Dissolved Oxygen Measurements Research Articles

Noise Reduction of Amperometric Electrochemical Sensor using Current Compensation on Transimpedance Amplifier for Dissolved Oxygen Measurement

In this paper, a study of noise reduction of an electrochemical sensor is presented. This study is initiated based on the fact that the signal from the electrochemical sensor has quite high noise. The current signal from the sensor is very weak and noisy due to high impedance and complex process on the sensor and measured media such as a solution of dissolved oxygen. The current is usually converted using a transimpedance amplifier with high voltage-to-current ratio by a feedback resistance, which usually also produces large noise due to high feedback resistance value. This will contribute to an additional noise to the natural noise of the sensor and measured media, causing more noisy result. A modified transimpedance amplifier is proposed to reduce the noise from the sensor and converter to increase signal-to-noise ratio. The modification employs a current compensation, so that the current noise is suppressed at the converter input. The noise and signal measurements at the output of the compensated transimpedance amplifier show noise reduction compared to the standard transimpedance amplifier and measurement error reduction of the measured dissolved oxygen down to 0.89%.

Carbon microspheres prepared from soluble starch hydrothermal carbonization for extending thermal stability of water-based drilling fluid

This study employed hydrothermal carbon microspheres (HCMs) as high-temperature stabilizers in drilling fluids. The HCMs were synthesized through a green hydrothermal carbonization method, using soluble starch as the precursor. The impact of HCMs on the thermal stability of xanthan, polyanionic cellulose and synthetic polymer solutions was assessed by comparing their rheological changes before and after thermal aging. The rheology and filtration properties of a polymer-based drilling fluid in the presence of HCMs were recorded before and after dynamic thermal aging at various temperatures for 16 h and static thermal aging at 200 °C for 96 h. The results demonstrated that HCMs effectively maintained stable rheology and low filtration loss following dynamic hot rolling at various temperatures and prolonged static thermal aging, surpassing the performance of conventional Na2SO3 and nano-SiO2 stabilizers. Mechanistic studies, including dissolved oxygen measurements, free radical detection, and cryo-scanning electron microscopy observations, revealed that HCMs can consume dissolved oxygen, scavenge free radicals, and physically crosslink polymers. This process prevents polymer thermo-oxidative degradation and ensures the stability of the drilling fluid. HCMs are novel, stable, sustainable, and highly effective high-temperature stabilizers for water-based drilling fluids. This study introduces a new application of biomass-derived hydrothermal carbonaceous materials for high-temperature drilling.

Acoustic measurements of photosynthetically formed gas bubble distributions in Posidonia oceanica seagrass meadows

The formation of gas bubbles on seagrass leaves commonly occurs during periods of high productivity in many aquatic ecosystems. Gas bubbles produced by seagrass meadows and subsequently released to the atmosphere can be a major component of primary production that is not quantified by measurements of dissolved oxygen. Acoustic propagation measurements have been explored as a possible tool for estimating photosynthetically relevant properties in situ. However, a lack of knowledge of bubble densities and size distributions has hindered acoustic attenuation as a quantitative measurement technique. Here we explore using measurements of acoustic backscattering from gas bubbles in and above Posidonia oceanica seagrass meadows as a more direct method for estimating bubble densities and size distributions. Acoustic backscattering data for this study was collected in September 2023 in Biodola Bay, Elba Island, Italy, using 1i–16 kHz linear frequency modulated pulses. Inversions of the broadband acoustic data yielded log-normal bubble size distributions with mean sizes between 0.4 and 0.5 mm in agreement with previously reported values. Estimated bubble densities yielded predicted attenuations in line with those found by propagation experiments. Results demonstrate the possible use of direct acoustic backscattering measurements as a supplement to dissolved oxygen measurements to better estimate rates of gas production which in turn can be used to better understand seagrass ecosystem properties, such as productivity and health.

