Changes In Water Temperature Research Articles

Multi-scale variability of hydrothermal regime based on wavelet analysis - The middle reaches of the Yangtze River, China

Water temperature is a major driver of riverine ecosystems and has an extremely significant impact on them. Understanding the multi-scale water temperature dynamics in a river basin is critical to analyze the water temperature status of rivers. In this study, the intra-annual and inter-annual time series of water temperature (WT) at Yichang station in the middle reaches of the Yangtze River over the past 62 years was analyzed using complex Morlet wavelet functions to reveal the complex structure of water temperature variation at multiple time scales. The ecological impact of water temperature changes on the reproduction of the “Four Major Chinese Carp” under the influence of the Three Gorges Dam (TGD). The results showed that the water temperature at Yichang Station has a multi-level time scale structure, with an increasing trend at the inter-annual scale from 1956 to 2017, but different variations at the seasonal scale, and the water temperature cycles at both the inter-annual and seasonal scales have time scale variations of about 8–14 years and 4–7 years, with obvious characteristics of WT variation stages. The inter-annual and summer scales will have low WT in 2017–2022 and high WT in 2023–2027, while the other seasonal scales will have high WT in the next few years, either in the short or medium term. The correlation between air temperature and WT is the most significant among the three drivers of air temperature, flow and rainfall, and the correlation between WT and the air temperature is the most significant in winter scale under the influence of the Three Gorges Dam construction. Since the completion of TGD in 2003, the summer drainage temperature has decreased and the breeding period of the “Four Major Chinese Carp” has been shortened by 30–40 days compared to that before the construction of TGD. The results of this study can be used as a basis for further exploration of the formation mechanism of river water temperature and provide a scientific basis for river ecological protection.

A modern snapshot of the isotopic composition of lacustrine biogenic carbonates – records of seasonal water temperature variability

Abstract. Carbonate shells and encrustations from lacustrine organisms provide proxy records of past environmental and climatic changes. The carbon isotopic composition (δ13C) of such carbonates depends on the δ13C of dissolved inorganic carbon (DIC). Their oxygen isotopic composition (δ18O) is controlled by the δ18O of the lake water and by water temperature during carbonate precipitation. Lake water δ18O, in turn, reflects the δ18O of atmospheric precipitation in the catchment area, water residence time and mixing, and evaporation. A paleoclimatic interpretation of carbonate isotope records requires a site-specific calibration based on an understanding of these local conditions. For this study, samples of different biogenic carbonate components and water were collected in the littoral zone of Lake Locknesjön, central Sweden (62.99∘ N, 14.85∘ E, 328 ma.s.l.) along a water depth gradient from 1 to 8 m. Carbonate samples of living organisms and subfossil remains in surface sediments were taken from the calcifying alga Chara hispida, from bivalve mollusks of the genus Pisidium, and from adult and juvenile instars of two ostracod species, Candona candida and Candona neglecta. Our results show that neither the isotopic composition of carbonates nor the δ18O of water vary significantly with water depth, indicating a well-mixed epilimnion. The mean δ13C of Chara hispida encrustations is 4 ‰ higher than the other carbonates. This is due to fractionation related to photosynthesis, which preferentially incorporates 12C into the organic matter and increases the δ13C of the encrustations. A small effect of photosynthetic 13C enrichment in DIC is seen in contemporaneously formed valves of juvenile ostracods. The largest differences in the mean carbonate δ18O between species are caused by vital offsets, i.e., the species-specific deviations from the δ18O of inorganic carbonate which would have been precipitated in isotopic equilibrium with the water. After subtraction of these offsets, the remaining differences in the mean carbonate δ18O between species can mainly be attributed to seasonal water temperature changes. The lowest δ18O values are observed in Chara hispida encrustations, which form during the summer months when photosynthesis is most intense. Adult ostracods, which calcify their valves during the cold season, display the highest δ18O values. The seasonal and interannual variability in lake water δ18O is small (∼ 0.5 ‰) due to the long water residence time in the lake. Seasonal changes in the temperature-dependent fractionation are therefore the dominant cause of carbonate δ18O differences between species when vital offsets are corrected. Temperature reconstructions based on paleotemperature equations for equilibrium carbonate precipitation using the mean δ18O of each species and the mean δ18O of lake water are well in agreement with the observed seasonal water temperature range. The high carbonate δ18O variability of samples within a species, on the other hand, leads to a large scatter in the reconstructed temperatures based on individual samples. This implies that care must be taken to obtain a representative sample size for paleotemperature reconstructions.

