Increase In Surface Water Temperature Research Articles

Interplay of UV-filter pollution and temperature rise scenarios on Mytilus galloprovincialis health: Unveiling sperm quality and adult physiology, biochemistry, and histology insights

Addressing the impacts of emerging contaminants within the context of climate change is crucial for understanding ecosystem health decline. Among these, the organic UV-filters 4-methylbenzylidenecamphor (4-MBC) and benzophenone-3 (BP-3) are widely used in cosmetics and personal care products. Their unique physico-chemical properties, along with their growing commercialization and consumption, have made them ubiquitous in aquatic environments through both direct and indirect releases, raising significant concerns about their potential threats to inhabiting biota. Additionally, increasing surface water temperatures exacerbate ecological risks, making it imperative to understand the implications for non-target species at different biological levels. This study investigated the short- and long-term effects of UV-filters 4-MBC or BP-3, at ecologically relevant concentrations, combined with current and predicted warming scenarios, on the performance and male reproductive health of Mytilus galloprovincialis mussel populations. Using biomarkers across sub-cellular, cellular, tissue, and individual levels, the study revealed significant physiological and biochemical impairments in both sperm cells and adults exposed to UV-filters. Temperature emerged as the primary driver influencing mussel responses and modulating the impacts of 4-MBC/BP-3, emphasizing their sensitivity to temperatures outside the optimal range and interactive effects between stressors. Specifically, sperm motility declined with increasing UV-filter concentrations, while temperature alone influenced ROS production, leading to compromised mitochondrial activity and DNA damage in the presence of combined stressors, indicative of potential reproductive impairments. Adults exhibited high UV-filter bioconcentration potential in whole tissues, compromised physiological status, morphophysiological changes in digestive glands, oxidative stress, and alterations in metabolic capacity, antioxidant defences, and biotransformation mechanisms, correlating with UV-filter exposure and temperature increase. Among the UV-filters tested, 4-MBC was the most detrimental, especially when combined with warming. Overall, this study underscores the vulnerability of M. galloprovincialis to cumulative stressors and highlights the importance of employing a multi-biomarker approach to assess and mitigate the impacts of stressors on coastal ecosystems.

Long-term water temperature changes in Seneca Lake and their nexus to climate change and human activities

While many freshwater lakes have witnessed a rapid increase in surface water temperatures, the trends in subsurface water temperatures are not well-understood. This study explored the long-term subsurface water temperature change and its connection to climate change and human activities in Seneca Lake. Utilizing linear regression and the Theil-Sen estimator, the study identified a significant monotonic temperature trend in the subsurface water. Principal component and contribution analyses revealed that climate changes, particularly air warming, were more critical in explaining water temperature patterns, and human activities such as land cover change could exacerbate the impact of climate change. Using remotely sensed surface water temperature data, the study found a significant positive correlation between thermal pollution and water temperatures in the northern region of the lake, and after incorporating control variables, the regression analysis suggested that the adverse effects of thermal pollution are primarily confined to the area adjacent to the power plant. This research can offer fresh insights into lake ecology improvement and management strategies.

Phytoplankton spring succession pattern in the Yellow Sea surveyed at Socheongcho Ocean Research Station

