Thermal variability and stream flow permanency in an alpine river system

Despite the importance of thermal conditions in influencing biodiversity of alpine river systems, knowledge of year round stream temperature variability is very limited. This paper advances understanding of alpine stream temperature dynamics using hourly resolution data collected over two consecutive years at five sites within a glacierized basin in the French Pyrénées. The potential utility of temperature for understanding river flow patterns at ungauged sites (most notably during winter) is explored. The results indicated marked heterogeneity in water column temperatures; groundwater streams were typically warmer and more thermally stable than those draining snow and ice. Based upon stream temperature patterns, it appears possible to differentiate between river flow conditions including: free‐flowing, surface freezing, dewatering and snow cover. Notably, groundwater‐fed streams appeared to exhibit greater flow permanency than meltwater‐fed streams, the latter freezing for extended periods. These new insights into long‐term alpine stream thermal conditions have major implications for understanding the strategies adopted by benthic macroinvertebrate taxa when overwintering, particularly where streams freeze. Copyright © 2006 John Wiley & Sons, Ltd.     

River Temperature Modelling by Strahler Order at the Regional Scale in the Loire River Basin,France

Daily water temperature was simulated at a regional scale during the summer period using a simplified model based on the equilibrium temperature concept. The factors considered were heat exchanges at the water/atmosphere interface and groundwater inputs. The selected study area was the Loire River basin (110 000 km²), which displays contrasted meteorological, hydrological and geomorphological features. To capture the intra‐basin variability of relevant physical factors driving the hydrological and thermal response of the system, the modelling approach combined a semi‐distributed hydrological model, simulating the daily discharge at the outlet of 68 subwatersheds (drainage area between 100 and 3700 km²), and a thermal model, simulating the average daily water temperature for each Strahler order in each subwatershed. Simulations at 67 measurement stations revealed a median root mean square error (RMSE) of 1.9°C in summer between 2000 and 2006. Water temperature at stations located more than 100 km from their headwater was adequately simulated (median RMSE < 1.5°C; ?0.5°C < median biases < 0.5°C). However, performance for rivers closer to their source varied because of the averaging of geomorphological and hydrological features across all the tributaries with the same Strahler order in a subwatershed, which tended to mask the specific features of the tributaries. In particular, this increased the difficulty of simulating the thermal response of groundwater‐fed rivers during the hot spells of 2003. This modelling by coupling subwatershed and Strahler order for temperature simulations is less time‐consuming and has proven to be extremely consistent for large rivers, where the addition of streambed inputs is adequate to describe the effect of groundwater inputs on their thermal regime. Copyright © 2015 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.     

WATER TEMPERATURE PATTERNS BELOW LARGE GROUNDWATER SPRINGS: MANAGEMENT IMPLICATIONS FOR COHO SALMON IN THE SHASTA RIVER,CALIFORNIA

Elevated stream temperature is a primary factor limiting the coho salmon (Oncorhynchus kisutch) population in California's Shasta River Basin. Understanding the mechanisms driving spatial and temporal trends in water temperature throughout the Shasta River is critical to prioritising river restoration efforts aimed at protecting this threatened species. During the summer, the majority of streamflow in the Shasta River comes from large‐volume, cold‐water springs at the head of the tributary Big Springs Creek. In this study, we evaluated the initial character of this spring water, as well as the downstream fate and transport of these groundwater inflows during July and August 2008. Our results indicated that Big Springs Creek paradoxically provided both cool and warm waters to the Shasta River. During this period, cool groundwater inflows heated rapidly in the downstream direction in response to thermal loads from incoming solar radiation. During the night time, groundwater inflows did not appreciably heat in transit through Big Springs Creek. These diurnally varying water temperature conditions were inherited by the Shasta River, producing longitudinal temperature patterns that were out of phase with ambient meteorological conditions up to 23 km downstream. Findings from this study suggest that large, constant temperature spring sources and spring‐fed rivers impart unique stream temperature patterns on downstream river reaches that can determine reach‐scale habitat suitability for cold‐water fishes such as coho salmon. Recognising and quantifying the spatiotemporal patterns of water temperature downstream from large spring inflows can help identify and prioritize river restoration actions in locations where temperature patterns will allow rearing of cold‐water fishes. Copyright © 2013 John Wiley & Sons, Ltd.     

