Increases In Stream Temperature Research Articles

Steelhead vulnerability to climate change in the Pacific Northwest

Summary Steelhead (Oncorhynchus mykiss) and other Pacific salmon are threatened by unsustainable levels of harvest, genetic introgression from hatchery stocks and degradation or loss of freshwater habitat. Projected climate change is expected to further stress salmon through increases in stream temperatures and altered stream flows. We demonstrate a spatially explicit method for assessing salmon vulnerability to projected climatic changes (scenario for the years 2030–2059), applied here to steelhead salmon across the entire Pacific Northwest (PNW). We considered steelhead exposure to increased temperatures and more extreme high and low flows during four of their primary freshwater life stages: adult migration, spawning, incubation and rearing. Steelhead sensitivity to climate change was estimated on the basis of their regulatory status and the condition of their habitat. We assessed combinations of exposure and sensitivity to suggest actions that may be most effective for reducing steelhead vulnerability to climate change. Our relative ranking of locations suggested that steelhead exposure to increases in temperature will be most widespread in the southern Pacific Northwest, whereas exposure to substantial flow changes will be most widespread in the interior and northern Pacific Northwest. There were few locations where we projected that steelhead had both relatively low exposure and sensitivity to climate change. Synthesis and applications. There are few areas where habitat protection alone is likely to be sufficient to conserve steelhead under the scenario of climate change considered here. Instead, our results suggest the need for coordinated, landscape‐scale actions that both increase salmon resilience and ameliorate climate change impacts, such as restoring connectivity of floodplains and high‐elevation habitats.

Potential impacts of climate change on growth and prey consumption of stream‐dwelling smallmouth bass in the central United States

AbstractSmallmouth bass (Micropterus dolomieu, SMB) is a broadly distributed, economically important species in the USA and Canada. Although previous research has suggested that projected climate warming may allow SMB to thrive beyond their current northern distribution, little research has been devoted to the population‐level effects of climate change on warm‐water fishes, including SMB. We modelled the impacts of projected climate change on growth of stream‐dwelling SMB along a north–south gradient in the central USA. Using downscaled regional projections from three global climate models, we generated scenarios for thermal habitat change for four populations (in Oklahoma, Missouri, Iowa and Minnesota) and used bioenergetics simulations to estimate prey consumption and growth under future projections. Bioenergetics simulations showed that prey consumption is expected to increase in all populations with moderate stream warming (2–3 °C). Growth potential is predicted to increase by 3–17% if not limited by food availability with stream warming by 2060 and was most pronounced for southern populations. For each 1 °C increase in stream temperature, SMB consumption would be expected to increase by about 27% and growth would increase by about 6%. Due to implications for species interactions, population performance and regulation of local fisheries, a better understanding of how SMB populations will respond to climate change is recommended for effective management and conservation.

Statistical modeling of daily and subdaily stream temperatures: Application to the Methow River Basin, Washington

Management of water temperatures in the Columbia River Basin (Washington) is critical because water projects have substantially altered the habitat of Endangered Species Act listed species, such as salmon, throughout the basin. This is most important in tributaries to the Columbia, such as the Methow River, where the spawning and rearing life stages of these cold water fishes occurs. Climate change projections generally predict increasing air temperatures across the western United States, with less confidence regarding shifts in precipitation. As air temperatures rise, we anticipate a corresponding increase in water temperatures, which may alter the timing and availability of habitat for fish reproduction and growth. To assess the impact of future climate change in the Methow River, we couple historical climate and future climate projections with a statistical modeling framework to predict daily mean stream temperatures. A K‐nearest neighbor algorithm is also employed to: (i) adjust the climate projections for biases compared to the observed record and (ii) provide a reference for performing spatiotemporal disaggregation in future hydraulic modeling of stream habitat. The statistical models indicate the primary drivers of stream temperature are maximum and minimum air temperature and stream flow and show reasonable skill in predictability. When compared to the historical reference time period of 1916–2006, we conclude that increases in stream temperature are expected to occur at each subsequent time horizon representative of the year 2020, 2040, and 2080, with an increase of 0.8 ± 1.9°C by the year 2080.