Photosynthetic nano fibers: Living microalgae packaging into polyvinyl alcohol nanofibers using an electrospinning method

AbstractAlthough microalgae are often studied for their biochemical extracts, utilizing them in a viable state opens new avenues for sustainable oxygenation in various systems. This study addresses the challenges of maintaining system homeostasis and presents an effective method for immobilizing live microalgae within poly(vinyl alcohol) (PVA) nanofibers using electrospinning technology. Characterization techniques, including scanning electron microscopy (SEM), fluorescence microscopy, Fourier‐transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC), were used to validate successful immobilization. Rheological studies were performed to investigate the influence of microalgae on the fiber morphology. Changing the PVA concentration, the fiber diameter could be regulated between 150 and 650 nm in the spinnable range. The addition of microalgae to the solution increased the viscosity of the prepared solution and reduced the resulting fiber diameter by approximately 2/3. Our results show that PVA nanofibers effectively encapsulate living microalgae and allow for sustained transport of nutrients and metabolites. The photosynthetic efficacy of the encapsulated microalgae was evaluated using dissolved oxygen measurements and showed two times higher rates of oxygen production and consumption compared with a film‐based approach. Our results show that PVA nanofibers effectively encapsulated living microalgae and allowed for the sustained transport of nutrients and metabolites. This innovative methodology provides a robust platform for immobilizing living microorganisms, with broad implications for applications ranging from regenerative medicine to sustainable agriculture.

Drift Characteristics of Sea-Bird Dissolved Oxygen Optode Sensors

Abstract The Sea-Bird 63 dissolved oxygen optode sensors used on various oceanographic platforms are known to drift over time. Corrections for drift are necessary for accurate dissolved oxygen measurements on the time scale of months to years. Here, drift on 14 Sea-Bird 63 dissolved oxygen optode sensors deployed on Spray underwater gliders over 5 years is described. The gliders with oxygen sensors were deployed regularly for 100-day missions as part of the California Underwater Glider Network (CUGN). A laboratory two-point calibration was performed on the oxygen sensor before and after glider deployment. Sensor drift during 100-day deployments was larger than during 100-day storage periods. Sensor behavior is modeled with a gain that asymptotically approaches 1.090 ± 0.005 with an e-folding time scale of 3.70 ± 0.361 years. At zero oxygen concentration, the sensor consistently reads around 3 μmol kg−1; a negative offset term is used in addition to the gain to correct the sensor oxygen. The correction procedure removes the error due to long time drift, one of the major sources of error, with an uncertainty of 0.5% (0.9% including outliers) or 0.5 μmol kg−1 depending on concentration, which improves the accuracy of the Sea-Bird 63 although uncertainty from other sources of error including the initial factory calibration and the sensor response time remain. Suggested procedures for implementing a two-point calibration procedure in the laboratory are discussed. Calibrations must be considered starting 6 months after initial factory calibration to keep error from sensor time drift under 1%. Significance Statement Dissolved oxygen measurements are widely used in oceanography. The optode sensors used to measure dissolved oxygen are known to drift over time. Here, the characteristics of drift for the oxygen optode sensor from Sea-Bird Scientific are described using a two-point calibration at zero and full saturation. The calibration procedure can be applied to oxygen optode sensors deployed on a variety of platforms when it is impractical to complete a multipoint calibration.

Observing the full ocean volume using Deep Argo floats

The ocean is the main heat reservoir in Earth’s climate system, absorbing most of the top-of-the-atmosphere excess radiation. As the climate warms, anomalously warm and fresh ocean waters in the densest layers formed near Antarctica spread northward through the abyssal ocean, while successions of warming and cooling events are seen in the deep-ocean layers formed near Greenland. The abyssal warming and freshening expands the ocean volume and raises sea level. While temperature and salinity characteristics and large-scale circulation of upper 2000 m ocean waters are well monitored, the present ocean observing network is limited by sparse sampling of the deep ocean below 2000 m. Recently developed autonomous robotic platforms, Deep Argo floats, collect profiles from the surface to the seafloor. These instruments supplement satellite, Core Argo float, and ship-based observations to measure heat and freshwater content in the full ocean volume and close the sea level budget. Here, the value of Deep Argo and planned strategy to implement the global array are described. Additional objectives of Deep Argo may include dissolved oxygen measurements, and testing of ocean mixing and optical scattering sensors. The development of an emerging ocean bathymetry dataset using Deep Argo measurements is also described.