INFLUENCE OF ENVIRONMENTAL INSTABILITY OF GROUNDWATER‐FED STREAMS ON HYPORHEIC FAUNA,ON A GLACIAL FLOODPLAIN,DENALI NATIONAL PARK,ALASKA

Macroinvertebrate community distributions were investigated within the benthic and hyporheic zone of five groundwater‐fed streams, on a floodplain terrace, in a glacierized catchment in Alaska, in summer 2008. The streams were characterized by a distinct gradient in environmental instability and provided an opportunity to determine whether the local variability in environmental instability of groundwater‐fed streams (reflecting differences in lengths of groundwater flow pathways) are of sufficient magnitude and frequency to influence macroinvertebrate community distribution. Individual measures of surface‐water temperature, streamflow, streambed stability and sediment size were incorporated into a multivariate index of environmental instability (IEI), using principal components analysis. In the hyporheic zone, a logarithmic association was observed between macroinvertebrate diversity and IEI and a quadratic association between abundance and IEI. The increase in diversity along the gradient of instability reflected a greater evenness of taxa caused by reduction in abundance of Chironomidae, combined with an increase in abundance of several less dominant taxa (Limnephilidae, Empididae, Baetidae and Simuliidae). At the surface, a quadratic association between diversity and IEI was observed, consistent with the intermediate disturbance hypothesis. Chironomidae, Nemouridae and Empididae presented contrasting surface and hyporheic distributions, indicating use of the hyporheic zone as a refuge. Moreover, covariance in the surface and hyporheic distribution of Limnephilidae and Chloroperlidae suggested the use of the hyporheic zone as an extension of the benthic habitat. The data indicate that local variability in environmental conditions between groundwater‐fed streams is sufficient to induce differences in macroinvertebrate communities and in the response of individual taxa. Copyright © 2012 John Wiley & Sons, Ltd.     

ON THE IMPORTANCE OF CONSIDERING CHANNEL MICROFORMS IN GROUNDWATER MODELS OF HYPORHEIC EXCHANGE

The infiltration of stream water in the sediment and its return to the stream—a process known here as hyporheic exchange flows (HEF)—is a critical control of the structure and functions of the stream ecosystem. River restoration programmes will increasingly require quantitative methods for evaluating this influence. Previous studies have already shown the potential of numerical groundwater models to characterize HEF and compare restoration scenarios. Although various sources of uncertainty are acknowledged, the potential effect of small streambed structures (or microforms), such as grains or ripples, embedded in channel‐unit scale structures (or macroforms), such as riffle‐pool sequences, is commonly ignored. Here, a simple conceptualization through a 2‐D vertical model is used to test whether (i) ignoring microforms in groundwater models at the macroform scale can impact estimations of residence times; (ii) microforms can influence HEF patterns driven by macroforms; and conversely (iii) the uncertainty of head measurements in stream piezometers can affect our understanding of HEF patterns. Results show that (i) residence times and flux estimations can be strongly affected by the modeller's choice to represent microform‐induced HEF or not; (ii) the interaction of the microform and macroform scales can induce various subsurface flow patterns; and (iii) the perceived significance of microform‐induced HEF is highly sensitive to the uncertainty of in‐stream measurements of subsurface heads. Little is known about the relative efficiency of these microform and macroform scales, which are effectively influencing exchange at different depths and interacting with each other. Future studies that consider biogeochemical cycling or streambed ecology should be placed in this context. It is also necessary to find ways of including this source of uncertainty in groundwater models of HEF. Copyright © 2012 John Wiley & Sons, Ltd.     

