Low Water Temperature Research Articles

Effect of ocean dynamic processes on the temporal-spatial pattern of persistent organic pollutants (PCB-153 and BDE-47) in the shelf seas

Field observations of persistent organic pollutants (POPs) in shelf seas presented abnormal phenomena such as high-concentration patches in offshore areas and different vertical profiles of POPs at the same location. We assumed that these phenomena were associated with the presence of bottom cold water mass (BCWM) in shelf seas and used a hydrodynamic-ecosystem-POP coupled model to confirm this hypothesis. Based on model results, with the formation of BCWM during summer, POPs accumulated inside BCWM due to their transport across the thermocline by the sorption to sinking particles. With the intensification of vertical mixing during winter, the release of POPs from BCWM induced high-concentration patches of POPs on the surface layer. Meanwhile, the low water temperature in winter was favorable for the gas deposition of POPs, which led to high surface concentrations of POPs. Because the accumulation of POPs in BCWM depended on the sorption of dissolved POPs by particles, not all types of POPs accumulated in BCWM. Some POPs even accumulated at the sea surface above the BCWM due to large gaseous deposition and weak sorption by particles. Using this feature, we proposed a prediction function for the accumulation of POPs in BCWM.

Oxygen 1s X-ray Photoelectron Spectra of Iridium Oxides as a Descriptor of the Amorphous-Rutile Character of the Surface.

Characterization of the surface of iridium oxide (IrOx) materials is of crucial importance to understand catalysts for the oxygen evolution reaction (OER) in low-temperature water electrolysis. While much of our current knowledge is based on well-defined single-crystal surfaces, surface-sensitive techniques like X-ray photoelectronic spectroscopy (XPS) are relevant to characterize the nanostructures considered. In this work, we describe a simple approach to use oxygen 1s spectra as an identifier of the amorphous/crystalline characteristics of iridium oxide structures from purely amorphous to purely crystalline. This conceptual approach was validated on seven commercially available materials. The presence of oxygen-associated defects in the surface moieties/species is shown even for purely crystalline materials with defect concentration increasing with greater amorphous character. This methodology provides us with an accessible ex situ descriptor of the catalyst surface as a baseline for further studies of the impact on catalytic properties.

Evaluating manganese removal in groundwater using pilot scale biofilters: The role of filter media characteristics during start-up

This study investigated the influence of filter media characteristics on manganese (Mn) removal in groundwater biofilters during the start-up phase. Six pilot scale biofilters containing three different granular activated carbons (GAC), two anthracite, and one sand media were run for 133 days to examine their Mn removal performance at a drinking water utility, while also monitoring ATP and bacterial growth as indicators of biological activity. Key findings demonstrate the critical role of media characteristics, especially for GAC media. Initial Mn adsorption on GAC, with its higher surface area, higher macropore volume, and surface charge, promoted physicochemical and biological oxidation, thus contributing to the early onset of Mn removal during the start-up of the GAC biofilters. In contrast, biological processes dominated Mn removal on anthracite and sand biofilters during start-up. As expected, the presence of Mn-oxidizing bacteria was detected in biofilters, and ATP levels were correlated to Mn removal until the biofilters were acclimated, showing the potential of ATP as an acclimation monitoring metric. Once acclimated, all biofilters consistently reduced Mn levels from 60.9 ± 4.5 µg/L to below 5 µg/L (>90 % removal), while concurrently removing iron, thereby highlighting the biofilter's effectiveness at low water temperatures (<15 °C). This study demonstrates the advantage of GAC media for Mn removal in biofilters during start-up in regions with lower water temperatures.

