Daily Water Temperature Research Articles

Development of improved deep learning models for multi-step ahead forecasting of daily river water temperature

Precise river water temperature (WT) forecasts are essential for monitoring water quality. This study addresses the limited use of signal decomposition in hybrid WT prediction models by proposing three methods: namely ensemble empirical mode decomposition (EEMD) on AdaBoost, long short-term memory (LSTM), and gated recurrent unit (GRU). These models integrate ensemble empirical mode decomposition (EEMD) with machine learning techniques for forecasting WT across multiple time horizons (one, three, and five days). The performance of implemented models were tested on two river stations located on the Clackamas River (USGS 14211010) and Willamette River (USGS 14211720). Some error measures comprising root mean square (RMSE), mean absolute error (MAE), coefficient of determination (R2), uncertainty coefficient in 95% confidence level (U95%), and mean absolute percentage error (MAPE) were applied in assessing the models’ performances. The performance of the proposed merged methods, including EEMD-AdaBoost, EEMD-LSTM, and EEMD-GRU, were compared with their simple forms. The outcomes illustrated that the hybrid models performed better than the relevant individual methods; however, the river WT forecasts of EEMD-LSTM and EEMD-GRU were found to be much closer to the observed data than those of the EEMD-AdaBoost method. The better accuracy of hybrid models compared to their corresponding simple ones can be explained by considering the potential of EEMD in separating intrinsic patterns and reducing the noises, leading to reliable forecasts of river WT time series. A performance comparison of the simple models also denoted the superiority of LSTM and GRU over the AdaBoost. The superior river WT forecasts at both stations during the testing stage were concluded for one day ahead at EEMD-GRU model (USGS 14211010: RMSE = 0.1929 ℃, MAE = 0.1489 ℃, R2 = 0.9988, U95% = 0.3745, MAPE = 1.3608%; USGS 14211720: RMSE = 0.1918 ℃, MAE = 0.1558 ℃, R2 = 0.9990, U95% = 0.3690, MAPE = 1.1790%).

Water Temperature, Prey Concentration and Salmonid Density Influence Daily Growth of Wild Juvenile Salmonids in Tributaries of the Upper Salmon River, Idaho (USA)

ABSTRACT Theory, experiments and field studies indicate that the somatic growth rate of freshwater consumers is shaped by the individual, additive and multiplicative effects of multiple factors, including consumer size and condition, temperature, prey resources and biotic interactions. While our understanding of how these factors affect wild populations of freshwater consumers is improving, the topic remains poorly studied, especially with respect to mobile species. Here, we report on an 8‐year, seven‐stream (n = 49 stream‐year combinations) observational study examining the individual and interactive effects of invertebrate prey concentration (F, mg/m3), mean daily water temperature (T, °C) and juvenile Chinook salmon (Oncorhynchus tshawytscha) density (D, fish/100 m2) on summer daily growth rates (%/d) of mobile, anadromous, juvenile Chinook salmon (age‐0+, n = 382) and sub‐yearling (age‐0+, n = 61) and yearling (age‐1+) steelhead trout (O. mykiss, n = 70) rearing in cold (mean daily summer: 12.1°C, range: 4.2°C–16.7°C) mountain tributaries of the Salmon River basin in central Idaho (USA). AICc model selection indicated that daily juvenile salmonid growth positively correlated with water temperature, prey biomass concentration, local juvenile Chinook density and the interaction between water temperature and food but with species and age‐specific differences. Water temperature was a covariate in all top‐ranked models, with daily growth (%/day) rate increasing (0.05%–0.23%/d) linearly with mean daily summer water temperature. In addition to a direct positive relationship with daily growth rate, there was evidence that prey concentration positively interacted with water temperature to accelerate daily growth (F × T). The positive relationship between juvenile salmonid daily growth rate and juvenile Chinook density is difficult to explain and could result from confounding factors. The individual success observed in these streams may contribute to population‐level benefits for the focal consumers, as prey‐rich, warm summers may result in larger individuals with higher energy reserves at the end of the summer/autumn growing season, contributing to improved overwinter survival. Our results, taken in combination with evidence from models, experiments and observational studies, have climate change implications. Current and predicted increases in water temperature will necessitate higher rates of prey consumption by aquatic ectothermic consumers to offset accelerated metabolic demands. Thus, to improve the resilience of mobile freshwater consumers in a warming climate, we suggest that natural resource managers not only consider physical and chemical habitat conditions but also biotic conditions, including the spatiotemporal quantity and quality of prey resources.

