Fish Kills Research Articles

Development of an Indirect Quantitation Method to Assess Ichthyotoxic B-Type Prymnesins from Prymnesium parvum.

Harmful algal blooms of Prymnesium parvum have recurrently been associated with the killing of fish. The causative ichthyotoxic agents of this haptophyte are believed to be prymnesins, a group of supersized ladder-frame polyether compounds currently divided into three types. Here, the development of a quantitative method to assess the molar sum of prymnesins in water samples and in algal biomass is reported. The method is based on the derivatization of the primary amine group and subsequent fluorescence detection using external calibrants. The presence of prymnesins in the underivatized sample should be confirmed by liquid chromatography mass spectrometry. The method is currently only partly applicable to water samples due to the low amounts that are present. The growth and cellular toxin content of two B-type producing strains were monitored in batch cultures eventually limited by an elevated pH. The cellular toxin contents varied by a factor of ~2.5 throughout the growth cycle, with the highest amounts found in the exponential growth phase and the lowest in the stationary growth/death phases. The strain K-0081 contained ~5 times more toxin than K-0374. Further investigations showed that the majority of prymnesins were associated with the biomass (89% ± 7%). This study provides the basis for further investigations into the toxicity and production of prymnesins.

Development and Launch of a Comprehensive Fish and Wildlife Reporting Mobile Application

Abstract This paper describes the conception, development, launch, marketing, and maintenance of the Florida Fish & Wildlife Conservation Commission Reporter (FWC Reporter), a mobile application (app) that the public can use to report fish and wildlife and environmental concerns to appropriate state agency offices. The FWC Reporter, launched in February 2018, is the first comprehensive reporting app developed by a fish and wildlife agency in the United States that we are aware of. On the basis of a consumer concept test and library research, the app's design incorporates elements of fast and frugal heuristics and inductive decision theory. The FWC developed this version of the app in-house with an open-source development package, and involves primarily email and telephone to send reports and facilitate communication with agency staff. From February 2018 through December 31, 2018, the FWC recorded over 1,000 downloads on Android and 4,308 on Apple devices, and 258 emailed reports. Since fish and wildlife reporting apps do not provide clear benefit to the user (low value proposition), it is crucial that offices receiving reports are proactive in building and maintaining their own reporting constituency. Engagement with the public is not only through active recruitment of app users, but also following up after a report is made so that the users know their efforts are appreciated. Two FWC programs demonstrated successful engagement, horseshoe crabs Limulus polyphemus and fish kills, as they received the most email reports. Other topics for any conservation or fish and wildlife agency to consider when developing their own reporting mobile app include download intention, adoption, continuance, habit formation, public and organizational acceptance, and marketing.

Co-occurring Notonecta (Hemiptera: Heteroptera: Notonectidae) Species Differ in Their Behavioral Response to Cues of Belostoma (Hemiptera: Heteroptera: Belostomatidae) Predation Risk

AbstractPredators affect prey through direct consumption as well as by inducing prey to defensively alter their phenotypes, including behavioral phenotypes, to maximize survival under predation risk. Closely related sympatric prey species with shared natural enemies may resolve behavioral trade-offs under predation risk differently. In a laboratory experiment, we investigated two co-occurring semiaquatic backswimmer congeners, which exhibit differences in their degree of habitat specialization across a gradient of habitat permanence. Notonecta irrorata Uhler primarily occur in ephemeral ponds, whereas Notonecta undulata Say are habitat generalists that are commonly found in both permanent and ephemeral ponds. We tested whether the two species differed in antipredator responses to both visual and chemical cues of a shared predator, the giant water bug, in a fully factorial design. The generalist species, N. undulata, exhibited reductions in activity in the presence of predator chemical cues only, whereas the specialist species, N. irrorata, remained consistently active across predator cue treatments. Our work shows that there are species-specific differences in how prey assess or respond to predation risk. The varying propensities of these backswimmer congeners to behaviorally respond to a shared predator, and differences in their behavior when exposed to different predation risk cues may be linked to underlying divergence in their life-history strategies.

