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.     

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.     

What Drives Warming Trends in Streams? A Case Study from the Alpine Foothills

We investigated the effects of climate warming and land‐use changes on the temperature and discharge of seven Swiss and Italian streams in the catchment of Lake Lugano. In addition, we attempted to predict future stream conditions based on regional climate scenarios. Between 1976 and 2012, the study streams warmed by 1.5–4.3 °C, whereas discharge showed no long‐term trends. Warming trends were driven mainly by catchment urbanization and two large‐scale climatic oscillations, the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation. In comparison, independent influences by radiative forcing due to increased atmospheric CO₂ were uncertain. However, radiative forcing was predicted to further increase stream temperature (to +3–7 °C), reduce summer discharge (to ?46%) and increase winter discharge (to +96%) between the present and 2070–2099. These results provide new insights into the drivers of long‐term temperature and discharge trends in European streams subject to multiple impacts. The picture emerging is one of transition, where greenhouse‐gas forcing is gaining ground over climate oscillations and urbanization, the drivers of past trends. This shift would impress a more directional nature upon future changes in stream temperature and discharge, and extend anthropogenic warming to rural streams. Diffusing future impacts on stream ecosystems would require adaptation measures at local to national scales and mitigation of greenhouse‐gas emissions at the global scale. Copyright © 2014 John Wiley & Sons, Ltd.     

Climate change impacts on native cutthroat trout habitat in Colorado streams

Headwater streams support vital aquatic habitat yet are vulnerable to changing climate due to their high elevation and small size. Coldwater fish are especially sensitive to the altered streamflow and water temperature regimes during summer low flow periods. Though previous studies have provided insights on how changes in climate and alterations in stream discharge may affect habitat availability for various native cutthroat trout species, suitable physical habitats have not been evaluated under future climate projections for the threatened Greenback Cutthroat Trout (GBCT) native to headwater regions of Colorado, USA. Thus, this study used field data collected from selected headwater streams across the current distribution of GBCT to construct one-dimensional hydraulic models to evaluate streamflow and physical habitat under four future climate projections. Results illustrate reductions in both predicted streamflow and physical habitat for all future climate projections across study sites. The projected mean summer streamflow shows greater decline (−52% on average) compared to the projected decline in mean August flow (−21% on average). Moreover, sites located at a relative higher elevation with larger substrate and steeper slope were projected to experience more reductions in physical habitat due to streamflow reductions. Specifically, streams with step-pool morphologies may experience grater changes in available habitat compared to pool-riffle streams. Future climate change studies related to coldwater fish that examine spatial variation in flow alteration could provide novel data to complement the existing literature on the thermal characteristics. Tailoring reintroduction and management efforts for GBCT to the individual headwater stream with adequate on-site monitoring could provide a more holistic conservation approach.     

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.     

Sensitivity of juvenile salmonid growth to future climate trends

Seasonal temperature and bioenergetic models were coupled to explore the impacts on juvenile salmonid growth of possible climate‐induced changes to mean annual water temperature and snowpack in four characteristic ecoregions. Increasing mean temperature increases juvenile growth in streams that currently experience cool spring temperatures. In streams with currently warm spring temperatures, an increase shortens the duration of optimal conditions and truncates growth. A loss of snow enhances growth in cool‐summer streams and decreases growth in warm‐summer streams. The relative impacts of such climate change trends will vary significantly across ecoregions. Copyright © 2010 John Wiley & Sons, Ltd.     

RESTORING SALMON HABITAT FOR A CHANGING CLIMATE

An important question for salmon restoration efforts in the western USA is ‘How should habitat restoration plans be altered to accommodate climate change effects on stream flow and temperature?’ We developed a decision support process for adapting salmon recovery plans that incorporates (1) local habitat factors limiting salmon recovery, (2) scenarios of climate change effects on stream flow and temperature, (3) the ability of restoration actions to ameliorate climate change effects, and (4) the ability of restoration actions to increase habitat diversity and salmon population resilience. To facilitate the use of this decision support framework, we mapped scenarios of future stream flow and temperature in the Pacific Northwest region and reviewed literature on habitat restoration actions to determine whether they ameliorate a climate change effect or increase life history diversity and salmon resilience. Under the climate change scenarios considered here, summer low flows decrease by 35–75% west of the Cascade Mountains, maximum monthly flows increase by 10–60% across most of the region, and stream temperatures increase between 2 and 6°C by 2070–2099. On the basis of our literature review, we found that restoring floodplain connectivity, restoring stream flow regimes, and re‐aggrading incised channels are most likely to ameliorate stream flow and temperature changes and increase habitat diversity and population resilience. By contrast, most restoration actions focused on in‐stream rehabilitation are unlikely to ameliorate climate change effects. Finally, we illustrate how the decision support process can be used to evaluate whether climate change should alter the types or priority of restoration actions in a salmon habitat restoration plan. Copyright © 2012 John Wiley & Sons, Ltd.     