Measurement and analysis of fish pond water temperature field in summer based on fiber Grating string.

To solve the problems of low detection efficiency and inability to adapt to distributed measurement in traditional detection methods, a water temperature field detection system based on a fiber Bragg grating string was designed. In this system, six fiber Bragg gratings with different center wavelengths are connected in series on a single fiber optic cable based on wavelength division multiplexing technology. The fiber Bragg grating string is encapsulated in stainless steel tube and vertically fixed in the measured water body of the fish pond. The space division multiplexing technology is employed to collect information from multiple fiber Bragg grating strings. Water temperature measurement experiments were conducted in the summer pond environment. The experimental results show that the daily variation curve of temperature in each water layer of the fish pond is relatively smooth and approximates a cosine function with a 24-hour period. In summer, the daily average water temperature in the pond is no more than 1°C higher than the average air temperature. The difference between the maximum and the minimum water temperature is approximately 2°C. During the daytime, the temperature gradually decreases from the surface to the deeper water layers, whereas at night, the temperature variation among the water layers is minimal. As depth increases, the amplitude of the water temperature curve oscillations gradually decreases, exhibiting exponential decay. However, the peak time gradually lags behind. There is a correlation between the temperatures of the water layers in the fish pond, and the smaller the distance between the water layers, the stronger the correlation. The experimental results obtained in this study are highly significant for real-time services in aquatic planting and aquaculture. Additionally, this measurement method can provide valuable reference and guidance for measuring temperature fields in other fluids.

150-year daily data (1870–2021) in lakes and rivers reveals intensifying surface water warming and heatwaves in the Pannonian Ecoregion (Hungary)

Study regionPannonian Ecoregion, Hungary. Study focusBridging the gap between atmospheric influences and aquatic environments, this study embarked on a comprehensive reconstruction of daily surface water temperatures across lakes and rivers within the Pannonian Ecoregion over an extensive period of 150 years (1870–2021). New hydrological insights for the regionThe analysis revealed a clear warming trend in waters over the past 150 years, and majority of this warming occurred in recent three to four decades (average warming rate: 0.317 °C/decade). Seasonal patterns indicated that winter and spring exhibited faster warming rates, followed by autumn and summer. There has been a significant increase in the number, duration, and intensity of heatwaves in both lakes and rivers, particularly pronounced in the last 30–40 years, and with the rise of air temperatures, river and lake heatwaves tend to intensity. These findings underscore the escalating impact of climate change on freshwater systems in the Pannonian Ecoregion, emphasizing the urgent need for mitigation measures. As the first study on river and lake heatwaves in Hungary and one of the few studies on river heatwaves worldwide, this study will provide reference for analysing extreme thermal events in aquatic systems.

Wpływ działalności antropogenicznej w dorzeczu górnego Dunaju na reżim temperatury wody Dunaju w Bratysławie

The man activity in the basin affects the water temperature in the increasingly higher levels (construction of water reservoirs, construction of thermal and nuclear power plants or drainage of waste water to streams). In this paper, we focused our attention on the evaluation of the impact of anthropogenic activity to increase the thermal load of the Danube River for the period 1926–2020 at the Bratislava (Slovakia) station. In the first part, the long-term trends of a series of monthly and annual water temperatures in the Danube (period 1931–2020) are identified. In the second part, the dependence of the range of daily water temperature values is analysed at the temperature of the atmosphere in Vienna. The impact of an increase in the temperature of the Danube water due to human activity was tried to identify for lower, average, and higher flows (for Danube discharge at Bratislava water gauge 1500 m3s-1, 2000 m3s-1, and 3000 m3s-1) by comparing two periods: 1932–1961, and 1991–2020. As the effect of water heating in the river stream is most noticeable during low flow (dry) periods and high air temperatures, only daily water and air temperature data from the warm months between May and September were used in the calculations. At monthly flow rates of 1500 m3s-1, the water temperature was, on average, 0.5°C higher during the period of 1991–2020 than it was during the period of 1932–1960. This growth could be attributed to human activities in the Danube basin above Bratislava (warming of water in the built tanks, the wastewater flow to the Danube flow, etc.)

