River Discharge Rates Research Articles

Sakawa River plume in Sagami Bay, Japan under weak wind condition: numerical simulation of coastal ocean dynamics and in situ observations for validation

AbstractThis study proposes a method for estimating river plume length from water levels and river discharge rates. A numerical model for coastal ocean dynamics was refined by comparing thermohaline fields calculated using the model with those measured off the mouth of the Sakawa River in Sagami Bay, Japan. The model successfully captured the reduction in salinity within the surface 1.0-m layer caused by riverine water transport. The simulated surface salinity maps revealed that the dynamic motions of the river plumes were primarily driven by one of the two diurnal occurrences of tidal current intensification. Regression analyses of the simulated results demonstrated that the river plume lengths were closely correlated with the water levels and river discharge rates, and that they could be accurately estimated from preceding river discharge rates under weak wind condition.

Impact of a Large Shallow Semi‐Enclosed Lagoon on Freshwater Exchange Across an Inlet Channel

AbstractThe impact of a large shallow semi‐enclosed lagoon on freshwater exchange across an inlet channel is investigated using an idealized numerical model. Lagoons are often found between a river mouth and the ocean; we focus on those where the river discharge rate is small and the inlet channel is narrower and deeper than the lagoon. Tides generate freshwater and oceanic‐water plumes across the channel; a stratified freshwater plume forms in the ocean from the late ebb to early flood phase, while a vertically well‐mixed oceanic‐water plume forms in the lagoon from the late flood to early ebb phase. The shallow depth of the lagoon increases the flow speed of the oceanic‐water plume, which results in the formation of a sharp and vertically well‐mixed salinity front within the lagoon. When this front moves toward the ocean during the ebb phase, vertical mixing increases where the bathymetry deepens and freshwater encounters oceanic water below. Without a dredged bottom slope, the impact of mixing would be greatly reduced within the shallow lagoon and channel, as the shallow depth would limit the subsurface intrusion of oceanic water. The narrow channel further causes the flow to converge and accelerate, enhancing both internal shear‐driven and bottom boundary‐layer mixing at the channel and increasing freshwater plume thickness where it enters the ocean. Sensitivity experiments showed that the role of tidal pumping in freshwater exchange across the channel increases when the lagoon area and tidal mixing increase and when the estuarine Richardson number decreases.

Freshwater resources around the reclaimed new land on the Eastern Hengsha Shoal in the Changjiang estuary

Reclaiming estuarine tidal flats is practiced to meet the growing demand for land. The reclaimed new land (RNL) on the Eastern Hengsha Shoal in the Changjiang Estuary is for agricultural production in Shanghai. Whether freshwater resources exist around the RNL has become a critical issue \caused by estuarine saltwater intrusion. In this study, the spatiotemporal saltwater intrusion and freshwater distribution around the RNL at different guarantee rates of river discharge using the improved 3D numerical model ECOM-si was investigated. Three water intakes on Hengsha Island and the northern edge of the RNL were set. The results showed that at different guarantee rates of river discharge during the dry season, there is a relatively sufficient suitable water intake time in the upper RNL. Nevertheless, there is a very limited suitable water intake time in the middle and lower RNL as the guarantee rate increases, especially in January and February. During the flood season, three water intakes can ensure sufficient suitable water intake time. The salinity around the RNL significantly increases under the combined effect of 50% and 95% guarantee rates with a 12 m/s northerly wind in February, resulting in a significant threat to the three water intakes. At the 50% guarantee rate, the suitable water intake times in February are 14.86, 9.78 and 3.53 days at three water intakes, respectively. At the 95% guarantee rate, the suitable water intake time in February is only 0.31 days in the upper RNL, and there is no freshwater in the middle and lower RNL. Overall, there is sufficient freshwater in the flood season and limited freshwater in the dry season for agriculture along the northern edge of the RNL.