Factors related to fish kill events in Mediterranean reservoirs

Fish kills are widespread visible events perceived by the civil society as a major cause for concern about water quality and ecosystem health. Investigations conducted so far have linked fish kills to multiple factors, but extensive studies examining quantitatively the likelihood of fish kills are missing. In the present study, factors related to fish kills in 67 Mediterranean reservoirs located in the Iberian Peninsula were investigated. Moreover, the variation in the likelihood of fish kills with the foreseen consequences of anthropogenically driven climate change upon temperature and precipitation was assessed. During the 23-year period studied (1995–2017) the number of fish kills per reservoir varied from 0 to 3 and happened mostly in Southern reservoirs and during the warmest months, particularly in June. Twelve explanatory variables showed significant differences between reservoirs with and without fish die-offs. Reservoir depth, surface area oxygen and chlorophyll a concentrations were the variables that, together, best discriminated between reservoirs with and without fish kills, explaining 67.2% of the total variation in the occurrence of fish die-offs. The variables retained in the mortality model explained unique parts of that variation, but a considerable amount of the explained variation was shared by all the variables. The number of fish kill events appears to be rising during the examined period and the projection made indicated an increase in the likelihood of fish kills towards the end of the 21st century, particularly for the RCP8.5 emission scenario, with the prevalence of fish kills reaching 0.865 in Southern reservoirs. In the future, oligotrophication is likely the only strategy to consistently reduce fish kills in Mediterranean reservoirs.

MULTI-TEMPORAL MODIS FOR DETECTION AND PUBLISHED LITERATURES FOR VALIDATION OF PHYTOPLANKTON BLOOMS IN SABAH AND SARAWAK, MALAYSIA

The coastal region of Sabah, Malaysia is mostly affected by harmful algal blooms (HABs) that often cause massive fish kills, and sometimes human casualties. Lack of a well-agreed, transparent and reproducible method, aperiodic nature and limited (technical) ability to monitor HAB at large regional scale, have all led to reinforced methodological improvement for bloom prediction, scientific management of coastal water resources, and regulatory attention. MODerate Resolution Imaging Spectroradiometer (MODIS), one of the well validated ocean colour sensors, enables acquiring high spectral resolution images, with short revisit time, freely accessible, and bay-wide coverage. Yet, the relative efficiency of MODIS-derived Chl-a (Chlorophyll-a), ABI (Algal Bloom Index), and nFLH (normalized Fluorescence Line Height) have not been compared in coastal regions of Malaysia. Fifteen MODIS Level 2 images acquired between 2005 and 2013 were considered as time series data that matched HAB events mentioned in previous studies. As historical real time in-situ data collection is often difficult (inaccessible), and thus unavailable; this project had to validate results obtained from literature, assuming that in-situ, would indicate HAB location at least during MODIS acquisition dates. Variations of HAB affected areas with temporal and spatial scales derived from bloom indices are shown in colour maps. Reliability of bloom information was measured by subjectively comparing HAB results provided by indices, and previously published in-situ results. ABI outperformed Chl-a and nFLH indices based on comparisons in both normal and HAB conditions occurring in the coastal waters of Sabah and Sarawak. The configuration and reliability retrieved from MODIS-ABI allowed their application in different likely tropical region as automated HAB monitoring systems and coastal water management programmes.

Karenia brevis causes high mortality and impaired swimming behavior of Florida stone crab larvae

The dinoflagellate Karenia brevis causes harmful algal blooms commonly referred to as red tides that are prevalent along Florida’s gulf coast. Severe blooms often cause fish kills, turbid water, and hypoxic events all of which can negatively impact local fisheries. The stone crab, Menippe mercenaria, is a ˜$25 million per year fishery that occurs primarily along Florida’s gulf coast. On the west Florida shelf, red tides occur from fall through spring, although severe blooms can occur during the summer. During the summer, stone crabs are reproductive and release larvae that are transported offshore where K. brevis blooms originate. This study determined the effects of K. brevis exposure on the survivorship, vertical swimming behavior, and oxygen consumption of stage-1 larval stone crabs. Survivorship was determined by exposing larvae to high (> 1 × 106 cells L−1) and medium (˜1 × 105 cells L−1) K. brevis concentrations for 96-hrs and were compared to controls that had no algae present. Larval swimming behavior (i.e., geotaxis) and oxygen consumption were monitored after 6-hr exposure to K. brevis. After 96-hrs of exposure, mortality was 100% and 30% for larvae in the high and medium concentrations of K. brevis, respectively, relative to the control. Larval swimming behavior was reversed in the K. brevis treatment; however oxygen consumption rates did not differ among treatments. These results suggest that severe blooms during the summer may reduce larval supply and serve as a potential bottleneck for new individuals recruiting into the fishery in years following a K. brevis bloom.

