Stream Temperature Impacts Because of Changes in Air Temperature,Land Cover and Stream Discharge: Navarro River Watershed,California, USA

Stream temperatures are critically important to aquatic ecology, especially cold‐water fish such as salmonids. Stream temperatures are influenced by multiple factors, including local climate, solar radiation on the stream channel, stream discharge volume and groundwater contributions. The Heat Source hydrodynamic and thermodynamic numerical model was used to evaluate temperatures in three stream reaches in the Navarro River watershed, California, USA. The model was calibrated and validated for summer 2015 conditions and then applied to scenarios that address changes in air temperatures, riparian forest cover and stream discharge. Modelling results indicate that stream temperatures are sensitive to changes in air temperatures and riparian forest cover and that higher discharge volume mitigates those impacts. Modelled stream maximum weekly average temperatures (MWAT) increased by 1.5–2.3°C in response to an air temperature increases of 3.5°C under low flow conditions (drought) but by only 0.9–2.0°C under moderate flow. Complete removal of riparian forest in a large‐scale forest fire would increase MWAT by 2.2–5.9°C in low discharges and by 1.0–4.4°C under moderate discharge. Riparian zone reforestation would decrease MWATs by less than 0.8°C, a modest change reflecting high existing shade on the modelled stream reaches. Comparison of identical climate and land cover change scenarios under low and moderate discharge conditions reveals that efforts to conserve stream discharge volume could be an effective mechanism to mitigate stream temperature increases. Copyright © 2016 John Wiley & Sons, Ltd.     

ASSESSING THE IMPACTS OF RIVER REGULATION ON NATIVE BULL TROUT (SALVELINUS CONFLUENTUS) AND WESTSLOPE CUTTHROAT TROUT (ONCORHYNCHUS CLARKII LEWISI) HABITATS IN THE UPPER FLATHEAD RIVER,MONTANA, USA

Hungry Horse Dam on the South Fork Flathead River, Montana, USA, has modified the natural flow regimen for power generation, flood risk management and flow augmentation for anadromous fish recovery in the Columbia River. Concern over the detrimental effects of dam operations on native resident fishes prompted research to quantify the impacts of alternative flow management strategies on threatened bull trout (Salvelinus confluentus) and westslope cutthroat trout (Oncorhynchus clarkii lewisi) habitats. Seasonal and life‐stage specific habitat suitability criteria were combined with a two‐dimensional hydrodynamic habitat model to assess discharge effects on usable habitats. Telemetry data used to construct seasonal habitat suitability curves revealed that subadult (fish that emigrated from natal streams to the river system) bull trout move to shallow, low‐velocity shoreline areas at night, which are most sensitive to flow fluctuations. Habitat time series analyses comparing the natural flow regimen (predam, 1929–1952) with five postdam flow management strategies (1953–2008) show that the natural flow conditions optimize the critical bull trout habitats and that the current strategy best resembles the natural flow conditions of all postdam periods. Late summer flow augmentation for anadromous fish recovery, however, produces higher discharges than predam conditions, which reduces the availability of usable habitat during this critical growing season. Our results suggest that past flow management policies that created sporadic streamflow fluctuations were likely detrimental to resident salmonids and that natural flow management strategies will likely improve the chances of protecting key ecosystem processes and help to maintain and restore threatened bull trout and westslope cutthroat trout populations in the upper Columbia River Basin. Copyright © 2011 John Wiley & Sons, Ltd.     

Riparian Forest Harvesting Effects on Maximum Water Temperatures in Wetland-sourced Headwater Streams from the Nicola River Watershed, British Columbia, Canada

