Stratification Period Research Articles

Time and depth variability of radon concentration and its relationship with other physicochemical parameters in an artificial lake subject to strong anthropogenic control.

Understanding the interaction between groundwater and surface water is crucial for an effective water management. This study investigates the vertical variability of radon gas (Rn-222) concentrations and other physicochemical parameters (pH, electrical conductivity, redox potential, and temperature) in an artificial lake (Aguieira Dam's reservoir) in the Mondego River, Portugal, that is intensively controlled by human factors. Over nine surveys conducted from May 2022 to September 2023, we observed significant vertical and temporal variations in these parameters, revealing complex patterns of water column stratification driven primarily by thermal dynamics and dam management practices. The study found that during periods of complete thermal stratification, Rn-222 concentrations were higher at mid-thermocline and at the riverbed, indicating traces of potential groundwater inputs, while at the epilimnion showed lower concentrations due to atmospheric exhalation. Conversely, during not complete stratification conditions, typically observed during higher water turbulence or lower water levels, the water column exhibited more homogeneous physicochemical profiles. Nevertheless, in some cases that could be related to increased precipitation prior to the sampling, it was observed also traces of groundwater input, highlighted by the radon tracer and confirmed by other physicochemical parameters. This study highlights the complex dynamics of water column stratification in artificial lakes whose inputs and outputs are heavily controlled by humans. The dam management itself is responsible for the complete inversion of the natural cycle of water level expected in a natural environment, thus these findings underscore the importance of considering both natural and anthropogenic factors in the management of water resources, particularly in dam-influenced systems, where vertical stratification and groundwater-surface water interactions can significantly impact water quality and the overall ecosystem health. This work contributes to a better understanding of the hydrological processes in dam-regulated river systems, providing insights for water resource management.

The influence of thermal and hypoxia induced habitat compression on walleye (Sander vitreus) movements in a temperate lake

BackgroundGlobally, temperate lakes are experiencing increases in surface water temperatures, extended periods of summer stratification, and decreases of both surface and deep water dissolved oxygen (DO). The distribution of fish is influenced by a variety of factors, but water temperature and dissolved oxygen are known to be particularly constraining such that with climate change, fish will likely feel the “squeeze” from above and below.MethodsThis study used acoustic telemetry to explore the effects of both thermal stratification and the deoxygenation of the hypolimnion on walleye (Sander vitreus) movements in a coastal embayment in Lake Ontario. Using historical water quality monitoring data, we documented seasonal and annual fluctuations in availability of both ‘suitable’ (all temperatures, DO > 3 mg/L) and ‘optimum’ (temperatures 18–23 °C, DO > 5mg/L) abiotic habitat for walleye and determined how these changes influenced walleye movements over a three-year period.ResultsHypoxia (< 3 mg/L DO) was present in Hamilton Harbour every summer that data were available (32 of the 42 years between 1976 and 2018), with a maximum of 68.4% of the harbour volume in 1990. We found that thermal stratification and a hypoxic hypolimnion greatly reduced the volume of suitable habitat during our telemetry study. The reduction of suitable habitat significantly reduced walleye movement distances, however as the summer progressed, this remaining suitable habitat warmed into their thermal optimum range which was found to increase walleye movement distances. Despite the seemingly poor conditions, tagged walleye remained in the harbour for most of the year, and were the fastest growing individuals compared to other sampled coastal subpopulations in Lake Ontario.ConclusionsAlthough we documented a reduction in the quantity of non-hypoxic habitat available to walleye, the water temperature of the remaining habitat increased throughout the summer into the physiologically optimum range for walleye and increased in metabolic quality. Many abiotic factors influence how, where, and what habitat fish choose to use, and this study reveals the importance of considering both habitat quality (temperature and dissolved oxygen) and quantity when evaluating fish habitat use and behaviour.