Annual and Interannual Variability in the Diffuse Attenuation Coefficient and Turbidity in Urbanized Washington Lake from 2013 to 2022 Assessed Using Landsat-8/9

Water clarity, defined in this study using measurements of the downwelling diffuse light attenuation coefficient (Kd) and turbidity, is an important indicator of lake trophic status and ecosystem health. We used in-situ measurements to evaluate existing semi-analytical models for Kd and turbidity, developed a regional turbidity model based on spectral shape, and evaluated the spatial and temporal trends in Lake Washington from 2013 to 2022 using Landsat-8/9 Operational Land Imager (OLI). We found no significant trends from 2013 to 2022 in Kd or turbidity when both the annual and full datasets were considered. In addition to the spring peak lasting from April through June, autumn Kd peaks were present at all sites, a pattern consistent with seasonal chlorophyll a and zooplankton concentrations. There existed no autumn peak in the monthly turbidity dataset, and the spring peak occurred two months before the Kd peak, nearly mirroring seasonal variability in the Cedar River discharge rates over the same period. The Kd and turbidity algorithms were thus each more sensitive to different sources of water clarity variability in Lake Washington.

Spatial and wavelet analysis of precipitation and river discharge during operation of the Three Gorges Dam, China

The Three Gorges Dam and Reservoir on the Yangtze River is one of the world's largest dams. After the dam's construction in 1997, the reservoir started filling up, expanding to a size of over 600 km2. Therefore, its possible influence on maintaining the size and water level of this waterbody is significant and concerning. This research utilized wavelet coherence analysis to examine the temporal correlation and phase coherence among various datasets, including dam injection (1998–2018) and discharge (2003–2018) data, ground station precipitation data along the Yangtze River (1998–2020), and river discharge raster maps 1998–2018. The analysis revealed a strong coherence between dam operation and river discharge rates, as well as a minor seasonal coherence between dam operation and precipitation. The periodic properties of the datasets indicate that, in addition to the general seasonal changes observed in the wavelet coherence analysis, other periodic signals in the datasets are also coherent over time. This coherence may be attributed to the simultaneous impacts of dam operation on precipitation and river discharge. The reasons for this coherence are still unknown, and further studies are required, incorporating information on soil moisture, groundwater levels, air humidity, and the monsoon, to understand how the dam affects them.

Role of inter-annual variability in the magnitude of river discharge on CO2 fluxes in the Godavari tidal river zone, India

Variations in the magnitude of river discharge may alter pH, pCO2 of surface water, and flux of CO2 to the atmosphere in the Tidal River Zone (TRZ). To test this hypothesis, a nearly decade-long time-series data of salinity, pH, and pCO2 data were collected and analyzed in the TRZ of Godavari River. The higher freshwater discharge occurred in the TRZ during the wet period (June to December) compared to the dry period (January to May). An increase in annual mean discharge was noticed between 2008 and 2019 due to surplus rainfall and the expansion of the hydropower plant. The surface water pH and pCO2 in the TRZ were controlled by the river discharge as evidenced by the linear positive and negative relationships with the rate of river discharge respectively. A strong relationship was observed between apparent oxygen utilization (AOU) and excess CO2 indicating a strong influence of heterotrophic activity on pCO2 levels in the TRZ. The respiration quotient (RQ) was above the aerobic respiration value of 1.35 indicating that terrestrial sources, such as sewage, and groundwater discharge, may have contributed to pH and pCO2 levels in the TRZ. The CO2 fluxes during the peak discharge period contribute to 48–88% of annual mean fluxes followed by moderate (12–52%) and dry periods (<4%). The annual mean CO2 emission amounted to 0.04 ± 0.05 TgC for the area of 36.9 × 106 m2 and increased at the rate of 0.005 TgC y−1 between 2008 and 2019 due to an increase in river discharge. The CO2 flux from the Godavari TRZ (0.04 TgC y−1) contributes to ∼0.2% of global tropical estuaries (18 TgC y−1). The CO2 flux contributed to ∼1.5% of the total carbon (both particulate and dissolved) exported from the Godavari TRZ to the Bay of Bengal and it is lower than the global mean contribution of 16%.