Dissolved Oxygen Relationships of Under‐Ice Water Column and Pore Water Habitat: Implications for Environmental Guidelines

Substantial reductions in dissolved oxygen concentration in freshwaters can negatively affect aquatic biota. Thus, existing regulatory criteria are designed to avoid environmental conditions that cause acute lethality, thereby reducing the likelihood of biological impairment. In North America, dissolved oxygen (DO) guidelines for protecting aquatic life assume that pore water and water column DO are correlated, with pore water values expected to be on average ≤3 mg/L below water column values. Our study assessed the validity of this assumption during the winter period of ice cover in a large, northern river ecosystem (Wapiti River, Alberta, Canada). We investigated the relationship between water column and pore water DO concentrations and examined whether this relationship was affected by industrial and municipal effluents. Water column DO fell from near saturation during open water periods to 80–84% under winter ice cover. DO concentrations in the pore water were significantly lower than in the water column at reference and effluent‐exposed sampling sites. Pore water DO values ranged widely from 0.27 to 13.28 mg/L. In contrast, water column DO concentrations (10.25–13.60 mg/L) were more narrowly distributed over the same period. Indeed, differences between winter pore water and water column DO were often as large as 9–12 mg/L and, notably, were significantly greater than the 3 mg/L difference upon which North American guidelines are based. Consequently, under‐ice DO concentrations of river pore water could not be accurately predicted from water column DO alone. Risk factors that may increase the potential for pore water DO to be more than 3 mg/L lower than water column values include the input of oxygen poor groundwater, infilling of the streambed with small inorganic and organic particles, water exchange rates between the water column and the streambed and effluent discharges that raise nutrient concentrations and biochemical oxygen demand. Given that low pore water DO was evident even in undeveloped reference sites, future work must establish the ecological relevance of chronic exposure to low, pore water DO and its impact on river biota. © 2016 Environment and Climate Change Canada. River Research Application StartCopTextStartCopText© 2016 John Wiley & Sons, Ltd.     

Heat exchanges and temperatures within a salmon spawning stream in the Cairngorms,Scotland: seasonal and sub‐seasonal dynamics

Stream temperatures are often used to predict salmonid embryo development; but there are very few medium‐term studies of the heat exchanges determining water column and bed temperatures. Furthermore, no research exists on the energy balance for sub‐arctic Scottish rivers. This paper reports results of a hydrometeorological study of a Cairngorm stream (Girnock burn, northeast Scotland) over the salmon spawning–hatch season (late October 2001 to mid‐April 2002) that aims: (1) to characterize seasonal and sub‐seasonal stream energy budget and thermal dynamics; and (2) to explain these variations with respect to meteorological and hydrological factors. In terms of average energy flux contributions, sensible heat (38.7%), the bed heat flux (37.0%) and friction at the stream bed and banks (24.3%) are heat sources, while latent heat (73.1%) and net radiation (26.9%) are heat sinks. All energy losses and 38.7% of heat gains occur at the air–water interface; and 61.3% of energy gains (including friction) take place at the water–channel bed interface. Typically, temperatures increase (+1.97°C) and show dampening of thermal response from the water column to depth in the stream bed. The most salient findings include: (1) the stream bed (atmosphere) is the dominant energy source (sink) for heating (cooling) channel water, which may be attributed to inferred heat advection by groundwater up‐welling into the bed of this upland stream; (2) sensible heat is the primary atmospheric energy source due to limited net radiation; (3) friction at the stream bed and banks is an important heat source. Energy budget terms and temperatures exhibit (sub‐)seasonal changes in response to meteorological and hydrological conditions; a schematic diagram is presented to summarize these results. This paper clearly illustrates the need for further medium‐ to long‐term empirical stream energy balance research to characterize heat flux dynamics and, thus, understand and predict water temperature variations over time‐scales of relevance to biological studies. Copyright © 2004 John Wiley & Sons, Ltd.     

