Increase In Water Temperature Research Articles

A Comparative Study of Phytoplankton Communities and Eutrophication Status in Two Urban Ponds Within Dhaka Metropolis

Changes in physicochemical water quality and plankton biomass over time can clearly indicate the eutrophication status of a water body. Urban ponds are particularly susceptible to cultural and natural eutrophication, making it essential to study their water quality and phytoplankton biomass. This study examined two urban ponds within the University of Dhaka campus: Shahidullah Hall Pond (SH-pond) and Museum Pond (Mu-pond). Common phytoplankton in both ponds included species like Pediastrum simplex, Melosira granulata var. angustata, Synedra nana, Ceratium sp., and Ceratium furcoides, along with zooplankton such as Brachionus sp., Keratella cochlearis, and copepod nauplii. The higher diversity of zooplankton compared to phytoplankton suggests that zooplankton overgrazing has reduced phytoplankton species composition. The study’s results indicate a clear trend of eutrophication in both ponds. Over three decades, SH-pond showed increases in water temperature (4.5°C), alkalinity (0.32 meq/L), dissolved oxygen (6.84 mg/L), soluble reactive phosphorus (21.35 μg/L), nitrate (137.77 μg/L), and chlorophyll-a (23.76 μg/L), with water transparency decreasing by 67 cm. Eutrophication indicators like dissolved oxygen, nitrogen, phosphorus, and phytoplankton biomass (chlorophyll-a) increased by 1.9, 1.82, 2.23, and 2.21 times, respectively, suggesting significant eutrophication in Sh-pond. In contrast, over 26 years, Mu-pond data showed decreases in water temperature (2.66°C), pH (0.18), conductivity (31 μS/cm), silica (12.17 mg/L), and chlorophyll-a (12.4 μg/L), but increases in dissolved oxygen (7.61 mg/L), soluble reactive phosphorus (1.16 μg/L), and nitrate nitrogen (170.75 μg/L). This suggests a slower rate of eutrophication in Mu-pond. Human intervention is a critical factor influencing eutrophication in urban ponds, highlighting the need for effective management systems. Dhaka Univ. J. Biol. Sci. 33(2): 15-26, 2024 (July)

Elevated temperature exacerbates pharmaceutical-induced oxidative stress in zebrafish (Danio rerio) larvae

There is growing evidence that rising global temperatures resulting from climate change may exacerbate the toxic effect of pollutants and heterotherms, including fish, in which homestatic mechanisms are directly influenced by environmental temperature will be most affected. Pharmaceuticals discharged into the environment are potentially harmful to wildlife as many of their drug targets are conserved across divergent phyla. Oxidative stress (OS) is a major mechanism by which many pharmaceutical contaminants can induce toxicity but this has received little consideration in the context of effects in wildlife. Further, these mechanisms are relatively poorly understood, particularly regarding multiple stressor interactions. We used transgenic TG(EpRE:mCherry) zebrafish, developed in our laboratory for detecting OS, as our experimental model. We show that the oxidative effects of high concentrations of pharmaceuticals from three different therapeutic classes (paracetamol, diclofenac and doxorubicin) are increased at temperatures elevated by 2–5 °C above those for zebrafish standard husbandry and relevant to their current natural environment (and predicted under the IPCC 2023 scenarios for intermediate to very high greenhouse gas emissions). These OS responses were primarily seen in the pronephros, liver, and gastrointestinal tract. The increase in OS at the increased water temperature may have resulted from the elevated temperature acting as a direct additive physiological stressor to the OS imposed by the drugs and/or via the temperature increasing the chemicals oxidative effect. For paracetamol, it appeared that the elevated responses at the higher temperature of 33 °C were in part due to an increase in uptake of the drug. Our data illustrate that risk assessments for chemicals inducing OS in fish (and likely other heterotherms) should consider the influence of temperature to ensure environmental protection in future environments.

Effects of changed water regime on the toxicity of silver nanoparticles (AgNPs) in tadpoles of Fejervarya limnocharis.