Impacts of Projected Climate Changes on Streamflow and Sediment Transport for Three Snowmelt‐Dominated Rivers in the Interior Pacific Northwest

Anthropogenic climate change is likely to have significant impacts on river systems, particularly on rivers dominated by seasonal snowmelt. In addition to altering the timing and magnitude of streamflow, climate change can affect the energy available to transport sediment, as well as the availability of sediment to be transported. These hydrologic changes are sensitive to local climate, which is largely controlled by topography, but climate models cannot resolve processes at these scales. Here, I investigate impacts of climate change on streamflow and suspended‐sediment transport for three snowmelt‐dominated rivers in the interior Pacific Northwest – the Tucannon River in Washington and the South Fork Coeur d'Alene and Red rivers in Idaho – using downscaled climate simulations from regional climate models (a range of three models plus an ensemble average) to drive a basin‐scale hydrologic model. The results indicate that climate change is likely to amplify the annual cycle of river discharge, producing higher winter discharge (increases in ensemble mean January discharge ranging from 4.1% to 34.4% for the three rivers), an earlier spring snowmelt peak (by approximately one month), and lower summer discharge (decreases in ensemble mean July discharge ranging from 5.2% to 47.2%), relative to a late 20th‐century baseline. The magnitude of the largest simulated flood under the ensemble‐average climate change scenario increases by 0.6–41.6% across the three rivers. Simulated changes in suspended‐sediment transport generally follow the changes in streamflow. These changes in discharge and sediment transport will likely produce significant impacts on the study rivers, including changes in flooding, physical habitat, and river morphology. Copyright © 2014 John Wiley & Sons, Ltd.     

Associations of watershed vegetation and environmental variables with fish and crayfish assemblages in headwater streams of the Pedernales River,Texas

Intermittent headwater streams serve important functions for humans and wildlife in semi‐arid rangelands. Increases in ashe juniper coverage in central Texas over recent decades are believed to have negatively impacted stream flows. Few studies have examined relationships between aquatic species and environmental factors in these systems as well as the influence of juniper coverage on assemblage structure. During summer 2003 and spring 2004, we examined species–environment relationships to infer potential effects of juniper cover on aquatic ecology relative to local‐scale and watershed‐scale environmental variables. Fish and crayfish species assemblages and physicochemical variables were investigated in spring‐fed headwater tributaries of the Pedernales River, Texas. Fish abundance was much higher in summer 2003, whereas crayfish abundance was higher in spring 2004. Fish species richness was lower during spring 2004, possibly due to below average precipitation during spring 2004 that reduced deep‐water refugia. Higher abundance of crayfish in spring 2004 samples was probably due to their ability to survive low‐flow conditions, and a release from fish predation pressure. Fish assemblage structure was more strongly associated with local abiotic factors during spring 2004 when flow was reduced, whereas structure during summer 2003 samples suggested a relatively greater influence of predation. In general, juniper cover was weakly associated with fish and crayfish assemblages, although it tended to be positively associated with relatively high‐quality habitat for sensitive taxa (flowing runs with coarse substrate; deep, connected pools). We suggest that intermediate levels of juniper cover in the region provide indirect benefits to aquatic organisms. However, short‐term, local environmental factors appear to have a much greater influence than watershed vegetation on fish and crayfish assemblages in these intermittent streams. Copyright © 2007 John Wiley & Sons, Ltd.     

Influence of tributaries on the longitudinal patterns of benthic invertebrate communities

