Oxygen Levels In Water Research Articles

Design of IoT-based monitoring system for temperature and dissolved oxygen levels in catfish aquaculture pond water

<span>One of the fish in Indonesian waters that has been successfully bred and cultivated is the catfish (Pangasius sp.). In catfish farming, there are several water quality factors that need to be considered, such as temperature and dissolved oxygen levels. Based on the existing description, it is very important to pay attention to the water quality of aquaculture ponds, especially temperature and dissolved oxygen levels for fish survival. This study aims to create an internet of things (IoT) based monitoring system for temperature and dissolved oxygen levels in catfish aquaculture pond water based on NodeMCU ESP8266. Monitoring system is using SEN0237 gravity analog dissolved oxygen sensor, DS18B20 sensor module, NodeMCU ESP8266, 20×4-character liquid-crystal display (LCD), micro secure digital (SD) card module, internet modem. Data from measurements of temperature and dissolved oxygen levels are stored online in the Adafruit.io database in the .csv format and on a micro secure digital (SD) card in the device in the .txt format. The lowest value of dissolved oxygen levels and temperature are 3.4 mg/L or 3.4 ppm and a temperature of 27.9 °C, respectively. Meanwhile, the highest value of dissolved oxygen levels and temperature are 4.6 mg/L or 4.6 ppm and temperature of 30.9 °C, respectively.</span>

Experimental investigation of dissolved oxygen improving aeration efficiency by hydraulic jumps

The dissolved oxygen (DO) level in water is vital for water quality and supporting aquatic life. Hydraulic jumps involve rapid flow changes from super-critical to sub-critical, visible at abrupt bed slope shifts, like at spillway bases in rivers or canals. The hydraulic jump efficiently mixes oxygen from air into water and offers a cost-effective method of aeration by entraining air bubbles in the stream to improve oxygen transfer compared to traditional systems. The objective of this experimental research is to investigate the aeration performance with hydraulic jump parameters and establish correlations crucial to measuring aeration (or transfer) efficiency. Relationships between transfer efficiency, jump height, jump length, sequent depth ratio, discharge, inlet Froude number, and channel bed slope were determined. To investigate the nature of such relationships, a series of experiments were conducted in a rectangular tilt flume to test the aeration performance of forced submerged hydraulic jumps with five different discharges and five different smooth bed slopes. The inlet Froude number before the jump varied from 2.18 to 8.23. Experimental observation confirms a positive relationship between transfer efficiency and jump control parameters. During experimentation, transfer efficiency was found to vary between 9.4 % and 34 %. This research includes estimating the optimal transfer efficiency due to hydraulic jumps, which can help hydraulic engineers in building structures that can revitalize any degraded stream.

Silver oxide integrated ionic polymer composite for wearable sensing and water purification

Integrating metal nanoparticles (NPs) with ionic polymer blends/composites showed immense interest for their potential in wearable sensors, soft robotic arms, flexible man-machine interfaces of biomedical devices, and water purification applications. However, conventional NPs attached ionic polymer composites exhibit limitations such as low sensitivity (ΔR/R), low total dissolved solids (TDS) reduction, and low phosphate (PO4-P) removal rate. Herein, ionic polymer composites (IPCs) using flower-shaped silver oxide (Ag2O) attached Poly (vinylidene fluoride) (PVDF)/ polyvinylpyrrolidone (PVP)/ionic liquid (IL) were designed and developed for wearable sensing and water purification. The IPCs demonstrated remarkably high ΔR/R values of 50, 10, and 3.5 corresponding to the wrist movement of 50°, finger movement of 180°, and chin movements respectively. The Ag2O-based IPC recorded a significant reduction of TDS from sewage water from 3405 ppm to 1035 ppm, elevated the dissolved oxygen (DO) levels in the sewage water from 1.2 mg/l to 6.8 mg/l, and removed approximately 87.38 % phosphate from sewage water. Due to the uniform distribution of Ag2O within pores of IPC, it demonstrated enhanced performance for wearable and wastewater treatment applications.

