Surface Water Layer Research Articles

Depth and temperature profiles reflect individual differences in the daytime diving behaviours of pelagic thresher sharks

We used acoustic telemetry to investigate the roles of depth and temperature in the daytime foraging behaviours of 13 tagged pelagic thresher sharks by monitoring their fine scale vertical movements in the Philippines. Cumulatively, pelagic thresher shark dives traversed the entire water column where they encountered temperatures that ranged from 33°C at the surface to 12°C at 250 m depths throughout the day, but the movements of individuals varied in the extent of both their deep and shallow water limits. Dives were not synchronized to diurnal cycles, and periodicity reflected cycles of similar dives, the dives themselves, deviations, cruising, and individuality. Pelagic thresher shark movements between the warm surface layer and cooler waters below the thermocline (155 – 175 m) may reflect a common Alopiid strategy that balances maintaining tolerable ambient water temperatures with opportunities to search for and forage on spatially patchy distributions of prey.

Fluxes of settling sediment particles and associated mercury in a coastal environment contaminated by past mining (Gulf of Trieste, northern Adriatic Sea)

PurposeAs the result of historical mining at Idrija (Slovenia), mercury (Hg) contamination in the Gulf of Trieste (northern Adriatic Sea) is still an issue of environmental concern. The element has been conveyed into the coastal area by the Isonzo/Soča River inputs of freshwater and suspended particles for centuries. This research aims to investigate the occurrence of Hg bound to the settling sediment particles (SSP) in the coastal water and to assess the sedimentary Hg fluxes.MethodsSettling sediment particles were collected at four sites located in the innermost sector of the Gulf, a shallow and sheltered embayment where the accumulation of fine sediments is promoted. Six sampling campaigns were performed under different environmental conditions in terms of discharge from the Isonzo River and 12 sediment traps were installed in the upper and bottom water column for SSP collection. Settling sediment particles (SSP) were collected approximately every 2 weeks and analysed for grain size and total Hg.ResultsSettling sediment particles (SSP) consisted predominantly of silt (77.7 ± 10.1%), showing a concentration of Hg ranging overall between 0.61 and 6.87 µg g−1. Regarding the daily SSP fluxes, the minimum (7.05 ± 3.26 g m−2 day−1) and the maximum (92.4 ± 69.0 g m−2 day−1) values were observed under conditions of low and high river discharge, respectively. The daily Hg fluxes displayed a notable variability, up to an order of magnitude, both in the surface water layer (3.07–94.6 µg m−2 day−1) and at the bottom (11.3–245 µg m−2 day−1), reaching the maximum values following periods of high river flow.ConclusionsThe Isonzo River inputs of suspended particulate matter continue to convey Hg into the Gulf of Trieste, especially following river flood events, which represent one of the most relevant natural factors affecting the variations of the Hg flux in the investigated area.

Features of Electrodeless Electrochemical Reactions

The article deals with reactions occurring under the action of active particles formed during the flash of a corona electric discharge between a solid electrode and the surface of a liquid – electrochemical reactions without an electrode. Reactions take place in a thin surface layer of water, where there are no electrodes, so the reactions are called electrodeless. The electrodes are used only to excite the reaction zone and do not directly participate in the reaction. The oxidation of organic compounds to carbon dioxide and water occurs in an electrodeless reaction.

Marine top secrets: Ichthyoplankton in surface water uncover hidden knowledge on fish diversity and distribution

Most marine fish species exploit the upper water layers during their early life stages, thus accounting for a considerable component of neuston communities. During this period, the early life stages of fish are subjected to coastal or oceanic currents, and developed and dispersed to ultimate adult habitats according to their specific ecological requirements. Despite the ecological importance of these pelagic communities, knowledge about species assemblages of fish eggs and larvae, particularly in an oligotrophic sea is scarce. To overcome this knowledge gap and to evaluate the contribution of such communities to invasive biology, we collected neuston ichthyoplankton above the coastal, shelf and bathyal waters of the Eastern Mediterranean Sea (Israeli coast), an oligotrophic basin prone to a dynamic invasion of tropical biota. To obtain species-level knowledge of fish diversity, we used DNA-based methods that uncovered the presence of 137 species which is one third of the total local Osteichthyes fauna, evidencing that neuston ichthyoplankton can be significantly diverse. In addition, we showed that neuston communities can provide new knowledge regarding cryptic or rare species, and have a potential to contain new non-indigenous species, by documenting fish larvae of three unreported species for the Mediterranean Sea. Last, we posit that ichthyoplankton biomonitoring in surface water layer can provide a holistic perspective regarding fish biodiversity throughout the marine environment.