ANALYSIS OF THE FLASH FLOOD EVENT AND RAINFALL DISTRIBUTION PATTERN ON RELAU RIVER BASIN DEVELOPMENT, PENANG, MALAYSIA

Typical disaster flooding and flash floods in Malaysia. Floods occur especially during the wet season within the geographical region area which is especially influenced by the northeast monsoon. So the sampling study was conducted in March 2019 in normal season. Cross-sectional measurements involving the measurement of river width, river depth and velocity were conducted at both sampling times. The main objective of this study was to identify the pattern of rainfall distribution and river discharge rate in the River Basin Relative when the flash flood event occurred. The average seasonal discharge value in the normal Relau River (Upstream) is 0.04 m3s-1, Relau River (Midstream) is 0.57 m3s-1, Relau River (Downstream) is 0.35 m3s-1. Whereas for Ara River (Midstream) is 0.78 m3s-1, Ara River (Downstream) is 0.19 m3s-1) and Kluang River (Upstream) is 0.18 m3s-1. The estimated value for flash flood shows that total water and sewer capacity that occurred during the flash floods was to increase the water level by five meters from the normal season water level with an estimated water velocity of m3s-1for this area. The reading shows the Relau River (Upstream) reading 5.18 m3s-1, the Relau River (Midstream) is m3s-1 the Relau River (Downstream) is 18.20 m3s-1. While for Ara River (Midstream) is 24.53 m3s-1, Ara River (Downstream) is 25.35 m3s-1) and Kluang River (Upstream) is 26.22 m3s-1.

Marine Plastic Drift from the Mekong River to Southeast Asia

Southeast Asia is the world’s most polluted area in terms of marine plastics. The Mekong River is one of the largest rivers in the area, and ranked as somewhere between the 8th- and 11th-biggest contributor to plastics in the world’s oceans. Here, we investigate how microplastics drift from the Mekong river to Southeast Asia, and which coastlines are most exposed. We identify potential factors (wind drift, rivers, vertical mixing and sinking rates) that affect plastic drift in the region using the OpenDrift model with realistic wind and ocean currents for simulations between three months (summer and winter) and 15 months. We find that the seasonal drift is influenced by the monsoon systems and that most of the plastics strand in the Philippines and Indonesia. In addition, the role of wind drift is significant in strong winds. Vertical mixing and sinking rates are unknowns that affect the relative importance of wind drift (near the surface) and ocean currents. Simulations with different terminal velocities show that, unsurprisingly, the higher the terminal velocities are, the closer they deposit to the source. In light of the large uncertainties in sinking rates, we find that the plastic distribution has large uncertainties, but is clearly seasonal and influenced by wind, vertical mixing, river discharge and sinking rates. The Philippines and Indonesia are found to have the coastlines that are most exposed to plastic pollution from the Mekong river. This study shows that simulations of marine plastic drift are very variable, depending on many factors and assumptions. However, it provides more detailed information on marine plastic pollution in Southeast Asia, and hopefully helps authorities take more practical actions.

Using environmental DNA metabarcoding to monitor fish communities in small rivers and large brooks: Insights on the spatial scale of information

Monitoring fish communities is central to the evaluation of ecological health of rivers. Both presence/absence of fish species and their relative quantity in local fish assemblages are crucial parameters to measure. Fish communities in lotic systems are traditionally monitored via electrofishing, characterized by a known limited efficiency and high survey costs. Analysis of environmental DNA could serve as a non-destructive alternative for detection and quantification of lotic fish communities, but this approach still requires further insights in practical sampling schemes incorporating transport and dilution of the eDNA particles; optimization of predictive power and quality assurance of the molecular detection method. Via a controlled cage experiment, we aim to extend the knowledge on streamreach of eDNA in small rivers and large brooks, as laid out in the European Water Framework Directive's water typology. Using a high and low source biomass in two river transects of a species-poor river characterized by contrasting river discharge rates, we found strong and significant correlations between the eDNA relative species abundances and the relative biomass per species in the cage community. Despite a decreasing correlation over distance, the underlying community composition remained stable from 25 to 300 m, or up to 1 km downstream of the eDNA source, depending on the river discharge rate. Such decrease in similarity between relative source biomass and the corresponding eDNA-based community profile with increasing distance downstream from the source, might be attributed to variation in species-specific eDNA persistence. Our findings offer crucial insights on eDNA behaviour and characterization of riverine fish communities. We conclude that water sampled from a relatively small river offers an adequate eDNA snapshot of the total fish community in the 300–1000 m upstream transect. The potential application for other river systems is further discussed.