Extreme hydrometeorological events induce abrupt and widespread freshwater temperature changes across the Pacific Northwest of North America

AbstractThe Pacific Northwest of North America experienced four extreme hydrometeorological events during 2021 including intense cold waves in mid-February and late December, the record-setting June heat dome, and catastrophic floods caused by two November atmospheric rivers. While the synoptic-scale patterns and terrestrial hydrological responses to these extreme events are well documented, scant information has been published on corresponding freshwater temperature responses. Here, we apply an observational database of hourly freshwater temperatures at 554 sites across the region to characterize their evolution during these four extreme hydrometeorological events. The two cold snaps and summer heat dome induced a general 1 °C decline and 2.7 °C increase, respectively, in water temperatures with subdued changes (+0.4 °C) during the mid-November floods. For 193 sites with long-term records, 478 daily maximum water temperatures were exceeded during the heat dome and 94 were surpassed during the flooding event, suggesting deleterious effects for water quality and aquatic species.

Impact of Duckweed (Lemna minor L.) Growing in Paddy Fields on Rice Yield and Its Underlying Causes

Duckweed growing in paddy fields (DGP) has substantially increased because of the effects of climate warming and/or eutrophication in irrigated water. Previous studies have primarily focused on investigating the effects of DGP as a nonchemical agent for enhancing rice productivity on nitrogen utilization in rice paddy fields. However, how DGP impacts rice yield remains poorly understood. Therefore, a field experiment with three representative rice cultivars was conducted to determine the effects of DGP on rice yield, considering ecological factors, photosynthetic capacity, spectral changes, and plant growth. The results showed that DGP significantly reduced the pH value by 0.6 and the daily water temperature by 0.6 °C, accelerated rice heading by 1.6 days and increased the soil and plant analyzer development (SPAD) and photosynthetic rate of leaves by 10.8% and 14.4% on average, respectively. DGP also markedly enhanced the values of various vegetation indices such as RARSc, MTCI, GCI, NDVI705, CI, CIrededge, mND705, SR705, and GM, and the first derivative curve of the rice canopy reflectance spectrum exhibited a ‘red shift’ phenomenon upon DGP treatment. Changes in the aforementioned factors may lead to average increases of 4.7% in plant height, 15.0% in dry matter weight, 10.6% in panicles m−2, 2.3% in 1000-grain weight, and ultimately a 10.2% increase in grain yield. The correlation observed suggested that the DGP-induced enhancement in grain yield can be achieved by reducing the pH and temperature of the paddy water, thus enhancing the SPAD value and photosynthesis of leaves and stimulating rice plant growth. These results could offer valuable theoretical support for the future sustainable development of agriculture and the environment through the biological synergy between rice and duckweed.

Prediction of daily river water temperatures using an optimized model based on NARX networks

Water temperature is an important physical indicator of rivers because it impacts many other physical and biogeochemical processes and controls the metabolism of aquatic species in rivers. Having a good knowledge of river thermal dynamics is of great importance. In this study, an advanced machine learning based model that is fast, accurate and easy to use, namely the nonlinear autoregressive network with exogenous inputs (NARX) neural network, was coupled with Bayesian Optimization (BO) algorithm for optimizing the number of NARX hidden nodes and lagged input/target values and the Bayesian Regularization (BR) backpropagation algorithm for the NARX training, to forecast daily river water temperatures (RWT). Long-term observed data from 18 rivers of the Vistula River Basin, one of the largest rivers in Europe, were used for model testing, and model performance was compared with the air2stream model. The results showed that the NARX-based model performs significantly better than the air2stream model in the calibration and validation stages, and can better capture the seasonal pattern and peak values of RWT. Input combinations impact the performance of the NARX-based model in RWT modeling, and air temperature and the day of the year (DOY) are the major inputs, while streamflow and rainfall play a minor role on modeling RWT at the Vistula River Basin. Considering that future times series of air temperatures are easily accessible from climate models and DOY is easy to be considered in the model, the NARX-based model can serve as a promising tool to investigate the impact of climate change on river thermal dynamics.