The effect of wood and temperature on juvenile coho salmon winter movement,growth, density and survival in side‐channels

In British Columbia, side‐channels have been built to compensate for lost salmonid habitat. Most are structurally simple with little in‐stream wood; however, they support high densities of juvenile coho salmon. We longitudinally divided in halves the top 100 m of two dead‐end artificial side‐channels, one side‐channel with low winter water temperatures (surface‐fed) and one with relatively higher water temperatures (groundwater‐fed), closed the downstream end of each side‐channel with two‐way traps, and treated only one half of each channel with bundles of wood. Trapped fish were marked daily and coho salmon movement, growth and smolt output were monitored for two years. Wood addition increased juvenile coho winter carrying capacity and spring smolt output only in the ‘colder’ surface‐fed side‐channel. In contrast, in the groundwater‐fed side‐channel, with relatively higher water temperatures, the wood treatment slightly reduced the channel's carrying capacity and the spring output of coho salmon smolts. Copyright © 2003 John Wiley & Sons, Ltd.     

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.     

Economic analysis of water temperature reduction practices in a large river floodplain: an exploratory study of the Willamette River,Oregon

This paper examines ecosystem restoration practices that focus on water temperature reductions in the upper mainstem Willamette River, Oregon, for the benefit of endangered salmonids and other native cold‐water species. The analysis integrates hydrologic, natural science and economic models to determine the cost‐effectiveness of alternative water temperature reduction strategies. A temperature model is used to simulate the effects of combinations of upstream riparian shading and flow augmentations on downstream water temperatures. Costs associated with these strategies are estimated and consist of the opportunity costs of lost agricultural production and recreation opportunities due to flow releases from an up‐stream reservoir. Temperature reductions from another strategy, hyporheic flow enhancement, are also examined. Restoration strategies associated with enhanced hyporheic cooling consist of removal/reconnection of current obstacles to the creation of dynamic river channel complexity. The observed reduction of summer water temperatures associated with enhanced channel complexity indicates that restoring hyporheic flow processes is more likely to achieve cost‐effective temperature reductions and meet the total maximum daily load (TMDL) target than conventional approaches that rely on increased riparian shading or/and combinations of flow augmentation. Although the costs associated with the hyporheic flow enhancement approach are substantial, the effects of such a long‐term ecological improvement of the floodplain are expected to assist the recovery of salmonid populations and provide ancillary benefits to society. Copyright © 2008 John Wiley & Sons, Ltd.     

典型山区小流域河床结构分布研究

本文选取了长江上游支流吊噶河作为典型小流域,通过详尽的实地现场考察,对吊噶河流域中河床结构的发育分布规律及其影响进行了统计分析。结果表明,河床演变过程中水流与河床结构相互适应与调整,不断趋向于平衡状态。河床结构越强的河段,消耗水流能量越大,从而接近平衡时能维持的坡降也往往越大。如果河段中坡降过大而河床结构没有充分发育,则河段因此处于不平衡状态,床面将受到冲刷。历史上经历剧烈下切作用的河段如V型深沟段,常常因发育较强的河床结构,维持住了高坡降,从而形成山区河流纵剖面上常见的台阶状突起。     

Seasonal Rearing Habitat in a Large Mediterranean‐Climate River: Management Implications at the Southern Extent of Pacific Salmon (Oncorhynchus spp.)

Pacific salmon (Oncorhynchus) use a variety of rearing environments prior to seaward migration, yet large river habitats and their use have not been well defined, particularly at the southernmost salmon range where major landscape‐level alterations have occurred. We explored juvenile Chinook salmon (Oncorhynchus tshawytscha) and steelhead (Oncorhynchus mykiss) presence along the river continuum and in main‐channel and off‐channel habitats of a regulated California Mediterranean‐climate river. Over an 8‐year period, off‐channels of the lower Mokelumne River exhibited slower and warmer water than the main‐channel. Probability of salmonid presence varied by stream reach and habitat types. Steelhead and Chinook salmon both demonstrated transitional responses to the dry season, with juveniles leaving off‐channels by midsummer. This corresponded to flow recession, increasing water temperatures, salmonid growth and end of emigration period. Main‐channel steelhead observations continued until the following storm season, which brought cool flood flows to reconnect off‐channels and the next juvenile cohort of both species to the river. Within arid climates, low‐gradient off‐channels appear more transiently used than in cooler and more northern humid climate systems. Within a highly regulated Mediterranean‐climate river, off‐channel habitats become increasingly scarce, disconnected or temperature limiting in low‐gradient reaches both seasonally and due to anthropogenic modifications. These observations may provide guidance for future management within large salmon streams. Copyright © 2015 John Wiley & Sons, Ltd.     

