Effects of glacial retreat on proglacial streams and riparian zones in the Coast and North Cascade Mountains

Proglacial stream development was studied in coastal British Columbia and Washington, focusing on reaches exposed by post‐Little Ice Age (LIA) glacier retreat, to address three principal questions: (i) Does the legacy of LIA glaciation influence the evolution of channel morphology? (ii) How long does it take for riparian forest to establish following glacier retreat? (iii) Can newly exposed proglacial streams provide suitable fish habitat? Channel morphologies were identified by field surveys of 69 reaches in 10 catchments. Riparian forest development and potential fish habitat were characterized in those reaches and an additional 22 catchments using GIS analysis. The landscape template imposed by the Quaternary glaciation appears to override most of the modern effects of the LIA in controlling channel‐reach morphology. Binary logistic regression analysis identified elevation and time since deglaciation as primary controls on the presence of riparian forest. At higher elevations, establishment of morphologically functional riparian forest could take several centuries, prolonged by channel instability associated with post‐LIA sediment inputs. Of the recently deglaciated streams included in this analysis, the majority (86%) of the total length was of suitable gradient for fish and could be accessed either by downstream populations or from adjacent lakes. Predicted maximum weekly average stream temperature (MWAT) indicated that the post‐LIA study streams were thermally suitable for cold‐water fish. A future scenario of glacier loss would cause a 14% decline in accessible cold‐water thermal habitat in post‐LIA streams. Decreased summer flows due to glacier retreat could further limit usable habitat by reducing stream depths and wetted perimeters. Copyright © 2013 John Wiley & Sons, Ltd.     

The headward extent of fluvial landforms and associated vegetation on massanutten mountain,Virginia

Variation in fluvial landforms and associated vegetation in the headward (upstream) direction has received little study and the controlling factors are not well understood. The relations among channel gradient, basin area, stream order, and the headward extent of fluvial landforms and vegetation was studied in 18 small basins and larger nearby stream reaches in the Massanutten Mountain area, northern Shenandoah Valley, Virginia. Low-order streams were traversed to their basin heads. Notice was made of the point or region of the disappearance of fluvial landforms. Indicator species were used to confirm landform identification. The studied landforms include the channel bar, channel shelf, floodplain, and terraces. Basin geomorphic characteristics were determined from topographic and geologic maps and ground surveys. Results suggest that gradient is the most important factor controlling the development of fluvial landforms. Floodplains have not developed along stream reaches where average channel gradients exceed 0.15. Channel shelves and associated vegetation occur farther upstream than floodplains.     

The influence of riparian vegetation on near‐bank turbulence: a flume experiment

Measurements from a fixed‐bed, Froude‐scaled hydraulic model of a stream in northeastern Vermont demonstrate the importance of forested riparian vegetation effects on near‐bank turbulence during overbank flows. Sections of the prototype stream, a tributary to Sleepers River, have increased in channel width within the last 40 years in response to passive reforestation of its riparian zone. Previous research found that reaches of small streams with forested riparian zones are commonly wider than adjacent reaches with non‐forested, or grassy, vegetation; however, driving mechanisms for this morphologic difference are not fully explained. Flume experiments were performed with a 1:5 scale, simplified model of half a channel and its floodplain, mimicking the typical non‐forested channel size. Two types of riparian vegetation were placed on the constructed floodplain: non‐forested, with synthetic grass carpeting; and forested, where rigid, randomly distributed, wooden dowels were added. Three‐dimensional velocities were measured with an acoustic Doppler velocimeter at 41 locations within the channel and floodplain at near‐bed and 0·6‐depth elevations. Observations of velocity components and calculations of turbulent kinetic energy (TKE), Reynolds shear stress and boundary shear stress showed significant differences between forested and non‐forested runs. Generally, forested runs exhibited a narrow band of high turbulence between the floodplain and main channel, where TKE was roughly two times greater than TKE in non‐forested runs. Compared to non‐forested runs, the hydraulic characteristics of forested runs appear to create an environment with higher erosion potential. Given that sediment entrainment and transport can be amplified in flows with high turbulence intensity and given that mature forested stream reaches are wider than comparable non‐forested reaches, our results demonstrated a possible driving mechanism for channel widening during overbank flow events in stream reaches with recently reforested riparian zones. Copyright © 2007 John Wiley & Sons, Ltd.     