Zeolite as a Tool to Recycle Nitrogen and Phosphorus in Paddy Fields under Straw Returning Conditions

Excess nitrogen (N) caused by straw returning to paddy fields undergoing flooding irrigation deteriorates the water quality. The purpose of this research was to use both simulated field and pot experiments to explore a new approach using zeolite to recycle this excess N. The results from simulated field experiments in stagnant water showed N adsorption with different zeolite applications (25, 50, 75, 100, 125, and 150 g L−1). Pot experiments revealed how straw and reused zeolite applications affected the concentrations of ammonia N (NH4+-N), nitrate N (NO3−-N), total N (TN), and total phosphorus (TP) in the surface water and soil layers of the paddy field. Zeolite showed a strong ability to adsorb NH4+-N in wastewater, even in a simulated drainage ditch (100 g L−1 zeolite adsorbed 74% NH4+-N). The zeolite recycled from the drainage ditch was still able to reduce N concentration caused by straw decomposition in the surface water. Zeolite adsorption reduced the peak values of NH4+-N, TN, and TP by 30%, 19%, and 5%, respectively. Based on these findings and conventional field designs, the use of 20 t ha−1 zeolite in the field is effective for recycling N and P. This research provides a sustainable development method to mitigate the water quality deterioration caused by straw returning to the field.

Vertical and seasonal variations in biofilm formation on plastic substrates in coastal waters of the Black Sea

Plastic contamination of the marine environment is an increasing concern worldwide. Therefore, it is important to understand the kinetics of biofilms on plastics to study their behavior, fate, and transport pathways in the ocean. In this study, the vertical and seasonal variations in biofouling formation on transparent polyethylene terephthalate (PET) plastic fragments in the Southwest Crimea coastal waters of the Black Sea were investigated. Biofilms were identified in the transient light as ‘dark spots’ on the plastic surface, for which the numbers, size, and area were measured using specialized software. The rate of biofouling in the surface water layer was lower than those found in the middle and near-bottom water column, which could be due to a damaging effect of turbulent mixing on the biofilm. The highest rates of biofouling and diverse community were observed during the summer. The epibiotic assembly was represented by diatoms (11 taxa), dinoflagellates (3 taxa), green algae, filamentous cyanobacteria, small flagellates, and ciliates. Significant differences between the biofouling rates observed in different seasons made it difficult to estimate the period of time the plastic substrate has been in the marine environment. It was proposed to use the green alga Phycopeltis arundinacea (Montgn) De Tender et al., 2015 as a bioindicator to study the age of the biofouling community. Discoid thalli were identified at all stages of colonization of the plastic fragments in different seasons. Results obtained in this study demonstrate that biofouling organisms may be good model organisms in revealing age of biofilm formation and longevity of plastic debris in the ocean. Consequently, it is proposed that such biofouling organisms could be used as target species to monitor the biodegradation of plastic debris.

Examples of the Water Dynamics Influence on the Spatial Distribution of Chlorophyll a Fluorescence Intensity in the Surface Layer of the Barents and Norwegian Seas

The influence of water dynamics on the spatial distribution of chlorophyll a fluorescence intensity in the surface layer of the Barents and Norwegian Seas, obtained during the 80-th cruise of the R/V “Akademik Mstislav Keldysh” using the flow-through measuring complex in August 2020, was demonstrated. The divergence of the current velocity field, calculated according to reanalysis data, was chosen as a parameter describing the dynamics of water masses. The application of the sliding correlations method allowed us to identify areas of the track with positive and negative correlations between the values of divergence and chlorophyll a fluorescence intensity. It is shown that a positive correlation is formed as a result of the vertical movement of the water surface layer, a negative one — may be a consequence of the water masses advection and the daily changes of the values of photosynthetically active radiation. The part of obtained results is confirmed by satellite data on the spatial distribution of chlorophyll a concentration.