Cutting-edge techniques in low-temperature electrochemical water splitting: advancements in hydrogen production

Abstract This review provides a comprehensive examination of strategies aimed at advancing low-temperature electrolysis for sustainable hydrogen production. It begins by exploring the significance and challenges associated with water splitting, followed by an in-depth discussion on the fundamentals of electrochemical water splitting and crucial performance indicators, including reversible hydrogen electrode potential, specific and mass activities, overpotential, Tafel slope, stability and durability, and Faradaic and energy efficiencies. The article then extensively discusses various emerging strategies, such as decoupled water electrolysis, hybrid water electrolysis (including reagent-sacrificing, pollutant-degrading, and value-added types), tandem water electrolysis, microbial electrolysis cells (covering reactor configurations, electrode materials, microbial populations, and substrates), and the application of external stimuli like ultrasonic, magnetic, and super gravity fields. Additionally, the challenges and advancements in seawater electrolysis are reviewed, with a focus on electrocatalysts, seawater electrolyzers, and future directions. Furthermore, the article addresses current challenges in electrolysis and electrolyzer development, offering perspectives on the future of these techniques. By delving into these strategies, this review aims to contribute to the advancement of clean energy technologies and the transition towards a hydrogen-based economy.

Enhancement of critical current density using micro-porous structure in a low-temperature water electrolysis

The critical current density (CCD), which limits the hydrogen production rate was measured by forming micro-porous structures on the cathode electrode in a low-temperature water electrolysis. Several micro-porous structures were formed by the electrodeposition method varying the current density during the deposition. A maximum 54% enhancement of the CCD was recorded compared to the plain surface. With the micro-porous structures, the superior capillary wicking effect allowed the electrolyte to penetrate the structure, resulting in the increased number of hydrogen nucleation sites. The increased hydrogen nucleation sites led to the decreased hydrogen bubble size and increased departed bubble density, which delayed formation of the hydrogen film leading to the CCD. The surface morphology revealed that the multiple pore layers with the interconnected pores exhibited superior capillary wicking effect compared to the open type single pore layer. It is expected that the results of present work stimulate further research regarding electrode surface design in the low-temperature water electrolysis.

Legionella in Primary School Hot Water Systems from Two Municipalities in the Danish Capital Region.

Legionella contamination in public water systems poses significant health risks, particularly in schools where vulnerable populations, including children, regularly use these facilities. This study investigates the presence of Legionella in the hot water systems from 49 primary schools across two municipalities in the Danish capital region. Water samples were collected from taps in each school, and both first-flush and stabile temperature samples were analysed for Legionella contents. The findings revealed that 97% of schools in Municipality 1 and 100% in Municipality 2 had Legionella in their hot water systems. The content of Legionella colonies was significantly higher in schools in Municipality 1, which was probably because of overall lower water temperatures. At stabile temperatures, 76% and 50% of the schools in the two municipalities exceeded the European Union's recommended limit of 1000 CFU/L. Stabile peripheral water temperatures were achieved after 3 min. Tap water temperatures above 54 °C and central tank temperatures above 59 °C were associated with Legionella contents below 1000 CFU/L. This study highlights the need for more stringent Legionella control procedures in schools, including higher water temperatures and refining Legionella reducing interventions with the addition of regular flow and draining procedures.

Innovative enhancements in solar still performance: A comprehensive study on wick-absorber configurations

This study introduces a new thermo-fluid analysis of using wick-absorbers to enhance solar still performance. Three configurations of wick absorbers were tested in a conventional single-slope solar still: (i) Case I: individual wick balls, (ii) Case II: zig-zag wick pattern, and (iii) Case III: rectangular wick array (grid-like pattern). The study evaluates multiple parameters, including saline water temperature, daily water productivity, Nusselt number, Sherwood number, thermal and exergy efficiencies, water cost, and payback period. The addition of an absorbing plate with an insulation layer led to lower saline water temperatures and shifted peak values. Compared to a traditional still, wick utilization enhanced water productivity by 45.8 %, 84.5 %, and 86 % for Cases I, II, and III, respectively, due to increased evaporation rates. This resulted in a relative enhancement in daily thermal efficiency by 64 %, 76 %, and 97.5 %, respectively. Additionally, four correlations were developed to describe Nusselt and Sherwood numbers, with a maximum deviation of 25 %. Economic analysis demonstrated cost-effectiveness, significantly reducing water cost and the payback period by 37 %, 39 %, and 44 % for Cases I, II, and III, respectively, compared to the conventional system.

