Coldwater Streams Research Articles

Experimental study of fixed and fluidized beds of PCM with an internal heat exchanger

This work presents the results of experiments performed in a thermal energy storage tank filled with particles, which was heated using hot air and then discharged with a cold water stream circulating inside a heat exchanger immersed in the bed. Both fixed- and fluidized-bed configurations were studied. The materials used were sand, which is a material commonly employed in sensible heat storage, and a granular phase change material (PCM), in which the phase change occurs over the temperature range of 40–50°C. Three different heat exchangers with different helical coil geometries were tested by measuring the temperatures in the bed and at the water inlet and outlet. Higher heat transfer coefficients between the bed and the water flow and higher heat exchanger effectiveness were observed for the heat exchanger with the greatest distance between coils, as it allows better contact between the bed particles and the heat exchanger surface when the particles are fluidized.

Large eddy simulation studies on the influence of turbulent inlet conditions on the flow behavior in a mixing tee

Mixing of coolant streams at significant temperature differences in a mixing tee occurs in the cooling systems (e.g. Residual Heat Removal System) of a nuclear power plant resulting in cyclical thermal fluctuations that may lead to high cycle thermal fatigue (HCTF) in the structure. The present study aims to numerically investigate such a scenario using the large-eddy simulation (LES) method. The LES is based on an experiment conducted at the fluid–structure interaction (FSI) test facility, University of Stuttgart. Hot and cold water streams flow in the main and branch pipes with a temperature difference (ΔT) of 117K. The mass flow rate ratio (main/branch) is 4:1.Two LESs with different inlet conditions are performed to study and compare the effect of each inlet condition on the flow behavior downstream of the mixing tee. They are (i) unperturbed inlet conditions and (ii) inlets with synthetic turbulence. The experimental inflow conditions result in an incompletely mixed thermally stratified flow marked by significant buoyancy effects. Assessment of parameters like mean temperature and velocity predicted by both LESs exhibit very little deviation with each other indicating the insignificant effect of inflow turbulence on the bulk flow. But the inclusion of inflow turbulence is seen to have a non-negligible effect in the assessment of parameters like temperature fluctuations, turbulent kinetic energy and temperature–velocity correlation. The prevailing flow conditions are not seen to induce any dominant frequency of near-wall temperature fluctuations, an important factor in thermal fatigue analysis. Energy content of these fluctuations mainly lies in the frequency range of 0.1–2Hz.

Stormwater Thermal Enrichment In Urban Watersheds

Thermal enrichment of coldwater streams by heated stormwater in summer months is often overlooked and even exacerbated by traditional management practices that typically account for flow moderation and pollutant removal only. Initiated in 1999, this study evaluated and identified innovative and traditional approaches to moderate this temperature impact by monitoring and analyzing the hydrologic and thermal regimes of an urban stormwater treatment system consisting of two traditional wet detention ponds and an enhanced natural wetland. Data analysis clearly shows temperature increases in the open detention ponds and the ability of the wetland to mitigate this thermal enrichment. Event-based thermal loading and temperature regime analysis indicated flow reduction via infiltration and effective vegetative cover in the wetland were the primary mechanisms for mitigating stormwater thermal enrichment. Using the concept of temperature equivalent, we also established the locations and strength of thermal enrichment areas. A heat transfer model was developed to simulate runoff temperature. Results indicated that rainfall characteristics, temperature difference between rainfall and the ground surface, and the runoff flow depth were the most important factors affecting runoff temperature. Recommendations identify the need for additional mechanisms (flow reduction/infiltration) beyond traditional detention pond discharge to mitigate solar heating of ponded water. Shading reduces direct heating of open channels. High albedo surfaces and shading reduce heat buildup in pavement, thus, diminishing heat transfer to runoff during rain events. Underground structures in contact with stormwater provide some limited benefits for reducing temperature of heated runoff This title belongs to WERF Research Report Series ISBN: 9781780404332 (eBook) ISBN: 9781843396833 (Print)

Projected impacts of climate change on stream salmonids with implications for resilience‐based management