Variation of stream temperature among mesoscale habitats within stream reaches: southern Appalachians

Stream mesoscale habitats have systematic topographic relationships to hyporheic flow patterns, which may create predictable temperature variation between mesoscale habitat types. We investigated whether systematic differences in temperature metrics occurred between mesoscale habitats within reaches of small streams tributary to the upper Little Tennessee River, southern Appalachians. Surface water temperature was recorded over three or four mid‐summer days in four mesoscale habitat types: riffle, main riffle, pool and alcove in 44 stream segments (sites). Temperature metrics were calculated for each mesoscale habitat relative to the mean value of the metric over the stream: Δ maximum temperature, Δ average maximum temperature and Δ maximum daily variation and also for each site: standard deviation of the maximum temperature and average diurnal variation (ADV). Sites were categorized as fully or partially forested. Pool tailouts had statistically significantly lower Δ maximum temperature and Δ average maximum temperature than riffle tailouts in partially forested sites, although differences were small. This was the opposite of what was expected in the presence of hyporheic exchange, indicating hyporheic exchange is not a dominant driver of mesoscale habitat temperatures at these sites. Temperature differences between mesoscale habitat units were small and unlikely to have ecological significance. We also evaluated relationships between stream temperature and riparian condition, watershed % impervious surfaces, watershed % non‐forested and elevation. ADV and standard deviation of the maximum temperature were significantly higher in partially forested sites, indicating that partially forested sites have greater temperature ranges and spatial variation of maximum temperatures. ADV decreased with elevation and increased with % impervious surfaces. Copyright © 2013 John Wiley & Sons, Ltd.     

Stream habitat provided by large wood at risk under drainage law

Watershed management efforts in agriculturally dominated landscapes of North America face nearly two centuries of laws and policies that encouraged habitat destruction. Although streams and wetlands in these landscapes are actively being restored using designs that incorporate science and engineering, watershed drainage laws can constrain action or impact passively restored or naturalized habitat. In general, drainage laws require removal of any riparian vegetation or wood deemed to obstruct flow in streams regulated as drains. We use a case study from Indiana (USA) to introduce the shortcomings of drainage laws for allowing large wood, which is an important habitat feature, to remain in stream ecosystems. Removals of large wood from monitored stream reaches in a regulated drain were associated with subsequent declines in fish biomass. Such legal activities represent an important environmental management problem that exists under drainage laws which apply to streams over a widespread geographic region of North America. Recent litigation in Wisconsin (USA) suggests that if state legislatures fail to update these antiquated laws, the courts may act in favour of science-based management of drains. The statutes and regulations that govern agricultural drainage warrant careful consideration if streams within drainage districts are to be managed to improve ecological function. © 2020 John Wiley & Sons, Ltd.     

Effects of forest stand age on the characteristics of logjams in mountainous forest streams

We measured longitudinal spacing and wood volume of channel‐spanning logjams along 30 1‐km reaches of forest streams in the Colorado Front Range, USA. Study streams flow through old‐growth (> 200 year stand age) or younger subalpine conifer forest. Evaluating correlations between the volume and longitudinal spacing of logjams in relation to channel and forest characteristics, we find that old‐growth forest streams have greater in‐stream wood loads and more jams per kilometer than streams in younger forest. Old‐growth forests have a larger basal area close to the stream and correlate with larger piece diameters of in‐stream wood. Jam volume correlates inversely with the downstream spacing for ramp and bridge pieces that can act as key pieces in jams. Most importantly, old‐growth streams have shorter downstream spacing for ramp and bridge pieces (< 20 m). Our results suggest that management of in‐stream wood and associated stream characteristics can be focused most effectively at the reach scale, with an emphasis on preserving old‐growth riparian stands along lower gradient stream reaches or mimicking the effects of old growth by manipulating the spacing of ramp and bridge pieces. Our finding that average downstream spacing between jams declines as wood load increases suggests that the most effective way to create and retain jams is to ensure abundant sources of wood recruitment, with a particular emphasis on larger pieces that are less mobile because they have at least one anchor point outside the active channel. Copyright © 2014 John Wiley & Sons, Ltd.     