Diagnosing Discrepancies between Observations and Models of Surface Energy Fluxes in a Midlatitude Lake

Abstract The physical processes of heat exchange between lakes and the surrounding atmosphere are important in simulating and predicting terrestrial surface energy balance. Latent and sensible heat fluxes are the dominant physical process controlling ice growth and decay on the lake surface, as well as having influence on regional climate. While one-dimensional lake models have been used in simulating environmental changes in ice dynamics and water temperature, understanding the seasonal to daily cycles of lake surface energy balance and its relationship to lake thermal properties, atmospheric conditions, and how those are represented in models is still an open area of research. We evaluated a pair of one-dimensional lake models, Freshwater Lake (FLake) and the General Lake Model (GLM), to compare modeled latent and sensible heat fluxes against observed data collected by an eddy covariance tower during a 1-yr period in 2017, using Lake Mendota in Madison, Wisconsin, as our study site. We hypothesized transitional periods of ice cover as a leading source of model uncertainty, and we instead found that the models failed to simulate accurate values for large positive heat fluxes that occurred from late August into late December. Our results ultimately showed that one-dimensional models are effective in simulating sensible heat fluxes but are considerably less sensitive to latent heat fluxes than the observed relationships of latent heat flux to environmental drivers. These results can be used to focus future improvement of these lake models especially if they are to be used for surface boundary conditions in regional numerical weather models. Significance Statement While lakes consist of a small amount of Earth’s surface, they have a large impact on local climate and weather. A large amount of energy is stored in lakes during the spring and summer, and then removed from lakes before winter. The effect is particularly noticeable in high latitudes, when the seasonal temperature difference is larger. Modeling this lake energy exchange is important for weather models and measuring this energy exchange is challenging. Here we compare modeled and observed energy exchange, and we show there are large amounts of energy exchange happening in the fall, which models struggle to capture well. During periods of partial ice coverage in early winter, lake behavior can change rapidly.

Estimation of the Thermally Reactive Layer in Lakes Based on Surface Water Temperature

AbstractHow fast does lake surface water temperature (LSWT) react to climate warming or cooling? The thermal response of lakes varies with the season and, typically, day‐to‐day fluctuations are larger in summer. The reason is that lakes are stratified systems where the thermally reactive volume is smaller in summer and, hence, its heat capacity (thermal inertia) is reduced. We define the dimensionless parameter δ as the ratio between the surface volume reacting to the net heat flux through the air‐water interface and the volume of the whole lake. By referring to a fully controlled case study obtained by means of a one‐dimensional physically based model (Simstrat), we investigate the variability of δ throughout the year and its dependence on LSWT. Then, we compare the results with the parameterization adopted in the hybrid data‐driven model air2water. Our analysis confirms that δ follows an exponential decay with increasing LSWT (i.e., a thinner surface layer in summer), and shows that this functional dependence varies between the warming and the cooling periods. These findings contribute to the understanding of the effect of a warming climate on water bodies and ecosystems by providing a simple tool to estimate the rate of change in lakes' water temperature.

Anomalous Temperature Interdicts the Reproductive Activity in Fish: Neuroendocrine Mechanisms of Reproductive Function in Response to Water Temperature.

Fish are poikilotherm and small changes in water temperature can greatly affect physiological processes including reproduction, which is regulated by complex neuroendocrine mechanisms that respond to climatic events. This review provides evidence that anomalous high and low temperature may directly affect reproduction in fish by suppressing the expression of genes in the reproductive neuroendocrine system. The grass puffer, Takifugu alboplumbeus, is an excellent animal model for studying the thermal regulation of reproduction, for they exhibit periodic spawning activities, which are synchronized with seasonal, lunar and daily cycles. In the grass puffer, the expression of the genes encoding gonadotropin-releasing hormone (GnRH) 1, kisspeptin, gonadotropin-inhibitory hormone (GnIH) and their receptors were markedly suppressed in the diencephalon of fish exposed to high temperature (28°C) when compared to normal temperature (21°C), followed by the decrease in the pituitary mRNA levels for follicle-stimulating hormone (FSH), luteinizing hormone (LH) and growth hormone (GH). On the other hand, the exposure to low temperature (14°C) also inhibited the expression of gnrh1, kiss2, gnih and their receptor genes in the brain and fshb, lhb, gh and prl in the pituitary. Taken together, it is plausible that anomalous high and low temperature may be a proximate driver of termination of reproduction by suppressing the activity of the reproductive GnRH/kisspeptin/GnIH system, possibly through direct action of temperature signals at transcription level.