Offshore windfarm construction elevates metabolic rate and increases predation vulnerability of a key marine invertebrate

A global increase in offshore windfarm development is critical to our renewable energy future. Yet, widespread construction plans have generated substantial concern for impacts to co-occurring organisms and the communities they form. Pile driving construction, prominent in offshore windfarm development, produces among the highest amplitude sounds in the ocean creating widespread concern for a diverse array of taxa. However, studies addressing ecologically key species are generally lacking and most research is disparate, failing to integrate across response types (e.g., behavior, physiology, and ecological interactions), particularly in situ. The lack of integrative field studies presents major challenges to understand or mitigate actual impacts of offshore wind development. Here, we examined critical behavioral, physiological, and antipredator impacts of actual pile driving construction on the giant sea scallop (Placopecten magellanicus). Benthic taxa including bivalves are of particular concern because they are sound-sensitive, cannot move appreciable distances away from the stressor, and support livelihoods as one of the world's most economically and socially important fisheries. Overall, pile driving sound impacted scallops across a series of behavioral and physiological assays. Sound-exposed scallops consistently reduced their valve opening (22%), resulting in lowered mantle water oxygen levels available to the gills. Repeated and rapid valve adductions led to a 56% increase in metabolic rates relative to pre-exposure baselines. Consequently, in response to predator stimuli, sound-exposed scallops displayed a suite of significantly weaker antipredator behaviors including fewer swimming events and shorter time-to-exhaustion. These results show aquatic construction activities can induce metabolic and ecologically relevant changes in a key benthic animal. As offshore windfarm construction accelerates globally, our field-based study highlights that spatial overlap with benthic taxa may cause substantial metabolic changes, alter important fisheries resources, and ultimately could lead to increased predation.

How Often Should Microbial Contamination Be Detected in Aircraft Fuel Systems? An Experimental Test of Aluminum Alloy Corrosion Induced by Sulfate-Reducing Bacteria.

Microbial contamination in aircraft fuel-containing systems poses significant threats to flight safety and operational integrity as a result of microbiologically influenced corrosion (MIC). Regular monitoring for microbial contamination in these fuel systems is essential for mitigating MIC risks. However, the frequency of monitoring remains a challenge due to the complex environmental conditions encountered in fuel systems. To investigate the impact of environmental variables such as water content, oxygen levels, and temperature on the MIC of aluminum alloy in aircraft fuel systems, orthogonal experiments with various combinations of these variables were conducted in the presence of sulfate-reducing bacteria. Among these variables, water content in the fuel oil demonstrated the most substantial influence on the corrosion rate of aluminum alloys, surpassing the effects of oxygen and temperature. Notably, the corrosion rate of aluminum alloys was the highest in an environment characterized by a 1:1 water/oil ratio, 0% oxygen, and a temperature of 35 °C. Within this challenging environment, conducive to accelerated corrosion, changes in the corrosion behavior of aluminum alloys over time were analyzed to identify the time point at which MIC intensified. Observations revealed a marked increase in the depth and width of corrosion pits, as well as in the corrosion weight-loss rate, starting from the 7th day. These findings offer valuable insights for determining the optimal frequency of microbial contamination detection in aircraft fuel systems.

Construction of Conjugated Organic Polymers for Efficient Photocatalytic Hydrogen Peroxide Generation with Adequate Utilization of Water Oxidation.

The visible-light-driven photocatalytic production of hydrogen peroxide (H2O2) is currently an emerging approach for transforming solar energy into chemical energy. In general, the photocatalytic process for producing H2O2 includes two pathways: the water oxidation reaction (WOR) and the oxygen reduction reaction (ORR). However, the utilization efficiency of ORR surpasses that of WOR, leading to a discrepancy with the low oxygen levels in natural water and thereby impeding their practical application. Herein, we report a novel donor-bridge-acceptor (D-B-A) organic polymer conjugated by the Sonogashira-Hagihara coupling reaction with tetraphenylethene (TPE) units as the electron donors, acetylene (A) as the connectors and pyrene (P) moieties as the electron acceptors. Notably, the resulting TPE-A-P exhibits a remarkable solar-to-chemical conversion of 1.65% and a high BET-specific surface area (1132 m2·g-1). Furthermore, even under anaerobic conditions, it demonstrates an impressive H2O2 photosynthetic efficiency of 1770 μmol g-1 h-1, exceeding the vast majority of previously reported photosynthetic systems of H2O2. The outstanding performance is attributed to the effective separation of electrons and holes, along with the presence of sufficient reaction sites facilitated by the incorporation of alkynyl electronic bridges. This protocol presents a successful method for generating H2O2 via a water oxidation reaction, signifying a significant advancement towards practical applications in the natural environment.