Water temperature was continuously recorded during the ice-free season between June/July and October/November at 90 sites with lentic and lotic stream sources distributed throughout the Nicola River watershed (British Columbia, Canada) in 1999, 2000, and 2001. The eight lentic-sourced stream temperature monitoring sites were located in two adjacent watersheds. The headwaters and riparian areas around the wetland outlet of the treatment watershed were harvested during the overwinter period between 1999 and 2000. Areas around and downstream of the headwater wetland outlet in the control watershed were not harvested. Reducing riparian shade by harvesting activities increased maximum stream temperatures in the treatment watershed by up to 1–2°C relative to the control watershed. Because of the general downstream cooling trends in lentic-sourced headwater streams, riparian harvesting activities in these regions have a reduced thermal impact relative to similar harvesting alongside lotic-sourced headwater streams, whose maximum stream temperatures may warm by up to 8°C following harvesting. The downstream influence of elevated maximum stream temperatures from riparian harvesting of lentic-sourced headwater streams appears to be localized, but persists for at least 2 years following harvesting. Both lentic-sourced treatment and control streams in the current study relaxed towards baseline equilibrium temperature estimated by the lotic-sourced watershed trend within several hundred meters of downstream travel distance, with cooling rates proportional to the distance from expected thermal equilibrium. Due to the heating in wetland-sourced stream reaches adjacent to riparian harvesting, the regions downstream of treatment areas cool more rapidly than similar regions in control watersheds as the stream attempts to achieve thermal equilibrium.     

Tributary confluences are dynamic thermal refuges for a juvenile salmonid in a warming river network

As rivers warm, cold‐water fish species may alleviate thermal stress by moving into localized thermal refuges such as cold‐water plumes created by cool tributary inflows. We quantified use of two tributary confluence plumes by juvenile steelhead, Oncorhynchus mykiss, throughout the summer, including how trout positioned themselves in relation to temperature within confluence plumes. At two confluences, Cedar and Elder creeks, along the South Fork Eel River, California, USA, we monitored temperatures using in situ logger grids throughout summer 2016. Fish were counted within confluences via snorkel surveys five times a day on 5 days at each site. We found diel and seasonal dependence on confluence use by steelhead, especially at the Cedar Creek confluence, where mainstem temperatures exceeded 28°C. At this site, fish moved into the confluence on the warmest days and warmest times of the day. Fish observed within the Cedar Creek confluence plume were most common in locations between 20–22°C, rather than the coldest locations (14.5°C). At Elder Creek, where mainstem temperatures remained below 24°C, there was little relationship between mainstem temperature and steelhead presence in the confluence plume. At both sites, steelhead distribution within plumes was influenced by spatial variation of temperature and mean temperature in surveyed grid cells. Our results show that cool tributaries flowing into warmer mainstem reaches (over 24°C) likely create important thermal refuges for juvenile steelhead. As mainstem rivers warm with climate change, cool‐water tributary inputs may become more important for sustaining cold‐water salmonids near the southern end of their range.     

The influence of riparian shade on lowland stream water temperatures in southern England and their viability for brown trout

Suitable thermal conditions in streams are necessary for fish and predictions of future climate changes infer that water temperatures may regularly exceed tolerable ranges for key species. Riparian woodland is considered as a possible management tool for moderating future thermal conditions in streams for the benefit of fish communities. The spatial and temporal variation of stream water temperature was therefore investigated over 3 years in lowland rivers in the New Forest (southern England) to establish the suitability of the thermal regime for fish in relation to riparian shade in a warm water system. Riparian shade was found to have a marked influence on stream water temperature, particularly in terms of moderating diel temperature variation and limiting the number of days per year that maximum temperatures exceeded published thermal thresholds for brown trout. Expansion of riparian woodland offers potential to prevent water temperature exceeding incipient lethal limits for brown trout and other fish species. A relatively low level of shade (20–40%) was found to be effective in keeping summer temperatures below the incipient lethal limit for brown trout, but ca. 80% shade generally prevented water temperatures exceeding the range reported for optimum growth of brown trout. Higher levels of shade are likely to be necessary to protect temperature‐sensitive species from climate warming. © Crown copyright 2010.     