Effects of hot water on the wettability of superhydrophobic metal surfaces

Super-hydrophobic surfaces were used in self-cleaning, anti-corrosion, anti-fog, drag reduction, oil–water separation, etc., but many super-hydrophobic surfaces were not resistant to hot water. Within a certain range, the change of hot water temperature had little effect on wettability, but beyond the range, the effect of water temperature on wettability was very significant. Here, the superhydrophobic metal surfaces of pure titanium, pure nickel, and 304 stainless steel with hierarchical micro-nano structures were prepared by nanosecond laser combined with heat treatment. By immersing in hot water at 25, 50, 75, and 100 °C, it was found that hot water could not significantly change the surface structure. At the same time, the content of total polar bonds on the metal surface increased, resulting in surface free energy rising. Thus, the superhydrophobicity of the surface was transformed into hydrophilicity with a water contact angle between 10 and 20°. This preparation method was non-toxic and pollution-free and was easy to repeat. The experimental results provided a reference for suppressing the change of superhydrophobic surface composition after hot water immersion.

The Effect of the Concentration of Copper Ions on the Unfrozen Water Content in Bentonites Measured with the Use of DSC Method

Studies on changes of unfrozen water content in calcium bentonite from Slovakia, with various concentrations of copper ions, were carried out using the method of differential scanning calorimetry (DSC). In this study, the influence of molar concentration of copper(II) chloride solution (1 M, 0.5 M, 0.25 M, 0.1 M), used to saturate clay, was analyzed, as well as the impact of copper ions contained in bentonite and how the copper concentration affects to changes of unfrozen water content versus temperature. The results suggest that new mineral phases originate in bentonite saturated with highly concentrated solutions due to the reaction with copper(II) chloride solutions. These minerals, identified based on XRD and SEM-EDS (X-ray Diffraction and Scanning Electron Microscopy with Energy Dispersive Spectroscopy) studies, are from the atacamite group. ANOVA (Analysis of Variance) has shown a statistically significant relationship between the unfrozen water content and the molar concentration of the solution used to saturate bentonite and between the unfrozen water content and the content of copper ions in the bentonite. The analysis of multiple regression has shown that the change of unfrozen water content in copper bentonites is related to the temperature change, specific surface, and the concentration of copper ions in the clay. An empirical equation was developed to estimate the content of unfrozen water at a given negative temperature in Cu-bentonites, in which the specific surface and copper ions concentration in the bentonite are the main parameters.

Simplified method for estimating discharge of microporous ceramic emitters for drip irrigation

Emitter discharge is an essential index in the hydraulic design, operation, and management of drip irrigation systems. Previous studies on the calculation of discharge have focused on traditional plastic emitters with labyrinth channels. Here, water flow in the pores of microporous ceramic emitter was analysed. A simplified method for calculating the discharge of microporous ceramic emitters was presented in the form of a model that took into account pore structure, water temperature, ceramic types, and emitter structural parameters, and was experimentally verified. Emitter structure was optimised with the goal of minimising material cost. The results showed that the discharge from microporous ceramic emitters varied significantly in different seasons due to water temperature change, and the higher water temperature was associated with a higher discharge. Discharge was increased by 39.10% when the water temperature changed from 20 °C to 35 °C. Discharge can be stabilised by adjusting operating pressure for different seasons. Discharge increased linearly with increasing operating pressure at the same water temperature. Compared with the sand-based microporous ceramic emitters, the clay-based microporous ceramic emitter had a relatively low discharge due to the fine particle size of its construction material.