Temperature increase and respiratory performance of macroinvertebrates with different tolerances to organic pollution

Respiration rates (mg O 2 g −1 AFDW h −1 ) of Leuctra hippopus , Sericostoma personatum , Helodes minuta , Gammarus pulex and Asellus aquaticus were studied across an oxygen gradient at 2.8 and 6.3 °C, corresponding to an expected 3.5 °C increase in Danish winter stream temperature. Species were selected from the Danish Stream Fauna Index (DSFI), representing an expected hierarchy of tolerance towards water quality degradation. We expected that low-ranking, tolerant species (i.e. indicators of bad water quality) would have the capacity to regulate their oxygen uptake relatively independently of oxygen availability (oxy-regulators) and high-ranking, sensitive species (i.e. indicators of good water quality) would be less able to do so (oxy-conformers). For all species respiration rate was higher (although non-significantly) at 6.3 °C. The species’ oxy-regulatory capacity did not consistently reflect their DSFI ranking. As expected, and in accordance with its DSFI ranking, A. aquaticus had the highest oxy-regulatory capacity with the ability to regulate O 2 uptake until an oxygen saturation of only 20%, which did not change with increasing temperature, emphasizing the robustness of A. aquaticus towards changes in the environment. S. personatum , H. minuta and G. pulex revealed no oxy-regulatory capacity. In contrast, the plecopteran L. hippopus did display an unexpected oxy-regulatory capacity. Though an increase in temperature changed L. hippopus ’ capacity to oxy-regulate (the critical limit increased from 32.5 to 43.5% oxygen), respiration rates did not change significantly in spite of the temperature increase. This result contradicts the general belief that stoneflies, because of their affinity to well oxygenated habitats, are conformers. Our findings call for further studies on the respiratory conformer–regulator concept and its role as an eco-physiological trait for bio-assessment.

Upper Thermal Tolerance of Mountain Whitefish Eggs and Fry

AbstractSome populations of Mountain Whitefish Prosopium williamsoni, a widely distributed native Rocky Mountain salmonid, have experienced catastrophic declines while other populations remain robust. To assess the possibility that the declines have arisen from climate‐related factors, several experiments were conducted to determine the upper thermal tolerances of embryos and fry and the effects of temperature on growth. Hatching of eggs was measured at 5.7, 6.4, 8.4, and 10.4°C (three replicates each). Survival and growth of fry were measured for 33 d at 5.7, 8.2, 11.8, 16.5, 19.1, 22.2, and 25.2°C (three replicates each). Mean hatching success was 96.7% (SD, 2.9) at 5.7°C, 98.3% (2.9) at 6.4°C, 90.0% (8.7) at 8.4°C and 38.3% (10.4) at 10.4°C. The ultimate upper incipient lethal temperature for fry was 23.6°C (95% CI, 23.5–23.7°C) after 7 d, which decreased with time to 22.6°C (22.1–23.0°C) after 33 d. The critical thermal maximum was 26.7°C (SD, 0.8) for fry acclimated to 13.4°C. The temperature for maximum growth was 13.8°C (95% CI, 10.8–16.8°C). Growth rates above and below the temperature for maximum growth decreased sharply to about 40% of the maximum at 5.7°C and 22.2°C. Based on these experimental data, the criteria for the protection of Mountain Whitefish fry are 21.6°C for acute water temperature and 16.8°C for chronic water temperature. The acute criterion for reproduction—based on the maximum temperature for successful incubation—is 8.4°C. The low upper thermal tolerance of Mountain Whitefish relative to those of other salmonids suggests that they will be very vulnerable to the increasing stream temperatures resulting from climate change.

Analysis of stream temperature and heat budget in an urban river under strong anthropogenic influences