The spring phytoplankton bloom is a critical event in temperate oceans typically associated with the highest productivity levels throughout the year. To investigate the bloom process in the Yellow Sea, daily data on physical, chemical, and phytoplankton taxonomic group biomass, calculated via the chemotaxonomic approach, were collected from late March or early April to late May between 2018 and 2020 at the Socheongcho Ocean Research Station. During early spring (late March to mid-April), phytoplankton biomass increased, accompanied by a decrease in nutrient levels, with Bacillariophyceae and Cryptophyceae being the dominant groups. As water temperature increased, a pycnocline began to develop in late April, leading to a peak of the phytoplankton bloom dominated by chlorophytes and Cryptophyceae. Network analysis suggested that this phytoplankton bloom was caused by the onset of vertical stratification induced by increased sea surface temperature. The chlorophyte peak induced phosphate limitation above the pycnocline, resulting in succession to Prymnesiophyceae and Dinophyceae. Following pycnocline formation, phytoplankton biomass below the pycnocline was dominated by Bacillariophyceae and Cryptophyceae, with decreasing or fluctuating trends depending on phosphate concentration. Apart from these general patterns, 2019 and 2020 both had distinctive traits. The 2019 data revealed lower phosphate concentrations than the other 2 years, leading to a smaller chlorophyte peak at the surface compared to 2018 and extreme phosphate limitation above the pycnocline. This limitation resulted in decreased biomass of late successional groups, including Prymnesiophyceae and Dinophyceae. Pycnocline formation was delayed in year 2020, and stratification was significantly weaker compared to the previous 2 years. Due to the pycnocline delay, the surface chlorophyte peak did not develop and no succession to late successional groups was observed. Instead, high levels of Bacillariophyceae and Cryptophyceae biomass were observed throughout the water column with no surface bloom. Thus, among various environmental factors, increasing surface water temperature and phosphate concentrations play pivotal roles in shaping phytoplankton bloom dynamics. Distinct yearly variation points to the broader impacts of climate shifts, emphasizing the need for continued marine monitoring.

Intraregional variability of exotic and native zooplankton in Basque coast estuaries (inner Bay of Biscay): effect of secondary dispersion, estuary features and regional environmental gradients

The zooplankton of five estuaries of the Basque coast (southeast Bay of Biscay) was surveyed in summer 2019 to check the intraregional spread of exotic species and analyse the cross-estuary differences in brackish and neritic communities related to the arrival of exotic species and the summertime geographic gradient of water temperature. Results revealed that all the studied estuaries have been colonized by Oithona davisae but not by Acartia tonsa and Pseudodiaptomus marinus. Environmental constraints due to estuarine hydrological features partly explained such differences, and the role of secondary spread opportunities remained less clear. Cross-estuary differences in the brackish community mainly reflected changes in the dominance of the native species Acartia bifilosa relative to different exotic copepod species. The neritic holoplankton differed in the contribution of thermophilic species in agreement with the thermal west–east increase of surface water temperature in the inner Bay of Biscay in summer. The detection of large numbers of larvae of the exotic crab Rhithropanopeus harrisii only in one of the estuaries highlighted the role of exotic benthic species in enhancing intraregional differences in estuarine meroplankton. Differences in the dominance of neritic or brackish species as a function of salinity and distance from coastline were also explored.

Can temperature rise change the impacts induced by e-waste on adults and sperm of Mytilus galloprovincialis?

Nowadays, it is of utmost importance to consider climate change factors, such as ocean warming, since the risk of negative impacts derived from increased surface water temperature is predicted to be high to the biodiversity. The need for renewable energy technologies, to reduce greenhouse gas emissions, has led to the increasing use of rare earth elements (REEs). Dysprosium (Dy) is widely used in magnets, motors, electrical vehicles, and nuclear reactors, being considered a critical REE to technology due to its economic importance and high supply risk. However, the increasing use of this element contributes to the enrichment of anthropogenic REEs in aquatic systems. Nevertheless, the information on the potential toxicity of Dy is limited. Moreover, the effects of pollutants can be amplified when combined with climate change factors. Thus, this study aimed to assess the effects of Dy (10 μg/L) in the species Mytilus galloprovincialis under actual (17 °C) and predicted warming conditions (21 °C). The Dy concentration in contaminated mussels was similar between temperatures, probably due to the detoxification capacity in individuals under these treatments. The combined stressors affected the redox balance, but higher impacts were caused by Dy and warming acting alone. In terms of cellular damage, although Dy acting alone was prejudicial to mussels, warming and both stressors acting together induced higher levels of LPO and PC. The histopathological effects of Dy in the digestive tubules were independent of the temperature tested. Regarding effects on sperm, only warming induced cellular damage, while both stressors, alone and together, impaired sperm movement. Overall, this study highlights that warming might influence the effects induced by Dy, but greater impacts were caused by the element. Eventually, the tested stressors may have consequences on mussels' reproduction capacity as well as their growth, abundance, and survival.