Seed germination of the medicinal plant Ferula gigantea

Ferula gigantea is a perennial herb valued for its medicinal and ornamental properties. The declining survival rate of F. gigantea in its natural habitat has prompted research on seed germination to aid relocation and conservation efforts. Here, we examined seed morphology through controlled experiments and investigated the impact of gibberellic acid (GA3) soaking and low-temperature stratification on seed germination. A 90-day low-temperature stratification period yielded the highest germination of 86.7%. In conclusion, pre-sowing low temperature stratification for 90 days is an effective method for improving seed germination in F. gigantea.

Sand Dunes as a Nature‐Based Solution to Mitigate Salt Intrusion in Stratified Estuaries

AbstractSalt intrusion in estuaries can pose a threat to drinking water extraction, irrigation, industries, and ecology. Key factors influencing the salt intrusion length include freshwater river flushing and vertical salt mixing. This study investigates the potential of estuarine sand dunes, that is, large‐scale rhythmic patterns, to serve as a nature‐based solution to mitigate salt intrusion. To this end, we adopt a two‐dimensional vertical (2DV) modeling approach, which numerically solves the flow and salt transport in an idealized single‐channel estuary. By varying the tidal amplitude and river discharge, three types of estuaries are modeled; a salt wedge, a strongly stratified and a strain‐induced periodic stratification estuary. Two types of dune configurations are considered: ’depth‐neutral’ dunes (preserving mean water depth) and ’deepening’ dunes (crest level equal to original bed level, rest of dune profile entirely below). Model results demonstrate that the presence of dunes can effectively reduce the salt intrusion length by several kilometers, compared to the scenario without dunes. Systematically varying dune geometry demonstrates that steeper (higher and shorter) dunes yield a stronger reduction in the salt intrusion length. Deepening dunes have the potential to generate sufficient mixing to overcome the adverse effects of channel deepening and, as such, can mitigate salt intrusion while maintaining navigability. As a naturally existing bedform, estuarine sand dunes present a promising nature‐based solution against salt intrusion without compromising accessibility to seaports.

Scarification with a Low Concentration of Acid Facilitates Water Acquisition and Minimizes Cold Stratification Duration, Improving the Seed Germination of Canadian Buffaloberry (Shepherdia canadensis (L.) Nutt.)

Canadian buffaloberry (Shepherdia canadensis (L.) Nutt.) is a perennial shrub known for its drought tolerance, nitrogen-fixing ability, and suitability for land reclamation and vegetation, particularly on nutrient-poor industrially disturbed soils in Alberta, Canada. Despite its ecological importance, commercial nurseries and greenhouses face challenges due to limited knowledge of optimizing seed germination and maintaining genetic diversity in cultivated seedlings. In this study, we investigated the interactive effect of cold stratification duration (0, 2, 4, 8, 12, and 16 weeks) and scarification time (control (no scarification), 1, and 4 h) on buffaloberry seed germination. The seed germination rate was tested using a factorial experiment with two factors arranged in a completely randomized design with four replications. Our findings indicate that scarification with a low concentration of acid for 1 h significantly enhances germination outcomes and shortens the required stratification period from 16 weeks to 12 weeks, achieving an optimal germination rate of 82%. Our novel approach using low-concentration acid to scarify Canadian buffaloberry seeds will help commercial greenhouses and forest nurseries improve seed germination, which utilizes this species for land reclamation and reforestation. Furthermore, this method can be adapted to improve germination in other native species with similar dormancy challenges, broadening its applications in ecological restoration efforts.