The Efficiency of Indigofera Leaves Meal Hydrolysate Utilization on Growth Performance of Leptobarbus hoevenii

This study was conducted to evaluate the efficacy of indigofera leaves meal hydrolysate (ILMH) on growth Leptobarbus hoevenii growth. This study employed five dietary treatments with varying levels of ILMH. Cellulase enzymes were used to hydrolyze Indigofera leaf meal, which was then combined with other feed ingredients. Three replicates of feed without ILMH, 10% ILMH, 20% ILMH, 30% ILMH, and 35% ILMH were included in the treatment-examination feed. Average initial fish weight was 1.27±0.01 g, and initial length was 4.28±0.07 cm. Weight observation was also conducted every two weeks. After six weeks of rearing, survival, final biomass, specific growth rate, and feed efficiency were observed. At the beginning and the end of maintenance, temperature, pH, and dissolved oxygen measurements were taken to determine the water's quality. Results that that the utilization of ILMH in L. hoevenii feed could substitute the use of soybean meal for 10-35% of the feed. Among all treatments, 10% ILMH-containing feed resulted in the highest growth and feed efficiency. This treatment had a 100% survival rate, a 1.78±0.05% specific growth rate, and a 53.28 ± 1.59% feed efficiency. According to the findings of this study, the utilization of 10% hydrolysate of indigofera leaf meal in feed was effective in enhancing L. hoevenii’s growth performance. Keywords: Efficiency, indigofera leaves, Leptobarbus hoevenii, hydrolysate, growth

Analysis Of Water Quality Conditions In Pearl Oyster (Pinctada maxima) Hatcheries in Karangasem Bali

Indonesia has a high potential for pearl oyster farming due to its diverse marine habitats, warm waters, and abundant supply of seaweed, which is the preferred food for pearl oysters. Indonesia is home to several species of pearl oysters, including the Pinctada maxima, which are prized for their large size and the quality of their pearls. Water quality plays a crucial role in the cultivation of Pinctada maxima. Factors such as temperature, pH, salinity, dissolved oxygen levels, and the presence of pollutants and pathogens can all impact the health and survival of Pinctada maxima. In addition to feed quality and seed availability, good water quality management is the key to the success of this biota seedling. This research was carried out by measuring parameters including temperature, salinity, pH, and dissolved oxygen levels in the waters temporally in the morning and evening every day of cultivation. Variables of ammonia, nitrite, total suspended solids, total bacteria, and vibrio bacteria were carried out once a week. The results of temperature measurements range from 28.2-290C. Measurement of total suspended solids 0 mg/l. pH measurements ranged from 8.1-8.3. Dissolved oxygen measurements ranged from 4.16-4.27 mg/l. Salinity measurements obtained results of 35 ppt. Ammonia measurements range from 0-1.55 mg/l. Nitrite measurements range from 0.012-0.026. Measurement of total bacteria obtained <1 X 101 cfu/ml from all samples. Measurement of total vibrio yielded <1 X 101 cfu/ml from all samples. Based on the research that has been done, the results show that water quality is still in the optimal range for pearl oyster (Pinctada maxima) hatchery activities.

Temporal variability of phytoplankton biomass and net community production in a macrotidal temperate estuary

Coastal zones play a significant role in Earth's biogeochemical processes. Within these regions, estuaries are particularly important due to their complex ecological interactions and spatial and temporal variability. The aim of this study was to apply a year long high-frequency (15 min) environmental data time series to identify both the timing and factors influencing phytoplankton blooms in the Southampton Water estuary. Dissolved oxygen measurements from an in situ deployed optode were applied to the open diel oxygen method to estimate daily integrated rates of gross primary production (GPP), ecosystem respiration (ER) and net community production (NCP). Additional water quality data including temperature, salinity, chlorophyll concentration and turbidity allowed the relationship between physical and biological processes occurring over different time scales to be investigated. The occurrence of major phytoplankton blooms during the spring-summer period were associated with critical values of estuarine water temperature and mean water column irradiance. In addition, neap tides were found to promote the initiation of phytoplankton blooms in late spring and summer months. Annual daily average NCP for the estuarine ecosystem presented an estimated net heterotrophic state (−0.8 mmol O2 m−2 d−1), although seasonal productivity events shifted this state for several days and sometimes weeks to net autotrophic conditions. The results of this study have demonstrated how high frequency in situ dissolved oxygen measurements from an optode can make a valuable contribution to understanding the key factors influencing bloom events in a temperate macrotidal estuary. This approach if applied more widely to other coastal sites could therefore contribute to consolidating global annual primary production budgets for coastal regions.