Summary Stream temperature variations of the Tama River, which runs through highly urbanized areas of Tokyo, were studied in relation to anthropogenic impacts, including wastewater effluents, dam release and water withdrawal. Both long-term and longitudinal changes in stream temperature were identified and the influences of stream flow rate, temperature and volume of wastewater effluents and air temperature were investigated. Water and heat budget analyses were also conducted for several segments of the mainstream to clarify the relative impacts from natural and anthropogenic factors. Stream temperatures in the winter season significantly increased over the past 20 years at sites affected by intensive and warm effluents from wastewater treatment plants (WWTPs) located along the mainstream. In the summer season, a larger stream temperature increase was identified in the upstream reaches, which was attributable to the decreased flow rate due to water withdrawal. The relationship between air and stream temperatures indicated that stream temperatures at the upstream site were likely to be affected by a dam release, while temperatures in the downstream reaches have deviated more from air temperatures in recent years, probably due to the increased impacts of effluents from WWTPs. Results of the water and heat budget analyses indicated that the largest contributions to water and heat gains were attributable to wastewater effluents, while other factors such as groundwater recharge and water withdrawal were found to behave as energy sinks, especially in summer. The inflow from tributaries worked to reduce the impacts of dam release and the heat exchanges at the air–water interface contributed less to heat budgets in both winter and summer seasons for all river segments.

The effects of increased stream temperatures on juvenile steelhead growth in the Yakima River Basin based on projected climate change scenarios

Stakeholders within the Yakima River Basin expressed concern over impacts of climate change on mid-Columbia River steelhead (Oncorhynchus mykiss), listed under the Endangered Species Act. We used a bioenergetics model to assess the impacts of changing stream temperatures—resulting from different climate change scenarios—on growth of juvenile steelhead in the Yakima River Basin. We used diet and fish size data from fieldwork in a bioenergetics model and integrated baseline and projected stream temperatures from down-scaled air temperature climate modeling into our analysis. The stream temperature models predicted that daily mean temperatures of salmonid-rearing streams in the basin could increase by 1–2 °C and our bioenergetics simulations indicated that such increases could enhance the growth of steelhead in the spring, but reduce it during the summer. However, differences in growth rates of fish living under different climate change scenarios were minor, ranging from about 1–5 %. Because our analysis focused mostly on the growth responses of steelhead to changes in stream temperatures, further work is needed to fully understand the potential impacts of climate change. Studies should include evaluating changing stream flows on fish activity and energy budgets, responses of aquatic insects to climate change, and integration of bioenergetics, population dynamics, and habitat responses to climate change.

Changes in Fish Community Structure and Effects on Blackside Dace (Chrosomus cumberlandensis) Populations Following Beaver Colonization in Davis Branch, Cumberland Gap National Historical Park, Bell County, Kentucky

Davis Branch in Cumberland Gap National Historical Park was considered important for the recovery of the Federally threatened Chrosomus cumberlandensis (Blackside Dace). Monitoring of the Davis Branch population began in 1990. Castor canadensis (North American Beaver) colonization was reported in 1994, and a series of dams have persisted in the upper section of the stream. The pervasive effects of Beavers on Blackside Dace populations were unknown. Our goals were: 1) to characterize the fish community structure and relative abundance of Blackside Dace within the assemblage, 2) to determine the direct and indirect effects of beaver dams on the fish community, and Blackside Dace population, 3) to monitor the age structure of the Blackside Dace population, and 4) to recommend management actions that will enhance the Blackside Dace population within Davis Branch. Fishes were collected from eight stations annually from 1990–2010, except for 2003–2005. Stations were delineated within downstream and upstream sections based on Beaver presence, and within three periods, prior (1990–1993), post (1994–2002), and recent (2006–2010). Fish community structure indicated distinct downstream and upstream assemblages prior to Beaver colonization, with the relative abundance of Blackside Dace approximately 6% and 18%, respectively. The fish assemblage and relative abundance of Blackside Dace shifted over time, with the relative abundance of Lepomis gulosus (Warmouth), Lepomis auritus (Redbreast Sunfish), and Chrosomus erythrogaster (Southern Redbelly Dace) increasing, and Blackside Dace decreasing; only 25 Blackside Dace were encountered from 2006–2010. Comparison of Blackside Dace age classes between the 3 periods indicated the 0 age class decreased over time and 1 and 2 age classes increased initially but eventually declined within both the downstream and upstream sections. It is speculated that the continued presence of beaver dams increased stream temperatures downstream and upstream, altered the flow regime, and changed the available habitat, thus creating conditions more suitable for centrarchid species and Southern Redbelly Dace, which probably preyed upon and out-competed Blackside Dace, respectively. It is recommended that the National Park Service and its partners 1) develop a Beaver management program, 2) return Davis Branch to its free-flowing, pre-Beaver condition, 3) significantly decrease nonnative species and decrease native centrarchid species to abundances prior to Beaver colonization, and 4) establish a Davis Branch Blackside Dace propagation and reintroduction program.