A multicatchment analysis of headwater and downstream temperature effects from contemporary forest harvesting

Stream temperature is a key physical water‐quality parameter, controlling many biological, chemical, and physical processes in aquatic ecosystems. Maintenance of cool stream temperatures during summer is critical for high‐quality aquatic habitat. As such, transmission of warm water from small, nonfish‐bearing headwater streams after forest harvesting could cause warming in downstream fish‐bearing stream reaches with negative consequences. In this study, we evaluate (a) the effects of contemporary forest management practices on stream temperature in small, headwater streams, (b) the transmission of thermal signals from headwater reaches after harvesting to downstream fish‐bearing reaches, and (c) the relative role of lithology and forest management practices in influencing differential thermal responses in both the headwater and downstream reaches. We measured summer stream temperatures both preharvest and postharvest at 29 sites—12 upstream sites (4 reference, 8 harvested) and 17 downstream sites (5 reference, 12 harvested)—across 3 paired watershed studies in western Oregon. The 7‐day moving average of daily maximum stream temperature (T_7DAYMAX) was greater during the postharvest period relative to the preharvest period at 7 of the 8 harvested upstream sites. Although the T_7DAYMAX was generally warmer in the downstream direction at most of the stream reaches during both the preharvest and postharvest period, there was no evidence for additional downstream warming related to the harvesting activity. Rather, the T_7DAYMAX cooled rapidly as stream water flowed into forested reaches ~370–1,420 m downstream of harvested areas. Finally, the magnitude of effects of contemporary forest management practices on stream temperature increased with the proportion of catchment underlain by more resistant lithology at both the headwater and downstream sites, reducing the potential for the cooling influence of groundwater.     

Carbon pools in stream‐riparian corridors: legacy of disturbance along mountain streams of south‐eastern Wyoming

Streams and their accompanying riparian environments are intrinsic components of terrestrial carbon cycling. However, they have been understudied in terms of the magnitude of their storage components and the role of disturbance in determining carbon storage capacity. This study presents partial carbon budgets for stream‐riparian corridors along six study reaches in mountain headwater streams of southeast Wyoming to evaluate the impact of tie‐driving, a historic disturbance legacy, on contemporary carbon storage. Detailed measurements of biomass were collected for in‐stream components of carbon including fine and coarse particulate organic matter and in‐stream large wood. Biomass was also estimated for riparian components including standing trees (live and dead), regenerating conifers, shrubs and herbaceous vegetation, downed wood, litter, and duff (partially decayed litter). Biomass was converted to carbon for all components and differences in storage were compared between tie‐driven and non‐driven reaches. Carbon content in riparian soils (to approximately 20 cm) was also measured. Twice the amount of carbon was stored in the riparian areas relative to the streams; most carbon was stored in standing trees (live and dead). While overall carbon storage within the riparian areas and streams were similar between disturbance conditions, the amount of carbon stored in large in‐stream wood and downed wood on the floodplain was significantly higher in systems that were not tie‐driven. The results of this study indicate that legacies of tie‐driving influence carbon storage within the region, while also capturing baseline estimates of carbon storage in the wake of recent bark beetle infestations. Copyright © 2015 John Wiley & Sons, Ltd.     

Fish assemblages in forest drainage ditches: Degraded small streams or novel habitats?