Satellite prediction of coastal hypoxia in the northern Gulf of Mexico

The growing number, size, and frequency of coastal hypoxia increasingly threaten marine ecosystem health and essential ecosystem services for human well-being. It is therefore urgent to use continuous and consistent observation and develop advanced tools to characterize and track the spatial and temporal change of coastal hypoxia. Satellite imagery with fine spatiotemporal resolution and global coverage has shown great potential for monitoring environmental changes, yet has rarely been applied to hypoxia mapping. To advance the understanding, we synthesized satellite-derived ocean color variables and dissolved oxygen measurements collected during 2014, and used random forest regression, lagged linear regression, and functional data analysis to estimate the spatiotemporal change of the hypoxia zone in the Gulf of Mexico. The three models achieved similar predictive accuracy (±1.2–1.4 mg/L dissolved oxygen), but the random forest regression performed the best in estimating the bottom dissolved oxygen from satellite-derived variables. Our models also revealed time lags of roughly 0–5 and 16–19 days between the surface water process (e.g., algae bloom and ocean warming) and bottom water hypoxia, which was rarely considered in previous hypoxia studies using satellite data. Finally, our models showed that the area of Gulf hypoxia increased gradually from May and reached a peak during mid-July and mid-August in 2014, and the hypoxia zone occurred in the estuary of the Mississippi River and Suwannee River during roughly 25% of summer days. In addition to predicting the size of hypoxic zones, our study provides additional information on where, when, and how long hypoxic zones persist with greater spatial details and enables modeling hypoxic zones at near-real-time (e.g., days) temporal scales. More importantly, we demonstrate the great potential of applying satellite remote sensing for spatially explicit hypoxia mapping, which could promote more cost-effective coastal hypoxia monitoring and assessment practices.

Precise method for accuracy and sensitivity improvement of a current mirror for very low current measurement on a dissolved oxygen biosensor

Dissolved oxygen measurements using an electrochemical biosensor and conventional current mirror with accurate results and the desired sensitivity are difficult to achieve, though this type of current mirror is used frequently to processbiosensor signals, providing a good response. However, it exhibits some drawbacks particularly due to mismatched transistors, which will lead to asymmetry between input and output currents. This asymmetry causes unwanted offset and gain error, reducing its accuracy, especially at very low current. A modified current mirror utilizing precise gate voltage adjustment of FETs is applied to match the transistors’ currents. The results show accuracy improvement of the modified current mirror compared to the conventional current mirror, where the improvements provide a very low accuracy error of 0.01%. In addition, the current mirror’s sensitivity can be adjusted by implementing this modification without increasing noise significantly.

Calibration method of multi-parameter compensation for optical dissolved oxygen sensor in seawater based on machine learning algorithm