Massive Outbreak of Aurelia coerulea in Geoje Bay, Korea

This study was carried out to elucidate the causes of massive outbreaks of Aurelia coerulea in Geoje Bay, Korea, from November 2022 to October 2023. Adult medusae consistently spawn with planulae, and the populations of A. coerulea in Geoje Bay could be categorized into current-year and overwintering populations. The current-year population began with the emergence of ephyrae in February and grew until October, while the overwintering population comprised a mixture of surviving current-year population and additional individuals that joined during the warm season. The size of the planulae are significantly larger than the annual average during the cold season. These results appear to be the energy accumulation of planulae for polyp formation under low water temperatures. Planulae form polyps within a temperature range of 5–25 °C, suggesting the possibility of year-round polyp recruitment. In Geoje Bay, the highest appearance rate of A. coerulea was in April (8.71 ± 12.5 ind. m−3), with ephyrae experiencing higher growth rates up to the young medusa stage. However, from April, a decline in zooplankton biomass resulted in reduced growth rates in adults, indicating that jellyfish growth was primarily regulated by food availability. Additionally, submersed oyster shells in oyster farms served as the main habitat for jellyfish polyps. A. coerulea populations were also characterized by the continuous spawning of planulae throughout the year. In conclusion, this study suggests that stable polyp habitats, abundant food supply during the initial developmental period of the population, and suitable ranges of water temperature were significant factors inducing the massive outbreak of A. coerulea in Geoje Bay, Korea.

Thermo-economic analysis of a solar district heating plant with an air-to-water heat pump

Solar district heating systems are essential in reducing carbon emissions and alleviating the energy crisis. By integrating with air-to-water heat pumps, it is possible to enhance the system’s efficiency and flexibility. However, the complementary mechanisms and coupling effects between the heat pump and the other components of the system are not clear. To address these issues, it is necessary to investigate the thermo-economic performance of the system, taking into account energy price fluctuations to achieve a more efficient and economically viable operational model. This study focuses on a solar district heating system in the Danish city of Ørum and investigates the impact of integrating a large-scale air-to-water heat pump. Based on energy and economic analyses, the impact of the heat pump on the system efficiency and the levelized cost of heat are investigated for 2020 and 2022. The results show that the heat pump can convert low-cost electricity into heat which will be stored in the tank, increasing the tank’s heat storage content by 1.2 times. The medium to low-temperature water in the tank can preheat the heat pump’s compressor, raising the COP of the heat pump from 3.3 to 3.5 and increasing the annual utilization cycle of the tank by 1.4 times by reducing the return water temperature to the bottom of the tank. Additionally, the system performance has been improved due to the installation of the heat pump, which increased the system COP from 1.22 in 2020 to 2.62 in 2022. Subsequently, the CO2 emission has been decreased from 192 kg/MWh to 74 kg/MWh with a larger share of sustainable energy. Due to the heat pump operation, the system-levelized cost of heat could be reduced to 68.6 EUR/MWh, compared to 94 EUR/MWh if the heat pump is removed. The investigation also revealed that the heat pump improved the flexibility of the heating system in response to energy prices, especially during the 2022 energy crisis in Europe. The findings of the paper provide a good reference for large solar heating applications.

Fish Health Altered by Contaminants and Low Water Temperatures Compounded by Prolonged Regional Drought in the Lower Colorado River Basin, USA.