Numerical investigation of nonlinear interaction between salinity- and sediment-induced stratification in highly turbid estuaries and coastal seas

ABSTRACT In highly turbid estuaries and coastal seas where freshwater rivers meet the salty ocean, both salinity-induced stratification (SaIS) and sediment-induced stratification (SeIS) are crucial in shaping total estuarine stratification. This study investigates the nonlinearity emerging from the interaction between SaIS and SeIS using a one-dimensional water column model over an erodible bed, driven by a longitudinal salinity gradient and oscillating tidal currents. The results reveal that total stratification deviates significantly from a simple addition of SaIS under clearwater conditions and SeIS under freshwater conditions, indicating a highly nonlinear interaction. The complex spatial and temporal patterns of the nonlinearity arise from the differing source-sink dynamics of salt and sediment. SaIS reduces SeIS during flood but intensifies it during ebb, whereas SeIS consistently strengthens SaIS. This nonlinearity, which exhibits notable flood-ebb asymmetry, is relatively insensitive to changes in tidal forcing compared to salinity gradient forcing, due to the conflicting effects of tidal currents on salinity straining, sediment diffusion, and turbulent mixing. These findings highlight the necessity of incorporating sediment's modulation of classical strain-induced periodic stratification due to salinity gradients in numerical models to improve predictions of buoyancy and stability in highly turbid estuarine and coastal systems.

New Generation Site and Estimated Propagation of Nonlinear Internal Waves Under Varying Background Stratification in the Northeastern East China Sea

AbstractThis study investigates the generation and propagation of nonlinear internal waves (NLIWs) in the northeastern East China Sea (ECS), focusing on the impact of time‐varying background stratification. Using satellite imagery and tide‐generating body force, 327 groups of NLIWs were identified from 93 MODIS images collected between 2015 and 2019 and classified into three distinct types based on their propagation directions—Type‐A (∼42%), Type‐B (∼38%), and Type‐C (∼20%)—each originating from different generation sites. Type‐B NLIWs were found to originate from a newly identified site near southwestern Fukue Island reported here for the first time, whereas Type‐A and Type‐C originated from the northern Okinawa Trough and southwestern Jeju Island, respectively. Seasonal variations in NLIW propagation speed using historical CTD data revealed an increase in the speed from winter to spring and fall, peaking in summer due to strong stratification. Although spatial distribution varied by season, propagation was generally faster in the eastern region than in the western region attributed to deeper thermoclines and higher density gradients. During field observation in May 2015, the observed NLIWs had an amplitude of 5–6 m, a characteristic width of 380–450 m, southwestward propagating directions, and a speed of ∼0.54 m s−1. An empirical model, used to track and predict these waves, confirmed their generation locations from southwestern Fukue Island (Type‐B) and indicated fast arrival speeds, influenced by time‐varying stratification conditions during the stratification period. These findings highlight the impacts of varying background conditions on NLIW propagation and would facilitate their prediction.

Environmental influences on the size and recruitment of inland Cisco populations in three Minnesota Sentinel lakes

Abstract Objective Cisco Coregonus artedi are a pelagic coldwater fish that are widely distributed throughout many lakes across Canada and the northern Midwest and play an important role as forage for large piscivores. Cisco are sensitive to oxythermal stress caused by a combination of warm epilimnetic temperatures and hypolimnetic hypoxia during peak stratification periods and are at risk from stressors such as climate change and land use changes. We hypothesized that interannual variability in the amount of oxythermal habitat and prey resources were associated with observed differences in size structure and recruitment success of different Cisco populations. This study evaluated the relationship between characteristics of three inland (non-Laurentian Great Lakes) Cisco populations, including maximum size and age-0 density, with environmental and biological factors such as pelagic oxythermal habitat, zooplankton availability, and Cisco density and biomass over a 7-year time series. Methods Targeted, standardized, annual pelagic sampling was conducted from 2013 to 2019 using hydroacoustic sonar and vertical gill nets to sample Cisco, vertical net tows to sample zooplankton, and temperature and dissolved oxygen profiles to measure oxythermal habitat. Linear regression and mixed-effect models were developed for two selected response variables: upper 95th percent total length (mm) and standardized age-0 density (fish/ha-m3). Result Cyclopoid copepod densities explained the most variability in the observed size differences, while age-1+ Cisco biomass best explained the variability in the age-0 density response variable. Additionally, the number of growing degree-days at dissolved oxygen of 3.0 mg/L explained variability in both response variables. Conclusion Results from this study document the importance of zooplankton prey, oxythermal habitat, and internal population dynamics on Cisco size and recruitment. This information provides fisheries managers with insights on the characteristics of inland lake systems that influence variability in Cisco populations and how this effects the vulnerability of this relatively important forage species on gape-limited predatory fish.