Measurement accuracy of optical dissolved oxygen sensor in actual seawater field is affected by many environmental factors. Traditional sensor calibration method is carried out by combining laboratory calibration experiment with field environmental factor correction. First, the influence of temperature on the sensor measurement results is added to the laboratory calibration experiment and model research. The measurement results are then corrected according to salinity and depth environmental factors in the field measurement. However, the influence of these environmental factors on the dissolved oxygen measurement results presents a multi-parameter nonlinear coupling characteristic. Nonlinear machine learning method is used in this study to investigate coupling mapping relationship between seawater multi-environmental factors and measured data of the sensor. A calibration device for controlling temperature, salinity, hydrostatic pressure, and dissolved oxygen concentration conditions and a matching multi-parameter calibration experimental process is designed and established. Analysis of the coupling relationship between multi-parameter conditions and their influence on the measurement of dissolved oxygen concentration showed that the established multi-parameter compensation calibration model achieves a calibration error of ±1 μmol L−1. Compared with existing compensation results after independent calibration of multi-parameters, the proposed model demonstrates better accuracy and rationality. The calibration sensor is tested in the laboratory and seawater field to verify the validity of the calibration model. Dissolved oxygen concentration measured by the sensor is basically consistent with reference measurement data and Winkler analysis value. Results showed that the multi-parameter calibration method based on machine learning can meet calibration requirements of the dissolved oxygen sensor in seawater with improved scientific rationality and calibration efficiency. Furthermore, the proposed method can be extended to other in situ measurement sensors in seawater while considering various environmental factor corrections.

A water quality barometer for Chesapeake Bay: Assessing spatial and temporal patterns using long-term monitoring data

This paper develops a barometer that indexes water quality in the Chesapeake Bay and summarizes quality over spatial regions and temporal periods. The barometer has a basis in risk assessment and hydrology, and is a function of three different metrics of water quality relative to numerical criteria: relative frequency of criterion attainment; magnitude of deviation from a numerical criterion; and duration of criterion attainment. Metrics associated with these features are calculated at the station level, allowing flexibility for simultaneously evaluating multiple stressors, different designated uses, and physical characteristics of the water. The barometer score is then created as a geometric mean of the three metrics. The water quality barometer (WQB) station scores may be spatially aggregated to report habitat scores across a spectrum of spatial resolutions (e.g., management segment, tidal subsystem, or the whole tidal bay). Dissolved oxygen measurements in the Chesapeake Bay collected during summer seasons of 1985 to 2020 are used to evaluate water quality. The WQB score and its bootstrapped confidence interval are reported at the station, segment, tidal subsystem and whole tidal bay levels. Notably, water quality interpreted through application of the WQB with dissolved oxygen concentration data and averaged over the 29-year period of record is good (i.e. protects aquatic living resources) in tributaries such as the James River, Rappahannock River and others; but is not as good in areas such as the Upper Tributaries and the York River. Recent summaries indicate that while the water quality is improving in much of the bay and its tidal tributaries, however, there is an indication of decline in quality in the period 20182020, especially in the upper regions of the Bay. The barometer is designed around using the time series data produced by the Chesapeake Bay Programs annual monitoring strategy; the approach has application to other large water bodies with large scale monitoring programs with extended time series or for integrating information from environmental sensor systems.

Non-Linear Autoregressive Dissolved Oxygen Prediction Model for Paddy Irrigation Channel

This study has proposed a non-linear autoregressive model to predict one-day ahead dissolved oxygen in paddy field irrigation channel. A 32-day data is obtained from Kampung Padang To’ La in Pasir Mas, Kelantan using off-the shelf water quality parameter sensors. Analysis has revealed no correlation between dissolved oxygen with pH and electrical conductivity. A non-linear autoregressive model is then developed using the dissolved oxygen measurements and artificial neural network. A prediction model developed using Levenberg- Marquardt algorithm yielded the best results with overall regression of 0.9253. The model has also passed all correlation tests and can therefore, be accepted.

Influence of radon gas removal on the oxygenation of thermal water bodies in the Paipa-Boyacá area

In this work, the effect of radon gas removal was studied for thermal water samples subjected to aeration and dissolved oxygen (DO) transfer processes. The prototype used in this work consisted of the application of a diffusion aeration system, usually used in water treatment processes, and the incorporation of a camera with the presence of LR-115 passive detectors, used for the measurement of radon gas. The Pylon ABC-6 active measurement method was used as a reference mechanism for radon gas concentration, while the dissolved oxygen measurement was measured simultaneously using a digital oximeter. The results obtained show that the DO transfer process is accompanied by an optimal removal of the radon gas present in the water samples, with a reception data of 1.5 ± 0.2 kBq·m-3, 61% of the value initially obtained. These data show that DO transfer processes have a great contribution to the removal of radon gas present in water bodies.