Efficient Biosynthesis of Acidic/Lactonic Sophorolipids and Their Application in the Remediation of Cyanobacterial Harmful Algal Blooms.

Cyanobacterial harmful algal blooms (CyanoHABs) pose significant threats to human health and natural ecosystems worldwide, primarily caused by water eutrophication, increased surface water temperature, and co-occurring microorganisms. Urgent action is needed to develop an eco-friendly solution to effectively curb the proliferation of CyanoHABs. Sophorolipids (SLs) are fully biodegradable biosurfactants synthesized by Starmerella bombicola. They can be classified into lactone and acid types. The lactone type displays strong antimicrobial activity, while the acid type exhibits good solubility, which make them ideal agents for mitigating CyanoHABs. Nevertheless, the broad utilization of SLs are hindered by their expensive production costs and the absence of effective genetic editing tools in the native host. In this study, we constructed recombinant strains capable of producing either acidic or lactonic SLs using the CRISPR-Cas9 gene editing system. The yields of acidic and lactonic SLs reached 53.64 g/L and 45.32 g/L in a shaking flask, respectively. In a 5 L fermenter, acidic SLs reached 129.7 g/L using low-cost glucose and rapeseed oil as substrates. The addition of 5 mg/L lactonic SLs effectively degraded cyanobacteria within 30 min, and a ratio of 8.25:1.75 of lactonic to acidic SLs showed the highest degradation efficiency. This study offers a safe and promising solution for CyanoHABs treatment.

Using historical catch data to evaluate predicted changes in fish relative abundance in response to a warming climate

Using models to predict future changes in species distributions in response to projected climate change is a common tool to aid management and species conservation. However, the assumption underlying this approach, that ecological processes remain stationary through time, can be unreliable, and more empirical tests are needed to validate predictions of biotic outcomes of global change. The scarcity of reliable historical and long‐term datasets can make these tests difficult. Moreover, incorporating abundance and multiple sampling methods can improve model predictions and usability for management. Our study 1) provides insight into how well models can predict environmental change under a warming climate, 2) incorporates multiple sampling gears and abundance data in modeling to better capture changes in populations and 3) shows the value of historical datasets for improving predictive models of population change. We used contemporary (2003–2019) and historical (1936–1964) abundance datasets of the North American fish largemouth bass Micropterus salmoides in lakes across the state of Michigan, USA. We developed Bayesian hierarchical models that leverage the use of multiple gears in contemporary lake surveys to estimate the relative catchabilities of largemouth bass for each gear and hindcast the models to predict historical abundance. Our estimates of relative density change over time were correlated with temperature change over time; increasing surface water temperature led to increasing largemouth bass density. Hindcasting models to historical lake temperatures performed similarly in predicting historical density to models predicting contemporary density. Our results suggest that models built using spatial environmental gradients can reliably predict population changes through time. Understanding the sampling methods and the environmental context of observational datasets can help researchers test for potential sampling biases and identify confounding factors that will improve predictions of future impacts of environmental change.

A review of lethal thermal tolerance among freshwater mussels (Bivalvia: Unionida) within the North American faunal region

Freshwater mussels of the order Unionida are currently one of the most imperiled groups of organisms in the North American faunal region. Accurate risk assessments and development of effective management strategies for remaining populations require knowledge of thermal limits in the face of increasing surface water temperature due to climate change and various anthropogenic factors. We conducted a systematic literature review of unionid mussels (order Unionida, families Margaritiferidae and Unionidae) in the North American faunal region to (1) summarize lethal thermal tolerance data by life stage and taxonomy, (2) discuss ecological and climate change implications of existing lethal tolerance data, and (3) identify needs for future research. We identified lethal tolerance estimates for only 28 of 302 species in the families Unionidae and Margaritiferidae. The mean acute median lethal temperatures were 32.8 °C for glochidia (19 species), 35.0 °C for juveniles (13 species), and 36.3 °C for adults (4 species). Generally, glochidia were less tolerant than juveniles or adults of the same species—but there were several exceptions. Generally, Amblemini had the highest acute and chronic thermal tolerance of all tribes followed by Anodontini, Pleurobemini, Lampsilini, and Quadrilini. Acclimation temperature affected lethal tolerance endpoints in less than half (52 of 145) of comparisons within species. Lethal tolerance data for additional species, combined with a comprehensive database of in situ surface water temperatures, would be useful for modeling the frequency and duration of lethal limit exceedance in North America and identifying populations currently living at or near their upper lethal limits.