Investigating the performance of a perforated pooled circular stepped cascade aeration system for intensive aquaculture

Aeration plays a crucial role in aquaculture to maintain adequate dissolved oxygen (DO) levels in water, which is essential for supporting aquatic life. However, traditional aeration systems such as paddlewheel aerators or diffused air aerators often come with high energy consumption, frequent maintenance, and greater operational costs. To address these challenges, this research paper presents the development and evaluation of a more sustainable and cost-effective aerator, named the perforated pooled circular stepped cascade aerator (PPCSC), for intensive aquaculture. Laboratory experiments were conducted in a masonry tank to assess the performance of the PPCSC aerator with different bottom radii (Rb) and discharges (Q). The results showed that the highest standard aeration efficiency (SAE) of 4.564 ± 0.6662 kg O2/kWh was achieved with a bottom radii (Rb) of 0.75 m and a discharge (Q) of 0.016 m3/s. A developed regression model was found to effectively evaluate the standard oxygen transfer rate (SOTR) and SAE for different Rb and Q values used in the PPCSC system. Both Rb and Q were found to significantly impact the SOTR and SAE of the PPCSC aerator. Overall, the PPCSC aerator is a promising option for small-scale tank-based intensive aquaculture due to its high performance and lower operational costs.

Analysis of Temperature, pH, and Electrical Conductivity of Water in Response to Taheri Consciousness Field 2

Water, as the most abundant molecule on Earth's surface and a vital component of living organisms, has always been the subject of investigation and analysis in the scientific community regarding its physicochemical properties and changes resulting from environmental variables. In previous studies on the effects of T-Consciousness Fields, changes in the pH and temperature of water as a result of exposure to these fields have been investigated. In this study, in addition to these two parameters, changes in the electrical conductivity of water molecules under the influence of T-Consciousness Field 2 have been examined, with the aim of finding a parameter of water that is more sensitive and responsive to T-Consciousness Fields. According to the results of this research throughout 8, 24, and 48 hours, changes in pH in the sample and control groups showed an increase, and temperature changes showed a decrease. Furthermore, changes in the electrical conductivity of water under the influence of T-Consciousness Field 2 were significant. To complement the current study, the examination of the levels of oxygen and carbon dioxide gases in pure water under the exposure of T-Consciousness Field 2 is on the agenda of the authors.

WATER QUALITY IN TEST PONDS: APPLICATION OF SAGO PULP-BASED CATFISH FEED IN UDAPI HILIR VILLAGE, MANOKWARI, WEST PAPUA

Research on water quality in test ponds based on the influence of the application of sago-based catfish food has been carried out in Udapi Hilir Village, Manokwari Regency. The effect of sago pulp composition was carried out on variations of rice bran: fish meal: sago pulp was 1:1:0.5, 1:1:1, 1:1:1,5, and rice bran: the fish meal was 1:1. This research explains the water quality of test ponds using physical and chemical parameter monitoring methods. The results of this study contain several chemical and physical parameters that exceed the quality standard threshold. The results of the proximate analysis showed that adding sago pulp provided a chemical value of the feed that was still following the recommended standards. The results of water quality tests carried out for 4 weeks showed an increase in TDS levels, without draining the test pool during the research. The average Nitrate (NO3 - ) has increased but is still below the quality standard of 10 mg/L. Nitrate (NO3 - ) concentrations are rising in all ponds for all treatments. Nitrate levels impact fish growth because they can lower water oxygen levels. Overall, the application of sago pulp as a raw material for catfish feed results in pond water quality that is still within the pond water quality standards so it has the potential as an alternative feed raw material.