AQUASEA hydrodynamic and transport model: Salinity and dissolved oxygen simulation in El-Burullus Lake (Nile Delta, Egypt) considering different boundary conditions

Burullus Lake, an Egyptian large shallow brackish-water Delta Lake, is affected by extensive human activities, the construction of fishponds nearby, and rapid social-economic development. This has impacted the health of the Lake's ecosystem. This study investigates the hydrodynamic and transport simulation model in Burullus Lake using the AQUASEA program, considering different boundary conditions. The model showed the flow circulation therein and that the velocity is maximum at the drain’s outfall and inlet locations. Self-purification capacity of the Lake occurs after about 27 days and Al-Khashah Drain sometimes pours water with salinity 30 ‰ and is responsible for increasing the salinity in the Lake to about 11 ‰. The verification and calibration of the model are based on salinity and dissolved oxygen measurements during the month of December 2019. The practice measurements of salinity and DO are close to the model results with a mean relative error value of 24.18% and 36.29, and a correlation coefficient value of 0.91 and 0.737, respectively. These results are in agreement with the actual observations but need more measurements to verify the model.

The Study of Clean Water Demand in Palangka Raya City, Central Kalimantan

Palangka Raya as the capital city of Central Kalimantan become the center lane economy leading to increase population growth and clean water demand. There are still areas experiencing water shortage problems because of the difficulty of distributing clean water. Objectives of this study were to determine the amount of water demand in 2016, 2020, 2025, 2030 and 2035 to fulfill the community requirements. Water quality and supply capacity at the intake system are also be the purposes of this study. In this study, the calculation of population projections using statistical methods in which to observe the rate of population growth of the past to estimate the number of people in the future. There are several methods that can be used to analyze the population growth in the future, specifically Arithmetic, Geometric, Linear Regression, Exponential, and Logarithmic. For water quality field survey was conducted to test parameters such as temperature, electrical conductivity, the amount of dissolved solids, pH, turbidity, salinity, and dissolved oxygen measurements. The method in this research was using Arithmetic method because the correlation can be said to be excellent compared to other methods. Results of this research were clean water demand discharge town of Palangka Raya with consecutive results as follows in 2016; 2020; 2025; 2030; 2035 amounted to 451.03 L/sec, 737.14 L/sec, 1,162.34 L/sec, 1,425.83 L/sec, 1,571.12 L/sec. In the aspect of water quality, source of raw water used PDAM Palangka Raya unqualified the standards in terms of pH value, so the use of water was not safe for the residents of Palangka Raya city.

Nitrogen supply and physical disturbance shapes Arctic stream nitrogen uptake through effects on metabolic activity

Abstract Climate change in the Arctic is altering the delivery of nutrients from terrestrial to aquatic ecosystems. The impact of these changes on downstream lakes and rivers is influenced by the capacity of small streams to retain such inputs. Given the potential for nutrient limitation in oligotrophic Arctic streams, biotic demand should be high, unless harsh environmental conditions maintain low biomass standing stocks that limit nutrient uptake capacity. We assessed the drivers of nutrient uptake in two contrasting headwater environments in Arctic Sweden: one stream draining upland tundra and the other draining an alluvial valley with birch forest. At both sites, we measured nitrate (NO3−) uptake biweekly using short‐term slug releases and estimated rates of gross primary production (GPP) and ecosystem respiration from continuous dissolved oxygen measurements. Catchment characteristics were associated with distinct stream chemical and biological properties. For example, the tundra stream maintained relatively low NO3− concentrations (average: 46 µg N/L) and rates of GPP (0.2 g O2 m−2 day−1). By comparison, the birch forest stream was more NO3− rich (88 µg N/L) and productive (GPP: 1.7 g O2 m−2 day−1). These differences corresponded to greater areal NO3− uptake rate and increased NO3− use efficiency (as uptake velocity) in the birch forest stream (max 192 µg N m−2 min−1 and 96 mm/hr) compared to its tundra counterpart (max 52 µg N m−2 min−1 and 49 mm/hr) during 2017. Further, different sets of environmental drivers predicted temporal patterns of nutrient uptake at these sites: abiotic factors (e.g. NO3− concentration and discharge) were associated with changes in uptake in the tundra stream, while metabolic activity was more important in the birch forest stream. Between sites, variation in uptake metrics suggests that the ability to retain pulses of nutrients is linked to nutrient supply regimes controlled at larger spatial and temporal scales and habitat properties that promote biomass accrual and thus biotic demand. Overall, constraints on biotic potential imposed by the habitat template determined the capacity of these high latitude streams to respond to future changes in nutrient inputs arising from climate warming or human land use. ​