AbstractThe sustainability of freshwater fisheries is increasingly affected by climate warming, habitat alteration, invasive species and other drivers of global change. The State of Michigan, USA, contains ecologically, socioeconomically valuable coldwater stream salmonid fisheries that are highly susceptible to these ecological alterations. Thus, there is a need for future management approaches that promote resilient stream ecosystems that absorb change amidst disturbances. Fisheries professionals in Michigan are responding to this need by designing a comprehensive management plan for stream brook charr (Salvelinus fontinalis), brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) populations. To assist in developing such a plan, we used stream‐specific regression models to forecast thermal habitat suitability in streams throughout Michigan from 2006 to 2056 under different predicted climate change scenarios. As baseflow index (i.e., relative groundwater input) increased, stream thermal sensitivity (i.e., relative susceptibility to temperature change) decreased. Thus, the magnitude of temperature warming and frequency of thermal habitat degradation were lowest in streams with the highest baseflow indices. Thermal habitats were most suitable in rainbow trout streams as this species has a wider temperature range for growth (12.0–22.5 °C) compared to brook charr (11.0–20.5 °C) and brown trout (12.0–20.0 °C). Our study promotes resilience‐based salmonid management by providing a methodology for stream temperature and thermal habitat suitability prediction. Fisheries professionals can use this approach to protect coldwater habitats and drivers of stream cooling and ultimately conserve resilient salmonid populations amidst global change.

Energy efficiency of permeate gap and novel conductive gap membrane distillation

This work presents numerical modeling results and flux experiments for a novel membrane distillation configuration called conductive gap membrane distillation (CGMD), as well as permeate gap membrane distillation (PGMD). CGMD has a conductive spacer in the gap between the membrane and condensing surface rather than more commonly used insulating materials. Flux measurements with two experimental systems are used to validate the numerical models for PGMD and CGMD. PGMD has 20% higher GOR (energy efficiency) than an air gap membrane distillation (AGMD) system of the same size, whereas CGMD can have two times higher GOR than even PGMD. Increasing gap effective thermal conductivity in CGMD has negligible benefits beyond kgap≈10W/mK under the conditions of this study. The direction of pure water flow in the gap has a significant influence on overall system energy efficiency, especially in the case of CGMD. Using a countercurrent configuration for the pure water flow in the gap relative to the cold stream leads to 40% higher GOR than flow cocurrent with the cold water stream.

Consecutive wildfires affect stream biota in cold- and warmwater dryland river networks

AbstractClimate change and fire suppression have altered fire regimes globally, leading to larger, more frequent, and more severe wildfires. Responses of coldwater stream biota to single wildfires are well studied, but measured responses to consecutive wildfires in warmwater systems that often include mixed assemblages of native and nonnative taxa are lacking. We quantified changes in physical habitat, resource availability, and biomass of cold- and warmwater oligochaetes, insects, crayfish, fishes, and tadpoles following consecutive megafires (covering >100 km2) in the upper Gila River, New Mexico, USA. We were particularly interested in comparing responses of native and nonnative fishes that might have evolved under different disturbance regimes. Changes in habitat and resource availability were related to cumulative fire effects, fire size, and postfire precipitation. The 2nd of 2 consecutive wildfires in the basin was larger and, coupled with moderate postfire discharge, resulted in increased siltatio...

A new species of Parakari (Ephemeroptera: Baetidae) from Guiana Highlands.

The genus Parakari was described from Guiana Highlands in southeastern Venezuela by Nieto & Derka in 2011 for two species inhabiting streams draining isolated, flat-topped table mountains called tepuis. A description of a third representative, Parakari roraimensis sp. n., is given here based on material collected from a coldwater stream at the foothills of Roraima-tepui (SE Venezuela). Detailed morphological descriptions of mature nymph and female adult are given. A differential diagnosis and a key to nymphs of the three Parakari species are provided.

A methodology for identifying ecologically significant groundwater recharge areas

A methodology has been developed to delineate recharge areas that support groundwater-dependent ecological features such as wetlands and coldwater streams. Numerical groundwater models are employed together with particle tracking techniques to link recharge areas to specific ecological features. Kernel density estimation methods are used to identify areas that contain the maximum number of particle endpoints per unit area. These high-density endpoint clusters are subsequently mapped as ecologically significant groundwater recharge areas (ESGRAs). The technique can be utilized with either finite-element or finite-difference groundwater models which are loosely coupled or fully integrated with a distributed hydrologic model. A good representation of both the surface water and the shallow groundwater system is required and the models should be based on a rigorous understanding of the regional, watershed and local-scale geologic, hydrogeologic and hydrologic setting. This manuscript describes how the methodology was employed to delineate ESGRAs for the Oro North, Oro South and Hawkestone Creeks subwatersheds, located in the northwest portion of the Lake Simcoe watershed in southern Ontario, Canada. The three study subwatersheds are connected to the Oro Moraine complex, a high-recharge feature that supports multiple watersheds and the regional groundwater flow system. A transient, integrated surface water/groundwater model was developed for the watersheds flanking the moraine and was calibrated to daily streamflow and groundwater-level observations. Particle tracking was then used to define the groundwater flow system between all streams and wetlands and the areas of recharge, and provided insight into the hydrologic function of the Oro Moraine. After optimization of the cluster analysis procedure, 24% of the 125-km² study area was mapped as having recharge areas that support significant ecological features. As required by the Lake Simcoe Protection Plan, the ESGRAs will be protected from future development to ensure the maintenance of the groundwater-fed ecosystems they support. The methodology described in this paper provides a consistent, objective and technically sound means of identifying and delineating ESGRAs, and has recently been applied to other watersheds in southern Ontario.