Nighttime warming and nitrogen addition effects on the microclimate of a freshwater wetland dominated by Phragmites australis

The critical impacts of microclimate on carbon (C) cycling have been widely reported. However, the potential effects of global change on wetland microclimate remain unclear, primarily because of the absence of field manipulative experiment in inundated wetland. This study was designed to examine the effects of nighttime warming and nitrogen (N) addition on air, water, and sediment temperature and also reveal the controlling factors in a Phragmites australis dominated freshwater wetland on the North China Plain. Nighttime warming increased daily air, water, and sediment temperature by 0.24 °C, 0.27 °C, and 0.36 °C, respectively. The diurnal temperature range of water was decreased by 0.44 °C under nighttime warming, whereas warming had no effect on diurnal temperature range of air and sediment. In addition, N addition caused a reduction of 0.20 °C and 0.14 °C in daily water and sediment temperature by increasing vegetation coverage. There was a significant interaction between nighttime warming and N addition on water temperature. Furthermore, the vapor pressure deficit is the main factor affecting the extent of the warming-induced increases in air temperature. The changes of height and leaf area index of Phragmites australis are responsible for the cooling effects in the N addition plots. This study provides empirical evidence for the positive climate warming – microclimate feedback in freshwater wetland. However, N deposition leads to decreased water and sediment temperature. Our findings highlight the importance of incorporating the differential impacts of nighttime warming and N addition on air, water, and sediment temperature into the predictions of wetland C cycling responses to climate change.

Warming surface and Lake heatwaves as key drivers to harmful algal Blooms: A case study of Lake Dianchi, China

Extreme heat events such as marine and atmospheric heatwaves, have catastrophic impacts on marine and terrestrial ecosystems. Recent studies have shown that the continuous warming of lake surfaces and enhancement of lake heatwaves (LHWs) have generated great research interest globally. However, the effects of LHWs on lake ecosystems, especially cyanobacterial harmful blooms (cHABs), remain unclear. This study reconstructed the daily Lake surface water temperature (LSWT) time series in Lake Dianchi from 1951 to 2020 using random forest. Trends and characteristics of LSWT and LHWs were identified, and their critical driving effects on cHABs were analyzed. Results showed that the LSWT in Lake Dianchi significantly increased with a rate of 0.26 °C/10a and with an abrupt changing point in 1992, coinciding with the first report of severe cHABs in Lake Dianchi. From 1951 to 2020, 141 LHWs were detected, of which 94.3 % occurred after 1992. Among all the potential climatic and water quality driving factors on Chlorophyll-a (Chla) variation, LSWT is the most important. Chla concentration and the intensity of LHWs were significantly correlated. The complex and strong interactions between LHWs and cHABs enable the suppression of cHABs only when both remain low. A case study in Lake Dianchi highlighted the critical driving effects of LSWT and LHWs on cHABs, suggesting that continuously warming surface and enhancing LHWs in the future will further challenge more specific and effective lake management strategies to suppress cHABs.

Heterogeneity in post-fire thermal responses across Pacific Northwest streams: A multi-site study

Over the past century, water temperatures in many streams across the Pacific Northwest (PNW) have steadily risen, shrinking endangered salmonid habitats. The warming of PNW stream reaches can be further accelerated by wildfires burning forest stands that provide shade to streams. However, previous research on the effect of wildfires on stream water temperatures has focused on individual streams or burn events, limiting our understanding of the diversity in post-fire thermal responses across PNW streams. To bridge this knowledge gap, we assessed the impact of wildfires on daily summer water temperatures across 31 PNW stream sites, where 10–100% of their riparian area burned. To ensure robustness of our results, we employed multiple approaches to characterize and quantify fire effects on post-fire stream water temperature changes.Averaged across the 31 burned sites, wildfires corresponded to a 0.3 – 1°C increase in daily summer water temperatures over the subsequent three years. Nonetheless, post-fire summer thermal responses displayed extensive heterogeneity across burned sites where the likelihood and rate of a post-fire summer water temperature warming was higher for stream sites with greater proportion of their riparian area burned under high severity. Also, watershed features such as basin area, post-fire weather, bedrock permeability, pre-fire riparian forest cover, and winter snowpack depth were identified as strong predictors of the post-fire summer water temperature responses across burned sites. Our study offers a multi-site perspective on the effect of wildfires on summer stream temperatures in the PNW, providing insights that can inform freshwater management efforts beyond individual streams and basins.