SPATIAL DISTRIBUTIONS OF NUTRIENTS AND CHLOROPHYLL-A: A POSSIBLE OCCURRENCE OF PHOSPHORUS AS A EUTROPHICATION DETERMINANT OF THE JAKARTA BAY

Phytoplankton blooms due to nutrient enrichment (eutrophication) have been considered as the primary factor causing several massive fish kills occurred in the Jakarta Bay. This study aims to determine the spatial variation of phytoplankton abundance based on chlorophyll-a concentration and its relationship with nutrient level and composition. A field observation was conducted in July 2015 measuring chlorophyll-a and nutrient concentrations. Chlorophyll-a was measured using fluorometer Trilogy AU-10 while nutrients was using spectrophotometer Shimadzu UV-1800. The result showed that chlorophyll-a concentration was relatively higher in the western compared to the eastern region of the Jakarta Bay. In addition, the western region was high in orthophosphate, nitrate and silicate while the eastern region was high in ammonium and nitrate. Statistical analysis shows that chlorophyll-a had the highest significant correlation against orthophosphate in the western region and chlorophyll-a had no significant correlation with nutrients in the eastern region. It seems that phosphorus was the primary determinant of chlorophyll-a variability with a concentration of orthophosphate of more than 0.028 mg P/L is required to increase chlorophyll-a concentration. In addition, low orthophosphate concentration (0.014 mg P/L) below its minimum requirement for maximum phytoplankton growth was likely the factor causing the absence of chlorophyll-a and nutrients relationship in the eastern region. In summary, phosphorus is seemingly the primary eutrophication determinant in the Jakarta Bay.

The impact of phenology on the interaction between a predaceous aquatic insect and larval amphibians in seasonal ponds

Phenology has an important effect on the life strategies of species that live in temporary waters. Predaceous aquatic insects are key components of communities associated with seasonal ponds. Since the life cycles of these predators and their prey are unusual in that they occur at different moments of the pond hydroperiod, differences in temporal overlap could change the strength of their interactions. This study analyzed the phenology of the giant water bug Belostoma bifoveolatum and its prey. Breeding phenology, nymph population, and prey phenology were studied extensively in three wetlands during the spring season. Experimental trials were carried out to evaluate prey consumption and prey preference. The results showed a strong overlap in phenology between the water bug and the Pleurodema thaul frog. The timing of tadpole and water bug nymph hatching could ensure high survival levels of the early immature stages of this insect. As giant water bugs develop, their prey selectivity experiences a shift—older nymphs and adults having a higher impact on tadpoles. The fluctuating climate of the Patagonian region probably influences the phenology of predator–prey assemblages in seasonal communities, and may have the potential to drive feeding performance and the strength of interspecific interactions.

Characterization of Francisella noatunensis subsp. orientalis isolated from Nile tilapia Oreochromis niloticus farmed in Lake Yojoa, Honduras.

Francisella noatunensis subsp. orientalis (Fno) is a Gram-negative, pleomorphic, facultative intracellular bacterial pathogen affecting a variety of cultured and wild fish species. Outbreaks of piscine francisellosis in warmwater fish have been documented worldwide; however, reports of Fno from Central America have been limited to a single documented outbreak in cultured tilapia in Costa Rica in 2007. From 2015 to 2017, Fno was consistently recovered from disease outbreaks in Nile tilapia Oreochromis niloticus cultivated in floating cages in Lake Yojoa, Honduras. Mortality rates during these outbreaks ranged from 50 to 85%. Fno was isolated by aerobic culture on selective media and identity confirmed by Fno-specific PCR. Repetitive extragenic palindromic PCR analysis revealed that the case isolates were genetically homogeneous with archived strains recovered from epizootics in cultured tilapia from Costa Rica and Mexico, suggesting the same strain of Fno was responsible for these otherwise unrelated fish kills. The current study provides only the second report of Fno in Central America and characterizes the first Fno outbreak in cultured fish in Honduras.

Retrospective and Predictive Investigation of Fish Kill Events.