ВЛИЯНИЕ МАССОВОГО РАЗВИТИЯ ЦИАНОБАКТЕРИЙ НА ФОРМИРОВАНИЕ КАЧЕСТВА ВОДЫ КУЙБЫШЕВСКОГО ВОДОХРАНИЛИЩА (ПРОБЛЕМА И ПУТИ РЕШЕНИЯ)

The process of mass development of cyanobacteria has a negative impact on the ecological state and water quality of the reservoirs of the Volga-Kama cascade, which are used for drinking water supply, fisheries and recreation. The main goal of the research is to assess the impact of the mass development of cyanobacteria on the formation of water quality using the example of the Kuibyshev reservoir in the context of global warming. Comprehensive observations were carried out in the period 2001-2021. on the largest in Europe Kuibyshev reservoir with seasonal, weekly and daily regime of water line regulation. The research results show that during the period of "water bloom" organic water pollution increases. So permanganate oxidation in summer exceeds the permissible value by 1.5-2.0 times, which creates problems in providing the population with high-quality drinking water. The mass development of cyanobacteria disrupts the oxygen regime of the reservoir. The seasonal variability of the dissolved oxygen concentration includes four periods, which differ in the different directions of the processes of formation of the oxygen regime. Within the year, two minima of the dissolved oxygen content are observed: winter and summer. In the summer minimum, the concentration of dissolved oxygen decreases to critical values, and is 4-5 mg/dm3. The mass development of cyanobacteria has a significant influence on the formation of the summer oxygen minimum. As a result of photosynthetic aeration, a thin surface layer of water supersaturated with oxygen is formed, which disrupts the process of oxygen absorption from the atmosphere in a significant part of the reservoir water area. Under conditions of growing nutrient load and global climate warming, the intensity and scale of the process of mass development of cyanobacteria in the Kuibyshev reservoir will only increase, which will lead to a further increase in oxygen deficiency, deterioration of water quality and the emergence of water use risks.

Changes in Hormonal Status of Aboriginal Fishes under the Impact of Agricultural Runoffs

Changes of cortisol, triiodothyronine, and thyroxine content in the blood plasma of perch, ruff, rudd and bleak under the impact of agricultural runoff from the adjacent territories to the water bodies were studied. Under the long-term exposure to the contaminated water, the weight and size of fish their growth rates specimens significantly decreased. The hormonal responses to the polluted waters impact are species-specific and partly depend on the ecological features of the species. Under the chronic impact of the polluted water, the cortisol content in blood plasma decreases and triiodothyronine content increases as compared to the control. The fishes occurring in the surface water layers create the thyroxine reserve in blood, and fishes which prefer the near-bottom layers use it to increase the triiodothyronine content. After treatment of the fields close to the reservoir with pesticides, the ruff and rudd develop the active stress reaction, the cortisol and thyroxine content in blood significantly increases. According to the considered indicators, the bleak is the most resistant to agricultural runoffs or possesses the ability to avoid toxic water pollution.

A Unique Application Methodology for the Use of Phosphorus Inactivation Agents and Its Effect on Phosphorus Speciation in Lakes with Contrasting Mixing Regimes

The efficiencies of the restoration of two lakes of varied morphometries and trophic states—meromictic, hypertrophic Lake Klasztorne Małe, and dimictic, eutrophic Lake Klasztorne Duże—with the use of the phosphorus inactivation method with sequential application of iron and aluminum compounds have been compared. The total dose of the agents applied for Lake Klasztorne Małe was 38 tons of PAX 18 (aluminum polychloride) and 14 tons of PIX 111 (iron chloride), and for Lake Klasztorne Duże, it was 74 tons of PAX 18 and 46 tons of PIX 111. After the application of the compounds, better efficiency of phosphate removal from the surface water layers was obtained in the case of the dimictic, eutrophic Lake Klasztorne Duże. The use of two doses of compounds did not lead to complete precipitation of phosphates from the bottom water layers of either lake. It is noteworthy that in the case of both lakes, inhibition of the internal loading process was observed. The obtained results for the Klasztorne lakes showed that the use of two types of compounds makes it possible to reduce the cost of restoration, and moreover, the dosing of iron salts in the coastal areas of the lakes ensures a higher level of ecological safety.