Climate change is viewed as one of the important causes of the amphibian population decline. Aspects of climate change like increase in water temperature and drying up of habitats have been underrepresented. The expanding production and usage of metal nanoparticles like silver nanoparticles (AgNPs) make them likely to end up in aquatic ecosystems. To arrive at a realistic assessment of the impact of AgNPs in a warming world, we have investigated the effects of temperature on the acute toxicity of AgNPs in tadpoles of Fejervarya limnocharis at 24, 48, 72 and 96h of exposure. The various aspects of sub-lethal toxicities of AgNPs with increase in temperature were also investigated. Besides, the effects of habitat desiccation on the sub-lethal toxicities of AgNPs in the tadpoles were analysed. The LC50 values of AgNPs at four different time points were found to be significantly different between the two different temperatures. Alterations in survival pattern, life history traits, amplifications in genotoxic potential and oxidative stress were observed with increased water temperature following AgNP exposure. The phenomenon of habitat desiccation was also found to significantly affect the toxicity of AgNPs with respect to alterations in mortality rate, time to metamorphosis and morphometric parameters of metamorphosed tadpoles. The findings suggest that changed water regime such as increased water temperature as well as reduction in water level accelerated the toxic effects of AgNPs in F. limnocharis tadpoles which is likely to affect their natural populations.

Assessing the impact of climate change and reservoir operation on the thermal and ice regime of mountain rivers using the XGBoost model and wavelet analysis

AbstractThis study presents an analysis of the influence of climatic conditions and the operation of a dam reservoir on the occurrence of ice cover and water temperature in two rivers (natural and transformed by reservoir operations) located in the Carpathian Mountains (central Europe). The analyses are based on data obtained from four hydrological and two climatological stations. The Extreme Gradient Boosting (XGBoost) machine learning model was used to quantitatively separate the effects of climate change from the effects arising from the operation of the dam reservoir. An analysis of the effects of reservoir operation on the phase synchronization between air and river water temperatures based on a continuous wavelet transform was also conducted. The analyses showed that there has been an increase in the average air temperature of the study area in November by 1.2 °C per decade (over the period 1984–2016), accompanied by an increase in winter water temperature of 0.3 °C per decade over the same period. As water and air temperatures associated with the river not influenced by the reservoir increased, there was a simultaneous reduction in the duration of ice cover, reaching nine days per decade. The river influenced by the dam reservoir showed a 1.05 °C increase in winter water temperature from the period 1994–2007 to the period 1981–1994, for which the operation of the reservoir was 65% responsible and climatic conditions were 35% responsible. As a result of the reservoir operation, the synchronization of air and water temperatures was disrupted. Increasing water temperatures resulted in a reduction in the average annual number of days with ice cover (by 27.3 days), for which the operation of the dam reservoir was 77.5% responsible, while climatic conditions were 22.5% responsible.

Postglacial ocean methane release from the northern South China Sea

Methane release into seawater and the atmosphere as a result of cold seepage activity is a sensitive indicator of global environmental change during the last glacial period. However, the link between postglacial ocean methane escape and possible increases in atmospheric methane concentration remains unclear, which hinders the evaluation of methane impact on climatic variability. In this study, lipid biomarkers were analyzed on samples from the Shenhu area in the South China Sea to reconstruct the marine gas hydrate variability since the last glacial time. The reconstructed methane release during the cool Last Glacial Maximum and Younger Dryas agreed well with previous findings. Interestingly, our results identified a pronounced methane outgassing at the end of Heinrich 1, which was likely triggered by the abrupt increase in intermediate water temperature. The occurrence of this gas hydrate dissociation before the drastic rise in atmospheric methane during Bølling-Allerød implied that the change in the gas hydrate reservoir could likely indirectly contribute to the initiation of the warming event, though more global evidence needs to be provided in the future.