Artificial drainage of forested wetlands to increase timber production has profoundly altered the hydrology of North-European landscapes during the 20th century. Nowadays, drainage ditches and small dredged streams can comprise most fluvial water bodies there, but the resulting ecological effects are poorly documented. In the current study, we explored, using fish as an indicator group, consequences of the transformation of natural stream networks to a mixture of natural and artificial watercourses. We asked whether the transformation results in impoverishment, enrichment or re-assembling of the communities both at watercourse and the landscape scales. We sampled fish in 98 sites in five well-forested regions in Estonia where ditches formed 83–92%, dredged streams 4–7%, and natural streams 3–10% of the total length of small watercourses. Based on a total of 6370 individual fish of 20 species, we found that, compared to natural streams, ditches had an impoverished fauna at both scales and both in terms of species richness and assemblage composition. Only natural streams hosted characteristic species (with Barbatula barbatula, Lampetra planeri and Lota lota emerging as significant indicators), while dredged streams had intermediate assemblages. The habitat factors explaining those drainage-related differences included a reduced flow velocity, loss of stream channel variability, less transparent water, and abundant aquatic vegetation. Hence, for stream-dwelling fish, drained forest landscapes represent degraded habitats rather than novel ecosystems, which contrasts with the transformation of terrestrial assemblages. Future studies should address whether that reflects the situation for whole aquatic assemblages, and how is the functioning of the hydrological systems affected. We suggest that the critical management issues for environmental mitigation of ditching effects on fish include basin scale spatial planning, protecting of the remaining natural streams, and rehabilitation of ditch channels in flat landscapes lacking beavers.     

Historical land use as a driver of alternative states for stream form and function in forested mountain watersheds of the Southern Rocky Mountains

We demonstrate how land use can drive mountain streams in the Southern Rockies across a threshold to induce an alternative state of significantly reduced physical complexity of form and reduced ecological function. We evaluate field data from 28 stream reaches in relatively laterally unconfined valleys and unmanaged forest that is either old‐growth forest or naturally disturbed younger forest, and 19 stream reaches in managed forest with past land use. We evaluate potential differences in stream form, as reflected in channel planform, cross‐sectional geometry, and in‐stream wood loads, and stream function, as reflected in pool volume and storage of organic carbon. Field data indicate a threshold of differences in stream form and function between unmanaged and managed stream reaches, regardless of forest stand age, supporting our hypothesis that the legacy effects of past land use result in an alternative state of streams. Because physical complexity that increases stream retentiveness and habitat can maintain aquatic‐riparian ecosystem functions, the alternative physical state of streams in managed watersheds creates a physical template for an alternative ecological state with reduced pool volume, organic carbon storage, and ecosystem productivity. We recommend maintaining riparian forests that can supply large wood to streams as a stream restoration technique in historically forested stream segments. Copyright © 2017 John Wiley & Sons, Ltd.     

Influence of a rock glacier spring on the stream energy budget and cold‐water refuge in an alpine stream

The thermal regimes of alpine streams remain understudied and have important implications for cold‐water fish habitat, which is expected to decline due to climatic warming. Previous research has focused on the effects of distributed energy fluxes and meltwater from snowpacks and glaciers on the temperature of mountain streams. This study presents the effects of the groundwater spring discharge from an inactive rock glacier containing little ground ice on the temperature of an alpine stream. Rock glaciers are coarse blocky landforms that are ubiquitous in alpine environments and typically exhibit low groundwater discharge temperatures and resilience to climatic warming. Water temperature data indicate that the rock glacier spring cools the stream by an average of 3 °C during July and August and reduces maximum daily temperatures by an average of 5 °C during the peak temperature period of the first two weeks in August, producing a cold‐water refuge downstream of the spring. The distributed stream surface and streambed energy fluxes are calculated for the reach along the toe of the rock glacier, and solar radiation dominates the distributed stream energy budget. The lateral advective heat flux generated by the rock glacier spring is compared to the distributed energy fluxes over the study reach, and the spring advective heat flux is the dominant control on stream temperature at the reach scale. This study highlights the potential for coarse blocky landforms to generate climatically resilient cold‐water refuges in alpine streams.     

Effects of human disturbance and riparian conditions on Odonata (Insecta) assemblages in eastern Amazon basin streams

Riparian vegetation is an important determinant of the physical, chemical, and biological condition of streams, and odonates are useful indicators of riparian condition. To identify environmental factors that structure Odonata assemblages in tropical forest streams, we collected adult odonate specimens and habitat data from 50 stream sites located in the Brazilian municipality of Paragominas (Pará state). We collected 1769 specimens representing 11 families, 41 genera, and 97 species. Of these species, 56 were Zygoptera, and 41 were Anisoptera. Improved environmental condition was reflected in increased Zygoptera species richness and reduced Anisoptera species richness. Channel shading was strongly and positively related to Zygoptera richness, and negatively to Anisoptera richness. Zygoptera species richness, but not Anisoptera species richness, was related positively to bank angle, quantity of wood in the stream bed, electrical conductivity, and decreased water temperature. Altered riparian vegetation structure was the principal determinant of odonate assemblage structure. Our results indicate that maintaining intact riparian vegetation is fundamental for conserving or re-establishing aquatic odonate assemblage structure.     