The goal of this study was to assess health of male Common Carp (carp, Cyprinus carpio) at four sites with a wide range in environmental organic contaminant (EOC) concentrations and water temperatures in Lake Mead National Recreation Area NV/AZ, US, and the potential influence of regional drought. Histological and reproductive biomarkers were measured in 17-30 carp at four sites and 130 EOCs in water per site were analyzed using passive samplers in 2010. Wide ranges among sites were noted in total EOC concentrations (>10Xs) and water temperature/degree days (10Xs). In 2007/08, total polychlorinated biphenyls (tPCBs) in fish whole bodies from Willow Beach (WB) in the free-flowing Colorado River below Hoover Dam were clearly higher than at the other sites. This was most likely due to longer exposures in colder water (12-14 °C) and fish there having the longest lifespan (up to 54 years) for carp reported in the Colorado River Basin. Calculated estrogenicity in water exceeded long-term, environmentally safe criteria of 0.1-0.4 ng/L by one to three orders of magnitude at all sites except the reference site. Low ecological screening values for four contaminants of emerging concern (CEC) in water were exceeded for one CEC in the reference site, two in WB and Las Vegas Bay and three in the most contaminated site LVW. Fish health biomarkers in WB carp had 25% lower liver glycogen, 10Xs higher testicular pigmented cell aggregates and higher sperm abnormalities than the reference site. Sperm from LVW fish also had significantly higher fragmentation of DNA, lower motility and testis had lower percent of spermatozoa, all of which can impair reproduction. Projections from a 3D water quality model performed for WB showed that EOC concentrations due to prolonged regional drought and reduced water levels could increase as high as 135%. Water temperatures by late 21st century are predicted to rise between 0.7 and 2.1 °C that could increase eutrophication, algal blooms, spread disease and decrease dissolved oxygen over 5%.

Driving net zero: Comprehensive evaluation of whole life carbon in domestic hot water systems

Low-temperature domestic hot water (DHW) systems provide significant carbon reduction benefits, supporting the UK’s 2050 net-zero target. Typically, low water volume applications do not need recirculation and storage when instantaneous heaters are employed, such applications can be more flexible in terms of temperature range and safety requirements. However, commercial applications may have high volumes of hot water and hence, will require high working temperatures to satisfy the recirculation requirements. This study developed a comprehensive toolkit to benchmark the embodied and operational carbon in terms of kgCO2e/m2 for various DHW systems, including equipment, refrigerants, and operational emissions. Analysis of seven DHW designs for an office building revealed that low-temperature systems consistently demonstrate the lowest whole-life carbon (WLC), underscoring the impact of grid decarbonisation and low-GWP refrigerants. The WLC results are normalised per square metre of floor area. Low-temperature systems showed the lowest WLC even with the inclusion of water treatment and chemical dosing systems.

Synergistic interaction of S-type heterojunction and sulfur vacancies in g-C3N5@Sv-ZnIn2S4 composites: Simultaneous promotion of complete 2,4-dichlorophenol mineralization and Cr(VI) reduction

Constructing efficient heterojunction photocatalysts is an effective measure for degrading pesticides and reducing heavy metals. In this study, g-C3N5@Sv-ZnIn2S4 (g-C3N5@Sv-ZIS) composite with large specific surface area has been successfully prepared by a simple low-temperature water bath method. The g-C3N5@Sv-ZIS composite showed complete mineralization of 2,4-dichlorophenol (2,4-DCP) and reduction of Cr(VI) within 60 min. The results of electron spin resonance spectroscopy, photoelectrochemical characterization, and energy band structure calculations indicated the formation of an S-type heterojunction at the interface of g-C3N5 and Sv-ZIS. In situ XPS analysis showed the transfer of photogenerated charges from g-C3N5 to Sv-ZIS. The molecular structure of 2,4-DCP was analyzed using frontier molecular orbital and electrostatic potential calculations. The possible degradation pathways of 2,4-DCP were proposed based on liquid chromatography– mass spectrometry results. Biotoxicity simulations of the intermediates revealed decreased toxicities. Furthermore, The kinetic rate constant of CZSv-200 for degrading 2,4-DCP and Cr(Ⅵ) in deionized water was approximately 2.20, 3.10 and 2.46, 4.03 times higher than that in lake and sewage plant water, respectively. The composites designed in this study provide reliable theoretical support for the removal of composite pollutants.