怒江源区小唐古拉山冻融过程水源解析

高寒地区径流的补给水源有冰雪融水、降水、地下水、土壤冻融水等类型,为了识别不同时期水源类型对水循环过程的影响,根据小唐古拉山一年野外气象观测资料与采集水样检测的同位素结果,运用统计学方法,分析研究了土壤温、湿度的变化特征以及相互之间的关系,并揭示高寒流域不同冻融过程中的水分来源。结果表明: ( 1) 土壤温度呈近似正弦曲线的周期性变化特征,与气温和相对湿度均呈极显著正相关,土壤湿度与土壤温度和气温均呈显著的正相关关系; ( 2) 依据活动层的土壤温度和土壤湿度的变化,将该区域的冻融过程划分为完全冻结期、融化过程期、完全融化期和冻结过程期; ( 3) 完全冻结期河流的水分来源主要是地下水( 山泉水) ; 融化过程期河流的水分来源主要是地下水( 山泉水) 和冰雪融水; 完全融化期河流的水分来源主要是地下水( 山泉水) 、大气降水、冰雪融水和土壤冻融水; 冻结过程期河流的水分来源主要是地下水( 山泉水) 。本研究成果可为高寒流域径流演变机理识别及适应气候变化提供支撑。     

The Isotope Hydrology of a Large River System Regulated for Hydropower

Impoundments, regulation and inter‐basin transfers associated with large hydropower developments affect runoff regimes, water residence times and stream water quality. We used stable isotopes to understand these effects on the river Tay system in Scotland, examining their spatial and temporal variation in surface waters at 22 sites. Spatial patterns of isotopes in stream water were consistent with those of precipitation, being more depleted in streams draining higher, colder northern headwaters and enriched in the milder western headwaters. To a lesser extent, spatial patterns also reflected effects of inter‐basin and intra‐basin water transfers at some sites. Temporal dynamics reflected precipitation inputs modulated by landscape properties, the presence of lakes and reservoirs, and regulation operations. Isotopic variability was highest in headwater tributaries with responsive soils and lowest downstream of lakes and reservoirs. Variability of isotopes in lower river sites was also damped as they integrate contributions from the rest of the catchment. Importantly, regulation from both reservoirs and inter‐basin transfers can distort simple input–output relationships for stable isotopes and affect catchment transit times with implications for water quality and in‐stream ecology. On the one hand, reservoirs and extension of natural lakes have created additional storage, potentially slowing flows; on the other, transfers have increased the volume and rates of water throughput in many of these water bodies, reducing hydraulic turnover times. Such effects tend to be quite localized and are not apparent at the larger catchment scale. Copyright © 2014 John Wiley & Sons, Ltd.     

Understanding the Thermal Regime of Rivers Influenced by Small and Medium Size Dams in Eastern Canada