Primary and Net Ecosystem Production in a Large Lake Diagnosed From High‐Resolution Oxygen Measurements

AbstractThe rates of gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP) provide quantitative information about the cycling of carbon and energy in aquatic ecosystems. In lakes, metabolic rates are often diagnosed from diel oxygen fluctuations recorded with high‐resolution sondes. This requires that the imprint of ecosystem metabolism can be separated from that of physical processes. Here, we quantified the vertical and temporal variability of the metabolic rates of a deep, large, mesotrophic lake (Lake Geneva, Switzerland–France) by using a 6‐month record (April–October 2019) of high‐frequency, depth‐resolved (0–30 m) dissolved oxygen measurements. Two new alternative methods (in the time and frequency domain) were used to filter low‐frequency basin‐scale internal motions from the oxygen signal. Both methods proved successful and yielded consistent metabolic estimates showing net autotrophy (NEP = GPP − R = 55 mmol m−2 day−1) over the sampling period and depth interval, with GPP (235 mmol m−2 day−1) exceeding R (180 mmol m−2 day−1). They also revealed significant temporal variability, with at least two short‐lived blooms occurring during calm periods, and a vertical partitioning of metabolism, with stronger diel cycles and positive NEP in the upper ∼10 m and negative NEP below, where the diel oxygen signal was dominated by internal motions. The proposed methods expand the range of applicability of the diel oxygen technique to large lakes hosting energetic, low‐frequency internal motions, offering new possibilities for unveiling the rich spatiotemporal metabolism dynamics in these systems.

Kelkit Çayı (Tokat) Epilitik Diyatomeleri

Bu çalışmada, Kelkit Çayı (Tokat) epilitik diyatomelerin aylık değişimi, yerleşim yeri altı ve tarım alanları altından seçilen iki istasyondan Mart-Aralık 2018 tarihleri arasında aylık periyotlarda alınan taş örneklerinde incelenmiştir. Çalışma süresince epilitik diyatomelere ait toplam 18 takson kaydedilmiştir. En fazla taksonla temsil edilen diyatome cinsleri Cymbella (3 takson) ve Nitzschia (3 takson) olurken, her iki istasyonda tüm aylarda kaydedilen diyatomeler arasındaki en yüksek nispi yoğunluklar ise Ulnaria ulna türüne ait olmuştur. İstasyonlardaki diyatomeler arasında Sorensen Benzerlik İndeksi ise %56,41 olarak bulunmuştur. Ayrıca istasyonlardan alınan su örneklerinde sıcaklık ve çözünmüş oksijen ölçümleri yapılmıştır. Ölçülen bu değişkenlerin epilitondaki diyatome gelişimini olumlu yönde etkilediği tespit edilmiştir. Epilitik florada tespit edilen diyatome türlerin nispi yoğunlukları belirlenmiştir. Elde edilen sonuçlara göre en düşük nispi yoğunluk 1. İstasyonda 4,76 olarak Mart ayında (Cymbella affinis ), 2. İstasyonda ise 2,83 olarak yine Mart ayında (Lindavia glomerata) kaydedilmiştir. En yüksek nispi yoğunluk değerleri dikkate alındığında ise 1. İstasyonda Navicula radiosa ve Ulnaria ulna türünde Aralık ayında (13,56), 2. İstasyonda ise Ulnaria ulna türünde Mart ayında (9,43) belirlenmiştir.