Dynamics of organic matter in the changing environment of a stratified marine lake over two decades

The marine lake (Rogoznica Lake), which fluctuates between stratified and holomictic conditions, is a unique environment on the eastern Adriatic coast affected by environmental changes. These changes are reflected in the warming of the water column, the apparent deoxygenation of the epilimnion, and the accumulation of organic matter (OM), toxic sulfide, and ammonium in the anoxic hypolimnion. Since the early 1990s, the volume of anoxic water has increased as the chemocline has moved to the surface water layer. A trend toward enrichment of refractory dissolved organic carbon (DOC) was observed in the anoxic hypolimnion, while a decreasing trend was observed in the oxic epilimnion in the spring DOC. At the same time, the most reactive surface-active fraction of DOC showed the opposite trend. In addition, there is evidence of accumulation of particulate organic carbon (POC) in the water column, followed by an increase in the fraction of POC in total organic carbon (TOC).On a multi-year scale (1996–2020), this work presents a unique time series of the dynamics of OM in the stratified marine system, showing a significant change in its quantity and quality due to climate and environmental variability. DOC-normalized surfactant activity is shown to be a good indicator of environmental change.

Assessment of the water quality of the Volga River in the area of the Podnovsky roadstead of oil tankers for nitrogen-containing compounds

In connection with the long stay of ships in the roadsteads and the influence of pollutants on the electrical conductivity of water and the corrosion rate of structural elements of the vessel, the article assesses the quality of the water of the Volga River in the area of ​​the Podnovsky roadstead of oil tankers. The purpose of this study is to assess the content of nitrogen-containing substances in the surface and bottom layers of the Volga River in the area of ​​​​the Podnovsky raid of oil tankers and the discharge of wastewater from the Nizhny Novgorod aeration station to determine the significance of the impact of its activities on the pollution of the water use facility. In the background section, an excess of the maximum permissible concentration of ammonium nitrogen was found to be almost four times higher. In the control section, there is a significant increase in ammonium nitrogen relative to the background by 34.5%. The maximum concentrations of ammonium nitrogen are found below the wastewater discharge in the surface water layer in the range of 1.8 - 1.3 maximum allowable concentrations. The maximum concentration of nitrites exceeded the maximum permissible value by 4.8 times.

Carbonaceous Materials Porosity Investigation in a Wet State by Low-Field NMR Relaxometry.

The porosity of differently wetted carbonaceous material with disordered mesoporosity was investigated using low-field 1H NMR relaxometry. Spin−spin relaxation (relaxation time T2) was measured using the CPMG pulse sequence. We present a non-linear optimization method for the conversion of relaxation curves to the distribution of relaxation times by using non-specialized software. Our procedure consists of searching for the number of components, relaxation times, and their amplitudes, related to different types of hydrogen nuclei in the sample wetted with different amounts of water (different water-to-carbon ratio). We found that a maximum of five components with different relaxation times was sufficient to describe the observed relaxation. The individual components were attributed to a tightly bounded surface water layer (T2 up to 2 ms), water in small pores especially supermicropores (2 < T2 < 7 ms), mesopores (7 < T2 < 20 ms), water in large cavities between particles (20−1500 ms), and bulk water surrounding the materials (T2 > 1500 ms). To recalculate the distribution of relaxation times to the pore size distribution, we calculated the surface relaxivity based on the results provided by additional characterization techniques, such as thermoporometry (TPM) and N2/−196 °C physisorption.