The OptoReg system: a simple and inexpensive solution for regulating water oxygen.

This paper describes an optocoupler-based regulation apparatus for saturation manipulation of oxygen in water (OptoReg). This system enables control of solenoid valves for oxygen and nitrogen gases using a FireSting-O2 meter, an optocoupler box and an electronic switch box. The hardware components connect to a computer through Universal Serial Bus (USB) cables. The control software is free and has a graphical user interface, making it easy to use. With the OptoReg system, any lab with a computer running Microsoft Windows operating system and a 4-channel FireSting-O2 meter can easily and cheaply set up four independently controlled systems for regulating water oxygen levels. Here, we describe how to assemble and run the OptoReg system and present a data set demonstrating the high precision and stability of the OptoReg system during static acclimation experiments and dynamic warming trials.

Understanding the vulnerability of surface–groundwater interactions to climate change: insights from a Bavarian Forest headwater catchment

Headwaters play a crucial role in maintaining forest biodiversity by providing unique habitats and are important for the regulation of water temperature and oxygen levels for downstream river networks. Approximately 90% of the total length of streams globally originate from headwaters and these systems are discussed to be especially vulnerable to impacts of climate change. This study uses an integrated hydrological model (HydroGeoSphere) in combination with 23 downscaled ensemble members from representative concentration pathways (RCPs) 2.6, 4.5 and 8.5 to examine how climate change affects water availability in a headwater catchment under baseflow conditions. The simulations consistently predict increasing water deficits in summer and autumn for both the near (2021–2050) and far future (2071–2099). Annual mean water deficits were estimated to be 4 to 7 times higher than historical levels. This is mainly due to a projected reduction in precipitation inputs of up to – 22%, while AET rates remain similar to those observed during the historical reference period (1992–2018). The declining groundwater storage reserves within the catchment are expected to result in a significant decline in surface water availability during summer and autumn, with a reduction in mean annual stream discharge by up to 34% compared to the reference period. Due to declining groundwater levels, upstream reaches are predicted to become intermittent in summer leading to a reduction of the total stream flow length by up to 200 m. Findings from this study will enhance our understanding of future water availability in headwater systems and may aid in the development of effective management strategies for mitigating local impacts of climate change and preserving these vulnerable ecosystems.

Metabolomic Profiling Reveals Differences in Hypoxia Response between Far Eastern and Siberian Frogs.

Anoxia is a significant challenge for most animals, as it can lead to tissue damage and death. Among amphibians, the Siberian frog Rana amurensis is the only known species capable of surviving near-zero levels of oxygen in water for a prolonged period. In this study, we aimed to compare metabolomic profiles of the liver, brain, and heart of the Siberian frog exposed to long-term oxygen deprivation (approximately 0.2 mg/L water) with those of the susceptible Far Eastern frog (Rana dybowskii) subjected to short-term hypoxia to the limits of its tolerance. One of the most pronounced features was that the organs of the Far Eastern frog contained more lactate than those of the Siberian frog despite a much shorter exposure time. The amounts of succinate were similar between the two species. Interestingly, glycerol and 2,3-butanediol were found to be significantly accumulated under hypoxia in the Siberian frog, but not in the Far Eastern frog. The role and biosynthesis of these substances are still unclear, but they are most likely formed in certain side pathways of glycolysis. Based on the obtained data, we suggest a pathway for metabolic changes in the Siberian frog under anoxia.

The upper temperature and hypoxia limits of Atlantic salmon (Salmo salar) depend greatly on the method utilized.