There has been little effort to understand how tributaries influence mainstem rivers at large scales beyond the immediate influence of the tributary and downstream of the mixing zone. Such knowledge is needed to create breaks in stream networks that can aid in the classification of stream valley segments and conservation studies that rely on the delineation of zones. We use benthic invertebrate assemblages to infer longitudinal gradients and discontinuities and relate these patterns to confluence symmetry ratio (CSR; the size ratio of the tributary basin to the mainstem basin upstream of the confluence). In addition, we briefly explore reach and catchment‐scale environmental influences. We found evidence for both gradual and abrupt longitudinal changes in benthic invertebrate communities. There was not a smooth continuous gradient but a sawtooth pattern with an overarching trend. Two major discontinuities were found: one associated with a large CSR = 0.74 and reach scale factors including predominance of sand and an abundance of benthic organic matter that provided a unique habitat; and a second associated with a large CSR = 0.64 and a transition from coarse textured morainal deposits to glaciolacustrine deposits. There were synchronous additions of some benthic invertebrates (e.g., Eukiefferiella brehmi, Antocha, Hydropsyche morosa, and Oligochaeta) showing an affinity for downstream reaches, whereas others showed an affinity for headwater reaches (e.g., Simulium tuberosum, Baetis tricaudatus, and Micropsectra). Benthic invertebrate communities were driven by a combination of confluence symmetry ratio, landscape, and reach scale factors that can confound interpretation.     

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.     

Arctic river temperature dynamics in a changing climate

Climate change in the Arctic is expected to have a major impact on stream ecosystems, affecting hydrological and thermal regimes. Although temperature is important to a range of in‐stream processes, previous Arctic stream temperature research is limited—focused on glacierised headwaters in summer—with limited attention to snowmelt streams and winter. This is the first high‐resolution study on stream temperature in north‐east Greenland (Zackenberg). Data were collected from five streams from September 2013 to September 2015 (24 months). During the winter, streams were largely frozen solid and water temperature variability low. Spring ice‐off date occurred simultaneously across all streams, but 11 days earlier in 2014 compared with 2015 due to thicker snow insulation. During summer, water temperature was highly variable and exhibited a strong relationship with meteorological variables, particularly incoming shortwave radiation and air temperature. Mean summer water temperature in these snowmelt streams was high compared with streams studied previously in Svalbard, yet was lower in Swedish Lapland, as was expected given latitude. With global warning, Arctic stream thermal variability may be less in summer and increased during the winter due to higher summer air temperature and elevated winter precipitation, and the spring and autumn ice‐on and ice‐off dates may extend the flowing water season—in turn affecting stream productivity and diversity.     

Thermal Influences on Life‐History Traits and Reproductive Effort of Introduced Pumpkinseed Sunfish Lepomis Gibbosus in the River Moselle Basin (Northeastern France)

The influence of local thermal regimes on juvenile growth rates, life‐history traits, and reproductive effort of introduced populations of pumpkinseed Lepomis gibbosus was examined in 11 water bodies in the River Moselle basin (northeastern France). Female pumpkinseed were collected during their reproductive period in mid‐June in 2009 and 2010, and water temperature was assessed over a 12‐month period in 2010. Annual thermal degree‐days above 10 °C varied from 1529 in a headwater site to 2722 in the Mirgenbach Reservoir, heated by cooling water from a nuclear power plant. Mean age at maturity varied from 1.3 to 2.2 and was inversely related to annual thermal degree‐days. The proportion of mature age‐1 females also increased with temperature, but neither mean total length at maturity nor gonadosomatic index was related to waterbody thermal regime. Body size at the end of the first year of life was unrelated to thermal regime, but the growth rate of immature age‐1 females in their second growing season was positively related to thermal degree‐days in the spring. Warmer water bodies showed elevated reproductive effort in age‐1 females when either early season gain in mass or mass at the beginning of the second growing season was controlled for; however, reproductive effort was unrelated to thermal regime in age‐2 and age‐3 females. Mean age at maturity was related to mean length at age 1 but not to mean length at age 2, in contrast to native North American and introduced European populations. We conclude that the life‐history response of pumpkinseed to warmer temperatures occurs primarily in age‐1 individuals and predict that climate warming will produce changes in pumpkinseed life‐history traits that will make the species more invasive in parts of Europe where the species is present but not actively spreading. Copyright © 2014 John Wiley & Sons, Ltd.     

STREAM HABITAT MODELLING FOR CONSERVING A THREATENED HEADWATER FISH IN THE UPPER CUMBERLAND RIVER,KENTUCKY

The conservation of stream biodiversity requires more explicit knowledge on the distribution of aquatic species within the context of their specific environmental settings and stresses. Although species distribution models (SDMs) have been widely used for organisms occupying contiguous spatial extents, the implementation of SDMs in relatively complex and segmented riverine networks is still at its early stage. In this study, we explicitly modelled the headwater stream habitat for the threatened blackside dace (Phoxinus cumberlandensis) endemic to the upper Cumberland River, Kentucky, USA. An occurrence record data set, along with variables describing stream properties and land use impacts, was used to predict the fish habitat suitability at the stream segment level. An approach combining geographic information systems and the maximum entropy species distribution modelling (MaxEnt) was adopted. Results demonstrated that natural conditions and land use disturbances, respectively, form the primary and secondary environmental constraints on the species' habitat. We generated regional‐scale management‐friendly maps showing subwatershed habitat suitability and locations of the clustered suitable habitats (hotspots) and thus set an example for spatially explicit management of threatened and endangered riverine species. This study demonstrates the usefulness of SDMs for stream network–based environments in the facilitation of biogeographic conservation efforts and studies. Copyright © 2012 John Wiley & Sons, Ltd.     