NUMERICAL INVESTIGATION OF A MANTLE HEAT EXCHANGER

The following work deals with numerical investigation of a storage tank equipped with a mantle annular cavity surrounding it. Heat is transferred via the working fluid flowing in the mantle side to the inner storage tank. Water at constant temperature of 60 oC enters the mantle to heat the tank and exits at a lower temperature. The study is carried out using the commercial software Ansys−Fluent to track the change of water temperature in the tank and mantle side during the simulated period of 60 minutes. Temperature contours of tank water and mantle water are drawn at several time intervals during the simulated period. The effects of changing working fluid mass flow rate were taken into account through three values, namely; 0.0077, 0.015 and 0.02 kg/s. Three values of mantle gap thickness; 10, 15 and 20 mm, and three values of mantle length; 250, 300 and 350 mm were applied in the simulation program and their effects were monitored and displayed. Results show that increasing the value of mass flow rate causes more heat transfer rate to the storage tank. The gap thickness of 10 mm which is the smallest value among the three applied values gave the best heat transfer rate and the mantle length of 300 mm was the optimum among the applied values. The heat transfer rate to the tank was studied in terms of tank mean temperature. The maximum mean tank temperature achieved at the end of the simulated period was 42oC.

Predicted changes in temperature, more than acidification, affect the shell morphology and survival of the girdled dogwhelk,Trochia cingulata(Linnaeus, 1771)

AbstractDespite the existing body of research that considers altered ocean temperature and acidification as co-occurring stressors, our understanding of the consequences of such shifts remains limited. This is particularly problematic in relation to predators such as whelks, as they can exert strong top-down control of communities yet, as calcifying ectotherms, they are likely to be vulnerable to climate change. This study assessed the effects of simultaneous changes in water temperature and pH on the South African girdled dogwhelk Trochia cingulata. For 12 weeks, whelks were exposed to three temperatures, 9 °C (cooling), 13 °C (current) and 17 °C (warming), each at three target pH levels, 8.0 (current), 7.7 (intermediate) and 7.5 (extreme). For each treatment shell thickness, strength and shape were measured after 6 and 12 weeks, while mortality was recorded daily. Survival was not affected by pH and was highest at 9 °C. Almost all whelks exposed to warming died within 2 weeks. After 6 weeks, shell strength declined significantly as acidity increased, regardless of temperature, and shells of whelks held at 9 °C were thinner. By 12 weeks, whelks exposed to cooling and extreme pH had the weakest shells. Notably, temperature no longer influenced shell thickness, but whelks held at 9 °C became globular in shape. These changes in shell morphology likely resulted from the increased cost of shell maintenance in cool, acidic conditions. The differences observed at 6 and 12 weeks demonstrate how responses can change over time, a point that should be kept in mind when assessing species sensitivities to changing environments. The dominant effect of temperature highlights that T. cingulata is particularly vulnerable to warming, while regional cooling may pose a challenge with respect to shell morphology.

Effect of reservoir size on water quality in coastal reservoirs during desalinization period using numerical model

Abstract Coastal reservoirs are water storage structures constructed near the river estuary to supply water to coastal areas. One of the most important aspects related to performance of these structures is the effect of reservoir size on the flow and water quality. For this purpose, MIKE3, a 3D numerical software was used in the present work. The case study included proposed a coastal reservoir located on the coastlines of the Caspian Sea in the vicinity of Tajan River estuary. To conduct this research, four types of reservoirs with different sizes were considered. Input parameters to the model included 5-year flood of Tajan River, initial reservoir salinity and ambient temperature data. The results showed that construction of a shallower reservoir due to better surface and depth mixing could achieve higher water salinity during the desalinization period. Furthermore, the greatest water temperature change value was determined after passing hydrograph peak discharge, which shows the effect of inflow on reservoir water quality. Finally, the results of water density revealed that the decreasing trend of water density occurred mostly due to the decreasing water salinity in the reservoir.

Seasonal Changes of Growth, Immune Parameters and Liver Function in Wild Chinese Sturgeons Under Indoor Conditions: Implication for Artificial Rearing.