One-pot synthesis of FeNi3/FeNiOx nanoparticles for PGM-free anion exchange membrane water electrolysis

Low-temperature anion exchange membrane water electrolysis (AEMWE) is one of the most promising technologies to produce green hydrogen. To date, membrane-electrode assembly (MEA) based on platinum group metal (PGM) electrocatalysts shows higher performance than PGM-free ones. Here, a single and easy synthesis for non-noble metal electrocatalysts (PGM-free) for both hydrogen and oxygen evolution reactions (HER and OER) was developed. Both electrocatalysts consist of FeNi3/FeNiOx nanoparticles obtained through chemical reduction using hydrazine. The electrocatalyst exhibits an overpotential of 210 mV and 234 mV for HER and OER respectively, at a current density of 10 mA cm−2 in 1 M KOH electrolyte, allowing a comparison between mass activity and geometric activity compared to PGM catalysts. In addition to a preliminary electrochemical characterization of the FeNi3/FeNiOx, the electrocatalyst were integrated into a pilot-scale AEMWE at both anode and cathode, which reaches (without iR-correction) 1.72 V and 1.94 V at a current density of 0.4 A cm−2 and 1 A cm−2 respectively at 60 °C. This PGM-free MEA outperforms the one based on Pt/C at cathode and RuO2 at anode with a voltage gap of 284 mV at 1 A cm−2. The aforementioned MEA was tested for 150 h with a discontinuous power profile, in order to get an idea of the possible degradation trends for a future industrial application, the reversible and irreversible voltage losses were calculated resulting in a degradation rate of 886 µV/h. This work demonstrates a simple and scalable synthesis of earth-abundant electrocatalytic materials for high-efficiency AEM water electrolysis.

Model-based evaluation of ammonia energy storage concepts at high technological readiness level

Ammonia is a promising carbon-free energy carrier since it can be stored as a liquid at mild conditions and its production process from hydrogen and nitrogen is established and efficient. Several Ammonia-to-Power concepts have been proposed in the literature, many of which employ not-yet-mature electrochemical technologies. We model the charging and discharging phases of three ammonia energy storage concepts in Aspen Plus seeking a compromise between efficient concepts and mature technologies. In the charging phase, ammonia is produced via the Haber–Bosch process using hydrogen from low-temperature water electrolysis for all the considered concepts. For the discharging phase, three ammonia conversion processes are modeled: (i) ammonia is thermally decomposed into nitrogen and hydrogen by using thermal energy from storage, and hydrogen is converted into electricity in a fuel cell; (ii) ammonia is thermally decomposed by using heat generated through the combustion of a fraction of the ammonia stream, and the produced hydrogen is supplied to a fuel cell; (iii) ammonia is used as a fuel in a combined power cycle. We compare these concepts with respect to roundtrip efficiency and levelized cost of electricity. The roundtrip efficiency and the levelized cost of electricity of the modeled concepts are ca. 30–34 % and 0.28–0.31 €kWh−1 (for an electricity purchase price of 0.03 €kWh−1). Concept (i) has both the highest roundtrip efficiency and the lowest levelized cost of electricity. We identify the process bottlenecks via an exergy analysis.

Green Hydrogen Production by Low-Temperature Membrane-Engineered Water Electrolyzers, and Regenerative Fuel Cells.

Green hydrogen (H2) is an essential component of global plans to reduce carbon emissions from hard-to-abate industries and heavy transport. However, challenges remain in the highly efficient H2 production from water electrolysis powered by renewable energies. The sluggish oxygen evolution restrains the H2 production from water splitting. Rational electrocatalyst designs for highly efficient H2 production and oxygen evolution are pivotal for water electrolysis. With the development of high-performance electrolyzers, the scale-up of H2 production to an industrial-level related activity can be achieved. This review summarizes recent advances in water electrolysis such as the proton exchange membrane water electrolyzer (PEMWE) and anion exchange membrane water electrolyzer (AEMWE). The critical challenges for PEMWE and AEMWE are the high cost of noble-metal catalysts and their durability, respectively. This review highlights the anode and cathode designs for improving the catalytic performance of electrocatalysts, the electrolyte and membrane engineering for membrane electrode assembly (MEA) optimizations, and stack systems for the most promising electrolyzers in water electrolysis. Besides, the advantages of integrating water electrolyzers, fuel cells (FC), and regenerative fuel cells (RFC) into the hydrogen ecosystem are introduced. Finally, the perspective of electrolyzer designs with superior performance is presented.