Modeling embryo survival: Genetic and environmental influences on eye-up rate in a north American Atlantic salmon selective breeding program

Selective breeding programs improve target traits but can also unintentionally change genetically correlated traits in the selected strain. The U.S. Department of Agriculture–Agricultural Research Service National Cold Water Marine Aquaculture Center (NCWMAC) in Franklin, Maine maintains a North American Atlantic salmon selective breeding program focused on improving commercially important traits (e.g., carcass weight). However, the program has experienced a significant decline in the percent of eyed embryos over its 14 years of operation, leading to concerns that reproductive performance was being unintentionally changed by selection for the target traits. The aims of this study were to 1) model eye up success as a potentially heritable trait utilizing the recorded pedigree and 2) assess the relationship between eye-up rate and environmental conditions experienced by the broodstock. Over 14 years of data encompassing 1537 full-sib families produced by 1537 dams and 885 sires was analyzed. Counts of eyed embryos and carcass weight were analyzed with a linear multi-trait trait model that included maternal genetic effects and a spawn year effect to determine the strength of genetic and environmental influences on the eyed embryo rate. To investigate the environmental influences in more detail, we assessed the correlation between water quality parameters in the broodstock rearing system observed over the same 14-year time period and the estimated spawn year effects. There was small heritability of the direct genetic effect (0.059 ± 0.009) and the maternal genetic effect (0.039 ± 0.013). Comparatively, the proportion of phenotypic variance explained by the maternal environmental effect was moderate (0.165 ± 0.012). The genetic correlations between carcass weight and eye up rate were very small and had a large amount of uncertainty. The correlation between the direct genetic effects on eye-up and carcass weight was −0.0528 ± 0.1469 while the correlation between the maternal genetic effect on eye-up and the direct genetic effect on carcass weight was 0.2030 ± 0.1791. The correlation between maternal common environmental effects on the two traits was also low at 0.0676 ± −0.0804. The effect of spawn year was statistically significant (p < 0.01), and the values were negatively correlated with mean un-ionized ammonia (mg/L, −0.56, p = 0.04,), nitrate concentrations (mg/L r = −0.65, p = 0.01) and temperature (°C, r = −0.61, p = 0.02) experienced by the broodstock prior to spawning. Overall, the results suggest that the decrease in eyed embryos over time was not caused by inadvertent selection but instead due to increases in water temperature and/or nitrogenous waste concentrations in the broodstock rearing system. Further investigation of the mechanisms behind these apparent environmentally induced declines and potential mitigation measures to prevent decreases in eye-up rates are needed.

Prediction of reproductive performance in wintering females of Siberian sturgeon (Acipenser baerii, Brandt) based on in vitro ovulation rate of isolated follicles

Early prediction of the reproductive success of sturgeon females is important both for artificial breeding conditions in sturgeon farms and for monitoring wild fish populations approaching spawning. This study demonstrated that ovarian follicles removed from wintering Acipenser baerii females can undergo in vitro ovulation when exposed to 17α,20β-dihydroxy-4-pregnen-3-one. The research was conducted from 2015 to 2021 and involved the examination of 110 wintering Siberian sturgeon females (A. baerii), with an average weight of 8–11 kg and an age range of 8–10 years. Selection of females for spawning was based on the polarization index (PI) at the time when the river temperature dropped to +8 °C. The selected females were overwintered in concrete flow-through tanks with water from the Volga River for approximately two months. At the end of this period, oocyte samples were collected for in vitro incubation. An increase in water temperature to 15 °C, which precedes spawning, was achieved by mixing with warm effluent from a regional power station. The reproductive success of females was evaluated based on fertilization and embryonic survival rates. High reproductive success was characterized by females with fertilization rates above 70% and hatching rates above 60%. We identified a positive correlation between the percentage of in vitro ovulated follicles and the in vivo fertilization and embryo survival rates, with correlation coefficients of Rsp = 0.60 and Rsp = 0.48, respectively. Statistical analysis showed that females whose in vitro ovulation rate of follicles exceeded 30% displayed high reproductive performance compared to those with an in vitro ovulation rate below 30%. The predictive accuracy of this criterion was determined by calculating the ratio of ranks between females with high and low reproductive performance, averaging 80.9% for fertilization and 77% for embryonic survival. Therefore, we propose a new criterion to select females of A. baerii for spawning based on the in vitro oocyte ovulation rate obtained from wintering individuals.