Seasonality has a significant effect on the physiology of fish, especially the effect of water temperature changes. In the present study, the growth, innate immune parameters and liver function indices of two rescued wild adult Chinese sturgeons under captive conditions were monitored for 1 year. The results showed that the total annual weight loss rate of the male was −4.58% and the total weight gain rate of the female was 24.12%, in which the weight of both individuals registered highly significant differences in summer, fall and winter (p < 0.01). The male Chinese sturgeon also exhibited negative specific growth rates (−0.1 to −0.8%) during spring to fall, whereas positive specific growth rates, ranging from 0.03 to 0.11%, were recorded in the female. Seasonality also affected the innate immune parameters of the two Chinese sturgeons, in which leukocytes had been increasing since spring and C-reactive protein (CRP) content was significantly higher (p < 0.05) in summer than fall in both individuals. The CRP level of the male Chinese sturgeon showed a significant increase from fall to winter (p < 0.05), suggesting that it may have contracted infection or inflammation during this study period. With the analysis of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), transaminase (AST:ALT) ratio, alkaline phosphatase, albumin to globulin ratio and triglycerides, it was found that the liver function of the captive Chinese sturgeons was adversely affected along seasonal changes, with the highest degree of liver impairment in winter. In combining observations from growth performance and changes in innate immune and liver function parameters, the present findings deduced that the male Chinese sturgeon under study was more susceptible to seasonal changes than the female. For better indoor culture of adult Chinese sturgeons, monitoring of hematological parameters to detect early signs of inflammation and liver function abnormality should be conducted with routine veterinary care during prolonged captivity.

Growth patterns of larval walleye pollock Gadus chalcogrammus from core and peripheral habitat differ in response to temperature

Walleye pollock (Gadus chalcogrammus) supports one of the world's largest fisheries and is a key species in North Pacific ecosystems. Its future as a sustainable fishery may be dependent on its ability to adapt to changing water temperatures under climate change. The largest global average increase in sea surface temperature has occurred in Alaska, and increasing temperatures are predicted. Here, we examined responses to a range of temperatures in the early life history of walleye pollock from a northern (core) and a southern (peripheral) part of their range using growth measurements and genetics (RADseq). Crosses were conducted to generate families with one female and three male adults from Shelikof Strait, AK and Puget Sound, WA. Offspring were reared to the late larval stage at three temperatures corresponding to low (1.5 °C), medium (5.8 °C), and high (∼12 °C) temperature relative to natural conditions. Alaska pollock outperformed Puget Sound pollock at the lowest temperatures, hatching earlier with a higher growth rate than Puget Sound pollock. At medium temperatures, Puget Sound and Alaska pollock grew at the same rate but Alaska pollock hatched sooner. The response to high temperatures was the same in both groups, characterized by early hatching at a small size and high growth rates. Genetic analysis did not show differences among family groups that survived different temperature treatments. Our results demonstrate local adaptation, although a link between genotype and phenotype was not found.

The Effect of Dietary Lactic Acid Bacteria on Intestinal Microbiota and Immune Responses of Crucian Carp (Carassius auratus) Under Water Temperature Decrease.

Temperature changes have a great impact on fish feeding, intestinal microorganisms, metabolism, and immune function. Therefore, it is necessary to develop effective methods to enhance the survival rates and growth of fish under water temperature changes. Lactic acid bacteria (LAB) are promising immunostimulatory feed additive, as demonstrated by their beneficial effects in several fish species. This study investigated the short-term effects of dietary LAB on intestinal microbiota composition and immune responses of crucian carp (Carassius auratus) when water temperature decreased from 30 ± 1°C to 18 ± 1°C. Lactococcus (L.) lactis 1,209 and L. lactis 1,242 with potential probiotics isolated from the intestine of Qinghai naked carp (Gymnocypris przewalskii) were selected as feed additives for the crucian carp feeding experiment. A total of 225 commercially available healthy crucian carp (250 ± 10 g) of similar age were kept in 30°C water for a week and then immediately transferred to 18 ± 1°C water, assigned to three dietary treatments for a 16-day feeding trial randomly: (1) HC, diets without additives (the control group); (2) HT, diets with 106 CFU/ml L. lactis 1,209; and (3) HL, with 106 CFU/ml L. lactis 1,242. Each group was set up with 3 replicates and each with 25 fish. The results showed that the mortality rate of crucian carp in HC, HT, and HL group was 50, 27, and 33%, respectively. High-throughput sequencing results displayed that the composition of the intestinal microorganism varied dynamically in response to different treatments and water temperature decrease. Among them, compared with the HC group, a higher abundance of Firmicutes and Proteobacteria, and a lower of Actinobacteria appeared in HT and HL. The cytokines heat shock protein 70 (HSP-70) in crucian carp intestinal tract significantly decreased when water temperature decreased (p < 0.05).