Changing Climatic Conditions Affect Surface Water Quality in Southwestern Louisiana in the United States

Climate change impacts on rising temperatures, changes on rainfall patterns,drought, flooding, sea level rise, glacier melts, and incidence of diseases andparasites are reported worldwide in recent decades. This study investigatesthe effects of changing climatic conditions – particularly air temperature andprecipitation, on surface water temperatures and other water quality param-eters, such as the conductivity, dissolved oxygen (DO), pH, and turbidity.A statistical analysis was performed on air temperature and precipitationdata from 1980 to 2005 to determine the changing climatic conditions. Thewater quality data for four waterbodies in southwestern Louisiana was also analyzed to examine trends between the air temperature and surface watertemperatures, precipitation and surface water temperatures, and precipitationand water quality parameters. There was an unexpected increase in surfacewater temperature with an increase in precipitation. As the precipitation andair temperature increased, so did the surface water temperature. This increasein surface water temperature was correlated with decrease in DO levels. Theincrease in precipitation also correlated with an increase in pH and turbidityin Bayou Plaquemine Brule. This study’s findings could be utilized in adynamic climate modeling system to provide more accurate predictions ofclimate change in southwestern Louisiana.

Macrobenthic diversity response to the atlantification of the Arctic Ocean (Fram Strait, 79°N) – A taxonomic and functional trait approach

This is the first study presenting temporal changes of the macrofauna biodiversity along the bathymetric gradient from the shelf to abyssal depths in the eastern Fram Striat. In this region, between 2004 and 2008, a significant increase in surface water temperature was observed due to the transport of Atlantic water from lower latitudes and was defined as a Warm Water Anomaly (WWA). Effects of the WWA in the eastern Fram Strait were observed across the entire food web, from the pelagic to the deep seafloor. The material for our study was collected before (in 2000) and after the WWA (in 2010 and 2017) at station depths ranging from 203 m to 5561 m. Samples of macrofauna and surface sediments were collected with use of a box corer to analyze species composition and functional traits, and environmental characteristics in sediments. We explore the influence of environmental changes on the structure (species composition and diversity) and functioning (functional trait composition and diversity) of macrofauna communities. An increase of primary production in surface waters during and after the WWA was reflected in a higher food availability at the seafloor from shelf to abyssal depths. Warming induced environmental changes led to an increase of macrofauna density and taxonomic diversity at all water depths. Macrofauna species composition significantly changed after the WWA. At all study sites, macrofauna functional diversity increased after the warm period. Functional trait composition changed significantly along the bathymetric transect. Despite changes in the taxonomic composition, macrofauna communities at the shallowest stations showed high functional redundancy, i.e., trait composition remained unchanged after the WWA. At water depths below 1500 m, where functional redundancy was significantly lower, functional trait composition changed significantly after the WWA. Our results suggest that macrofauna communities on the shelves are more resistant to environmental changes compared to deep-sea assemblages in the eastern Fram Strait.

해수온도차발전-히트펌프 복합 사이클의 국내 적용성 검토

Due to industrialization and urbanization, the energy used by humankind is rapidly increasing, and side effects such as global warming and climate change are appearing. In order to respond to these international problems, research on new and renewable energy is continuously being carried out. In this study, OTEC-Heat pump combined cycle for domestic application was studied.BR Electricity was produced by OTEC through the increased surface water temperature and direct cooling using deep water discharge water in the summer were constructed. A heat pump using seawater is at higher temperature than outside air in the winter. In this study, energy cost and carbon dioxide emissions were compared with existing diesel power generation, EHP cooling, and kerosene heating systems. By applying OTEC, it was possible to produce 757.7 MWh of electricity per year, and through direct cooling, it was possible to save 98% of energy compared to EHP and 82% of energy compared to kerosene heating through a seawater heat pump.