A case study on single basin solar still augmented with wax filled metallic cylinders

This experimental study introduces a novel approach to enhancing solar still performance through the integration of wax-filled rods, marking a significant advancement in solar desalination technology. These rods, innovatively designed to absorb and store both sensible and latent heat during peak solar radiation hours, release this stored energy gradually, particularly during the evening and night. This unique mechanism results in a notable and consistent increase in water temperature within the modified solar still after 17:00, setting it apart from conventional models. The study's findings reveal that the modified solar still achieves a 12.8 % higher cumulative distillate yield and a 16.3 % increase in efficiency compared to traditional solar stills. Furthermore, this enhancement translates into a 6.3 % reduction in distillate production costs, underscoring the economic viability and superior performance of the modified design.

Impact of Temperature on the Growth Performance, Survival Rate, Osmoregulation, Dissolved Oxygen and Physiological Changes of Freshwater Tilapia (Oreochromis mossambicus)

For many aquatic species, any changes in water temperature affect their survival. This study was performed to investigate the effect of rising temperature on the growth parameters, protein content, dissolved oxygen content, moisture content osmoregulation, and physiological activity of freshwater Tilapia (Oreochromis mossambicus). The experiments were set in plastic fish tanks, the experimental tank placed in direct sunlight and the control tank in shade, and measuring temperature and pH daily, with proper aeration and feed was provided. The study found that increasing water temperature led to higher mortality rates and low survivability percentages in fish, with a higher growth rate in the experimental group with a pH range of 5.7 to 8.2. High dissolved oxygen levels were recorded during the experimental period, with a mean difference of 26.56 compared to the control group, possibly causing restless movement in fish. The study revealed that the alkalinity of water decreases with increasing temperature. The study found that increased salinity led to a significant increase in growth performance, indicating an increase in metabolic rate, and a decrease in alkaline nature. The difference between the mean protein value in the experimental and control groups is 0.896mg/ml. Thermal limitations may negatively impact O. mossambicus physiological responses, impacting aquaculture production due to predicted global climate change-induced water temperature changes.

Remarkable shifts in the megabenthic community structure over four decades in Tokyo Bay, Japan, in relation to environmental variations

We investigated long-term changes in the megabenthic community in Tokyo Bay, Japan, using data from fisheries-independent trawl surveys conducted from 1977 to 2023. In addition, we examined the potential relationship between changes in biotic communities and environmental conditions. The total abundance and biomass exhibited an increasing trend until 1987, followed by a substantial decline from the late 1980s to the 1990s due to a decrease in small to medium-sized fish and crustacean species. Meanwhile, a marked increase in the number of large fish (including elasmobranchs), mollusks, and echinoids, was observed in the 2000s. These shifts in the megabenthic community structure were correlated with an increase in water temperature and a decrease in nutrient concentrations and copepod densities. Cumulative evidence suggests that a remarkable shift in the megabenthic community structure occurred between the 1970s and the 2020s, which was possibly associated with variations in the environmental conditions in Tokyo Bay.

Has climate change over the last ten years caused a banalisation of diatom communities in Cypriot streams?

To unveil possible changes in diatom communities in Cypriot streams over the last ten years or so, we selected samples from the years 2020, 2021, and 2022 for the “recent” dataset (N = 119) and samples from the years 2010 and 2011 for the “historical” dataset (N = 108). Biotic homogenization has become a truly global phenomenon. Here we show that, over the last ten years, in response to increased water temperature, conductivity, and discharge variability due to climate-change, Cypriot stream diatom communities include a higher number of trivial (= widespread, tolerant, and opportunistic), aerial, and thermophilic species, have reduced β-diversity and increased nestedness. Moreover, IndVal analysis shows that indicator species from the historical dataset were characteristic, often relatively rare species, while the indicators of the recent dataset were a group of typical trivial, eutraphentic, and thermophilic species. As is almost always the case, the diatom communities we studied were subjected to multiple stressors, often affecting them in opposite ways. Besides the increase in trivial species, the reduction in β-diversity, and the rise in nestedness mentioned above, the diatom assemblages we studied also showed an increase in α-diversity that could be due to a moderate reduction in nutrients in several sites. High-ecological-integrity ecosystems, such as springs, waterfalls, and dripping rock-walls, in particular springs that were shown to be excellent hydrologic refugia in climates heavily affected by climate change, and the stream sites close to them should be carefully protected, as they can be refugia for sensitive and characteristic species that can recolonize the adjacent streams after adverse climatic events.