Effects of elevated water temperature on fish and macroinvertebrate communities below small dams

Many studies have investigated the ecological changes that occur below dams that release cold, hypolimnetic water, but very few studies have looked at the effects of the release of warm, surface waters. The effect of small, surface release dams on downstream thermal regimes is a major habitat concern for many cold‐water systems, however. The objective of this study was to examine the effects of summer temperature increases due to impoundment on downstream fish and macroinvertebrate communities in cold‐water streams. We sampled fish, macroinvertebrates and habitat upstream and downstream of dams on ten rivers during the summers of 1998 and 1999. Changes in mean summer temperature downstream varied from a cooling of 1 °C to an increase of more than 5 °C. Increasing temperatures downstream coincided with lower densities of several cold‐water fish species, specifically brown trout (Salmo trutta), brook trout (Salvelinus fontinalis) and slimy sculpin (Cottus cognatus) while overall fish species richness increased downstream. Density of mottled sculpin (Cottus bairdi), another cold‐water species, was not related to temperature changes below the dams. Macroinvertebrates showed shifts in community composition below dams that increased temperature. This study provides information useful for determining the extent of impact of these small, surface release dams, which are abundant across the country. Copyright © 2003 John Wiley & Sons, Ltd.     

Cooler,bigger; warmer,smaller: Fine-scale thermal heterogeneity maps age class and species distribution in behaviourally thermoregulating salmonids

Behavioural thermoregulation is a survival strategy that occurs in response to an exceedance of thermal stress-inducing thresholds. When salmonids experience exceedance of these thresholds, they seek regions of colder water, known as thermal refuges. During an extreme temperature event of summer 2021 (main stem ~31.5°C) a large aggregation of Atlantic salmon (Salmo salar—all age classes) and brook trout (Salvelinus fontinalis—>20 cm) was observed on the Little Southwest Miramichi River in New Brunswick, Canada. Using a drone-mounted thermal infrared (TIR) sensor, fine-scale TIR imagery of the occupied refuge was acquired. Polarized glasses were worn by an onshore observer to make visual observations. Constructing maps from these data we examined the spatial distribution of fish, and the corresponding temperature of the areas they occupied. Salmonids were found to be distributed by age class and species, with the distribution driven by the mosaic of temperatures in the refuge. Young of the year (YOY), 1+, 2+ and adult Atlantic salmon occupied areas with average temperatures ~30.1, 28.8, 25.7 and 21.9°C, respectively; whilst mature brook trout occupied areas ~21.8°C. Noteworthy is the observation of thermally aggregating young of the year Atlantic salmon, and the range in temperatures they occupied (~8°C). One isolated, shallow, cold water patch (~22°C) exclusively held YOY Atlantic salmon. Our findings highlight the importance of several different thermal characteristics of thermal refuges and their link to salmonid occupancy and can aid the design of ecologically meaningful thermal refuge augmentation/restoration projects.     

Characterizing physical habitat preferences and thermal refuge occupancy of brook trout (Salvelinus fontinalis) and Atlantic salmon (Salmo salar) at high river temperatures

Anthropogenic influences, including climate change, are increasing river temperatures in northern and temperate regions and threatening the thermal habitats of native salmonids. When river temperatures exceed the tolerance levels of brook trout and Atlantic salmon, individuals exhibit behavioural thermoregulation by seeking out cold‐water refugia – often created by tributaries and groundwater discharge. Thermal infrared (TIR) imagery was used to map cold‐water anomalies along a 53 km reach of the Cains River, New Brunswick. Trout and salmon parr did not use all identified thermal anomalies as refugia during higher river temperature periods (>21°C). Most small‐bodied trout (8–30 cm) were observed in 80% of the thermal anomalies sampled. Large‐bodied trout (>35 cm) required a more specific set of physical habitat conditions for suitable refugia, that is, 100% of observed large trout used 30% of the anomalies sampled and required water depths >65 cm within or adjacent to the anomaly. Densities of trout were significantly higher within anomalies compared with areas of ambient river temperature. Salmon parr were less aligned with thermal anomalies at the observed temperatures, that is, 59% were found in 65% of the sampled anomalies; and densities were not significantly different within/ outside anomalies. Salmon parr appeared to aggregate at 27°C, and after several events over 27°C variability in aggregation behaviour was observed – some fish aggregated at 25°C, others did not. We stipulate this is due to variances of thermal fatigue. Habitat suitability curves were developed for velocity, temperature, depth, substrate, and deep water availability to characterize conditions preferred by fish during high‐temperature events. These findings are useful for managers as our climate warms, and can potentially be used as a tool to help conserve and enhance thermal refugia for brook trout and Atlantic salmon in similar systems.     