Results of growing Siberian sterlet juvenile in the conditions of the Beloyarsk Fish Hatchery of the Krasnoyarsk region

Studies on the rearing of sterlet from wild and grown producers were carried out in the production conditions of the fish-breeding enterprise TOSP "Beloyarsk Fish-breeding Plant" of the Federal State Budgetary Institution "Glavrybvod" (Krasnoyarsk) in 2020 and 2022. With a complete transition to external nutrition, the sterlet larva was placed in pools with a planting density of 6 thousand copies / m2. Water consumption was 20-23 l/min. As the larvae grew, they were planted, and at the time of reaching an average weight of 1 g, the planting density was 2 thousand copies / m2. With an increase in water consumption to 25-30 l/min. The average daily water temperature during the growing period ranged from 12.5-17.0 °C. The content of oxygen dissolved in water was in the range of 9.1-11.0 mg/l. Different approaches to methods of growing larvae have been studied. To compare and evaluate our results, we used instructions and standards developed by the Glavrybvod of Russia and used for island farms. In 2020, up to 10 days, the larva was grown only using artemia nauplia. Then, the starting compound feed was gradually introduced. The feed was diluted in water and distributed at the beginning simultaneously with artemia, then alternating feedings. Coma was broadcast at 30-minute intervals up to 20 days of growing and at the end of the growing period after 1 hour. For 20 days, they have completely switched to compound feeds. As a result of the study, it was revealed that it is more rational to introduce starter feeds in the form of dust from the moment the sterlet larvae start feeding. This technique made it possible to reduce the time of growing juveniles to a standard weight of 1 g for five days, with approximately equal preservation of juveniles.

Биотехнические показатели товарного выращивания красноклешневого рака в прудовой аквакультуре в условиях юга России

Work was carried out on commercial cultivation of the australian red-clawed crayfish Cherax quadricarinatus in the pond aquaculture of the Astrakhan region in the summer-autumn period of 2021 and 2022. During the exper-iment, young crayfish were studied, formed in 5 groups in accordance with the initial average weight of 0.17, 0.18, 1.8, 5.1 and 7.8 g and cultivated in ponds with an area of 0.1 hectares each. The duration of cultivation was 62-99 days, depending on the groups under consideration. During the work, the main size and mass characteristics of cancers in each group were determined, linear growth, weight gain, bio-mass, survival, overall cancer productivity, and the yield of marketable products were calculated. Also, the hydrochemical parameters of the environment and the feed base of the ponds were monitored, the values of which characterized the condition of the ponds as satisfactory for the cultivation of crayfish. The average daily water temperature during the work period was in the range of 24.0-25.0 ºC on average. It is determined that the optimal period of cultivation of ARCC under natural temperatures should be at least 3 months. The average weight of young crayfish planted in ponds for cultivation can be 0.2-8.0 g, depending on the tasks set: obtaining a larger number of crayfish within an average weight of 40 g, obtaining a smaller number, but larger individuals (60-80 g). It is most effective to plant juveniles of an average weight of at least 2 g in ponds. Cultivation of early ARCC juveniles in ponds in the South of Russia to produce commercial cancers is less effective, but it is possible due to the highest yield of commercial products per hectare of area among the groups of cancers under consideration. The hydrochemical regime of reservoirs must meet the biological requirements of the species. The condition of ponds, and in particular, the rapid development of aquatic vegetation in the water column during cultivation can significantly reduce the natural cancer productivity of reservoirs.

Seasonal and Inter-Annual Variability of Water Temperature in Petrozavodsk Bay of Lake Onega

Abstract—Based on year-round measurements of water temperature at an autonomous station (an anchored chain equipped with temperature sensors), the features of the temperature and ice regimes of the Petrozavodsk Bay of Onega Lake in modern climatic conditions were studied; the dates and duration of the main hydrological phenomena in the water area of the bay were specified. In the abnormally warm winter of 2019–2020, the water area of the Petrozavodsk Bay was not completely covered with ice for the first time in a long period of observations; in the area of the measurement station, ice fields were observed from late January to mid-March. The duration of ice-covered period in the next two winters was 3.5 and 5 months. Data were obtained on the timing of the onset and duration of the spring under-ice convection, a phenomenon that plays an important role in the thermal regime of the lake at the end of winter. It is shown that 2016, 2021 and 2022 spring under-ice convective mixing lasted 4–6.5 weeks, covering the entire water column by the end of ice period. Mixing of the water column after breaking the ice (spring homothermy) continued for another 3–4 weeks. In the spring of 2020, under-ice convection was not observed; spring overturn continued for two months from mid-March to mid-May. The dates of the upward transition of water temperature through 4°C in the years of measurements (5–19 May) were ahead of the long-term average by 2–3 weeks (end of May). Thermal stratification was established from 12 to 27 May and existed for 3–3.5 months. Complete mixing of the water mass of the bay took place in late August–early September, and then, until ice settling, the water column cooled in a state of homothermy. Immediately before ice formation, the water temperature dropped to very low values and did not exceed 0.1°С in the water column. The period with an average daily water temperature of the surface layer of the Petrozavodsk Bay above 10°C lasted from 121 to 144 days during the years of measurements.