Contrasting effects of climate change on denitrification and nitrogen load reduction in the Po River (Northern Italy)

An increase in water temperature is one of the main factors that can potentially modify biogeochemical dynamics in lowland rivers, such as the removal and recycling of nitrogen (N). This effect of climate change on N processing deserves attention, as it may have unexpected impacts on eutrophication in the coastal zones. Intact sediment cores were collected seasonally at the closing section of the Po River, the largest Italian river and one of the main N inputs to the Mediterranean Sea. Benthic oxygen fluxes, denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) rates were measured using laboratory dark incubations. Different temperature treatments were set up for each season based on historical data and future predictions. Higher water temperatures enhanced sediment oxygen demand and the extent of hypoxic conditions in the benthic compartment, favoring anaerobic metabolism. Indeed, warming water temperature stimulated nitrate (NO3−) reduction processes, although NO3− and organic matter availability were found to be the main controlling factors shaping the rates between seasons. Denitrification was the main process responsible for NO3− removal, mainly supported by NO3− diffusion from the water column into the sediments, and much more important than N recycling via DNRA. The predicted increase in the water temperature of the Po River due to climate change may exert an unexpected negative feedback on eutrophication by strongly controlling denitrification and contributing to partial buffering of N export in the lagoons and coastal areas, especially in spring.Graphical

Seasonal environmental transitions and metabolic plasticity in a sea-ice alga from an individual cell perspective

Sea-ice microalgae are a key source of energy and nutrient supply to polar marine food webs, particularly during spring, prior to open-water phytoplankton blooms. The nutritional quality of microalgae as a food source depends on their biomolecular (lipid:protein:carbohydrate) composition. In this study, we used synchrotron-based Fourier transform infra-red microspectroscopy (s-FTIR) to measure the biomolecular content of a dominant sea-ice taxa, Nitzschia frigida, from natural land-fast ice communities throughout the Arctic spring season. Repeated sampling over six weeks from an inner (relatively stable) and an outer (relatively dynamic) fjord site revealed high intra-specific variability in biomolecular content, elucidating the plasticity of N. frigida to adjust to the dynamic sea ice and water conditions. Environmental triggers indicating the end of productivity in the ice and onset of ice melt, including nitrogen limitation and increased water temperature, drove an increase in lipid and fatty acids stores, and a decline in protein and carbohydrate content. In the context of climate change and the predicted Atlantification of the Arctic, dynamic mixing and abrupt warmer water advection could truncate these important end-of-season environmental shifts, causing the algae to be released from the ice prior to adequate lipid storage, influencing carbon transfer through the polar marine system.

Wettability behavior of DTMS modified SiO2: Experimental and molecular dynamics study

In this research, the wetting behavior of SiO2 modified with dodecyltrimethoxysilane (DTMS) was explored using both experimental and molecular dynamics (MD) simulation approaches. The experimental results reveal that DTMS can chemically bond to the SiO2 surface, and the contact angle (CA) reaches the maximum value of 157.7° when the mass of DTMS is twice that of SiO2. The different wetting behaviors caused by DTMS grafting were analyzed by CA fitting, ionic pairs, concentration distribution, molecule orientation, and interfacial interaction energy. The results demonstrate that a 25% DTMS grafting rate resulted in a maximum CA of 158.2°, which is ascribed to the disruption of interfacial hydrogen bonding and changes in the hydration structure caused by DTMS grafting. Moreover, the above hydrophobic SiO2 model shows a slight decrease in CA as the water temperature increases, which is consistent with the experimental findings. In contrast, an opposite change was observed for the pristine SiO2 model. Although the higher water temperature enhances the diffusion capacity of water molecules in both models, the difference in interfacial interactions is responsible for the change in CA. We hope this finding will contribute to a deeper understanding of the wetting adjustment of SiO2.