Fish kill investigations are critical to understanding threats to aquatic ecosystems and can serve as a measure of environmental disruption as well as an early indicator of emerging disease. The goal of this study was to analyze historical data related to such events among wild fish populations in Minnesota in order to assess the quality and completeness of the data and potential trends in fish kills. After excluding events with incomplete data (e.g., in which the location was not reported), we analyzed 225 unique fish kills from 2003 to 2013 that were recorded in two Minnesota Department of Natural Resources databases. The most reported fish kills occurred during 2007 (n=41) and during the month of June (n=81) across all years. Centrarchid species were present in the most fish kills (138), followed by cyprinid and ictalurid species, which were present in 53 and 40 events, respectively. Environmental factors were the most common cause of death reported. Models of environmental factors revealed that the maximum nighttime land surface temperature was the most critical factor in fish mortality, followed by changes in primary productivity and human disturbances. During the course of this study, data gaps were identified, including underreporting, inconsistent investigation, and the lack of definitive diagnoses, making interpretation of our results challenging. Even so, understanding these historical trends and data gaps can be useful in generating hypotheses and advancing data collection systems for investigating future fish kills. Our study is a primer investigation of fish kills providing information on the plausible areas, seasons, and fish groups at risk that can guide active environmental monitoring and epidemiological surveillance of fishes.

New Records of Anuran Predation by Giant Water Bugs of the Genus Lethocerus in Argentina (Hemiptera: Belostomatidae)

The aim of this paper is to report 10 predation events of anuran amphibians by giant water bugs of the genus Lethocerus in different localities in northeastern Argentina. With the exception of Scinax fuscovarius and Physalaemus biligonigerus, they are all new records of adult anurans being prey to these invertebrates. We conclude that this interaction is of extremely importance in the regulation of amphibian populations and should be studied in a thorough manner.

Overview of Decadal Ecosystem Changes in the Western Arabian Sea and the Occurrence of Algal Blooms

Gradual decadal changes have taken place in the Western Arabian Sea over the last 50 years. These changes have affected wind speeds, atmospheric and sea surface temperature, thermohaline stratification, shoaling of the oxycline, and dust/iron inputs. A decrease in nitrate supply of the photic layer have caused an increase in annual frequency of harmful algal blooms and fish kills. Along with that, a decrease in diatom biomass and a shift from red Noctiluca to green Noctiluca during the northeast monsoon was observed during the last two decades, Even though these are the same species they have very different nutritional modes. The red one is a heterotroph with a preference for grazing diatoms, while the green one has a symbiont and thus it is a mixotroph. Recent results suggest that this shift may be caused by the shoaling oxycline since the green one grows better under low oxygen because the symbiont produces oxygen for its host. The western Arabian Sea is temporally and spatially complex. With the recent advances in remote sensing of the ocean, a further understanding of these temporal and spatial changes can be gained through analyzing frequent images with opportunistic ground-truthing.

Overview of Decadal Ecosystem Changes in the Western Arabian Sea and the Occurrence of Algal Blooms

Gradual decadal changes have taken place in the Western Arabian Sea over the last 50 years. These changes have affected wind speeds, atmospheric and sea surface temperature, thermohaline stratification, shoaling of the oxycline, and dust/iron inputs. A decrease in nitrate supply of the photic layer have caused an increase in annual frequency of harmful algal blooms and fish kills. Along with that, a decrease in diatom biomass and a shift from red Noctiluca to green Noctiluca during the northeast monsoon was observed during the last two decades, Even though these are the same species they have very different nutritional modes. The red one is a heterotroph with a preference for grazing diatoms, while the green one has a symbiont and thus it is a mixotroph. Recent results suggest that this shift may be caused by the shoaling oxycline since the green one grows better under low oxygen because the symbiont produces oxygen for its host. The western Arabian Sea is temporally and spatially complex. With the recent advances in remote sensing of the ocean, a further understanding of these temporal and spatial changes can be gained through analyzing frequent images with opportunistic ground-truthing.

The Shift of Traditional Agroecosystems in the in Eastern Arc Catchments of Tanzania