Destratification of a Eutrophic Reservoir in South Korea Using a Novel Convectional Water Circulation System (CWCS)

Replication of natural mixing through artificial water circulation techniques, such as convectional water circulation systems (CWCS), can break thermal stratification in stagnant water and suppress algal blooms. Here, the field performance of a novel CWCS was evaluated in a eutrophic reservoir (Shingal reservoir, South Korea) for three seasons between September 2016 and September 2018. The CWCS was deployed in a corner of stagnated water in the reservoir. The changes in water temperature and dissolved oxygen (DO) concentrations at different water depths were examined at the deployment site and two control sites within the stagnant area during the 2016 and 2017 seasons. In 2018, the performance of the CWCS in replicating natural mixing was assessed by monitoring water temperature changes at different depths at the CWCS unit deployment site and a comparison site with natural water flow. The differences in water temperature and DO concentrations between the epilimnion and the hypolimnion were significantly smaller at the deployment site than at the control sites, demonstrating the effectiveness of the CWCS in vertical and horizontal mixing as well as in oxygen transfer. The findings of the field study revealed that the CWCS effectively induced natural-like mixing without disturbing the hypolimnion.

Effects of Temperature on the Timeliness of eDNA/eRNA: A Case Study of Fenneropenaeus chinensis

Environmental DNA (eDNA) technology has been successfully applied to detect organisms in various aquatic ecosystems. However, eDNA has been proven to exist for a long time in environmental samples. The timeliness of eDNA detection results largely depends on the rate of molecular degradation. Environmental RNA (eRNA) is considered an excellent complementary tool because most researchers believe that RNA degrades faster than DNA in vitro, while, to the best of our knowledge, the number of published articles related to eRNA is very limited. To address an important knowledge gap, this study focused on the response mechanism of eRNA degradation to water temperature change as compared with eDNA. Changes in the concentration of eDNA and eRNA of the mitochondrial cytochrome c oxidase subunit 1 (COI) gene from Fenneropenaeuschinensis were detected at four temperatures (10, 15, 20 and 25 °C). The results showed that the degradation rate of eDNA increased with an increase in temperature. The degradation rate constants ranged from 0.011 to 0.486 h−1 and the degradation time ranged from 8 to 383 h for eDNA. The degradation rate of eRNA changed slightly with an increase in temperature. The degradation rate constants ranged from 0.190 to 0.379 h−1 and the degradation time ranged from 11 to 22 h for eRNA. eRNA showed better stability under temperature change and maintained a faster degradation rate at low temperatures. These results provide answers to the questions of whether eRNA and eDNA degradation rates are fast or slow. Furthermore, this study may suggest the potential superiority of eRNA over eDNA and promote further study of eRNA in future research.

A case study of paleoenvironmental interactions during the Miocene Climate Optimum in southwestern Paratethys

The marine system of the Mediterranean-Paratethys region in the Middle Miocene was influenced by the global climatic changes corresponding to the Miocene Climate Optimum. The latter was characterized by global warming of deep oceanic waters succeeded by a decrease of wind activity and ocean water circulation together with a decline in oceanic productivity. This study provides a detailed paleoenvironmental and depositional history of the Middle Miocene deposits from Mt. Požeška Gora (the east part of Croatia). Stable carbon and oxygen isotope data with foraminiferal fauna coupled together with palynological data indicate both seasonal and long-term changes in surface water temperatures, nutrient contents, and salinity. Furthermore, it was possible to determine two phases of Middle Miocene flooding in the studied marine system: (a) a shallow, high nutrient marginal sea strongly affected by freshwater inputs corresponding to the thermal maximum and periods with enhanced precipitation during the Miocene Climate Optimum, and (b) a younger deeper marginal sea with a developed seasonal stratification, rather intermediate nutrient availability and reduced fresh-water inputs. Based on the microbiostratigraphy and strontium isotope stratigraphy (87Sr/86Sr) coupled with previously published high-precision geochronology, the timing of the first and second flooding can be correlated with the Langhian age - ≤15.4 Ma and 14.6 Ma, respectively Possibly, the properties of the surficial waters that were described as a part of the flooding phases in individual time intervals can indicate changes in circulation patterns as a result of potential influence of the open-sea water masses.