In this study, Atlantic salmon were: (i) implanted with heart rate (fH) data storage tags (DSTs), pharmacologically stimulated to maximum fH, and warmed at 10°Ch-1 (i.e. tested using a 'rapid screening protocol'); (ii) fitted with Doppler® flow probes, recovered in respirometers and given a critical thermal maximum (CTmax) test at 2°Ch-1; and (iii) implanted with fH DSTs, recovered in a tank with conspecifics for 4 weeks, and had their CTmax determined at 2°Ch-1. Fish in respirometers and those free-swimming were also exposed to a stepwise decrease in water oxygen level (100% to 30% air saturation) to determine the oxygen level at which bradycardia occurred. Resting fH was much lower in free-swimming fish than in those in respirometers (∼49 versus 69beatsmin-1) and this was reflected in their scope for fH (∼104 versus 71beatsmin-1) and CTmax (27.7 versus 25.9°C). Further, the Arrhenius breakpoint temperature and temperature at peak fH for free-swimming fish were considerably greater than for those tested in the respirometers and given a rapid screening protocol (18.4, 18.1 and 14.6°C; and 26.5, 23.2 and 20.2°C, respectively). Finally, the oxygen level at which bradycardia occurred was significantly higher in free-swimming salmon than in those in respirometers (∼62% versus 53% air saturation). These results: highlight the limitations of some lab-based methods of determining fH parameters and thermal tolerance in fishes; and suggest that scope for fH may be a more reliable and predictive measure of a fish's upper thermal tolerance than their peak fH.

Monitoring the pH and temperature of IoT-based fish farming using Arduino

The Internet of Things (IoT) based intelligent Fish farming refers to the integration of various IoT devices and sensors into traditional fish farming practices to monitor and optimize various aspects of the fish farming environment such as water temperature, pH levels, oxygen levels, and feed schedules. This can help to improve the overall health and wellbeing of the fish, reduce waste, and increase productivity and efficiency. IoT devices can also be used to track the growth and health of individual fish, allowing farmers to make data-driven decisions about when to harvest or move fish to different tanks. The use of IoT technology can also help to detect potential health issues or environmental problems early on, allowing farmers to take preventative measures to minimize the impact on their fish. Overall, smart fish farming using IoT has the potential to revolutionize the way fish are farmed, making the process more sustainable, efficient, and profitable. The project focuses on an IoT-enabled smart fish farming system. In order to deal with them, the system is coupled with an irrigation system. Indonesia’s weather is erratic. This system's microcontroller is an Arduino ESP32. The temperature sensor DSb18B20 and the soil moisture sensor DF Robot are used to regulate the environment. Both a computer and a smartphone are used to display the results.

Development of a Platform for Monitoring the Levels of Dispersed Oxygen in River Components of a Water Supply Micro Basin Using Programmable Microcontrollers

The Internet of Things (IoT) has become widespread. Widely used worldwide, it already penetrates all spheres of life, and its symbiosis with the environment has become increasingly important and necessary. IoT in life sciences has gained much importance because it minimizes the costs associated with field research, shipments, and transportation of the sensors needed for physical and chemical measurements. This study proposes an IoT water monitoring system in real time that allows the measurement of dissolved oxygen levels in water at several monitoring points in a difficult-to-access location, the Pirapo River, in southern Brazil, responsible for supplying water to large urban centers in the region. The proposed method can be used in urban and rural areas for consumption and quality monitoring or extended to a modern water infrastructure that allows water providers and decision makers to supervise and make optimal decisions in difficult times. The experimental results prove that the system has excellent perspectives and can be used practically for environmental monitoring, providing interested parties with experiences acquired during the system implementation process and timely relevant information for safe decision making.