Evaluating the performance of topobathymetric LiDAR to support multi-dimensional flow modelling in a gravel-bed mountain stream

Stream biophysical processes are commonly studied using multi-dimensional numerical modelling that quantifies flow hydraulics from which parameters such as habitat suitability, stream carrying capacity, and bed mobility are derived. These analyses would benefit from accurate high-resolution stream bathymetries spanning tens of kilometres of channel, especially in small streams or where navigation is difficult. Traditional ground-based survey methods are limited by survey time, dense vegetation and stream access, and are usually only feasible for short reaches. Conversely, airborne topobathymetric LiDAR surveys may overcome these limitations, although limited research is available on how errors in LiDAR-derived digital elevation models (DEMs) might propagate through flow models. This study investigated the performance of LiDAR-derived topobathymetry in support of multi-dimensional flow modelling and ecohydraulics calculations in two gravel-bedded reaches (approximately 200 m long), one morphologically complex and one morphologically simple, and at the segment scale (32 km-long stream segment) along a 15 m-wide river in central Idaho, USA. We compared metre and sub-metre-resolution DEMs generated from RTK-GPS ground and Experimental Advanced Airborne Research LiDAR-B (EAARL-B) surveys and water depths, velocities, shear stresses, habitat suitability, and bed mobility modelled with two-dimensional (2D) hydraulic models supported by LiDAR and ground-surveyed DEMs. Residual statistics, bias (B), and standard deviation (SD) of the residuals between depth and velocity predicted from the model supported by LiDAR and ground-survey topobathymetries were up to −0.04 (B) and 0.09 m (SD) for depth and −0.09 (B) and 0.20 m s⁻¹ (SD) for velocity. The accuracy (B = 0.05 m), precision (SD = 0.09 m), and point density (1 point m⁻²) of the LiDAR topobathymetric survey (regardless of reach complexity) were sufficient to support 2D hydrodynamic modelling and derivative stream habitat and process analyses, because these statistics were comparable to those of model calibration with B = 0 m and SD = 0.04 m for water surface elevation and B = 0.05 m s⁻¹ and SD = 0.22 m s⁻¹ for velocity in our investigation. © 2020 John Wiley & Sons, Ltd.     

Numerical simulation of the impact of sediment supply and streamflow variations on channel grain sizes and Chinook salmon habitat in mountain drainage networks

Climatically driven changes in streamflow and hillslope sediment supply could potentially alter stream surface grain size distribution patterns and thereby impact habitat for a number of threatened and endangered in‐stream fish species. Relatively little is known about hydrograph (shape, peak flow) influence or the relative importance of chronic and episodic hillslope inputs on channel conditions. To better understand these external drivers, we calculated sediment routing through a gravel‐bedded river network using a one‐dimensional (1D) bedload transport model. We calculated changes in grain sizes and estimated Chinook salmon habitat suitability caused by a dry year and an extreme flood hydrograph, and chronic (diffusive, overland flow) or pulse (landslide, debris flow) hillslope sediment supplies. To obtain accurate channel conditions, a relatively high reference Shields stress, representative of steep mountain streams, was needed. An extreme event flood without any hillslope sediment inputs caused widespread bed coarsening and a decrease in aquatic habitat. Chronic sediment input combined with this hydrograph eliminated any changes in grain size and habitat, although when combined with a dry year flow, caused systematic bed fining. The influence of a given hydrograph therefore highly depends on the hillslope sediment supply. Regardless of the flow hydrograph or sediment pulse timing, grain size distribution or location, pulse sediment inputs did not cause widespread grain size changes despite being 100 times the total chronic input volume. Widespread and continuous hillslope sediment inputs may influence channel grain sizes and aquatic habitat more than a single discrete sediment pulse. Depending on the magnitudes of flow hydrograph and sediment supply alterations, climate change may induce no differences in grain sizes or very dramatic changes with significant consequences for long‐term sustainability. Copyright © 2013 John Wiley & Sons, Ltd.     