A MULTITAXONOMIC APPROACH TO UNDERSTANDING LOCAL‐ VERSUS WATERSHED‐SCALE INFLUENCES ON STREAM BIOTA IN THE LAKE CHAMPLAIN BASIN,VERMONT, USA

Twenty‐one stream reaches in northwestern Vermont were surveyed to assess the relative influence of local‐ and watershed‐scale variables on stream biotic assemblages including fish, aquatic macroinvertebrates and birds. Data were collected during the summers of 2003 and 2004 and included quantitative and qualitative geomorphic and habitat assessments (local‐scale) and land‐use characterization and modelled annual flow and sediment loading (watershed‐scale). Biotic assemblages were surveyed to capture characteristics related to abundance, diversity and composition. Principal components analysis (PCA) was used to generate sets of factors representing unique scenarios of geophysical data derived from various spatial extents within the watershed. These factors were then used as the independent variables in multiple regression models using the biotic data as the dependent variables. Forty significant models were built from the combination of the eight scenarios and 11 dependent variables. Fish assemblage diversity and composition were influenced by a combination of local‐scale and watershed‐scale variables; however, the qualitative local data were more predictive than the quantitative data. Local‐scale data and sediment (model‐derived) were important factors in building significant macroinvertebrate models. Bird abundance and species richness were best predicted using local geomorphic characteristics and the qualitative local data. Our results reinforce the concept that whereas both local‐ and watershed‐scale variables affect stream biota, their relative influence depends upon the individual ecology of each taxon. In order to address these issues, comprehensive watershed management, restoration and conservation plans would benefit from assessments at multiple scales and from geomorphological, watershed and multitaxonomic perspectives. Copyright © 2010 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.     

Statistical tools for thermal regime characterization at segment river scale: Case study of the Ste‐Marguerite River

Suitable thermal fish habitats are constrained by both maximum and minimum temperature tolerances. A multivariate and geostatistical approach was developed to estimate stream thermal characteristics at the river segment scale. Data from 22 temperature‐monitoring stations during summer 2007 were used to estimate monthly maximum temperature as well as thermal characteristics such as the number of events, the cumulative degree–days and the associated duration over specific temperature thresholds of 19 and 21°C. The probability of exceeding these temperature thresholds has also been interpolated. The methodology relies on the construction of a multivariate space using physiographic and hydrological characteristics of gauging stations as inputs in a canonical correlation analysis (CCA). A geostatistical interpolation technique, ordinary kriging, was subsequently used to perform interpolation in the physiographical space constructed using CCA. Results from this study were obtained for thermal characteristics estimated into two different interpolation spaces: (1) a 7 metrics space, and (2) an 8 metrics space. Cross‐validation technique has been performed and satisfactory results were obtained. Kriging thermal characteristics (magnitude and duration) into the 7 metric space for a 19°C threshold exceedance leads to best results with Relative Root Mean Square Error (RRMSE) ranging between 9.66 and 15.08%. The study shows that kriging in a multivariate space is a promising tool for water resources managers, especially in cases where risk mapping for lethal or sub‐lethal temperature thresholds may be required for a specific fish species. Copyright © 2010 John Wiley & Sons, Ltd.     