Projected climate change impacts on the hydrology and temperature of Pacific Northwest rivers

A dominant river‐tracing‐based streamflow and temperature (DRTT) model was developed by coupling stream thermal dynamics with a source‐sink routing model. The DRTT model was applied using 1/16 degree (∼6 km) resolution gridded daily surface meteorology inputs over a ∼988,000 km2 Pacific Northwest (PNW) domain to produce regional daily streamflow and temperature simulations from 1996 to 2005. The DRTT results showed favorable performance for simulation of daily stream temperature (mean R2= 0.72 and root‐mean‐square error = 2.35°C) and discharge (mean R2 = 0.52 and annual relative error = 14%) against observations from 12 PNW streams. The DRTT was then applied with a macroscale hydrologic model to predict streamflow and temperature changes under historical (1980s) and future (2020s, 2040s, and 2080s) climate change scenarios (IPCC AR4) as they may affect current and future patterns of freshwater salmon habitat and associated productivity of PNW streams. The model projected a 3.5% decrease in mean annual streamflow for the 2020s and 0.6% and 5.5% increases for the 2040s and 2080s, respectively, with projected increase in mean annual stream temperatures from 0.55°C (2020s) to 1.68°C (2080s). However, summer streamflow decreased from 19.3% (2020s) to 30.3% (2080s), while mean summer stream temperatures warmed from 0.92°C to 2.10°C. The simulations indicate that projected climate change will have greater impacts on snow dominant streams, with lower summer streamflows and warmer summer stream temperature changes relative to transient and rain dominant regimes. Lower summer flows combined with warmer stream temperatures suggest a future with widespread increased summertime thermal stress for coldwater fish in the PNW region.

Diurnal timing of warmer air under climate change affects magnitude, timing and duration of stream temperature change

AbstractStream temperature will be subject to changes because of atmospheric warming in the future. We investigated the effects of the diurnal timing of air temperature changes – daytime warming versus nighttime warming – on stream temperature. Using the physically based model, Heat Source, we performed a sensitivity analysis of summer stream temperatures to three diurnal air temperature distributions of +4 °C mean air temperature: i) uniform increase over the whole day, ii) warmer daytime and iii) warmer nighttime. The stream temperature model was applied to a 37‐km section of the Middle Fork John Day River in northeastern Oregon, USA. The three diurnal air temperature distributions generated 7‐day average daily maximum stream temperatures increases of approximately +1.8 °C ± 0.1 °C at the downstream end of the study section. The three air temperature distributions, with the same daily mean, generated different ranges of stream temperatures, different 7‐day average daily maximum temperatures, different durations of stream temperature changes and different average daily temperatures in most parts of the reach. The stream temperature changes were out of phase with air temperature changes, and therefore in many places, the greatest daytime increase in stream temperature was caused by nighttime warming of air temperatures. Stream temperature changes tended to be more extreme and of longer duration when driven by air temperatures concentrated in either daytime or nighttime instead of uniformly distributed across the diurnal cycle. Copyright © 2012 John Wiley & Sons, Ltd.

RESTORING SALMON HABITAT FOR A CHANGING CLIMATE

ABSTRACTAn 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.

The paradox of cooling streams in a warming world: Regional climate trends do not parallel variable local trends in stream temperature in the Pacific continental United States

Temperature is a fundamentally important driver of ecosystem processes in streams. Recent warming of terrestrial climates around the globe has motivated concern about consequent increases in stream temperature. More specifically, observed trends of increasing air temperature and declining stream flow are widely believed to result in corresponding increases in stream temperature. Here, we examined the evidence for this using long‐term stream temperature data from minimally and highly human‐impacted sites located across the Pacific continental United States. Based on hypothesized climate impacts, we predicted that we should find warming trends in the maximum, mean and minimum temperatures, as well as increasing variability over time. These predictions were not fully realized. Warming trends were most prevalent in a small subset of locations with longer time series beginning in the 1950s. More recent series of observations (1987–2009) exhibited fewer warming trends and more cooling trends in both minimally and highly human‐influenced systems. Trends in variability were much less evident, regardless of the length of time series. Based on these findings, we conclude that our perspective of climate impacts on stream temperatures is clouded considerably by a lack of long‐term data on minimally impacted streams, and biased spatio‐temporal representation of existing time series. Overall our results highlight the need to develop more mechanistic, process‐based understanding of linkages between climate change, other human impacts and stream temperature, and to deploy sensor networks that will provide better information on trends in stream temperatures in the future.