Brook Trout Distribution, Genetics, and Population Characteristics in the Driftless Area of Minnesota

AbstractThe Driftless Area in southeastern Minnesota is on the southwestern edge of the native range of Brook Trout Salvelinus fontinalis. It was assumed that native Brook Trout were extirpated from this region in the early 1900s due to degraded stream conditions and stockings of eastern‐origin Brook Trout and European Brown Trout Salmo trutta. Our objectives were to examine Brook Trout populations in the region to determine their spatial and genetic distribution and quantify population characteristics. Information on presence or absence of Brook Trout was gathered by electrofishing 174 streams in southeastern Minnesota. Brook Trout were present in 68% of coldwater streams compared with only in 3% in the early 1970s. The increase is likely due to increasing stream discharge throughout the Driftless Area, enabling recolonization or successful establishment of stocked populations. Streams with higher base flow discharge also had higher abundance, larger size at maturity, and larger Brook Trout present. Genetic data on 74 populations were analyzed to characterize genetic variation within populations, assess genetic structure among populations, and determine possible origins. Numerous populations were not associated with known hatchery sources but were primarily composed of geographic groupings that could represent remnant lineages. Although population characteristics were similar among genetic origins, potentially remnant populations should be given conservation priority because they have proven their ability to sustain themselves in this region. Management actions that emphasize maintaining or increasing stream base flows throughout the region will likely enhance remnant Brook Trout populations in the Driftless Area.Received July 25, 2014; accepted March 17, 2015

Landscape Prediction and Mapping of Game Fish Biomass, an Ecosystem Service of Michigan Rivers

AbstractThe increased integration of ecosystem service concepts into natural resource management places renewed emphasis on prediction and mapping of fish biomass as a major provisioning service of rivers. The goals of this study were to predict and map patterns of fish biomass as a proxy for the availability of catchable fish for anglers in rivers and to identify the strongest landscape constraints on fish productivity. We examined hypotheses about fish responses to total phosphorus (TP), as TP is a growth‐limiting nutrient known to cause increases (subsidy response) and/or decreases (stress response) in fish biomass depending on its concentration and the species being considered. Boosted regression trees were used to define nonlinear functions that predicted the standing crops of Brook Trout Salvelinus fontinalis, Brown Trout Salmo trutta, Smallmouth Bass Micropterus dolomieu, panfishes (seven centrarchid species), and Walleye Sander vitreus by using landscape and modeled local‐scale predictors. Fitted models were highly significant and explained 22–56% of the variation in validation data sets. Nonlinear and threshold responses were apparent for numerous predictors, including TP concentration, which had significant effects on all except the Walleye fishery. Brook Trout and Smallmouth Bass exhibited both subsidy and stress responses, panfish biomass exhibited a subsidy response only, and Brown Trout exhibited a stress response. Maps of reach‐specific standing crop predictions showed patterns of predicted fish biomass that corresponded to spatial patterns in catchment area, water temperature, land cover, and nutrient availability. Maps illustrated predictions of higher trout biomass in coldwater streams draining glacial till in northern Michigan, higher Smallmouth Bass and panfish biomasses in warmwater systems of southern Michigan, and high Walleye biomass in large main‐stem rivers throughout the state. Our results allow fisheries managers to examine the biomass potential of streams, describe geographic patterns of fisheries, explore possible nutrient management targets, and identify habitats that are candidates for species management.Received May 20, 2014; accepted November 6, 2014

Acid mine drainage and stream recovery: Effects of restoration on water quality, macroinvertebrates, and fish