Chronology of rainbow trout reproduction in a warmwater tributary of the Chattahoochee River: using an invasive species as an indicator of watershed integrity

The Chattahoochee River near Atlanta, Georgia, USA is a stocked tailwater trout (Salmonidae) fishery and rainbow trout (Oncorhynchus mykiss) have been found to spawn in selected warmwater tributary streams. Because these stocked fish enter non‐stocked waters and produce offspring that reside year‐round, they are technically invasive. One tributary in particular, Cabin Creek, has had documented spawning activity for three consecutive years since the stream was monitored. We chronicled the production of the 2006 year‐class of rainbow trout in this small, warmwater tributary to the Chattahoochee River. Based on electrofishing samples and otolith microstructure, the 2006 year‐class of trout were produced from spawning that occurred from 6 February 2006 to 10 March 2006. Fish from this year‐class grew from an average size of 34.28 mm total length (TL) on 26 April 2007 to 102.00 mm TL on 14 May 2007, which is an average increase in size of 67.72 mm over a 383‐day period or 0.18 mm/day. Water temperatures in the stream were near the lethal limits for rainbow trout, reaching a maximum of 24.57°C on 1 August 2006 and a maximum 7‐day average maximum (M7DAM) of 22.99°C on 7 August 2006. The watershed of Cabin Creek is one of the least urbanized in the area, protected from development within lands owned by the National Park Service, with high levels of forest cover, which facilitates rainbow trout young‐of‐year survival through the summer. Thus, the documented spawning and young‐of‐year survival of this invasive species appears to be indicative of high forested watershed integrity. Copyright © 2008 John Wiley & Sons, Ltd.     

Salmonid Spawning Runs and Estimated Ova Production in Normandale Creek of Lake Erie

The Normandale Creek study area (2,531 m²)provides spawning and nursery grounds for lake-run coho salmon (Oncorhynchus kisutch), rainbow trout (Salmo gairdneri), and brown trout (Salmo trutta), In 1973–74, 59 adult salmonids (58% rainbow trout, 39% coho salmon, and 3% brown trout) ascended the stream between 31 October and 12 May. Upstream movements were significantly related to peak stream discharge (r = 0.21) and highly significantly related to discharge occurring on the day following the peak freshet (r = 0.34). Despite a highly significant correlation (r = 0.29) between flow and water temperature, the latter factor is not significantly related with upstream movement of adult fish. Coho salmon spawned at water temperatures of 1 to 10° C between 2 November and 19 December, rainbow trout at 1 to 15° C between 9 November and 14 May, and brown trout at 7° C between 4 and 5 November. Of 86 nests constructed, 60% were disturbed by re-use or sand deposition. From a calculated deposition of 90,403 ova, it is estimated that some 22% survived to emergence.     

Can water level stations be used for thermal assessment in aquatic ecosystem?

Many studies focus on stream water temperature (WT) because it is considered a key ecological factor. However, few of them have investigated the use of WT data from water level monitoring networks, which often measure WT as ancillary data. Our study was conducted in southern Belgium at a high temporal resolution with continuous data recorded at intervals of 10 min between 2012 and 2016 and large spatial scale greater than 16,000 km². This study aimed to assess whether a regional water level network (140 stations) is reliable for continuous WT monitoring based on a Bland–Altman analysis with WT collected through a European monitoring network (Water Framework Directive). This study also investigates whether WT data acquired by water level stations can be used to perform both state‐of‐the‐art visualization of thermal regimes and spatio‐temporal queries for specific ecological monitoring. We found that the water level stations were reliable tools in recording continuous WT in the streams of the study area. The temperature difference between the two WT monitoring networks was ?0.57°C on average. Our positive results promote the use of WT from water level stations in order to globally characterize the thermal regime of streams as well as to provide spatial or temporal information on this regime at high frequencies. As an example, our data showed the effectiveness for brown trout (Salmo trutta fario L.) in spatializing thermal risk areas related to the thermal requirement of this fish species; in 2015, 19% of stations located in brown trout fish zone recorded temperatures above 25°C.     