Combining a Multi-Lake Model Ensemble and a Multi-Domain CORDEX Climate Data Ensemble for Assessing Climate Change Impacts on Lake Sevan.

Global warming is shifting the thermal dynamics of lakes, with resulting climatic variability heavily affecting their mixing dynamics. We present a dual ensemble workflow coupling climate models with lake models. We used a large set of simulations across multiple domains, multi-scenario, and multi GCM- RCM combinations from CORDEX data. We forced a set of multiple hydrodynamic lake models by these multiple climate simulations to explore climate change impacts on lakes. We also quantified the contributions from the different models to the overall uncertainty. We employed this workflow to investigate the effects of climate change on Lake Sevan (Armenia). We predicted for the end of the 21st century, under RCP 8.5, a sharp increase in surface temperature and substantial bottom warming , longer stratification periods (+55days) and disappearance of ice cover leading to a shift in mixing regime. Increased insufficient cooling during warmer winters points to the vulnerability of Lake Sevan to climate change. Our workflow leverages the strengths of multiple models at several levels of the model chain to provide a more robust projection and at the same time a better uncertainty estimate that accounts for the contributions of the different model levels to overall uncertainty. Although for specific variables, for example, summer bottom temperature, single lake models may perform better, the full ensemble provides a robust estimate of thermal dynamics that has a high transferability so that our workflow can be a blueprint for climate impact studies in other systems.

Investigating Taste and Odour Characteristics in a Drinking Water Source: A Comprehensive 3-Year Monitoring Study.

The monitoring of drinking water quality is a vital public health concern together with taste and odour (T&O) episodes, an emerging global problem causing a loss of public trust to the quality of water. Our objective was to monitor water quality of an important drinking water source and also the production dynamics of geosmin and 2-methylisoborneol (2-MIB) which cause taste and odour problems in the lake. The trophic status of the lake was classified as mesotrophic. 2-MIB was positively correlated temperature while geosmin was positively correlated with depth. Other physicochemical parameters related with water quality did not show significant correlation with geosmin and 2-MIB. The highest 2-MIB and geosmin concentrations were detected during the thermal stratification period in 2016 and 2018 by gas chromatography-mass spectrometry (GC-MS). Cyanobacteria and Actinobacteria were detected in geosmin & 2-MIB detected samples as potential taste and odour producers by PCR. Selected samples were analysed with metabarcoding and Planktothrix, Pseudanabaena, Cyanobium, Streptomyces, and Nocardioides were detected as potential geosmin & 2-MIB producers. Micrococcus, Rhodococcus, Acinetobacter, Comamonas, Novosphingobium, Sphingopyxis, Pseudomonas, Sphingomonas, Stenotrophomonas and Flavobacterium were identified as potential geosmin & 2-MIB degraders. The results highlighted the significant role of the autochthonous bacterial community, temperature and thermal stratification in the taste and odour dynamics of a drinking water source.

Backed pieces at Sharbithat SHA-10 (Sultanate of Oman)

Sharbithat 10 (SHA-10) was discovered in 2017 during the first extensive survey of the northern part of the Dhofar region. Located on a vast mesa surrounded by wadi deltaic branches and abundant sources of flint, SHA-10 is characterized by flint scatters, dwellings, and cairns. Initial test trenches revealed a single period stratification sequence, highlighting a rich marine faunal composition and intense flintknapping activity. The fishing equipment, typical of coastal sites from this period, accompanies a distinctive lithic industry comprising blades, backed pieces, and tanged points. Through the study of technological processes leading to the manufacture of these artefacts, analysis of the points’ morphological variability, and examination of the prevalence of backed bladelets, new hypotheses regarding coastal subsistence strategies and chronological issues have emerged. However, the potential co-occurrence of different facies complicates a chronological definition which can be partly clarified by radiocarbon data results. In this communication, we present a preliminary study of this unique assemblage, discuss its chrono-typological implications, and explore their significance within the framework of South Arabian prehistory.