Acid mine drainage (AMD) is a prominent threat to water quality in many of the world’s mining districts as it can severely degrade both the biological community and physical habitat of receiving streams. There are relatively few long-term studies investigating the ability of stream ecosystems to recover from AMD. Here we assess watershed scale recovery of a cold-water stream from pollution by AMD using a 1967 survey of the biological and chemical properties of the stream as a pre-restoration benchmark. We sampled water chemistry, benthic macroinvertebrates, and fish throughout the watershed during the spring and summer of 2011. Water chemistry results indicated that pH and total alkalinity increased post-restoration, while acidity, sulfate, and iron concentrations decreased. Watershed-level taxa richness, local taxa richness, biomass, diversity, and density of macroinvertebrates were significantly higher post-restoration; however, %EPT was not significantly different. Fish species richness, density, and brook trout density were all significantly higher post-restoration. These results provide clear evidence that both abiotic and biotic components of streams can recover from AMD pollution.

Use of first‐order tributaries by brown trout (Salmo trutta) as nursery habitat in a cold water stream network

AbstractMany investigators have examined the importance of suitable in‐stream habitat and flow regime to salmonid fishes. However, there is much less known about the use of small (<5 l·s−1 discharge) first‐order streams within a larger stream network by salmonids. The purpose of this study was to evaluate the use of small headwater streams by juvenile brown trout Salmo trutta in the Emmons Creek stream network in Wisconsin, USA, and to determine whether abundance was related to habitat variables in these streams. Fishes in eight spring‐fed first‐order streams were sampled during a 7‐month period using a backpack electroshocker and measured for total length. Habitat variables assessed included stream discharge, water velocity, sediment composition and the abundance of cover items (woody debris and macrophytes). Densities of YOY trout ranged from 0 to 1 per m2 over the course of the study and differed among first‐order streams. Stepwise multiple regression revealed discharge to be negatively associated with trout density in spring but not in summer. All other habitat variables were not significantly related to trout density. Our results demonstrate the viability of small first‐order streams as nursery habitat for brown trout and support the inclusion of headwater streams in conservation and stream restoration efforts.

Revised Predictive Model for Successful Introduction of Native Ohio Brook Trout (Salvelinus fontinalis) in Select Streams in Geauga and Lake Counties, Ohio a

Eight cold-water streams in Lake and Geauga Counties, Ohio were evaluated to develop a revised predictive model to assess future streams for the introduction of threatened native Ohio Brook Trout (Salvelinus fontinalis). A 15-month study was conducted, ending May 2010, in streams where Brook Trout were previously introduced during the years 1997-2002. Fifty percent of the sixteen original reintroduction streams failed to support the establishment of self-sustaining populations of Brook Trout, indicating there were additional factors contributing to their success and failure. Of the 8 streams included in this study, 4 streams were designated successful, 2 variable, and 2 failed, in terms of the Brook Trout’s ability to establish self-sustaining populations by the Ohio Department of Natural Resources (ODNR). Multivariate statistical methods including Principal Component Analysis (PCA) and Agglomerative Hierarchical Cluster Analysis (AHCA) were implemented to determine the most important characteristics in Brook Trout stream selection. Factors found to be significant for Brook Trout success were stream velocities within the range of 1.4-4.7 cm/s, high hydraulic conductivity of the headwater bedrock aquifer (K>4.7 x 103 cm/s), lighter average δ18O ‰ (-9.8 to -10.4), either high percent canopy cover (40%-55%) or high percent instream cover (18%-37%), a high number of cold-water adapted benthic macroinvertebrate cold-water taxa (10-16 species), yearly average hyporheic water temperature of 4.6°C-17.2°C, average surface water turbidity of 7 to 31 NTU and long-term surface water temperature and dissolved oxygen monitoring over both winter and summer seasons is recommended prior to Brook Trout introduction to ensure their sustainability.