ESTIMATING THERMAL REGIMES OF BULL TROUT AND ASSESSING THE POTENTIAL EFFECTS OF CLIMATE WARMING ON CRITICAL HABITATS

Understanding the vulnerability of aquatic species and habitats under climate change is critical for conservation and management of freshwater systems. Climate warming is predicted to increase water temperatures in freshwater ecosystems worldwide, yet few studies have developed spatially explicit modelling tools for understanding the potential impacts. We parameterized a nonspatial model, a spatial flow‐routed model, and a spatial hierarchical model to predict August stream temperatures (22‐m resolution) throughout the Flathead River Basin, USA and Canada. Model comparisons showed that the spatial models performed significantly better than the nonspatial model, explaining the spatial autocorrelation found between sites. The spatial hierarchical model explained 82% of the variation in summer mean (August) stream temperatures and was used to estimate thermal regimes for threatened bull trout (Salvelinus confluentus) habitats, one of the most thermally sensitive coldwater species in western North America. The model estimated summer thermal regimes of spawning and rearing habitats at <13°C and foraging, migrating, and overwintering habitats at <14°C. To illustrate the useful application of such a model, we simulated climate warming scenarios to quantify potential loss of critical habitats under forecasted climatic conditions. As air and water temperatures continue to increase, our model simulations show that lower portions of the Flathead River Basin drainage (foraging, migrating, and overwintering habitat) may become thermally unsuitable and headwater streams (spawning and rearing) may become isolated because of increasing thermal fragmentation during summer. Model results can be used to focus conservation and management efforts on populations of concern, by identifying critical habitats and assessing thermal changes at a local scale. Copyright © 2012 John Wiley & Sons, Ltd.     

A Comparison of the Temperature Regime of Short Stream Segments under Forested and Non‐Forested Riparian Zones at Eleven Sites Across North America

When forested riparian zones are cleared for agriculture or development, major changes can occur in the stream temperature regime and consequently in ecosystem structure and function. Our main objective was to compare the summer temperature regimes of streams with and without forest canopy cover at multiple sites. The secondary objective was to identify the components of the stream heat budget that had the greatest influence on the stream temperature regime. Paired stream reaches (one forested and one non‐forested or ‘open’) were identified at 11 sites distributed across the USA and Canada. Stream temperature was monitored at the upstream and downstream ends of 80 to 130‐m‐long reaches during summer, and five variables were calculated to describe the stream temperature regime. Overall, compared with forested reaches, open reaches tended to have significantly higher daily mean (mean difference = 0.33 ± 1.1°C) and daily maximum (mean difference = 1.0 ± 1.7°C) temperatures and wider daily ranges (mean difference = 1.1 ± 1.7°C). Mean and maximum daily net heat fluxes in open reaches tended to be greater (or less negative) than those in forested reaches. However, certain sites showed the opposite trends in some variables because of the following: (i) Daily mean and maximum temperatures were biased by differences in inflow temperature between paired reaches and (ii) inputs of cold groundwater exerted a strong influence on temperature. Modelling and regression results suggested that within sites, differences in direct solar radiation were mainly responsible for the observed differences in stream temperature variables at the daily scale. © 2014 The Authors. River Research and Applications published by John Wiley & Sons, Ltd.     

Body mass and growth of overwintering brown trout in relation to stream habitat complexity