Ensemble of models shows coherent response of a reservoir’s stratification and ice cover to climate warming

Water temperature, ice cover, and lake stratification are important physical properties of lakes and reservoirs that control mixing as well as bio-geo-chemical processes and thus influence the water quality. We used an ensemble of vertical one-dimensional hydrodynamic lake models driven with regional climate projections to calculate water temperature, stratification, and ice cover under the A1B emission scenario for the German drinking water reservoir Lichtenberg. We used an analysis of variance method to estimate the contributions of the considered sources of uncertainty on the ensemble output. For all simulated variables, epistemic uncertainty, which is related to the model structure, is the dominant source throughout the simulation period. Nonetheless, the calculated trends are coherent among the five models and in line with historical observations. The ensemble predicts an increase in surface water temperature of 0.34 K per decade, a lengthening of the summer stratification of 3.2 days per decade, as well as decreased probabilities of the occurrence of ice cover and winter inverse stratification by 2100. These expected changes are likely to influence the water quality of the reservoir. Similar trends are to be expected in other reservoirs and lakes in comparable regions.

Experimental Investigation of a Prototype Thermal Refuge for Trout

Recent years have seen an increase in surface water temperatures in several streams and fisheries, which has a detrimental effect on cold-water species such as trout. One possibility to resolve this issue is to create localized refugia of colder water generated through active cooling. The current work focuses on a prototype thermal refugia design and field testing. Various configurations of the prototype thermal refugia were tested in a stream, which could benefit from additional refugia regions. The prototypes featured a staggered, tube-bundle heat exchanger placed inside an enclosure with an aperture. The results demonstrate that in remote locations, man-made refugia can be provided. While the base enclosure (91.5 cm × 91.5 cm × 45.8 cm) allowed for excess mixing with the warmer free stream and resulted in low performance (dimensionless temperature difference of θ¯avg= 0.07), additional modifications improved performance. By utilizing a panel or an extension, the dimensionless temperature difference quadrupled (θ¯avg= 0.26) while the average heat transfer per dimensionless temperature difference was reduced to approximately one-fifth (1.92 kWth/θ¯avg) of the base enclosure. But these configurations increased the standard deviation of the temperature differences inside the refugia due to localized cooling. The combination of the panel and the extension did not further increase the standard deviation but resulted in an even higher dimensionless temperature difference (θ¯avg= 0.55) and a lower heat transfer per dimensionless temperature difference (0.81 kW/θ¯avg). This suggests that the enclosure design can be used to achieve a desirable temperature differential while maintaining a reasonable spatial fluctuation in that temperature difference and power requirement.

Latitudinal variation in diversity and abundance of mesopelagic fishes associated with change in oceanographic variables along 110°E, south-east Indian Ocean

As part of the second International Indian Ocean Expedition, an oceanic transect from 39.5°S to 11.5°S along 110°E in the south-eastern Indian Ocean enabled concurrent oceanographic measurements and sampling of early stages of mesopelagic fishes within the upper 500 m of the water column. Notable oceanographic features along the generally oligotrophic transect included an increase in surface water temperature from 12 to 28 °C from south to north and low salinities at both ends of the transect. High salinity Subtropical Surface Water was evident over the central part of the transect and low dissolved oxygen occurred at depth at the northern end where tropical waters were influenced by the Indonesian Throughflow. Throughout the study region larval fish stages were generally concentrated in the epipelagic zone. Species richness, abundance and diversity of fishes (n = 166 species) increased towards the tropical waters. The families Myctophidae (lanternfishes; 60 species), Phosichthyidae (lightfishes; 2 species) and Gonostomatidae (bristlemouths; 5 species) were numerically dominant. Clustering of integrated abundance data (0–500 m depth) revealed four major fish assemblages along the transect. When linked to oceanographic variables, multivariate multiple regression indicated that surface temperature, surface salinity and dissolved oxygen at 400 m depth provided the best fitting model explaining fish distribution patterns. Where possible, comparisons have been made with early data collected along this 110° E line in the 1960s during the first International Indian Ocean Expedition.