Land use and surface water withdrawal effects on fish and macroinvertebrate assemblages in the Susquehanna River basin, USA

Water withdrawals in the Susquehanna River basin, USA, are increasing due to burgeoning shale gas extraction activities. In order to determine if flow alteration resulting from shale gas industry surface water withdrawals impacts fish and macroinvertebrate assemblages in lotic habitats, data were collected upstream and downstream of 12 withdrawal and three reference sites in headwater, cold water, and large warm water streams. Watershed size ranged from 4 to 517 km2 and average daily withdrawals ranged from 0.05 to 1.4 million liters. Analysis of withdrawal data indicated that approved withdrawals far exceeded actual withdrawals across all stream types. The largest withdrawals relative to stream size were from headwater streams, where on average 6.8% of average daily flow was withdrawn daily. Fish and macroinvertebrate assemblage similarity at study sites depended largely on stream sampled, rather than position upstream or downstream of withdrawals. Regression techniques were employed to determine if catchment-level variables or withdrawal metrics best described variation in fish and macroinvertebrate metrics shown to be sensitive to flow alteration. The catchment-level variables were responsible for the majority of observed variation in fish metrics. Macroinvertebrate models performed poorly, indicating that the stream sampled or variables not included in the analyses were responsible for the majority of variation. Overall, evidence suggests impacts of shale gas withdrawals within the Susquehanna basin are limited at the present state of flow alteration. Potential reasons include protective measures such as pass-by flow restrictions, which require withdrawals to cease when flows drop below a predetermined low flow threshold, maximum instantaneous and daily withdrawal limits, and recent initiation of withdrawals (1–3 years of operation).

Metrics for assessing thermal performance of stormwater control measures

Urban runoff can impact the thermal regime of surface waters and degrade valuable aquatic ecosystems. Some stormwater control measures (SCMs) have been shown to mitigate the effects of thermally-enriched runoff, but previous studies lacked consistency when characterizing the thermal behavior of SCMs. Ecologically-relevant parameters such as maximum outflow temperature, duration of temperatures exceeding thresholds for coldwater species, and thermal load have all been considered in past research. Standard metrics that properly represent the downstream impacts of urban stormwater were needed. This paper evaluated thermal metrics to provide designers and regulators with catchment-scale methods for assessing thermal performance and compliance. It was concluded that multiple metrics must be employed to account for both thermal load and biologically-based reference temperature limits. Metrics for temperature evaluations were broken out by data requirements. When only SCM temperature data are available, event mean temperature estimation appears to be the most rigorous metric. Groundwater temperature may also be employed as a surrogate metric for SCM discharge temperatures if conservative protection of coldwater stream health is desired. When SCM temperature and flow data exist, thermal load reductions should be explored.Efficacy of the low impact development (LID) strategy for temperature mitigation (retaining onsite greater than the 95th percentile storm event) was evaluated using field-collected permeable pavement data. Based on these data, retaining the 95th percentile storm event was determined to be an effective technique for thermal protection of surface waters.However, the most rigorous metrics involve long-term temperature and flow data from local reference streams. The best metric currently available is the uniform continuous above threshold (UCAT) method, in which it is necessary to consider continuous exposure duration when comparing against biological thresholds. These analyses can be tailored to specific species of interest within a targeted ecoregion. Combined with thermal load and mixing analysis in-stream, the UCAT method can provide a real-world estimation of the impacts of development. Additionally, evaluation of mixing zones in-stream should also be employed to adequately assess thermal impacts. However, these methods are the most data intensive.The metrics discussed in this paper can be used to inform new and existing design methodologies for regulating stormwater temperature, duration, and thermal load.

Family-Level Benthic Macroinvertebrate Communities Indicate Successful Relocation and Restoration of a Northeast Iowa Stream

A major stream relocation and restoration project was started in 2004 near Dorchester, Iowa. The project converted riparian cropland and stream bank trees to native tallgrass prairie vegetation while relocating Brook Creek to its original streambed. The goal of this project was to restore Brook Creek to conditions comparable with South Pine Creek, a nearby reference coldwater stream that was used as a model for Brook Creek. Benthic macroinvertebrates were monitored in 2005, 2007, 2010, and 2012 in both Brook Creek and South Pine Creek. Benthic macroinvertebrate family-level taxonomic richness, Ephemeroptera/Plecoptera/Trichoptera (EPT) family richness, and family-level biotic indices (FBI) were calculated. We found that Brook Creek’s FBI values were lowered and EPT richness values increased significantly from 2005 to 2012, indicating establishment of a high quality benthic macroinvertebrate community. Benthic macroinvertebrate communities in Brook Creek became increasingly similar to South Pine Creek over the course of this study as evidenced by a principle component analysis and percent similarity, from a 28.72% similarity in 2005 to 62.54% similarity in 2012. These results demonstrate the successful reestablishment of a benthic macroinvertebrate assemblage following stream reconstruction and similarity to a high-quality reference stream.