The effects of land use at different spatial scales on instream features in agricultural streams

The conversion of forests into agriculture has been identified as a key process for stream homogenization. However, the effects of this conversion can be scale-dependent. In this context, our aim was to identify the influence of different land uses at different spatial scales (catchment, drainage network and local) on instream features in agricultural streams. We defined six classes of land use: native forest, reforestation, herbaceous and shrubs, pasture, sugarcane and other categories. We obtained 22 variables related to instream, riparian area, stream morphology and water physicochemical characteristics in 86 stream reaches. To identify and isolate the effect of different land uses at different spatial scales on instream features, we performed a partial redundancy analysis (p-RDA). Different land uses and scales influenced instream features and defined two stream groups: (i) homogeneous streams with a higher proportion of sand substrate and instream grasses that were associated with the proportion of herbaceous vegetation at the local scale and with pasture at all scales and (ii) heterogeneous streams with a higher physical habitat integrity associated with the proportion of forest and sugarcane at the local and catchment scales. Land use at the catchment scale affected the physicochemical water properties and stream morphology, whereas stream physical habitat (i.e., substrate, instream cover, marginal vegetation and stream physical habitat condition) was mainly influenced by land use at the local scale (i.e., 150 m radius). Pure catchment, drainage network and local land uses explained 9%, 7% and 4%, respectively, of the total variation of instream features. Thus, to be most effective, stream conservation and restoration efforts should not be limited to only one scale.     

Modeling the functional influence of vegetation type on streambank cohesion

The important role of vegetation in adding cohesion and stabilizing streambanks has been widely recognized in several aspects of fluvial geomorphology, including stream restoration and studies of long‐term channel change. Changes in planform between braided, meandering, and anabranching forms have been attributed to the impacts of vegetation on hydraulic roughness and bank stability. However, these studies focus either on flume studies where analog vegetation is used, or case studies featuring one species, which is commonly invasive. We present functional differences of bank‐stabilizing root characteristics and added cohesion, with vegetation categorized as woody and non‐woody and by the vegetation groups of trees, shrubs, graminoids, and forbs. We analyzed root morphology and tensile strength of 14 species common to riparian areas in the southern Rocky Mountains, in field sites along streambanks in the montane and subalpine zones of the Colorado Front Range. Using the vegetation root component (RipRoot) of a physically‐based bank stability model (BSTEM), we estimated the added cohesion for various sediment textures with the addition of each of the 14 species. Significant differences exist between woody and non‐woody vegetation and between the four vegetation categories with respect to the coefficient of the root tensile strength curve, lateral root extent, and maximum root diameter. Woody vegetation (trees and shrubs) have higher values of all three parameters than non‐woody species. Tree roots add significantly more cohesion to streambanks than forb roots. Additionally, rhizomes may play an important role in determining the reach‐scale effects of roots on bank stabilization. Differences in root characteristics and added cohesion among vegetation categories have several important implications, including determining the likelihood of planform change, developing guidelines for the use of bank‐stabilizing vegetation, and linking the effect of vegetation to geomorphic structure that can benefit ecosystem functioning. Copyright © 2014 John Wiley & Sons, Ltd.     

Growth, condition and energy stores of Arctic grayling fry inhabiting natural and artificial constructed Arctic tundra streams