Although small and medium‐size dams are prevalent in North America, few studies have described their year‐round impacts on the thermal regime of rivers. The objective of this study was to quantify the impacts of two types of dams (run‐of‐river, storage with shallow reservoirs) on the thermal regime of rivers in eastern Canada. Thermal impacts of dams were assessed (i) for the open water period by evaluating their influence on the annual cycle in daily mean water temperature and residual variability and (ii) for the ice‐covered winter period by evaluating their influence on water temperature duration curves. Overall, results showed that the run‐of‐river dam (with limited storage capacity) did not have a significant effect on the thermal regime of the regulated river. At the two rivers regulated by storage dams with shallow reservoirs (mean depth < 6 m), the annual cycle in daily mean water temperature was significantly modified which led to warmer water temperatures in summer and autumn. From August to October, the monthly mean water temperature at rivers regulated by storage dams was 1.4 to 3.9°C warmer than at their respective reference sites. During the open water period, the two storage dams also reduced water temperature variability at a daily timescale while increased variability was observed in regulated rivers during the winter. Storage dams also had a warming effect during the winter and the winter median water temperature ranged between 1.0 and 2.1°C downstream of the two storage dams whereas water temperature remained stable and close to 0°C in unregulated rivers. The biological implications of the altered thermal regimes at rivers regulated by storage dams are discussed, in particular for salmonids. Copyright © 2016 John Wiley & Sons, Ltd.     

Temporal and spatial variations of runoff composition revealed by isotopic signals in Nianchu River catchment,Tibet

Understanding the hydrology of glaciated catchments is an important step in assessing the vulnerability of water resources to a changing climate. Based on multi-isotopes of water (²H, ¹⁸O and ³H) and dissolved radon (²²²Rn), the temporal and spatial variabilities of major hydrological processes along the main flow and tributaries in the Nianchu River catchment were examined and the isotopic response to climate variation was identified. Geographic variation in changes of isotopic composition that differ from other rivers in the Nianchu River catchment was apparent. Along the direction of runoff, river δ¹⁸O exhibited more depletion, which was closely related to water mixing and groundwater discharge. End-member mixing analysis using isotopic tracers suggested that annual recharge from summer rainfall and glacial meltwater maintained the surface water resources (their respective contributions rate were 65.9% and 26.5%); groundwater had a significant contribution on runoff in the dry season (about 46.6%). Summer rainfall and meltwater rapidly infiltrated through a series of faults and fissures and were, stored in underground reservoirs and released to runoff in the dry season, thereby ensuring rapid circulation and renewal of water resources (annual renewal proportion was about 40%). It was concluded that rainfall infiltration, meltwater and groundwater storage play important roles in the hydrology of this alpine-cold catchment. Similar to a general alpine-cold catchment, the stable isotopes (δ²H, δ¹⁸O) of river runoff will gradually be enriched, while groundwater reserves will increase in the Nianchu River catchment as a result of climate warming and an acceleration of glacial-melting.     

PAIRED STREAM–AIR TEMPERATURE MEASUREMENTS REVEAL FINE‐SCALE THERMAL HETEROGENEITY WITHIN HEADWATER BROOK TROUT STREAM NETWORKS

Previous studies of climate change impacts on stream fish distributions commonly project the potential patterns of habitat loss and fragmentation due to elevated stream temperatures at a broad spatial scale (e.g. across regions or an entire species range). However, these studies may overlook potential heterogeneity in climate change vulnerability within local stream networks. We examined fine‐scale stream temperature patterns in two headwater brook trout Salvelinus fontinalis stream networks (7.7 and 4.4 km) in Connecticut, USA, by placing a combined total of 36 pairs of stream and air temperature loggers that were approximately 300 m apart from each other. Data were collected hourly from March to October 2010. The summer of 2010 was hot (the second hottest on record) and had well below average precipitation, but stream temperature was comparable with those of previous 2 years because streamflow was dominated by groundwater during base‐flow conditions. Nonlinear regression models revealed stream temperature variation within local stream networks, particularly during warmest hours of the day (i.e. late afternoon to evening) during summer. Thermal variability was primarily observed between stream segments, versus within a stream segment (i.e. from confluence to confluence). Several cold tributaries were identified in which stream temperature was much less responsive to air temperature. Our findings suggested that regional models of stream temperature would not fully capture thermal variation at the local scale and may misrepresent thermal resilience of stream networks. Groundwater appeared to play a major role in creating the fine‐scale spatial thermal variation, and characterizing this thermal variation is needed for assessing climate change impacts on headwater species accurately. Copyright © 2013 John Wiley & Sons, Ltd.     