Ice-ice disease in cultivated eucheumatoid seaweeds: The perspectives of farmers

ABSTRACT Eucheumatoid seaweeds, encompassing the genera Kappaphycus and Eucheuma, are widely cultivated globally, particularly in tropical regions. However, ice-ice disease (IID) poses a significant challenge to their production, causing substantial economic losses. This study aimed to elucidate the factors contributing to IID in eucheumatoid seaweeds, focusing on the perspectives of seaweed farmers in Sibutu, Tawi-Tawi, Philippines. A mixed methods approach was employed, utilizing both one-to-one interviews (n = 96) and focus group discussions. The majority of the interviewed farmers were male, aged between 31 and 60 years, with extensive experience (11‒25 years) in seaweed cultivation. Notably, all participants possessed a familiarity with IID since childhood. Farmers described IID as a pathological condition affecting eucheumatoid seaweeds, characterized by the emergence of white and soft areas on the seaweed thalli. The initial stages of the disease manifest as a pale discolouration of the thalli and the presence of epiphytes or debris. Several environmental factors were identified by the farmers as contributing to IID incidence, including high or low water temperatures, low salinity (particularly after heavy rainfall), stagnant water currents, nutrient deficiencies, inadequate seedling quality, and poor farm management practices. Additionally, deepwater (nearshore) farms were reported to be more susceptible to IID. Farmers noted that easterly winds could exacerbate the disease by facilitating the infestation of epiphytes on the seaweed. Furthermore, the prevalence of IID was observed to be highest during the dry and hot season. Kappaphycus striatus was identified by the farmers as being more susceptible to IID compared with K. alvarezii and Eucheuma denticulatum. The negative impact of IID on farmers’ livelihoods was also highlighted. Some mitigation strategies employed by the farmers included the application of inorganic nutrient enrichments (e.g. ammonium phosphate (16–20-0, N-P-K) and complete (14–14-14, N-P-K) fertilizers), frequent relocation of infected seaweed to different farms, and the cultivation of more IID-resistant species.

A sustainable high-performance bamboo fiber composite material for cryogenic engineering

Exploring the application and development of biomass materials in the field of special engineering in line with the principles of green development. This work investigates the mechanical and thermal properties response of bamboo scrimber (BS) with different densities and resin contents at room temperature and ultra-low temperatures (-196 °C). The results showed that ultra-low temperatures significantly enhanced the modulus of rupture (increase of 143.9 %), modulus of elasticity (125.0 %), compressive strength (150 %), and shear strength (165 %) of BS due to the cell shrinkage at low temperature and physical phase transition of internal water. The failure modes of BS at ultra-low temperatures transitioned from ductile to brittle, compared with that at room temperature. Furthermore, BS with lower-density exhibited better thermal insulation (thermal conductivity < 0.55 W/mK) and dimensional stability (CTE < 6 1/k−6). These findings established a research base for broadening the application areas of BS for cryogenic engineering applications.