Dissolved Organic Matter of the Surface Water Layer of Gelendzhik Bay in September 2021 According to Fluorimetry and Lidar Measurements

Dissolved Organic Matter of the Surface Water Layer of Gelendzhik Bay in September 2021 According to Fluorimetry and Lidar Measurements

Efficient simulation of stochastic seismic response of long-span bridges in river valleys using hybrid BEM-FEM

Determining ground motions is essential for seismic analysis of long-span bridges located at complex sites. However, there is a lack of earthquake records for local site conditions. Thus, this study focused on the effect of local site conditions on the stochastic response of long-span high-pier rigid frame bridges crossing a valley with an overlying water layer. For this purpose, a hybrid boundary element and finite element method (BEM-FEM) is proposed to investigate the stochastic seismic response of long-span bridges at such a complex site. First, a simulation method for 3-D spatially varying ground motions ascribed to wave scattering from irregular surface topography, sedimentary soil, and water layers was established based on the BEM combined with the spectral representation method. Furthermore, the statistical properties of the bridge response were explored based on the FEM and Monte Carlo simulations. The advantage of this work is that it reveals how the seismic wave propagation in this particular valley topography and water layer affects the stochastic response of the bridge considered. Moreover, the results indicate that seismic wave scattering leads to a significant energy redistribution of the input waves in the tri-directions related to the surface location, and a decrease in the coherency loss functions at all frequencies. Owing to this change, the peak ground accelerations (PGAs), bridge response means, and response variability are doubled. The beneficial effect of the water layer on the PGAs is weakened, while the adverse effect of hydrodynamic pressure dominates. The parameter analysis results demonstrate that a 10-m-deep sedimentary soil layer produces a 47% increase in the internal force of the pier bottom. The solid-liquid dynamic coupling effect should be accurately quantified for bridges located at saturated sites. Considering the local site conditions, the coefficient of variation (COV) of the response of the pier top exceeded 0.3, indicating strong randomness.

ПРОСТРАНСТВЕННО-ВРЕМЕННАЯ ИЗМЕНЧИВОСТЬ ГИДРОХИМИЧЕСКИХ ХАРАКТЕРИСТИК В ПОВЕРХНОСТНОМ СЛОЕ ВОД ТРОПИЧЕСКИХ ШИРОТ АТЛАНТИЧЕСКОГО ОКЕАНА

The work is devoted to the modern distribution of hydrochemical parameters in the surface layer of waters of tropical latitudes of the Atlantic Ocean. The materials were collected based on the results of two expeditions onboard the R/V “Academik Mstislav Keldysh” – AMK 79 (2019–2020) and AMK 87 (2021–2022). Four longitudinal transatlantic sections were considered. The hydrochemical characteristics of the Canary upwelling areas, the zones of aerosol transport from the desert regions of Africa, the areas of influence of the river discharge of the Rio de la Plata are described in detail.

Modeling and Prediction of Environmental Factors and Chlorophyll a Abundance by Machine Learning Based on Tara Oceans Data

It is of great theoretical and practical significance to understand the inherent relationship and evolution patterns among various environmental factors in the oceans. In this study, we used scientific data obtained by the Tara Oceans Project to conduct a comprehensive correlation analysis of marine environmental factors. Using artificial intelligence and machine learning methods, we evaluated different methods of modeling and predicting chlorophyll a (Chl-a) concentrations at the surface water layer of selected Tara Oceans data after the raw data processing. Then, a Pearson correlation and characteristic importance analysis between marine environmental factors and the Chl-a concentrations was conducted, and thus a comprehensive correlation model for environmental factors was established. With these obtained data, we developed a new prediction model for the Chl-a abundance based on the eXtreme Gradient Boosting (XGBoost) algorithm with intelligent parameter optimization strategy. The proposed model was used to analyze and predict the abundance of Chl-a abundance of TOP. The obtained predicted results were also compared with those by using other three widely-used machine learning methods including the random forest (RF), support vector regression (SVR) and linear regression (LR) algorithms. Our results show that the proposed comprehensive correlation evaluation model can identify the effective features closely related to Chl-a, abundance, and the prediction model can reveal the potential relationship between environmental factors and the Chl-a concentrations in the oceans.