A study of the temperature distribution in the OTEC cold water pipe using a heat and mass transfer approach

Abstract The difference between sea water temperature at a depth of around 1000 m and sea water temperature at sea level is generally used as a parameter in the design of Ocean Thermal Energy Conversion (OTEC). In practice, electricity generation is determined by the difference between the temperature of the cold seawater coming out of the Cold Water Pipe (CWP) and the temperature of the seawater at the surface. The temperature of cold sea water increases due to heat transfer experienced by cold sea water flowing through the CWP, which comes into contact with surrounding sea water which has a higher temperature. This in turn provides a lower actual temperature difference, and therefore reduces the design power capacity. However, many previous studies did not consider these lower temperature differences. This may be acceptable for cases with practically small heat transfer such as CWP with low thermal conductivity combined with good insulation used in 1000 m CWP vertical floating systems. Unfortunately, this may not be the case for many of OTEC’s proposed alternative sites, which are located on land systems that require CWP lengths of five km or more. This raises the need for careful investigation to determine the temperature of the sea water coming out of the CWP, where it is necessary to calculate the temperature distribution of the cold sea water flowing through the CWP. This paper aims to estimate the temperature distribution of cold sea water flowing through the CWP and the increase in temperature of cold sea water leaving the CWP. Analysis based on the principles of mass and heat transfer was carried out in this research, where modelling was carried out numerically using a finite volume approach. For the case considered, the change in sea water temperature at CWP from depth to the surface occurs 1-3°C, which is the accumulation of each change in sea water depth. The results of this research illustrate that designing an OTEC system with a long CWP must consider the temperature distribution of cold sea water flowing through the CWP to produce a more realistic design.

Depth-dependent warming of the Gulf of Eilat (Aqaba)

The Gulf of Eilat (Gulf of Aqaba) is a semi-enclosed basin situated at the northern end of the Red Sea, renowned for its exceptional marine ecosystem. To evaluate the response of the Gulf to climate variations, we analyzed various factors including temperature down to 700 m, surface air temperature, and heat fluxes. We find that the sea temperature is rising at all depths despite inconclusive trends in local atmospheric variables, including the surface air temperature. The Gulf’s sea surface temperature (SST) warms at a rate of a few hundredths of a degree Celsius per year, which is comparable to the warming of the global SST and the Mediterranean Sea. The increase in sea warming is linked to fewer winter deep mixing events that used to occur more frequently in the past. Based on the analysis of the ocean-atmosphere heat fluxes, we conclude that the lateral advection of heat from the southern part of the Gulf likely leads to an increase in water temperature in the northern part of the Gulf. Our findings suggest that local ocean warming is not necessarily associated with local processes, but rather with the warming of other remote locations.

Pathways linking watershed development and riparian quality to stream water quality and fish communities: Insights from 233 subbasins of the Great Lakes region

Anthropogenic stressors such as urban development, agricultural runoff, and riparian zone degradation impair stream water quality and biodiversity. However, the intricate pathways that connect these stressors at watershed and riparian scales to stream ecosystems—and their interplay with climate and hydrology—remain understudied. In this study, we used Partial Least Squares (PLS) path modeling to examine these pathways and their collective impacts on stream water quality and fish community structures across 233 watersheds in the Great Lakes region. Our study suggests that moderate levels of watershed development enhance overall fish richness, potentially due to increased water temperature and nutrient availability, but reduces both the percentages and richness of cold water and intolerant taxa. Riparian quality exerts indirect effects on water quality with climate and stream order serving as key mediators. Complementing our SEM analysis, we also used Multiple Linear Regression (MLR) models and identified a significant positive relationship between the proportion of clay and agricultural land with TN concentrations. However, TP concentrations are influenced by a more complex set of interactions involving developed areas, soil, and slope. These findings emphasize the necessity of adopting integrated management strategies to preserve the health and integrity of freshwater ecosystems in the Great Lakes region. These strategies should integrate watershed and riparian protection measures while also taking into account the effects of climate change and specific local conditions.