The purpose of this study was to identify the drivers of the shift of traditional agro-ecosystems and their implication on catchment resources management of Eastern Arc Catchments of Tanzania. Lower Mngeta and Upper Zigi water catchments are situated within Eastern Arc Mountains of Tanzania. Household questionnaire, key informant interviews and focus group discussion were used for collecting primary data. The findings indicated that most of the participants (85.9% and 90.4% in Lower Mngeta and Upper Zigi catchments respectively) depend on subsistence rain-fed agriculture for their livelihoods. However, there are significant changes in production as a result of land fertility deteriorating and negative climatic changes (seasonal shift). This has become a major challenge for most of the farmers. To cope with agro-ecosystem dynamics, farmers in the study areas use both traditional and modern strategies as illustrated in the results section. While tradition always reported to be inexpensive, some modern agro-ecosystem practices reported to cause siltation, killing of fish and herbal plants, easy rotting of seeds (for maize) and bad aroma (for rice)in spite of having a high rate of return. It was also reported that depletion of traditions and norms of conduct, accelerated by multi-cultural interaction from immigrants, have led to deterioration of traditional agriculture practices. Moreover, arrival of agriculture companies and introduction of spice farming was reported to have caused manpower imbalance, unequal distribution of natural resources and less diversity of indigenous plants. The study concludes that communities are much into economic opportunity derived from agro-ecosystem than stewarding it. The study recommends that the effort restoring catchment ecosystem should come from both traditional and modern strategies so as to harmonize and accommodate environmental, economic and traditional values.

Ethical Considerations in Exploiting, Culturing and Killing Fish towards Animal Rights in Islam

Human show cruelty to fish during exploiting, culturing, killing, experimentation and amusement. Presently, overexploitation of marine fishes is a serious problem worldwide. More than 50% of total fish production is now raised in aquafarms where many fish suffer from parasitic infections, diseases, and debilitating injuries in culture systems. Every year, millions of fish are caught in nets and on hooks. Many of them are tortured just for sports. Fishes are also regularly used for scientific experiments. Many of them are killed by unethical ways. Among all animals, human is the main culprits in causing harms to animals including fishes by damaging their ecosystems. To secure animal rights, modern bio-ethics started to be developed in the last century. The principle of modern bio-ethics is very similar to the principle of Islamic bio-ethics. Therefore, modern bio-ethics might be guided by Islamic bio-ethics, which was well established in the 7th century. According to Islam, God gave the human being responsibility to look after animals, to protect them, and not to abuse or threaten them. Human is not permitted to kill animals just for sports or amusements. God created the universe in a perfect balance and human should not disturb this. Therefore, human may exploit and culture food (fish and other organisms) and ornaments without destroying aquatic ecosystems. Islam prescribes a set of rules to treat animals with the utmost kindness and compassion. However, Islamic direction can be integrated with science to ensure minimum stress, pain and suffering when killing animals including fishes.

Effects of Karenia brevis harmful algal blooms on fish community structure on the West Florida Shelf

Blooms of the Karenia brevis dinoflagellate can create devastating effects on marine communities off the west coast of Florida when they release a suite of neurotoxins known as brevetoxins (PbTx). These blooms, informally referred to as red tides, can cause massive fish kills, necessitate closures of shellfish fisheries, and can even leave lingering toxins that impact shelf communities long after the bloom has dissipated. Much effort has been put into studying K. brevis bloom initiation and dynamics, however, predicting the impact of these blooms on Florida’s fish and fisheries is problematic because K. brevis cell counts and fish mortality is not well correlated. Ecopath with Ecosim (EwE) is an ecosystem modelling platform that is used in this study to simulate K. brevis bloom effects on the West Florida Shelf ecosystem. The model produced for this study, which has been named the West Florida Shelf K. brevis model, is an application of the EwE modelling platform that employs a recently developed time series to index K. brevis bloom severity. This index was used to drive bloom-related mortality as a fishing fleet in the model in a historical reconstruction scenario from 1980 to 2009. The study suggests that K. brevis blooms can impose top-down food web effects causing trophic cascades. Piscivores, planktivores and detritivores experienced biomass increases when bloom-related mortality was applied, while invertebrate eaters and omnivores experienced biomass decreases. Changes in community structure and biodiversity are evidenced by effects on species evenness and richness. The model indicated an overall improvement in fits to observational time series of biomass and catch when using the K. brevis index. These results provide evidence that K. brevis mortality should be considered in population models, particularly for species with low predation mortality such as gag.

Lost in translation: the German literature on freshwater salinization.