Summer Thermal Thresholds of Fish Community Transitions in Connecticut Streams

AbstractThermal tolerances have been studied for individual fish species but few have investigated how stream fish assemblages respond along a temperature gradient and which thermal ranges act as a threshold, triggering discernible community change. The purpose of this study was to define summer temperature thresholds of fish community transitions in Connecticut streams. The program Threshold Indicator Taxa Analysis suggested that the coldwater class had a June–August mean water temperature < 18.29°C, the coolwater class 18.29–21.70°C, and a warmwater class > 21.70°C. Significant indicator species of coldwater streams were Slimy Sculpin Cottus cognatus and Brook Trout Salvelinus fontinalis. Significant indicator species of warmwater streams were Cutlip Minnow Exoglossum maxillingua, Smallmouth Bass Micropterus dolomieu, Rock Bass Ambloplites rupestris, Brown Bullhead Ameiurus nebulosus, Redbreast Sunfish Lepomis auritus and Yellow Bullhead A. natalis. The narrow 3.41°C temperature range between the coldwater and warmwater thresholds was designated as a coolwater transition zone, with potential for the presence of both coldwater and warmwater species and lack of species uniquely associated with this thermal range. Our approach based on a robust set of water temperature and fish community data should be applicable to other temperate regions and will be useful for informing development of thermal criteria, application of multimetric indices, and planning for anticipated effects of climate change.Received July 2, 2013; accepted October 8, 2013Published online January 30, 2014

Paragyrodactylus variegatusn. sp. (Gyrodactylidae) fromHomatula variegata(Dabry De Thiersant, 1874) (Nemacheilidae) in Central China

Paragyrodactylus variegatus n. sp. (Monogenea: Gyrodactylidae) is described from the fins and body surface of Homatula variegata (Dabry de Thiersant, 1874) living in cold-water streams in the Qinling Mountains of central China. It represents the third known species in the genus, with all species parasitizing Asian river loaches (Cypriniformes: Nemacheilidae). The new species resembles most closely Paragyrodactylus iliensis Gvosdev and Martechov, 1953 , but is diagnosed by its marginal hooks being longer than 19 μm, a sickle longer than 4 μm, a sickle aperture shorter than the sickle distal width, and absence of a ventromedial indentation in the haptoral accessory hard part. Scanning electron microscopy reveals a central foramen in the haptoral accessory hard part, and small knob-like protuberances on the heel and toe of the marginal hook sickle. A partial 18S (448 bp) and complete ITS-1, 5.8S, and ITS-2 (1,139 bp) rDNA sequences are provided. A preliminary phylogenetic analysis based on the partial 18S gene, which included all sequenced genera of the Gyrodactylidae, suggests P. variegatus n. sp. is basal within Gyrodactylus sensu lato. It is proposed that the genus is a relict freshwater lineage parasitizing river loaches in the mountain plateaus of central Asia.

Thermal Pollution Mitigation in Cold Water Stream Watersheds Using Bioretention

AbstractThis study examines the use of bioretention as a strategy to reduce the thermal impact associated with urban stormwater runoff in developing cold water stream watersheds. Temperature and flow data were collected during 10 controlled runs at a bioretention facility located in Blacksburg, Virginia. It was determined that bioretention has the ability to reduce the temperature of thermally charged stormwater runoff received from an asphalt surface. Significant reductions in peak and average temperatures (p < 0.001) were observed. However, this facility was unable to consistently reduce the temperature below the threshold for natural trout waters in Virginia. The ability of bioretention to reduce runoff volume and peak flow rate also serves to reduce the hydrothermal impact. An average thermal pollution reduction of nearly 37 MJ/m3 was calculated using an adopted threshold temperature of 20°C. Based on the results of this study, it was concluded that properly designed bioretention systems have the capability to reduce the thermal impact of urban stormwater runoff on cold water stream ecosystems.

Thermodynamic analysis of non-isothermal mixing's influence on the energy target of water-using networks

In this paper, a thermodynamic analysis of non-isothermal mixing's influence on the energy target of water-using network is presented. Firstly, water streams in the network are divided into two categories, and then based on the classification all the non-isothermal mixing patterns between two streams are defined. Through thermodynamic analysis from energy composite curve of hot and cold water streams, the influences of non-isothermal mixing on the energy target of water-using network are explored and some mixing rules are obtained, which can be used to simplify the heat exchanger network of a given water-using system and improve the system's energy performance through identifying the beneficial non-isothermal mixings. The applicability of these rules is illustrated by an example in the paper and the result is very encouraging.