Experimental study on effect of submergence depth on steam jet shape characteristics in direct contact condensation

The phenomenon of direct contact condensation is frequently utilized in the industrial sector due to low driving potential requirements and proficient heat and mass transfer characteristics. This experimental study investigates the influence of nozzle submergence depth by condensing steam through a straight pipe (SP) and converging-diverging (CD) nozzle. The effect of operating conditions i.e. steam pressure and water temperature in addition to nozzle geometry were also studied on steam cavity shape characteristics. Six different shapes were manifested including unstable, conical, ellipsoidal, cylindrical, divergent, and double expansion-contraction. The dimensionless penetration length of plumes was observed in a range of 1.46–3.91 and 2.14–4.41 for the CD and SP nozzle, respectively while the maximum expansion ratio was determined to be 1–1.25 for the CD nozzle and 1.16–1.58 for the SP nozzle. It has been observed that jet length increases with an increase in submergence depth, steam pressure, and water temperature. The maximum expansion ratio was observed to decrease with the increase in submergence depth and increase with an increase in steam pressure and water temperature. The empirical correlations for dimensionless penetration length were developed and predicted results were found to be lying between ±10 % and ±7 % for CD and SP nozzle respectively.

Idiosyncratic phenology of greenhouse gas emissions in a Mediterranean reservoir

AbstractExtreme hydrological and thermal regimes characterize the Mediterranean zone and can influence the phenology of greenhouse gas (GHG) emissions in reservoirs. Our study examined the seasonal changes in GHG emissions of a shallow, eutrophic, hardwater reservoir in Spain. We observed distinctive seasonal patterns for each gas. CH4 emissions substantially increased during stratification, influenced predominantly by the increase in water temperature, net ecosystem production, and the decline in reservoir mean depth. N2O emissions mirrored CH4's seasonal trend, significantly correlating to water temperature, wind speed, and gross primary production. Conversely, CO2 emissions decreased during stratification and displayed a quadratic, rather than a linear relationship with water temperature—an unexpected deviation from CH4 and N2O emission patterns—likely associated with photosynthetic uptake of bicarbonate and formation of intracellular calcite that might be exported to sediments. This investigation highlights the imperative of integrating these idiosyncratic patterns into GHG emissions models, enhancing their predictive power.

Validation of a new acoustic telemetry transmitter for the study of predation events in small fishes.

Acoustic telemetry has emerged as an important tool for studying the movement and behavior of aquatic animals. Predation-sensing acoustic transmitters combine the functions of typical acoustic transmitters with the added ability to identify the predation of tagged animals. The objective of this paper was to assess the performance of a newly miniaturized acid-based predation-sensing acoustic transmitter (Innovasea V3D; 0.33 g in air). We conducted staged predation events in the laboratory where acoustically tagged rainbow trout (Oncorhynchus mykiss) were fed to largemouth bass (Micropterus nigricans) at 3.3-7.0, 9.0-10.8, 16.0-20.0, and 22.0-25.8°C. We also conducted false-positive tests where tagged rainbow trout were held at 10.0 and 16.8°C without the risk of predation. Predation events were successfully identified in 92% of the staged predation trials. Signal lag (i.e., the time required for a predation tag to indicate that predation occurred) ranged from 0.11 to 6.29 days and decreased strongly with increasing water temperature and increased with increasing body mass of the tagged prey. Tag retention in the gut of the predator was much more variable than signal lag and was influenced by water temperature and individual predators but not by prey mass. No false positives were detected after 60 days at either temperature (n = 27 individuals). Although the relationships between water temperature, signal lag, and retention time are likely species-specific, the data reported here provide useful information for the use of these transmitters to study predation in wild fishes, especially for temperate, freshwater fish.