Evidence of Climate Change Based on Lake Surface Temperature Trends in South Central Chile

Lake temperature has proven to act as a good indicator of climate variability and change. Thus, a surface temperature analysis at different temporal scales is important, as this parameter influences the physical, chemical, and biological cycles of lakes. Here, we analyze monthly, seasonal, and annual surface temperature trends in south central Chilean lakes during the 2000–2016 period, using MODIS satellite imagery. To this end, 14 lakes with a surface area greater than 10 km2 were examined. Results show that 12 of the 14 lakes presented a statistically significant increase in surface temperature, with a rate of 0.10 °C/decade (0.01 °C/year) over the period. Furthermore, some of the lakes in the study present a significant upward trend in surface temperature, especially in spring, summer, and winter. In general, a significant increase in surface water temperature was found in lakes located at higher altitudes, such as Maule, Laja and Galletué lakes. These results contribute to the provision of useful data on Chilean lakes for managers and policymakers.

Community shifts from eukaryote to cyanobacteria dominated phytoplankton: The role of mixing depth and light quality

Abstract Lake stratification strengthens with increasing surface water temperatures, thereby reducing the depth of the mixed layer. Phytoplankton communities are not only exposed to different nutrient availability within a mixed water column, but also to different light quality. We conducted controled laboratory and mesocosm experiments to investigate phytoplankton, especially cyanobacteria, responses to different light quality and mixing depths. Our mesocosm experiment allowed the manipulation of mixing depth in situ by a mesocosm approach and to follow the effects of changing mixing depth on the phytoplankton community composition. Our laboratory experiment allowed the control of temperature and light quantity. To investigate the effect of light quality on phytoplankton, we created a light gradient from full photosynthetic active radiation to a reduced blue spectrum. In both experiments, shifts in phytoplankton community composition from eukaryote to cyanobacteria occurred at shallow mixing depth with higher availability of photosynthetic active radiation. Our results from the mesocosm experiment support the idea that reduced mixing depth can promote cyanobacterial abundance. With our laboratory experiment, we were able to manipulate light quality independent of temperature, available nutrients and light intensity influencing phytoplankton abundance. Results from the laboratory experiments support our hypothesis that a shift in light spectrum alone is a driver, strong enough to enhance cyanobacteria occurrence. Most of the previous studies dealing with cyanobacterial blooms have investigated temperature and eutrophication effects. Certainly, these are major factors for the growth of phytoplankton, but our experiments show that other aspects, such as the quality of light, must be also taken into account to explain cyanobacterial blooms. Such shifts in the phytoplankton community from eukaryote to cyanobacteria dominated communities will have strong consequences for food web dynamics. Several cyanobacteria specific traits, (e.g., toxin production, lack of essential fatty acids, and inedibility through production of large colonies) reduce transfer efficiencies of energy and matter between phyto‐ and zooplankton and therefore can influence higher trophic levels such as fish.

Rapidly expanding lake heatwaves under climate change

Lake heatwaves—prolonged periods of hot surface water temperature in lakes—have recently been shown to increase in intensity and duration, with numerous potential implications for aquatic ecosystems. However, an important physical attribute of lake heatwaves that has not yet been investigated is their spatial extent, and how it varies within a warming world. Here, we show that the spatial extent of lake heatwaves, defined as contiguous regions within a lake that simultaneously experience extreme warm conditions, is increasing in the largest group of freshwater lakes on Earth, The Laurentian Great Lakes. We show that the maximum spatial extent of lake heatwaves is sensitive to inter-annual variations in winter ice cover and the timing of stratification onset in spring. Notably, we find that a lengthening of the warm summer season and, in turn, an overall increase in surface water temperature, stimulates the development of larger lake heatwaves. On average, our results suggest that the mean spatial extent of lake heatwaves has increased two-fold since 1995. We anticipate this rapid expansion of lake heatwaves to have widespread implications for heat-related impacts on aquatic species.