A Stream Water Availability Model of Upper Indus Basin Based on a Topologic Model and Global Climatic Datasets

Integrated water resources management at river basin scales and evaluation of effects of climate change on regional water resources require quantitative estimates of space-time variability of monthly discharges within a river network. This study demonstrates that such estimates, which can be called stream water availability, for regional river basins with meager or nonexistent gauge data, can be obtained by combining continuity models of hydrological processes, flow routing, and topology of the river basin. The hydrologic processes can be adequately modeled using high quality databases of hydrologic significance. A stream water availability model is presented for Upper Indus Basin (UIB) utilizing the most up-to-date datasets for topography, temperature, precipitation, net radiation, land cover, soil type, and digital atlas. Multiple datasets have been evaluated and the ones with best accuracy and temporal coverage have been selected for the final model. Upper Indus River and its major tributaries are highly significant in regional water resources management and geopolitics. However, UIB is a poorly studied and largely ungauged river basin with an area of 265,598 km² and extremely rugged topography. Several factors, the chief ones being the challenging terrain and the trans-boundary nature of the basin, have contributed to this knowledge gap. Hydro-climatologically it is a complex basin with a significant cryospheric component. The spatial and temporal variation of the principal climatic variables, namely precipitation, net radiation, and temperature has been thoroughly accounted for in the development of a stream water availability model based on a process model coupled with a topologic model and a linear reservoir model of river flow routing. Model calculations indicate that there are essentially two hydrologic regimes in UIB. The regime that is truly significant in contributing stream flows, originates from the UIB cryosphere containing outstanding glaciers and snowfields. The other regime, generated from wet precipitation and melt water from seasonal snow covers is insignificant due to high rates of infiltration and evaporation in the semi-desert environment prevailing at elevations below perennial snow and ice covers. In general, the modeled stream flow characteristics match with the sparse discharge measurements that are available. Flow in the Indus considerably increases at its confluence with Shyok River and further downstream where other tributaries form the north join the main stem. At or near the outlet of the basin stream flow can vary from less than 800 m³ s^− 1 in the winter and spring to nearly 8,000 m³ s^− 1 in the peak summer and can persist to over 1,500 m³ s^− 1 in the autumn. The importance of snow and glacial melt in Indus River discharge is apparent and any global or regional climate change affecting the equilibrium line elevation of the snow fields in the Karakoram will have a profound influence on the water availability in the Indus. Estimates are made for per capita water availability in Ladakh and Gilgit-Baltistan territories, controlled by India and Pakistan respectively. Geopolitical significance and climate change effects are discussed briefly.     

The effect of Keepit Dam on the temperature regime of the Namoi River,Australia

Modifications to water temperature caused by the release of hypolimnetic water from thermally stratified reservoirs pose a major threat to the aquatic biota of lowland rivers in Australia's Murray–Darling basin. Keepit Dam is earmarked as one of several deep‐release structures in the basin causing ecologically significant temperature modification over a large length of river. This study utilized discrete and continuously monitored historical water temperature data from stream gauging stations, together with reservoir thermal profile data, to assess the impacts of Keepit Dam on the thermal regime of the Namoi River. Modifications to selected components of the river's annual temperature cycle were quantified in relation to a pre‐dam temperature regime estimated from statistical models incorporating catchment, hydrological and sample attributes. Keepit Dam has modified the thermal regime of the Namoi River. The effect was greatest immediately downstream from the dam where the annual maximum daily temperature was approximately 5.0 °C lower and occurred three weeks later than the pre‐dam condition. This change was sufficient to disrupt thermal spawning cues for selected Australian native fish species. The magnitude of disturbance progressively diminished with distance from the dam. Key aspects of the river's annual temperature cycle were largely restored to the pre‐dam condition within 100 river km downstream from the dam, which is closer than previous estimates. However, there was marked inter‐annual variation in the magnitude of thermal modification and ecological impact as a result of year to year changes in tributary flow and reservoir behaviour. Copyright © 2002 John Wiley & Sons, Ltd.