects on both stream and riparian food webs. Theory predicts that allochthonous prey should increase density of subsidised predators, thereby increasing predation on in situ prey and causing a negative indirect effect via apparent competition. However, short-term experiments have produced either positive or negative indirect effects. These contrasting results may be due to characteristics of the subsidies and individual consumers, but could also result from differences in experimental designs. 5. New study approaches are needed to better determine the direct and indirect effects of reciprocal prey subsidies. Experiments coupled with comparative research will be required to measure their effects on individual consumer fitness and population demographics. Future work should investigate whether reciprocal prey fluxes stabilise linked stream–riparian ecosystems, explore how landscape context affects the magnitude and importance of subsidies, and determine how impacts of human disturbance can propagate between streams and riparian zones via these trophic linkages. Study of these

Measurements of groundwater–stream water interactions are increasingly recognized as important to understanding the ecology of fishes and other organisms in stream and riparian ecosystems. However, standard measurement techniques are often feasible only at small spatial scales, in areas with easy access, or in systems with relatively fine substrata. We developed simple new techniques for installing minipiezometers and obtaining estimates of vertical hydraulic gradient, hydraulic conductivity, and specific discharge in gravel and cobble streambeds that allowed for large numbers of measurements to be obtained in remote locations. Our approach yielded values comparable to those obtained through more traditional methods. Consequently, these techniques may provide a labor cost-efficient way for detecting groundwater−stream water interaction patterns that are critical labor-attributes of stream and riparian systems at multiple scales.

The distribution and abundance of bull trout (Salvelinus confluentus) spawning were affected by geomorphology and hyporheic groundwater - stream water exchange across multiple spatial scales in streams of the Swan River basin, northwestern Montana. Among spawning tributary streams, the abundance of bull trout redds increased with increased area of alluvial valley segments that were longitudinally confined by geomorphic knickpoints. Among all valley segment types, bull trout redds were primarily found in these bounded alluvial valley segments, which possessed complex patterns of hyporheic exchange and extensive upwelling zones. Bull trout used stream reaches for spawning that were strongly influenced by upwelling. However, within these selected reaches, bull trout redds were primarily located in transitional bedforms that possessed strong localized downwelling and high intragravel flow rates. The changing relationship of spawning habitat selection, in which bull trout selected upwelling zones at one spatial scale and downwelling zones at another spatial scale, emphasizes the importance of considering multiple spatial scales within a hierarchical geomorphic context when considering the ecology of this species or plans for bull trout conservation and restoration.

The Swan Basin in Montana is considered a stronghold of regional significance for the bull trout Salvelinus confluentus, a native char whose populations are fragmented and declining throughout its range. We used correlation analysis to examine spatial and temporal variation of bull trout redd count data (1982–1995) relative to geomorphic and land-use factors among nine principal spawning tributaries of the Swan River. Bull trout redd numbers were positively correlated with the extent of alluvial valley segments bounded by knickpoints and negatively correlated with the density of logging roads in spawning tributary catchments. The density of logging roads in spawning tributary catchments was not significantly correlated with geomorphic factors. Temporal trends among the principal spawning streams were variable. In four of the nine principal spawning streams, redd numbers increased significantly during the survey period, and in the remaining streams, redd numbers showed no significant change. Chang...

We measured large woody debris (LWD) in 20 known bull trout (Salvelinus confluentus) spawning stream reaches from logged and wilderness watersheds in northwestern Montana. Mean bankfull width of stream reaches was 14.1 m ranging from 3.9 to 36.7 m. Streams were large enough to move LWD and form aggregates. We determined the characteristics of individual pieces of LWD that were interactive with the stream channel. Large, short pieces of LWD attached to the stream bank were the most likely to be positioned perpendicular to stream flow, while large, long pieces either tended to be parallel to the flow or, when attached, were most apt to extend across the channel thalweg. Observations indicated that the majority of pools were formed as scour pools by either very large LWD pieces that were perpendicular to the stream or multipiece LWD aggregates. Among reaches in wilderness watersheds, ratios of large to small LWD, attached to unattached LWD, and with and without rootwads were relatively consistent. However, among reaches with logging in the watershed, these ratios varied substantially. These results suggest that logging can alter the complex balance of delivery, storage, and transport of LWD in northern Rocky Mountain streams, and therefore, the likely substantive change in stream habitats. Resume : Nous avons mesure les gros debris ligneux (GDL) dans 20 troncons de cours d'eau servant de frayeres a l'omble a tete plate dans des bassins exploites par l'industrie forestiere et des bassins sauvages du nord-ouest du Montana. La largeur moyenne des troncons a pleins bords etait de 14,1 m, avec une fourchette de 3,9 m a 36,7 m. Les cours d'eau etaient assez larges pour que les GDL se deplacent et forment des agregats. Nous avons determine les caracteristiques des morceaux de GDL qui interagissaient avec le chenal. Les morceaux gros et courts attaches a la berge etaient les plus susceptibles de se positionner perpendiculairement au courant, tandis que les morceaux gros et longs se placaient parallelement au courant ou, s'ils etaient attaches, etaient les plus susceptibles de se placer en travers du thalweg du chenal. Les observations ont montre que la majorite des fosses sont le resultat de l'affouillement cause soit par de tres gros morceaux de GDL perpendiculaires au courant, soit par des agregats composes de plusieurs morceaux de GDL. Parmi les troncons des bassins sauvages, les rapports des gros aux petits GDL, des GDL attaches aux GDL non attaches, des GDL avec et sans attaches racinaires, etaient relativement constants, alors qu'ils variaient considerablement parmi les troncons des bassins soumis a l'exploitation forestiere. Ces resultats permettent de penser que l'exploitation forestiere peut alterer l'equilibre complexe de l'apport, de l'installation et du transport des GDL dans les cours d'eau du nord des Montagnes Rocheuses, et donc occasionner des modifications potentiellement importantes des habitats lotiques.