Combining Landsat TIR‐imagery data and ERA5 reanalysis information with different calibration strategies to improve simulations of streamflow and river temperature in the Canadian Subarctic

AbstractArctic and Subarctic environments are among the most vulnerable regions to climate change. Increases in liquid precipitation and changes in snowmelt onset are cited as the main drivers of change in streamflow and water temperature patterns in some of the largest rivers of the Canadian Arctic. However, in spite of this evidence, there is still a lack of research on water temperature, particularly in the eastern Canadian Arctic. In this paper, we use the CEQUEAU hydrological‐water temperature model to derive consistent long‐term daily flow and stream temperature time series in Aux Mélèzes River, a non‐regulated basin (41 297 km2) in the eastern Canadian subarctic. The model was forced using reanalysis data from the fifth‐generation ECMWF atmospheric reanalyses (ERA5) from 1979 to 2020. We used water temperature derived from thermal infrared (TIR) images as reference data to calibrate CEQUEAU's water temperature model, with calibration performed using single‐site, multi‐site, and upscaling factors approaches. Our results indicate that the CEQUEAU model can simulate streamflow patterns in the river and shows excellent spatiotemporal performance with Kling‐Gupta Efficiency (KGE) metric >0.8. Using the best‐performing flow simulation as one of the inputs allowed us to produce synthetic daily water temperature time series throughout the basin, with the multi‐site calibration approach being the most accurate with root mean square errors (RMSE) <2.0°C. The validation of the water temperature simulations with a three‐year in situ data logger dataset yielded an RMSE = 1.38°C for the summer temperatures, highlighting the robustness of the calibrated parameters and the chosen calibration strategy. This research demonstrates the reliability of TIR imagery and ERA5 as sources of model calibration data in data‐sparse environments and underlines the CEQUEAU model as an assessment tool, opening the door to its use to assess climate change impact on the arctic regions of Canada.

Spatial and seasonal variability of sub–daily water temperature dynamics in the lowland agricultural catchment of the Wkra River

Spatial and seasonal variability of sub–daily water temperature dynamics in the lowland agricultural catchment of the Wkra River

Warming of the Willamette River, 1850–present: the effects of climate change and river system alterations

Abstract. Using archival research methods, we recovered and combined data from multiple sources to produce a unique, 140-year record of daily water temperature (Tw) in the lower Willamette River, Oregon (1881–1890, 1941–present). Additional daily weather and river flow records from the 1850s onwards are used to develop and validate a statistical regression model of Tw for 1850–2020. The model simulates the time-lagged response of Tw to air temperature and river flow and is calibrated for three distinct time periods: the late 19th, mid-20th, and early 21st centuries. Results show that Tw has trended upwards at 1.1 ∘C per century since the mid-19th century, with the largest shift in January and February (1.3 ∘C per century) and the smallest in May and June (∼ 0.8 ∘C per century). The duration that the river exceeds the ecologically important threshold of 20 ∘C has increased by about 20 d since the 1800s, to about 60 d yr−1. Moreover, cold-water days below 2 ∘C have virtually disappeared, and the river no longer freezes. Since 1900, changes are primarily correlated with increases in air temperature (Tw increase of 0.81 ± 0.25 ∘C) but also occur due to alterations in the river system such as depth increases from reservoirs (0.34 ± 0.12 ∘C). Managed release of water affects Tw seasonally, with an average reduction of up to 0.56 ∘C estimated for September. River system changes have decreased variability (σ) in daily minimum Tw by 0.44 ∘C, increased thermal memory, reduced interannual variability, and reduced the response to short-term meteorological forcing (e.g., heat waves). These changes fundamentally alter the response of Tw to climate change, posing additional stressors on fauna.