Variable-retention riparian harvesting effects on riparian air and water temperature of sub-boreal headwater streams in British Columbia

A 5-year (2002–2006) before–after control impact study was initiated in three watersheds of the British Columbia central interior to assess the ability of a variable retention riparian treatment to maintain fish habitat conditions in small sub-boreal streams (<2m width). This paper presents findings for the stream shade and air and stream temperature component of the study. Eight streams were studied to assess stream shade, riparian air, and stream water temperature response during summer months to a policy retention level of at least 10stems of merchantable timber per 100m of channel length. After harvesting there was a significant decrease in shade as well as an increase in air and stream temperature at all treatment sites. Riparian harvesting reduced stream shade by 30–50% from pre-harvest levels but shade was recovering to pre-harvest levels 2–3years after harvesting. Mean weekly average and maximum air temperatures at treatment sites increased more than 3°C compared to control locations. Mean weekly average and maximum stream temperatures at treatment sites increased by as much as 5 and 6°C, respectively. Despite the recovery of shade measured at the water surface, mean and maximum water temperatures remained significantly higher at treatment sites than control sites. The discrepancy between shade recovery and temperature response indicates that vegetative surface height receiving radiation must be considered along with shade. Shade from overstory may be more effective at maintaining riparian air and stream temperatures than lower understory because it can limit energy transfer to lower layers of the forest canopy and ground surface.

Headwater stream temperature: Interpreting response after logging, with and without riparian buffers, Washington, USA

We examined stream temperature response to forest harvest in small (<9ha) forested headwater catchments in western Washington, USA over a seven year period (2002–2008). These streams have very low discharge in late summer X¯≈0.3Ls-1) and many become spatially intermittent. We used a before–after, control-impact (BACI) study design to contrast the effect of clearcut logging with two riparian buffer designs, a continuous buffer and a patch buffer. We focused on maximum daily temperature throughout July and August, expecting to see large temperature increases in the clearcut streams (n=5), much smaller increases in the continuously buffered streams (n=6), with the patch-buffered streams (n=5) intermediate. Statistical analyses indicated that all treatments resulted in significant (α=0.05) increases in stream temperature. In the first year after logging, daily maximum temperatures during July and August increased in clearcut catchments by an average of 1.5°C (range 0.2 to 3.6°C), in patch-buffered catchments by 0.6°C (range −0.1 to 1.2°C), and in continuously buffered catchments by 1.1°C (range 0.0 to 2.8°C). Temperature responses were highly variable within treatments and, contrary to our expectations, stream temperature increases were small and did not follow expected trends among the treatment types. We conducted further analyses in an attempt to identify variables controlling the magnitude of post-harvest treatment responses. These analyses showed that the amount of canopy cover retained in the riparian buffer was not a strong explanatory variable. Instead, spatially intermittent streams with short surface-flowing extent above the monitoring station and usually characterized by coarse-textured streambed sediment tended to be thermally unresponsive. In contrast, streams with longer surface-flowing extent above the monitoring station and streams with substantial stream-adjacent wetlands, both of which were usually characterized by fine-textured streambed sediment, were thermally responsive. Overall, the area of surface water exposed to the ambient environment seemed to best explain our aggregate results. Results from our study suggest that very small headwater streams may be fundamentally different than many larger streams because factors other than shade from the overstory tree canopy can have sufficient influence on stream energy budgets to strongly moderate stream temperatures even following complete removal of the overstory canopy.

What are the effects of wooded riparian zones on stream temperature?