In winter, juvenile salmonids hide within the substrate during the day and emerge to feed on drifting invertebrates at night. In channelized streams, where the streambed heterogeneity has been artificially reduced, suitable microhabitats (low‐flow refugia) may be in short supply. Therefore, restoration of stream habitat by enhancement structures might improve the overwintering conditions of juvenile salmonids. We used a set of artificial streams to test whether individually‐marked juvenile brown trout of two age‐classes (age‐0 and age‐1 trout) loose mass during the winter differently in channelized and semi‐natural streams. Fish of both age‐classes lost mass early in the winter (November to January), but age‐0 fish in the channelized streams lost more of their initial mass than did the restored‐stream fish (ca. 10% vs. 2.5% on average, respectively). They then exhibited zero‐growth in both treatments in late winter (January to April), and by early spring (May), the channelized‐stream fish had completely caught up for their greater initial mass loss. In control tanks where the fish were fed continuously, age‐0 trout exhibited zero‐growth from November to January, then gaining mass constantly through the rest of the experiment. Significant time*treatment interaction was also detected for age‐1 trout, but all differences were caused by the faster growth of fish in the control tanks, whereas the two channel treatments did not differ significantly. The shortage of suitable sheltering sites in the channelized streams apparently intensified competition and caused greater initial mass loss in age‐0 trout. Furthermore, growth compensation exhibited by juvenile trout may have negative impacts on the long‐term fitness of individuals. Therefore, by increasing the amount of sheltering sites, in‐stream restoration may have potential to enhance the overwintering success of juvenile salmonids. Copyright © 2010 John Wiley & Sons, Ltd.     

Spatial variability of thermal regimes and other environmental determinants of stream fish communities in the Great Lakes Basin,Ontario, Canada

Temperature is one of the most important environmental variables in stream ecosystems because it affects the growth, survival and distribution of stream biota. This study examined if the spatial variability of thermal regimes and 18 other environmental variables were associated with fish communities in watersheds throughout the Great Lakes Basin (GLB), Ontario. The thermal regimes were defined as regimes 1, 2 and 3 and had maximum water temperatures of 26.4, 28.4 and 23.5°C, and spring warming rates of 0.20, 0.12 and 0.10 °C d^?1, respectively. The spatial variability of the thermal regimes (VTR) within the watersheds was summarized into four VTR groups: S1, S2, M23 and M123. Stream sites in S1 watersheds had temperatures characteristic of regime 1 whereas stream sites in S2 watersheds followed regime 2. M23 watersheds had sites with a mix of regimes 2 and 3 whereas M123 watersheds had all three thermal regimes at sites throughout watersheds. Canonical correspondence analysis (CCA) indicated that 16% of the variation in fish communities was related to the spatial VTR in the watersheds. Forward selection CCA indicated that elevation, the S1 VTR group, sparse forest cover, wetland area, base flow index (groundwater discharge potential), flow and industrial stress explained 42% of the variance in the fish communities. Simplified indicator species analysis (ISA) showed that different species could be used as indicators for each of the VTR groups. Human activities such as industrial development, deforestation, groundwater withdrawal and flow alteration all may affect the environmental variables related to stream fish communities. Copyright © 2010 John Wiley & Sons, Ltd.     

A Statistical Model for Managing Water Temperature in Streams with Anthropogenic Influences

Streams in the Pacific Northwest (Oregon, Washington, British Columbia) face rising summer temperatures and increasing anthropogenic influence, with consequences for fish populations. Guidance is needed in small managed watersheds for setting reservoir release rates or for the restriction of water extractions to meet the needs of fish and aquatic ecosystems. Existing environmental flow methods focus on discharge rates and do not typically consider water temperatures, and detailed thermal models are too complex for widespread implementation. We used multiple logistic regression to develop statistical models for estimating the probability of exceeding a salmonid stream temperature threshold of 22 °C as a function of discharge and maximum daily air temperatures. Data required are air temperature, stream temperature and stream discharge over a minimum of one summer. The models are used to make minimum discharge recommendations under varying forecast weather conditions. The method was applied to nine streams in the Pacific Northwest. Minimum recommended discharge generally ranged from 23% to 86% of mean annual discharge and was higher than observed low flows in most streams. Comparison of the new method to existing methods for Fortune Creek in British Columbia indicated that total season discharge volumes could be reduced while meeting thermal requirements. For other streams, it was evident that high water temperatures cannot be managed by increasing discharge, as the discharge required would be greater than natural discharge and higher than achievable by management. The statistical method described in this paper allows for a risk‐based approach to discharge management for fish habitat needs.     