75-Year dynamics of the Black Sea phytoplankton in association with eutrophication and climate change

Based on a database containing species records obtained from 1948 to 2022 and a hydrochemical database, long-term changes in the biomass and taxonomic structure of phytoplankton in the deep-sea basin of the Black Sea were analysed in the stratified period from April to October. Over 75years, a significant increase in concentration of nitrate, a weak increase in phosphate and a strong decrease in dissolved silicate were observed in the nutricline. The biomass of diatoms and total phytoplankton increased several times during the peak of eutrophication in 1991-1993, then decreased by the 2000s and has again shown an increasing trend in the last 15years. The number of species dominant in biomass has halved from the 1940s-60s to the 2010s. The primary beneficiaries were the large- and medium-celled diatoms Pseudosolenia сalcar-avis and Proboscia alata, as well as the coccolithophore Emiliania huxleyi, the main dominant species of the last decade. Most noticeable was the increase in the amplitude and duration of the regular annual May-July bloom of E. huxleyi. Over the past three decades, its biomass has increased by more than an order of magnitude, accounting for about 40% of the total phytoplankton biomass. Development of the large- and medium-celled diatoms, as well as the decrease in biomass of silicoflagellates, can be, at least partly, associated with the long-term decline in dissolved silicate in the upper layers. The trend towards a decrease in dinoflagellate biomass is probably associated with increased mixing intensity in the water column. Over the study period, the total phytoplankton biomass was positively related to nitrate stock in the water column. Short-term period (from one to several years) interannual variability was influenced predominantly by hydrophysical processes, primarily the intensity of winter convection. After cold winters with intense involvement of deep nutrients in the upper layers, the biomass of diatoms, coccolithophores and total phytoplankton increased. Thus, fluctuations in winter weather or local climate reduced or enhanced the effect of eutrophication, sometimes leading to the time gap between the peak in nitrate stock and phytoplankton biomass. The case of the Black Sea illustrates the complex pattern of the response of a marine ecosystem to the simultaneous impacts of anthropogenic and climate changes, leading to significant alterations in the functioning of the biological carbon pump.

Resolving spatially complex interactions between hydrodynamics and biogeochemical processing in a large reservoir with metalimnetic oxygen deficits

Resolving spatially complex interactions between hydrodynamics and biogeochemical processing in a large reservoir with metalimnetic oxygen deficits

Self-image, self-esteem, anxiety, and functional capacity in patients undergoing open-structure rhinoplasty

Rhinoplasty may improve negative psychological aspects, such as mild to moderate body dysmorphic disorder; however, the repercussions on the self-image and quality of life of patients after the procedure are unknown. To evaluate self-image, self-esteem, anxiety, and functional capacity of patients undergoing open-structure rhinoplasty. A primary, analytical, clinical, longitudinal, and prospective study was conducted, which included 30 female patients, aged between 18 and 50 years with elongated nose and nasal hump, who underwent open and structured rhinoplasty. All procedures were performed by a team from the Rhinology DCP/Unifesp. The Rosenberg Self-Esteem Scale -EPM, BDSS, BDD-YBOCS, SF-36, SRQ-20, and STAI (T/E) questionnaires were administered before the surgery and at 6, 12, and 18 months after surgery. The results showed statistically significant differences in the Rosenberg scale -EPM (p=0.017), BDSS (p<0.001), BDD (p=0.006), SF-36 (p=0.041), SRQ-20 (p=0.012), and STAI-T (p=0.001) scores in general analyses. Additionally, the statistically significant changes persisted in various stratified postoperative periods. In the qualitative analysis, there was only statistical significance for the classification of the BDSS score, where the "Absent" (absence of body dysmorphism) index increased from 70.0% in the preoperative state to 96.7% in 18 months postoperatively. The "Present" (presence of body dysmorphism) index fell from 30.0% to 3.3% in the same period (p=0.001). Open-structure rhinoplasty improved the patients' self-image, self-esteem, anxiety, and mental health.