Warming of the lower Columbia River, 1853 to 2018

AbstractWater temperature is a critical ecological indicator; however, few studies have statistically modeled century‐scale trends in riverine or estuarine water temperature, or their cause. Here, we recover, digitize, and analyze archival temperature measurements from the 1850s onward to investigate how and why water temperatures in the lower Columbia River are changing. To infill data gaps and explore changes, we develop regression models of daily historical Columbia River water temperature using time‐lagged river flow and air temperature as the independent variables. Models were developed for three time periods (mid‐19th, mid‐20th, and early 21st century), using archival and modern measurements (1854–1876; 1938–present). Daily and monthly averaged root‐mean‐square errors overall are 0.89°C and 0.77°C, respectively for the 1938–2018 period. Results suggest that annual averaged water temperature increased by 2.2°C ± 0.2°C since the 1850s, a rate of 1.3°C ± 0.1°C/century. Increased water temperatures are seasonally dependent. An increase of approximately 2.0°C ± 0.2°C/century occurs in the July–Dec time‐frame, while springtime trends are statistically insignificant. Rising temperatures change the probability of exceeding ecologically important thresholds; since the 1850s, the number of days with water temperatures over 20°C increased from ~5 to 60 per year, while the number below 2°C decreased from ~10 to 0 days/per year. Overall, the modern system is warmer, but exhibits less temperature variability. The reservoir system reduces sensitivity to short‐term atmospheric forcing. Statistical experiments within our modeling framework suggest that increased water temperature is driven by warming air temperatures (~29%), altered river flow (~14%), and water resources management (~57%).

Camera traps reveal that terrestrial predators are pervasive at riverscape cold-water thermal refuges.

Perceived predation risks by terrestrial predators are major ecological forces in aquatic systems, particularly for aggregating fish. Riverscape thermal refuges are discrete, localized cold-water patches where fish temporarily aggregate to buffer against heat events. Predation pressures by terrestrial predators at thermal refuges may decrease the thermoregulatory benefits of refuge use, but quantifying such effects can be challenging and controversial when sampling can impose additional stress on fish. We passively monitored terrestrial predator visitation patterns and predation at four thermal refuges in the Housatonic River, Connecticut, USA, between May 18th and September 29th, 2022, with camera traps, a common wildlife monitoring method. Specifically, we (1) assessed diel visitation patterns by different categories of terrestrial predators at thermal refuges and determined if patterns varied among predator categories or with prevailing environmental conditions, and (2) estimated the probability of predation by hour of the day combined across all predator categories, quantifying general predation pressures at refuges. We detected at least one terrestrial predator at a thermal refuge each day, and mean hourly visitation rates (count/h) were highly variable across predator categories and sampling dates. The most supported generalized additive mixed model indicated that terrestrial predator visitation rates (count/h/day) varied with mean daily river discharge and water temperature differential, and relationships differed across categories of terrestrial predators. We observed 22 separate predation attempts on thermoregulating salmonids and predicted that the probability of predation by any terrestrial predator increased from 0.002 to 0.017 throughout a 24 h day (p = .004). Camera traps provided novel evidence that terrestrial predators are pervasive at riverine thermal refuges, which is relevant for refuge conservation and management globally. We recommend the implementation of a coordinated monitoring network across riverine thermal refuges using camera traps, further enriching our ecological understanding of cumulative predator effects in refuges across complex riverscapes.

Karst Terrain Promotes Thermal Resiliency in Headwater Streams

The response of stream ecosystems to climate change will depend in part on groundwater processes that reduce the sensitivity of streams to atmospheric conditions. We investigated the thermal sensitivity of streams across a gradient of groundwater inputs defined by karst terrain (carbonate parent materials) in the headwaters of the Potomac River basin in eastern North America. We collected stream temperature data and quantified thermal sensitivity for 30 sites from the relationship between daily mean water and air temperatures. Our analysis demonstrates that thermal sensitivity is lower for streams in karst terrain than elsewhere, and that the effect of karst terrain is more important than effects of elevation or basin size in this regard. Our study indicates the importance of karstic groundwater for stream thermal resiliency and suggests the importance of riparian vegetation for maintaining stream temperatures elsewhere. Our study also provides a simple and rapid method for climate change research that can be implemented in conjunction with watershed organizations and citizen science networks.