Application of concentration and 2-dimensional stable isotope measurements of methane to constrain sources and sinks in a seasonally stratified freshwater lake

Methane (CH4) emissions from aquatic systems have recently been comprised to account for up to 50% of global CH4 emissions, with lakes representing one of the largest CH4 sources within this pool. However, there is large uncertainty associated with CH4 emissions from freshwater environments to the atmosphere, because of a lack of understanding in the spatial and temporal dynamics of CH4 sources and sinks, as well as underlying mechanisms and processes. In this study, we investigated the concentrations and stable carbon (δ13C-CH4) and hydrogen (δ2H-CH4) isotope composition of CH4 in a small eutrophic lake (Lake Willersinnweiher) with seasonal stratification and its spatial and temporal variation. We found that while supersaturation of CH4 in the entire water column was present throughout the whole year, the isotopic composition of CH4 in sediment and water column varied depending on lake stratification, physiochemical conditions, and lake depth. During the stratification period, isotopic characteristics of pelagic surface water CH4 differed from littoral and sedimentary CH4, suggesting likely mixing of CH4 from different sources including vertical and lateral input as well as groundwater input and potentially oxic methane production in the mixed surface water layer. Aerobic CH4 oxidation indicated by a strong increase in both δ13C-CH4 and δ2H-CH4 values at the bottom of the oxycline was found to significantly reduce upward migrating CH4 released at the sediment-water interface. In the sediment, stable isotope characteristics of CH4 showed an increasing dominance of the acetoclastic CH4 formation pathway from the pelagic towards the littoral area. Furthermore, the occurrence of sulfate-dependent anaerobic methane oxidation in the sediment was suggested by an increase in δ13C-CH4 and δ2H-CH4 values. During the mixing period, the isotopic CH4 composition of the water column was distinctively less negative than during the stratification period potentially resulting from a greater impact of groundwater CH4 input compared to the stratification period. Our findings implicate that the application of concentrations and dual isotope measurements of CH4 is a promising approach for constraining CH4 sinks and sources in Lake Willersinnweiher and potentially other small lakes to clearly disentangle the complex CH4 dynamics in lakes both spatially and seasonally.

From inshore to offshore: distribution of microplastics in three Italian seawaters

A comprehensive understanding of the concentration of microplastics (MPs) in seawaters is essential to implement monitoring programs and understand the impacts on ecosystems, as required by the European legislation to protect the marine environment. In this context, the purpose of this study is to investigate the composition, quantity, and spatial distribution of microplastics from coastal to offshore areas in three Italian seawaters. In addition, the distribution of microplastics between surface and subsurface water layers was analyzed in order to better understand the dynamics of MPs in the upper layers of the water column. A total number of 6069 MPs (mean total concentration of 0.029 microplastics · m−2) were found to be heterogeneous in type, shape, and color. In general, MPs concentrations decrease with coastal distance, except when environmental forcings are predominant (such as sea currents). Moreover, the amount of surface MPs was almost four times that of subsurface microplastics, which consisted mostly of fibers. In light of these results, it becomes clear how critical it is to plan remediation actions and programs to minimize microplastic accumulations in the sea.

Characteristics of the Image System based on Photon Density Waves in Observing Underwater Objects through a Waved Surface

The wavy surface effect on the resolution of optical imaging systems employing narrow modulated probing beams is studied. Relations are formulated connecting the complex amplitudes of the photon density waves (propagating through the wavy interface and the water layer) to the main parameters of the problem. These relations consider the finite waves height and the change in the photon trajectory length due to random refraction of rays upon entering the water. The optical transfer function of the wavy surface and the beam scattering function averaged over the ensemble of surface waving realizations are introduced. The dependences of these functions on the surface waves integral parameters, namely, the elevations and slopes dispersions, are examined. The contributions of surface waving and water layer to the generation of optical transfer functions and to the overall signal level from an underwater object when it is imaged using photon density waves are estimated. It is shown that in a certain range of depths, spatial frequencies, and illumination beam modulation frequencies, the systems employing photon density waves can demonstrate advantages over the systems with stationary illumination.