Human activities have globally increased and altered the ion concentration of freshwater ecosystems. The proliferation of potash mines in Germany (especially intense in the early 1900s) constitutes a good example of it. The effluents and runoff coming from potash mines led to extreme salt concentrations (e.g. 72 g l-1 of total salt content, approx. 149 mS cm-1) in surrounding rivers and streams, causing ecosystem degradation (e.g. massive algal blooms and fish kills). This promoted scientific research that was mostly published in German, thereby being neglected by the wide scientific community. Here, the findings of the German literature on freshwater salinization are discussed in the light of current knowledge. German studies revealed that at similar ion concentrations potassium (K+) can be the most toxic ion to freshwater organisms, whereas calcium (Ca2+) could have a toxicity ameliorating effect. Also, they showed that salinization could lead to biodiversity loss, major shifts in the composition of aquatic communities (e.g. dominance of salt-tolerant algae, proliferation of invasive species) and alter organic matter processing. The biological degradation caused by freshwater salinization related to potash mining has important management implications, e.g. it could prevent many European rivers and streams from reaching the good ecological status demanded by the Water Framework Directive. Within this context, German publications show several examples of salinity thresholds and biological indices that could be useful to monitor and regulate salinization (i.e. developing legally enforced salinity and ion-specific standards). They also provide potential management techniques (i.e. brine collection and disposal) and some estimates of the economic costs of freshwater salinization. Overall, the German literature on freshwater salinization provides internationally relevant information that has rarely been cited by the English literature. We suggest that the global editorial and scientific community should take action to make important findings published in non-English literature more widely available.This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.

A-, B- and C-type prymnesins are clade specific compounds and chemotaxonomic markers in Prymnesium parvum

Harmful blooms formed by planktonic microalgae (HABs) in both freshwater and coastal waters regularly lead to severe mortalities of fish and invertebrates causing substantial economic losses of marine products worldwide. The mixotrophic haptophyte Prymnesium parvum is one of the most important microalgae associated with fish kills. Here 26 strains of P. parvum with a wide geographical distribution were screened for the production of prymnesins, the suspected causative allelochemical toxins. All investigated strains produced prymnesins, indicating that the toxins play an important role for the organism. The prymnesins can be classified into three types based on the length of the carbon backbone of the compound and each algal strain produced only one of these types. Biogeographical mapping of the prymnesin distribution indicated a global distribution of each type. In addition, phylogenetic analyses based on internal transcribed spacer (ITS) sequences revealed monophyletic origin of all prymnesin types and clades could therefore be defined based on the toxic compound. It might be that evolution of new species within the P. parvum species complex is driven by changes in toxin type or that they are a result of it. Such a correlation between chemotype and phylotype has never been documented before for a harmful microalga. Chemotaxonomy and ITS-type classification may thus be used to further delimit the P. parvum species complex.

Is Submarine Groundwater Discharge (SGD) Important for the Historical Fish Kills and Harmful Algal Bloom Events of Mobile Bay?

Large-scale fish and crustacean kills, locally known as Jubilees, and harmful algal blooms (HABs) have been occurring in Mobile Bay (Alabama) for more than a century. In fact, the first record describing a Jubilee event in Mobile Bay during 1867 was the first ever-documented case of mass mortalities of marine animals caused by hypoxia. To evaluate the importance of submarine groundwater discharge (SGD) in the occurrence of Jubilees and HABs in Mobile Bay, a 3-year study was conducted using a multi-method approach. Significant spatial and temporal variations of SGD were revealed in the bay only by applying a combination of geochemical and shallow geophysical techniques. The development of seasonal hypoxia observed in bay waters in areas impacted by Jubilees was the result of anoxic SGD inputs, which magnitude and spatial distribution were controlled by shallow lithological heterogeneities created during the modern development of the bay. Although when compared to the river discharge SGD contributed between 0.2 (wet season) and 5% (dry season) of the total freshwater inputs to Mobile Bay, 80% of the total SGD in the bay occurred in areas ecologically impacted by hypoxia and Jubilees. In these areas, SGD comprised up to 37% of the total water inputs during the dry season, coinciding with the time of the year when Jubilees and HABs occur. In conclusion, while SGD might not be a significant source of fresh water to Mobile Bay or other estuaries worldwide, enhanced SGD caused by site-specific lithological heterogeneities can have a critical role in the development of hypoxia and ecological issues in nearshore waters.

Features of measuring dynamic biochemical parameters in the middle Ob

Indicators that reflect metabolic processes of living organisms in the water of the middle course of the Ob River were measured in different seasons of 2016 and 2017. In the winter period, the processes of catabolism predominate. They intensify in mid-February. At this time a sharp decrease in dissolved oxygen (O2) in the water is observed, which results in fish kills. The most intense catabolic processes occur in March, before the river ice breakup. In summertime there is no difference between the day and night periods. It is probable that the internal heterogeneity of water flows has a more significant effect on dynamic indices than the processes of photosynthesis.