Predicted increases in stream temperature due to climate change will have a number of direct and indirect impacts on stream biota. A potential intervention for mitigating stream temperature rise is the use of wooded riparian zones to increase shade and reduce direct warming through solar radiation. To assess the effectiveness of this intervention, we conducted a systematic review of the available evidence for the effects of wooded riparian zones on stream temperature. We searched literature databases and conducted relevant web searches. Inclusion criteria were: subject - any stream in a temperate climate; intervention - presence of trees in the riparian zone; comparator - absence of trees in the riparian zone; outcome measure - stream temperature. Included studies were sorted into 3 groups based on the scale of the intervention and design of the study. Two groups were taken forward for synthesis; Group 1 studies comparing water temperature in streams with and without buffer strips/riparian cover and Group 2 comparisons of stream temperatures in open and forested landscapes. Temperature data were extracted and quantitative synthesis performed using a random effects meta-analysis on the differences in mean and maximum temperature. Ten studies were included in each of Groups 1 and 2. Results for both groups suggest that riparian wooded zones lower spring and summer stream temperatures. Lowering of maximum is greater than lowering of mean temperature. Further analysis of environmental variables that might modify the effects of the intervention was not possible using the limited set of studies. Wooded riparian zones can reduce stream temperatures, particularly in terms of maximum temperatures. Because temperature is known to affect fish, amphibian and invertebrate life history, the reported effect sizes are likely to have a biological significance for the stream biotic community. Consequently investment in creation of wooded riparian zones might provide benefits in terms of mitigating some of the ecological effects of climate change on water temperature. Considerable uncertainty lies in the environmental variables that may modify the cooling effect of wooded riparian zones, and therefore it is not possible to identify when the use of this intervention for cooling would be most valuable.

Bank thermal storage as a sink of temperature surges in urbanized streams

A poorly-studied benefit of bank storage is the ability of the streambed to act as a thermal sink to streams influenced by urban runoff (e.g. bank thermal storage. Headwater streams, with their low thermal inertia, are particularly susceptible to thermal pollution. We utilize numerical modeling to quantify the amount of heat exchanged with the subsurface during temperature surges, which we define as greater than a 1 C stream temperature increase in 15 min. We base our study on Boone Creek, a low-order stream in northwestern North Carolina with stream discharge and temperature data dating to March 2006. The catchment is heavily urbanized, and although the stream is of moderate gradient, it is fed by tributaries that lose up to 200 m/km. The combined effect of urbanization and steep gradient produces a flashy response: stream discharge averages 0.10 m3/s, but may increase up to two orders of magnitude during storm events. These events also affect stream and streambed temperatures. Four summers of monitoring (2006–2008, 2010) indicate that 71 temperature surges occurred with a mean temperature increase of 2.39 C and a maximum increase of 6.36 C. We model generic storm events based on typical Boone Creek storms and streambed hydrogeology with the U.S.G.S. finite-difference groundwater flow and heat transport code VS2DH. The one-dimensional model domain includes a diurnally-oscillating stream temperature and specified head at the upper boundary, a constant streambed temperature and head at the lower boundary, and gaining stream conditions. Reference storm simulations use a temperature increase of 3.66 C and a stream stage increase of 0.66 m. Simulations show that at a depth of 4.5 cm, nearly half of the temperature-surge signal has dissipated and lag times are 30 min. By a depth of 9.5 cm, however, peak temperatures are only one-third of storm levels and lag times are 2 h. At depths beyond 49.5 cm, the perturbation is less than 0.1 C and lags the storm event by more than 17.5 h. Storm influence extends to a depth of 2 m and persists for days. Sensitivity simulations suggest that hydraulic conductivity, sediment heat capacity, and thermal conductivity are the most sensitive model parameters. Calculations show that temperature-surge induced heat storage in the simulated streambed is 72% of the heat storage in the stream.

Response of western Oregon (USA) stream temperatures to contemporary forest management

A replicated before–after-control-impact study was used to test effectiveness of Oregon’s (USA) riparian protection measures at minimizing increases in summer stream temperature associated with timber harvest. Sites were located on private and state forest land. Practices on private forests require riparian management areas around fish-bearing streams; state forest’s prescriptions are similar but wider. Overall we found no change in maximum temperatures for state forest streams while private sites increased pre-harvest to post-harvest on average by 0.7 °C with an observed range of response from −0.9 to 2.5 °C. The observed increases are less than changes observed with historic management practices. The observed changes in stream temperature were most strongly correlated with shade levels measured before and after harvest. Treatment reach length, stream gradient, and changes in the upstream reach stream temperature were additionally useful in explaining treatment reach temperature change. Our models indicated that maximum, mean, minimum, and diel fluctuations in summer stream temperature increased with a reduction in shade, longer treatment reaches, and low gradient. Shade was best predicted by riparian basal area and tree height. Findings suggest that riparian protection measures that maintain higher shade such as the state forests were more likely to maintain stream temperatures similar to control conditions.