Prediction of outflow temperature of reservoir based on theory-guided machine learning models and optimization of operation for improving outflow temperature

The proportion of hydropower within the energy-resource structure is gradually increasing. However, the construction of reservoirs inevitably leads to ecological and environmental issues, especially the release of low-temperature water in summer and its detrimental effects on fish spawning and reproduction. These issues can be alleviated by optimizing the reservoir operation scheme, but the large amount of time required for predicting the reservoir outflow temperature emerges as the primary constraint. In this study, we considered Pubugou (PBG) Reservoir and proposed an efficient and high-precision prediction method for reservoir outflow temperature based on theory-guided machine learning (TGML) algorithms. This method was applied to the multi-objective optimization of the reservoir operations, and an optimization operation plan was proposed to improve the outflow temperature. The research results indicate that the LightGBM machine learning model shows good predictive performance, with a maximum deviation of no more than 1 °C in predicting the outflow temperature. There is a significant competitive relationship between reservoir power generation and the outflow temperature. Compared with the current operational scheme, the maximum power operation plan results in a 4.4% increase in total power generation but causes the average outflow temperature during the fish spawning period to decrease by 0.1 °C. The total power generation of the improved outflow temperature operation scheme was 0.8% lower than that of the actual scheme, but the average outflow temperature during fish spawning increased by 0.2 °C. Properly increasing the discharge flow from the reservoir and lowering the water level can thus help alleviate the issue of outflow temperature.

Thermodynamic analysis of a new tandem dual-temperature air source heat pump with ejector

This paper presents a conventional air source heat pump cycle (CHPC) and two dual-temperature air source heat pump cycles (DTHPC1 and DTHPC2). DTHPC1 employs two condensers, while DTHPC2 adds an extra compressor and combines the ejectors on top of DTHPC1. Compared with the conventional heat pump cycle, the new dual-temperature heat pump DTHPC2 can provide hot water at one additional temperature and still have high performance. In this paper, the refrigerants R1234yf and R1234ze(E) were selected as suitable for the cycle conditions. The cycle performance under different conditions was simulated and compared based on energy analysis methods and exergy analysis methods. The main performance parameters included COPh, ηex, etc. The results demonstrate that the COPh and ηex of DTHPC2 and DTHPC1 are greater than those of CHPC under identical conditions. Specifically, at an ambient temperature of approximately -10 °C, high-temperature hot water of approximately 65 °C, and low-temperature hot water of approximately 35 °C, the COPh of DTHPC2 and DTHPC1 increased by 45% and 32.7%, respectively, in comparison to CHPC. Similarly, the ηex of DTHPC2 and DTHPC1 increased by 27.1% and 28.9%, respectively.

Tidal pumping and intertidal groundwater springs create pronounced spatiotemporal thermal variability in a coastal lagoon

AbstractIntertidal groundwater springs provide thermally stable, nutrient‐rich freshwater that causes fine‐scale variability in water temperature and salinity and promotes biodiversity in coastal estuaries and lagoons. In this study, we combined three thermal sensing techniques to elucidate summer water temperature patterns at the mouths of intertidal groundwater springs and the ambient coastal lagoon in Prince Edward Island, Canada. Thermal infrared imagery captured the spatiotemporal variability in relative temperatures of the lagoon channel and cold‐water plumes from the springs. Thermal anomalies due to the springs were detected at the surface throughout a tidal cycle, suggesting that the thermal plumes were buoyant. Fiber‐optic distributed temperature sensing paired with temperature loggers near the spring outlets recorded groundwater temperatures at low tide (~ 7°C) but ambient lagoon temperatures (up to 26°C) at high tide due to the vertical thermal gradient in the stratified water column. Calculated estuarine Richardson numbers throughout the study confirm intertidal spring buoyancy due to salinity differences. The fiber‐optic distributed temperature sensing results revealed pronounced variations in temperature as evidenced by spatial (3.7°C) and temporal (5.5°C) standard deviations over the cable length during the study and lower mean lagoon bed water temperatures at high tide (22.5°C) than low tide (24.3°C) due to heat advection from tidal pumping. Lagoon temperatures fluctuate at diurnal (solar) and semi‐diurnal (tidal) frequencies. The findings emphasize the efficacy of a multi‐technology approach to reveal fine‐scale and dynamic thermal processes that drive temperature patterns and habitat distribution in coastal lagoon ecosystems and highlight the thermal influence of intertidal springs.