Relative impacts of increases of solar radiation and air temperature on the temperature of surface water in a shallow, eutrophic lake

Abstract We monitored lake surface water temperatures from 1992 to 2019 in Lake Kasumigaura, a shallow lake in Japan. We hypothesized that increases of shortwave radiation had increased surface water temperatures and heat fluxes more than had the increases of air temperature. We used the heat flux analyses and the sensitivity analyses to test the hypothesis. The fluxes of solar radiation gradually increased during the study period in a manner consistent with the phenomenon of global brightening. The increase was especially apparent in the spring. The rate of increase of surface water temperature was especially significant in May. Air temperature did not significantly increase in May, but it increased significantly in June (0.40 °C decade−1). A sensitivity analysis of the heat fluxes at the lake surface (shortwave radiation, longwave radiation, latent heat flux, and sensible heat flux) revealed that surface water temperature was more sensitive to changes of shortwave radiation than to air temperature during the spring. Although other factors such as inflows of groundwater and river water may also have impacted surface water temperatures, the increase of solar radiation appeared to be the major factor responsible for the increase of surface water temperature during the spring in Lake Kasumigaura.

Deeper waters are changing less consistently than surface waters in a global analysis of 102 lakes

Globally, lake surface water temperatures have warmed rapidly relative to air temperatures, but changes in deepwater temperatures and vertical thermal structure are still largely unknown. We have compiled the most comprehensive data set to date of long-term (1970–2009) summertime vertical temperature profiles in lakes across the world to examine trends and drivers of whole-lake vertical thermal structure. We found significant increases in surface water temperatures across lakes at an average rate of + 0.37 °C decade−1, comparable to changes reported previously for other lakes, and similarly consistent trends of increasing water column stability (+ 0.08 kg m−3 decade−1). In contrast, however, deepwater temperature trends showed little change on average (+ 0.06 °C decade−1), but had high variability across lakes, with trends in individual lakes ranging from − 0.68 °C decade−1 to + 0.65 °C decade−1. The variability in deepwater temperature trends was not explained by trends in either surface water temperatures or thermal stability within lakes, and only 8.4% was explained by lake thermal region or local lake characteristics in a random forest analysis. These findings suggest that external drivers beyond our tested lake characteristics are important in explaining long-term trends in thermal structure, such as local to regional climate patterns or additional external anthropogenic influences.

Global changes may be promoting a rise in select cyanobacteria in nutrient-poor northern lakes.

The interacting effects of global changes-including increased temperature, altered precipitation, reduced acidification and increased dissolved organic matter loads to lakes-are anticipated to create favourable environmental conditions for cyanobacteria in northern lakes. However, responses of cyanobacteria to these global changes are complex, if not contradictory. We hypothesized that absolute and relative biovolumes of cyanobacteria (both total and specific genera) are increasing in Swedish nutrient-poor lakes and that these increases are associated with global changes. We tested these hypotheses using data from 28 nutrient-poor Swedish lakes over 16years (1998-2013). Increases in cyanobacteria relative biovolume were identified in 21% of the study sites, primarily in the southeastern region of Sweden, and were composed mostly of increases from three specific genera: Merismopedia, Chroococcus and Dolichospermum. Taxon-specific changes were related to different environmental stressors; that is, increased surface water temperature favoured higher Merismopedia relative biovolume in low pH lakes with high nitrogen to phosphorus ratios, whereas acidification recovery was statistically related to increased relative biovolumes of Chroococcus and Dolichospermum. In addition, enhanced dissolved organic matter loads were identified as potential determinants of Chroococcus suppression and Dolichospermum promotion. Our findings highlight that specific genera of cyanobacteria benefit from different environmental changes. Our ability to predict the risk of cyanobacteria prevalence requires consideration of the environmental condition of a lake and the sensitivities of the cyanobacteria genera within the lake. Regional patterns may emerge due to spatial autocorrelations within and among lake history, rates and direction of environmental change and the niche space occupied by specific cyanobacteria.