Murray cod waterhole woes

During bouts of prolonged drought and little to no river flow, waterholes are a haven for freshwater fishes. However, as humans divert more water for their own use and as global temperatures rise, these small bodies of water are increasingly vulnerable to climbing temperatures and low oxygen levels. Fortunately, some fishes are able to change quickly to cope with high temperatures, and occasionally these changes also help them do better with low oxygen levels. But size matters when it comes to dealing with these stressors. Big fish are thought to deal with low oxygen better than small fish, and small fish are thought to deal better with high temperatures, but all are likely to be vulnerable when both stressful circumstances occur simultaneously. To investigate how body size influences a fish's ability to tolerate both high heat and low oxygen, Darren McPhee, with researchers from the University of Queensland and the Queensland Department of Regional Development, Australia, turned to massive Murray cod – which can grow to the size of a giant panda (over 100 kg) – to find out how they deal with the combined threat.Working with fish ranging from 0.2 g to 3 kg, the team transferred the animals to water at temperatures mimicking a hot summer (28°C). After 4 weeks, all of the cod, regardless of size, increased the temperature at which they lose their balance (known as the upper thermal limit), indicating that the cod are able to deal with persistent high temperatures. But when the team tested the fish's abilities to remain upright at high temperatures as the water oxygen levels decreased, their ability to tolerate heat declined. Surprisingly, the fish's body sizes had an unusual impact on their ability to withstand high temperatures when their oxygen supply was restricted. As expected, when the fish had access to well-oxygenated water (100% and 50% oxygen saturation), the smaller animals coped better with high temperatures than the big fish. But this pattern flipped when the oxygen levels in the water were low (30% and 16% oxygen saturation), where the largest fish tolerated the high temperatures better than the smaller fish. Intriguingly, this didn't mean that the big fish were thermal tolerance champions. At the lowest oxygen level (16% oxygen saturation), the mid-sized fish coped best with the high temperatures.The scientists also tested how short-term and persistent exposure to different temperatures affected the cod's ability to survive low oxygen in several different ways. In the short term (less than 24 h), fish exposed to high temperatures breathed faster and lost their balance at an oxygen level twice as high as what they would normally handle. But when exposed to a high heat for 4 weeks, the responses to low oxygen weren't quite as drastic. Again, the largest cod were the least bothered by decreasing oxygen – not changing their breathing frequency and taking longer to lose their balance (unlike the little fish).Although Murray cod of all sizes demonstrated an amazing ability to cope with high temperatures in the lab, McPhee and colleagues also went into the wild to check the water quality of three Queensland waterholes that are much loved by the cod. The researchers found that the fish are living dangerously close to the edge – at the limit of the high temperatures and low oxygen levels that they can endure – especially during the summer. And, as the smallest cod are most vulnerable to the combined stress of high temperature and low oxygen, this slow-growing species is at genuine risk from catastrophic loss if their littlest ones succumb in the face of the deadly duo.

Hypoxia and Anoxia Tolerance in Diploid and Triploid Eastern Oysters at High Temperature

Increasing reliance on the use of triploid oysters to support aquaculture production relies on their generally superior growth rate and meat quality over that of diploid oysters. Reports of elevated triploid mortality have generated questions about potential trade-offs between growth and tolerance to environmental stressors. These questions are particularly relevant as climate change, coastal activities, and river management impact water salinity, temperature, nutrients, pH, and oxygen levels within key estuarine oyster growing areas. In particular, the co-occurrence of warm water temperatures and low dissolved oxygen concentration (DO) events are increasingly reported in estuaries, with potentially lethal impacts on sessile, oyster resources. To investigate potential differences in DO tolerance, diploid and triploid market-sized or seed oysters were exposed to continuous normoxia (DO > 5.0 mg L–1), hypoxia (DO < 2.0 mg L–1), and anoxia (DO < 0.5 mg L–1) at 28°C and their mortalities were monitored. The hemolymph of the market-sized oysters was collected to measure cellular and biochemical changes in response to hypoxia and anoxia, whereas their valve movements were also measured. In general, about half of market-sized oysters died within about 1 wk under anoxia (LT50: 5.7–8.9 days) and within about 2 wk under hypoxia (LT50: 11.9–19.4 days) with diploid oysters tending to die faster than triploid oysters. Seed oysters took longer to die than market-sized oysters under both anoxia (LT50: 9.5–12.1 days) and hypoxia (LT50: 21.8–25.0 days) with diploid oysters (LT50: 9.5–11.8 days) dying slightly faster than triploid oysters (LT50: 11.8–12.1 days) under anoxia. Hemolymph pH decreased and plasma calcium and glutathione concentrations increased with decreasing DO, with values under anoxia being different than those under normoxia. Hemocyte density was also lower under anoxia than under either normoxia or hypoxia. Overall, few differences in physiological responses to hypoxia and anoxia were found between diploid and triploid oysters suggesting that ploidy (2N versus 3N) had limited effect on the tolerance and response of eastern oysters to low DO.