Stream temperature dynamics within a New Zealand glacierized river basin

Knowledge of river thermal dynamics for glacierized basins is limited, despite the high sensitivity of these systems to climatic change/variability. This study examined spatio‐temporal water column and streambed temperature dynamics within a New Zealand glacierized river basin over two melt seasons. Water column temperature was recorded at three sites along the mainstem channel and four hillslope/groundwater‐fed tributaries. Air temperature, precipitation and stream discharge were monitored to characterize hydroclimatological conditions. Streambed temperature was monitored at the upper and lower main river sites at 0.05, 0.2 and 0.4 m depth. Water column temperature rose on average 0.6°C km^?1 along the glacier‐fed mainstem. Temperature was elevated during warmer periods but the downstream increase was reduced due to greater meltwater production (consequently a larger total stream flow volume for atmospheric heating) plus a proportional reduction in warmer groundwater contributions. Hillslope/groundwater‐fed tributaries yielded a range of temperature patterns, indicating variable sourcing (meltwater or rainfall) and residence times. In the upper basin, streambed temperature was warmer than the water column, suggesting groundwater upwelling; however, during high runoff events, water column and streambed temperature converged, indicating downwelling/heat advection by channel water. At the lower site, streambed temperature mirrored the water column, suggesting greater surface water/atmospheric influences. Key drivers of stream thermal regime were: (1) relative water source contributions, (2) prevailing hydroclimatological conditions, (3) distance from source, (4) total stream flow volume and (5) basin factors (specifically, valley/channel geomorphology and riparian forest). High magnitude precipitation events produced a contrasting stream thermal response to that reported elsewhere. In contrast to European alpine research, streams showed a reduced thermal range owing to the relatively mild, wet melt season climate. This New Zealand case study highlights the importance of understanding basin‐specific modification of energy and hydrological fluxes for accurate prediction of stream thermal dynamics/habitat and ecological response to climatic variability and change. Copyright © 2007 John Wiley & Sons, Ltd.     

Identifying Temperature Thresholds Associated with Fish Community Changes in British Columbia,Canada, to Support Identification of Temperature Sensitive Streams

We collected fish samples and measured physical habitat characteristics, including summer stream temperatures, at 156 sites in 50 tributary streams in two sampling areas (Upper Fraser and Thompson Rivers) in British Columbia, Canada. Additional watershed characteristics were derived from GIS coverages of watershed, hydrological and climatic variables. Maximum weekly average temperature (MWAT), computed as an index of summer thermal regime, ranged from 10 to 23 °C. High values of MWAT were associated with large, warm, low relief watersheds with a high lake influence. Measures of community similarity suggested that the fish community changed most rapidly through a lower transition zone at an MWAT of about 12 °C and an upper transition zone at an MWAT of about 19 °C. These results were confirmed using existing fisheries inventory data combined with predictions of MWAT from a landscape‐scale regression model for the Thompson River watershed. For headwater sites in the Chilcotin River watershed (which drains into the middle Fraser River), the relative dominance of bull trout versus rainbow trout (based on inventory data) decreased with increasing predicted MWAT although the distinction was not as clear as for the Thompson River sites. The fish communities in these watersheds can be characterized in terms of very cold water (bull trout and some cold water species), cold water (salmonids and sculpins) and cool water (minnows and some cold water salmonids). The two transition zones (ca 12 and 19 °C) can be used to identify thresholds where small changes in stream temperature can be expected to lead to large changes in fish communities. Such clear, quantifiable thresholds are critical components of a management strategy designed to identify and protect vulnerable fish communities in streams where poor land use practices, alone or in combination with climatic change, can lead to changes in stream temperatures. Copyright © 2015 John Wiley & Sons, Ltd.     

Climate change will both exacerbate and attenuate urbanization impacts on streamflow regimes in southern Willamette Valley,Oregon

Interactions between climate change and urbanization may affect stream ecosystems in unexpected ways. With an integrated modelling framework, we assessed the combined hydrological impacts of climate change and urbanization under historical and future climate regimes across varied development scenarios in three watersheds in the Willamette Valley, Oregon. First, through an agent‐based land use change model Envision, we created four development scenarios that consisted of 2 × 2 combinations of regional growth (compact population growth in urban cores vs. dispersed growth into rural areas) and stormwater management scenarios (with vs. without integrated stormwater management, ISM). ISM was defined as the integration of strategic organization of land uses with site‐scale stormwater best management practices. Next, two future climate regimes were developed by statistically downscaling projections from two general circulation models (CanESM2 and CNRM‐CM5) that performed well in replicating historical climate. The hydrological assessment of these scenarios was then conducted with the Soil and Water Assessment Tool. Using 10 ecologically significant flow metrics, we evaluated each scenario based on the magnitude of change in each metric and the degree to which such changes could be mitigated. Climate change alone led to a drying trend in flow regimes under both future climates. Combined with urbanization, it magnified changes in six of 10 metrics but attenuated impacts for three other measures of flashiness in at least one basin. The combination of compact growth and ISM effectively mitigated alterations for seven (out of nine) metrics sensitive to the combined impacts in at least one basin, with ISM being more effective than compact growth. The modelling framework teased out both nuanced differences and generalizable trends in hydrological impacts of urbanization and climate change and offers key methodological innovations towards an integrated framework capable of linking landscape planning mechanisms with the goal of sustaining stream ecosystem health.