Juvenile north-temperate and Arctic fishes are faced with trade-offs between energy allocation to growth and energy storage (primarily lipids) prior to over-wintering. We determined classical morphometric (fork length, body weight and condition factor) and biochemical (whole body triglycerides, muscle RNA/DNA ratio, muscle proteins) measures of growth and condition in individual young-of-the-year (YOY) Arctic grayling (Thymallus arcticus). Grayling were collected just prior to over-wintering in late August (approximately 50 days after swim-up) from two natural streams and five locations within a 3.4 km long artificial stream constructed as a fish habitat compensation project and diversion channel for the diamond mining industry in Northwest Territories, Canada (64°45′N). Fork lengths, body weights and whole body triglyceride levels in grayling collected from all sites along the artificial stream were significantly lower than fish collected from one of the natural streams. Condition factor (weight-at-length) was not different among grayling collected from natural and artificial streams. Muscle proteins were lower in grayling collected from four sites along the artificial stream compared to the natural streams. In contrast, muscle RNA/DNA ratios were greater in grayling collected from two sites in the artificial stream compared to natural streams. There were no consistent differences in any variable among grayling collected at the five artificial stream sites or among grayling collected from the two natural streams. The higher RNA/DNA ratios and lower fork lengths, whole body triglycerides and muscle proteins in grayling inhabiting the artificial stream are consistent with energy still being primarily allocated to growth in these fish at this late stage of summer. Individuals that are both larger and possess greater energy storage in the form of triglycerides are more likely to survive the long over-wintering period at this latitude. Our results suggest that YOY grayling using the artificial stream as nursery habitat will likely face increased over-winter mortality, thus raising concerns over the use of fish presence, spawning and rearing as criteria for the initial success of artificial streams as habitat compensation measures in Arctic tundra regions. Further research is needed to determine the potential consequences of reduced size and energy storage in juvenile fishes in order to assess the viability of stream fish habitat compensation and restoration projects associated with industrial development in Arctic tundra regions.     

A conceptual model for the longitudinal distribution of wood in mountain streams

Wood load, channel parameters and valley parameters were surveyed in 50 contiguous stream segments each 25 m in length along 12 streams in the Colorado Front Range. Length and diameter of each piece of wood were measured, and the orientation of each piece was tallied as a ramp, buried, bridge or unattached. These data were then used to evaluate longitudinal patterns of wood distribution in forested headwater streams of the Colorado Front Range, and potential channel‐, valley‐ and watershed‐scale controls on these patterns. We hypothesized that (i) wood load decreases downstream, (ii) wood is non‐randomly distributed at channel lengths of tens to hundreds of meters as a result of the presence of wood jams and (iii) the proportion of wood clustered into jams increases with drainage area as a result of downstream increases in relative capacity of a stream to transport wood introduced from the adjacent riparian zone and valley bottom. Results indicate a progressive downstream decrease in wood load within channels, and correlations between wood load and drainage area, elevation, channel width, bed gradient and total stream power. Results support the first and second hypotheses, but are inconclusive with respect to the third hypothesis. Wood is non‐randomly distributed at lengths of tens to hundreds of meters, but the proportion of pieces in jams reaches a maximum at intermediate downstream distances within the study area. We use these results to propose a conceptual model illustrating downstream trends in wood within streams of the Colorado Front Range. Copyright © 2009 John Wiley & Sons, Ltd.     

Riparian land use and stream habitat regulate water quality

Riparian land use is a key driver of stream ecosystem processes but its effects on water quality are still a matter of debate when proposing measures to improve freshwater quality. The aim of this study was to examine the influence of riparian land use on stream habitat and water chemistry, and to assess in what extent stream habitat also affects water quality. To that end, we selected eight reaches in the Ave River basin (northwestern Portugal) and compared longitudinal variations in water chemistry and stream habitat between reaches with different land use (urban, agricultural and natural), and between reaches with natural riparian areas and different habitats. Stream habitat was assessed using the Fluvial Functional Index, the HABSCORE, and the Riparian Forest Quality Index. Longitudinal variations in water chemistry were determined measuring differences in concentrations of ammonium, nitrate, phosphate and oxygen, and conductivity, pH and temperature between the downstream and the upstream ends of each reach. Nitrate concentration tended to decrease along reaches with more natural riparian areas and to increase along reaches with more urban and agricultural land uses. Longitudinal variations in water chemistry also differed between reaches with natural riparian areas, suggesting that water quality also depends on stream habitat. Moreover, longitudinal variation in water chemistry was proven a simple, useful and low-cost approach to assess the influence of land cover and stream habitat on water quality. Overall results demonstrated that both riparian land use and stream habitat influence water quality and that riparian forests are essential to reduce nutrient export to downstream ecosystems.