The Miocene Climatic Optimum at the interface of epicontinental sea and large continent: A case study from the Middle Miocene of the Eastern Paratethys

The Miocene Climate Optimum (MCO) and the subsequent Miocene Climate Transition (MCT) are important biotic, environmental and geologic events. Here we address whether this holds true for the epicontinental Eastern Paratethys Sea (today's Black – Caspian Sea region). Two Tarkhanian – lower Chokrakian sequences of Middle Miocene age in the Kerch Peninsula were investigated using foraminifera, calcareous nannofossils, molluscs, fish otoliths, spores and pollen, oxygen and carbon stable isotopes and strontium isotope stratigraphy (SIS). Our results show that the marine environment during the Tarkhanian to early Chokrakian in the study area was characterized by open shelf conditions (near upper part of lower sublittoral zone), variable water column stratification and bottom water oxygen levels. Biostratigraphy and new SIS data suggest an age of >15.5 (∼16.0?) – 14.75 Ma for the Tarkhanian, which implies a considerably longer duration (> 0.75 Ma vs. 0.1 Ma) than was previously suggested. The maximum transgression seen in the middle Tarkhanian could be dated to ∼15.5–15.1 Ma and correlates with the highstand of sequence Bur 5/Lan 1 (15.2 Ma) and terminal phase of the MCO. The vegetation indicates a gradual change from subtropical humid (early Tarkhanian) to arid (early Chokrakian) conditions, which reflect the MCT. The climate change in the Eastern Paratethys occurred slightly earlier than in the Central Paratethys, possibly related to the existence of the large flat Eurasian continent.

Clasts derived from rhizocretions in shallow-marine Miocene clastic deposits of northern Hungary: an example of zombie structures

Disc- and cylindrical-shaped clasts of fine-grained calcareous and ferruginous rock, each with a central tunnel, occur in shallow marine brackish Miocene sandy deposits of the Egyházasgerge Formation in Hungary. Previously, these have been interpreted as enigmatic biogenic (?) structures. After field and laboratory examination and comparisons with sub-recent rhizoclasts in subsoils developed on Quaternary fine-grained deposits in SE Poland, they are re-interpreted as redeposited rhizocretions possibly washed out of the coeval continental deposits of the Salgótarján Lignite Formation. Most are fragmented and abraded. They are termed rhizoclasts and are presented as an example of zombie structures inherited from another environment where they played a different role. Such rhizoclasts can be considered as an indicator of the source of the clastic material transported from a vegetated landmass on which moderate or poorly drained soils develop and plant roots penetrate the fine-grained substrate. In such soils, iron was mobilized, then fixed by oxidation, as the water table and oxygen levels fluctuated.

High-resolution characterization of the development and decay of seasonal hypoxia in the Gulf of Riga, Baltic Sea

The Gulf of Riga is a shallow basin in the eastern Baltic Sea connected to the Central Baltic Sea via shallow straits. Seasonal oxygen depletion occurs in the deep layer of the gulf. We conducted hourly measurements of dissolved oxygen, temperature, and salinity in the deep layer (50 m) of the gulf and observed the full cycle of development and relaxation of hypoxia in 2021. Hypoxia (&amp;lt;2.9 mg l-1) first occurred on 27 June and was observed for 71 days until its complete decay on 22 October. Average oxygen decline of 0.10 mg l-1 d-1 from saturation in mid-April until mid-July and 0.04 mg l-1 d-1 onwards until the end of August were observed. This seasonal pattern was superimposed by short-term variability in time scales from hours to days and was probably caused by inertial oscillations, (sub)mesoscale processes, deep layer currents, and pycnocline movements. Ventilation events with a relatively low impact and duration of up to ten days occurred in the deep layer due to the inflows of the saltier water from the Central Baltic. The inflowed water originated from the upper layer in winter and the thermocline in summer and was almost saturated in oxygen. Mostly mixing with existing oxygen-depleted water in the Gulf of Riga, but also local consumption declined the oxygen levels in the inflow water before it arrived at the observing station. Monthly standard deviations in oxygen varied from 0.3 to 2.8 mg l-1 and illustrated the added value of Eulerian measurements to complement the conventional monitoring.