Effects of Environmental Water Transfers on Stream Temperatures

Low streamflows and warm stream temperatures currently limit habitat and productivity of trout, including native Lahontan cutthroat trout in Nevada's Walker Basin. Environmental water transfers, which market water from willing sellers to instream uses, are evaluated to improve instream habitat. We use River Modelling System, an hourly, one‐dimensional hydrodynamic and water quality model, to estimate current and potential environmental water transfer effects on stream temperatures. Model runs simulate a range of environmental water transfers, from 0.14 to 1.41 cms, at diversions and reservoirs for wet year 2011 and dry year 2012. Results indicate that critically warm stream temperatures generally coincide with low flows, and thermal refugia exist in East Walker River, a tributary of the Walker River. Environmental water transfers reduce maximum stream temperatures by up to 3 °C in dry years and are more effective in dry years than wet years. This research suggests that environmental water transfers can enhance instream habitat by improving water quality as well as increasing instream flow. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of habitat restoration on post‐emergence displacement of brown trout (Salmo trutta L.): A case study in a Northern Swedish stream

During the 19th and 20th centuries, Swedish streams were channelized to facilitate the commercial transport of timber on water. Stream‐dwelling fish were affected by the consequent reduction in habitat quality. To mitigate the effects on salmonids, which sustain important recreational fisheries, many streams have been restored through the replacement of boulders into the channel since the early 1980s. However, the effects of restoration on salmonids remain poorly known. This study assesses the effect of habitat restoration on the post‐emergence displacement of brown trout (Salmo trutta L.) fry. Hatchery‐raised fry were released in a third‐order stream canalized for timber floating in northern Sweden, and the effect of restoration on displacement was assessed. The short‐term (24 h) displacement of trout fry was reduced from 10.1 to 2.3% of fry released following restoration. Water velocity accounted for 89.4% of the variation in fry displacement across years and sites. Post‐summer recruitment (the proportion of introduced juvenile trout remaining in the study reaches 60 days after the emergence) increased approximately three fold after restoration. These findings suggest that habitat restoration benefit trout populations through substantial reductions of fry displacement and possible contributions to juvenile recruitment. Copyright © 2009 John Wiley & Sons, Ltd.     

Response of epiphytic diatom communities from the tailwaters of glen Canyon Dam,Arizona, to elevated water temperature

The composition of epiphytic diatom communities from the cold tailwaters (12°C) of Glen Canyon Dam, Arizona, was analysed after a 2 wk incubation period at 12°C, 18°C and 21°C. There was a significant change in diatom composition between 12°C and 18°C, while no significant changes occurred between 18°C and 21°C. This suggests that a temperature threshold exists between 12°C and 18°C for the diatom flora in the tailwaters of Glen Canyon Dam. At the two higher water temperatures, smaller and closely adnate taxa became more important numerically than larger, upright, cold water stenotherms. The potential importance of this compositional shift in epiphytic diatoms on macroinvertebrate grazers has management implications regarding different release programs from reservoirs.     

长江流域水系划分与河流分级初步研究

将推荐的水系划分与河流分级Horton法相结合,通过合理选取最小河流(流域)单元、科学制作河流树状图表,初步研究了长江流域(不含太湖水系)的河流分级。研究结果显示:①推荐将长江水系划分为干流水系与雅砻江、岷江、嘉陵江、乌江、洞庭湖、汉江、鄱阳湖、太湖8个支流水系;② 581条河流基本特性资料的收集、整理与分析表明长江流域河流的河长与流域面积约为0.5次方关系,选取流域面积不小于2 000 km²或河长不小于100 km的河流为最小河流(流域)单元,确定长江流域(不含太湖水系)河流总数为374条;③以岷江水系为例,精心制作了长江流域各水系的河流树状图表,树状图显示了河流隶属关系、分级数、河长、流域面积等特性;④长江流域(不含太湖水系)最高河流分级数为6级。按河流统计:6级1条(0.3%),5级3条(0.8%),4级6条(1.6%),3级14条(3.7%),2级71条(19.0%),1级279条(74.6%);按水系统计:岷江、嘉陵江、鄱阳湖为5级,干流、雅砻江、洞庭湖、汉江为4级,乌江为3级。