Marine Fe cycling linked to dynamic redox variability, biological activity and post-depositional mineralization in the 1.1 Ga Mesoproterozoic Taoudeni Basin, Mauritania

Marine Fe cycling linked to dynamic redox variability, biological activity and post-depositional mineralization in the 1.1 Ga Mesoproterozoic Taoudeni Basin, Mauritania

The episodic dynamics of salt transport in the Waitematā Estuary, a well-mixed estuary in New Zealand

The episodic dynamics of salt transport in the Waitematā Estuary, a well-mixed estuary in New Zealand

The influence of mixing on seasonal carbon dioxide and methane fluxes in ponds

Inland waters are important sources of the greenhouse gases carbon dioxide (CO2) and methane (CH4). Ponds have amongst the highest CO2 and CH4 fluxes of all aquatic ecosystems, yet seasonal variation in fluxes remain poorly characterized, creating challenges for accurately estimating annual emissions. Further, ponds can exhibit a range of mixing regimes, yet the impact of mixing regimes on gas emissions remains unclear. Here, we assessed annual dynamics of CO2 and CH4 in four temperate ponds (Minnesota, USA) that varied in mixing regimes. The ponds ranged from annual sinks to sources of CO2 (−1 to 15 mol m−2 yr−1) and were all significant sources of CH4 (4.3–8.2 mol m−2 yr−1), with annual fluxes in CO2 equivalents of 1.8–4.1 kg CO2-eq. m−2 yr−1. Mixing regimes impacted CO2 and CH4 dynamics, as stratified periods were associated with more anoxia, greater accumulation of gases in the bottom waters, higher emissions of CH4, and lower fluxes of CO2. Ponds with stronger summer stratification also had increased CO2 and CH4 fluxes associated with fall turnover. Overall, the two ponds with the strongest stratification had higher annual fluxes (2.6, 4.1 kg CO2-eq. m−2 yr−1) compared to the two ponds that more frequently mixed (1.8, 2.2 kg CO2-eq. m−2 yr−1).

Thermal structure variations and influence factors in a subtropical reservoir, China: explanations from multiple research methods

ABSTRACT Revealing the subtle variations in thermal structure in a reservoir is crucial for accurately understanding the interaction between water and the carbon cycle. This study provides a detailed description of the thermal structure of Dalongdong reservoir, a representative subtropical stratified reservoir in Guangxi, China. It unveils the three stable state changes in water – mixing, microstratification, and stratification – along with their influencing factors. The study emphasizes air temperature (AT) as the primary factor influencing water temperature (WT) stability, followed by water level. Cross-correlation analysis shows that adjacent WTs experience a prolonged response hysteresis during the stratification period, while the mixing period exhibits a shorter hysteresis. Wavelet analysis revealed that AT and surface-layer WT exhibited a dominant oscillation period of 16–32 h. The periodicity of other water layers is not obvious. This framework can help to enhance our understanding of material cycles and protection of the water environment.

Seasonal deoxygenation in a shallow coastal embayment: The role of stratification and implications for water-quality monitoring.

Seasonal deoxygenation in a shallow coastal embayment: The role of stratification and implications for water-quality monitoring.

Planktonic foraminifera response to the azores high and industrial-era global warming in the central-western Mediterranean Sea

Planktonic foraminifera response to the azores high and industrial-era global warming in the central-western Mediterranean Sea