Bayesian network models for environmental flow decision‐making: 1. Latrobe River Australia

AbstractCurrent methods underpinning environmental flow (eFlow) decisions often lack transparency, do not adequately consider uncertainties and rarely include adaptive management principles. We report the development and application of an eFlow Bayesian Network (BN) model that links four flow components with an ecological model to predict the spawning and recruitment of two important native fish species, the Australian Grayling and River Blackfish, in the highly regulated and flow‐stressed lower Latrobe River in Victoria, Australia. Autumn high flows, in conjunction with low stream temperature, are critical for Grayling spawning. The BN model was used to predict the probability of spawning and recruitment of these two native fish species for four flow scenarios. Quantitative data, flow simulation models and expert judgement were used to parameterize the BN model. The model results showed clearly that currently, and into the future, there is a very low likelihood of spawning and recruitment of Australian Grayling in the lower Latrobe. River Blackfish are minimally affected by the predicted reductions in flow and increased stream temperatures. Management scenarios aimed at modifying flows and stream temperatures to increase the likelihood of successful spawning and recruitment of Australian Grayling were assessed. Self‐sustaining populations of Australian Grayling could conceivably be achieved in the upper reaches of this river if fish passage was provided through an on‐stream reservoir. A major benefit in building and applying an eFlow BN model is that it can facilitate meaningful analysis and discussion of the ecological effects of particular eFlow regimes. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Influence of Fire on Native and Nonnative Salmonid Populations and Habitat in a Western Montana Basin

AbstractAnticipated increases in the frequency and severity of wildfire may threaten the persistence of native salmonid populations in headwater streams in western North America. This study used extensive pre‐ and postfire data to assess whether wildfire leads to hypothesized declines in native westslope cutthroat troutOncorhynchus clarkii lewisiand bull troutSalvelinus confluentuspopulations along with increases in the prevalence and abundance of nonnative brook troutS. fontinalis. Postfire cutthroat trout density was negatively correlated with the proportion of basin area that burned at moderate to high severity, but the declines in density after fires were less pronounced for bull trout and brook trout. Recovery of cutthroat trout was generally rapid in severely affected reaches. Contrary to expectation, there was no evidence of a marked increase in abundance or invasion by brook trout after wildfire. Brook trout exhibited the most severe declines in debris flow–affected reaches among all species and exhibited less recovery in severely burned reaches than did cutthroat trout. Increased stream temperature was the most significant habitat change that followed wildfire, the mean maximum water temperature during summer months increasing by 2–6°C in severely burned reaches. In contrast, burned area percentage was unrelated to large woody debris density, the percentage of surface fines, substrate diversity, or the percentage of pool habitat. The characteristically high variability in fish and habitat responses to wildfire will continue to pose a challenge for the understanding and management of fire in aquatic ecosystems.

The influence of wildfire extent and severity on streamwater chemistry, sediment and temperature following the Hayman Fire, Colorado

The 2002 Hayman Fire was the largest fire in recent Colorado history (558 km2). The extent of high severity combustion and possible effects on Denver’s water supply focussed public attention on the effects of wildfire on water quality. We monitored stream chemistry, temperature and sediment before the fire and at monthly intervals for 5 years after the fire. The proportional extent of a basin that was burned or that burned at high severity was closely related to post-fire streamwater nitrate and turbidity. Basins that burned at high severity on &gt;45% of their area had twice the streamwater nitrate and four times the turbidity as basins burned to a lower extent; these analytes remained elevated through 5 years post-fire. In those basins, the highest post-fire streamwater nitrate concentrations (23% of USA drinking water standards) were measured during spring, the peak discharge period. Summer streamwater was 4.0°C higher in burned streams on average compared with unburned streams; these persistent post-fire stream temperature increases are probably sufficient to alter aquatic habitat suitability. Owing to the slow pace of tree colonisation and forest regrowth, recovery of the watersheds burned by the Hayman Fire will continue for decades.