Operating performance analysis of cold and heat sources composite based on ground source heat exchanger and hot water exchange tanks

Aiming at the air-conditioning system of underground space engineering, it is proposed to use ground source heat exchanger and hot water exchange tanks in parallel as a composite cold and heat source, which can simultaneously achieve energy-saving requirements. In order to explore the operating heat transfer characteristics of the composite cold and heat source system, a mathematical model of buried pipes and hot water exchange tanks was established. The simulation analysis of the influencing factors such as inlet temperature and fluid flow rate shows that under the condition of small flow rate, increasing the fluid flow rate can significantly improve the buried pipe and the hot water tank and the heat exchange effect; the greater the temperature difference between the inside and outside of the pipe, the better the heat exchange effect of the heat exchanger, under the same flow rate, the heat transfer coefficient of the spiral coil is KDN15>KDN20>KDN25. According to three different load conditions, the flow ratio of the composite cold and heat source is optimized and analyzed. The results show that as long as the flow ratio is properly controlled, the composite cold and heat source can meet the cooling requirements of the air-conditioning system under different working conditions. There is an optimal flow ratio between the heat sources. The greater the ratio R of the extreme working condition load change value to the standard working condition load value, the smaller the value of the optimal flow ratio, and it is not affected by the loop flow rate and the inlet water temperature change.

Spatio-temporal Changes in the Regime of Rivers in the Pripyat River Catchment and Climate Change

In work features of a hydrological regime of catchments of the river of the Pripyat in climate change are considered. Researches of meteorological characteristics of the given territory show the tendency to growth, both temperatures of air, and precipitation, evaporation from a surface of water and ground also show the tendency to increase. That is not unequivocally reflected in change of a course of hydrological characteristics waters objects of territory. On a part of pools of the rivers the mid-annual runoff of water in the rivers in time tends to growth, and Change of levels of subsoil waters decreases for parts - on a turn - here, as a rule, tends a course in time opposite to a mid-annual runoff of water in the rivers. Change of the maximal temperature of water in the rivers in time repeats the tendency of a course of a runoff of water in them, i.e. at increase in a runoff of water in the rivers - the maximal temperature increases, and at reduction - decreases. The increase in temperature of a superficial component of a runoff of the rivers occurs because of the general increase in temperature of air in considered territory. Silt charge waters in all territory decreases, despite of increase in quantity of atmospheric precipitation and increases or reduction of a runoff of water in the rivers. The relationship between the water runoff layer and precipitation and soil moisture has a certain time delay. The average annual water temperature over time shows a tendency to increase at almost all stations, while the change in the maximum water temperature in rivers over time has a multidirectional tendency and to a greater extent depends on the change in water depth in the river, a decrease in high water maximums and frequent thaws, etc. The studies carried out show that the preservation of moisture in thick layers of soil (0 cm-100 cm) contributes to an increase in water flow in rivers and in the modern conditions of Polesie of Ukraine this will solve a number of problems with the provision of high-quality water resources for various industries and the population.

Effects of dimensionality on the performance of hydrodynamic models for stratified lakes and reservoirs

Abstract. Numerical models are an important tool for simulating temperature, hydrodynamics, and water quality in lakes and reservoirs. Existing models differ in dimensionality by considering spatial variations of simulated parameters (e.g., flow velocity and water temperature) in one (1D), two (2D) or three (3D) spatial dimensions. The different approaches are based on different levels of simplification in the description of hydrodynamic processes and result in different demands on computational power. The aim of this study is to compare three models with different dimensionalities and to analyze differences between model results in relation to model simplifications. We analyze simulations of thermal stratification, flow velocity and substance transport by density currents in a medium-sized drinking-water reservoir in the subtropical zone, using three widely used open-source models: GLM (1D), CE-QUAL-W2 (2D) and Delft3D (3D). The models were operated with identical initial and boundary conditions over a 1-year period. Their performance was assessed by comparing model results with measurements of temperature, flow velocity and turbulence. Our results show that all models were capable of simulating the seasonal changes in water temperature and stratification. Flow velocities, only available for the 2D and 3D approaches, were more challenging to reproduce, but 3D simulations showed closer agreement with observations. With increasing dimensionality, the quality of the simulations also increased in terms of error, correlation and variance. None of the models provided good agreement with observations in terms of mixed layer depth, which also affects the spreading of inflowing water as density currents and the results of water quality models that build on outputs of the hydrodynamic models.