Seasonal effects, spatial distribution, and possible sources of microplastics in the Chao Phraya River estuary, Thailand

Microplastics (MPs) in estuaries are sources of plastic debris that enter the marine environment. However, there is limited information on the seasonal effect on the accumulation of MPs in the estuaries of Thailand. The abundance and spatial distribution of MPs in the dry and wet seasons were investigated in the Chao Phraya River estuary, and possible emission sources were traced. Dominant factors affecting the distribution patterns of MPs have also been reported. All collected water samples contained MPs, with a mean abundance of 4.0 ± 2.8 × 105 particles/km2 in the wet season and 5.2 ± 3.3 × 105 particles/km2 in the dry season. Fragments were mostly observed, with polypropylene and polyethylene being the dominant polymers. The findings also showed that accumulation of MPs was directly influenced by the river discharge rate into the estuary. Further, the spatial distribution of MPs was closely related to seasonal variations in sea surface currents. Microplastic pollution status with seasonal variations and possible emission sources could provide important information to the government and local environmental organizations for MP pollution prevention and future MP studies in estuarine environments.

Structure and variability of the Pechora plume in the southeastern part of the Barents Sea

The Pechora River forms the large Pechora River plume in the southeastern part of the Barents Sea (also called the Pechora Sea). Many previous works addressed water masses in the Barents Sea, however, the Pechora plume received relatively little attention, therefore, many basic aspects of its structure and variability remain unknown. In this study, we focus on spreading of the Pechora plume in the Pechora Sea during ice-free periods. Based on the extensivein situmeasurements and satellite observations, we describe the dependence of area and spatial characteristics of the Pechora plume on wind forcing, river discharge rate, and spring ice conditions. We reveal three general types of Pechora plume spreading, which are determined by the external forcing conditions. Joint analysis of a large set ofin situand satellite data provided opportunity to study the variability of the Pechora plume on the synoptic, seasonal, and interannual time scales. We reveal regular advection of the Pechora plume through the Kara Strait into the Kara Sea. In addition, we describe formation of a significant area of increased salinity within the Pechora plume formed during wind-induced coastal upwelling events. The results of this research are of key importance for understanding the physical, biological, and geochemical processes in the Pechora Sea and the adjacent areas of the Barents and Kara seas.

Synoptic and Seasonal Variability of Small River Plumes in the Northeastern Part of the Black Sea

Small river plumes are typical features at many coastal regions in the World Ocean. These water masses have relatively small areas and volumes; however, due to their energetic dynamics localized in a thin surface layer, they strongly affect coastal circulation, water quality, and ocean-atmosphere interaction. In this study, we investigate external factors, which govern synoptic and seasonal variability of small river plumes, and, therefore, affect land-ocean fluxes of fluvial water and biogeochemically important material. We use numerical modeling to simulate small river plumes at the northeastern part of the Black Sea. We describe the response time of small river plumes to changes in river discharge and wind forcing conditions, which determines variability of river plumes at different time scales. We reveal that the influence of river plumes on coastal processes depends not only on total annual river discharge volume, but also on temporal distribution of high-discharge and low-discharge periods. Seasonal and synoptic features of local atmospheric circulation could strongly modify the relation between river plume characteristics and river discharge rate. The results obtained in this study are important for better assessment of delivery and fate of river-borne suspended and dissolved matter, as well as floating litter in coastal areas.

Riverine Litter Flux to the Northeastern Part of the Black Sea

Rivers are among the main sources of marine litter, especially for semi-isolated sea areas with high populations and intense economic activity. The semi-isolated Black Sea located in the Eastern Europe is an example of such an area, whose watershed basin is under high anthropogenic pressure. In this study, we report the results of the first long-term monitoring program of floating litter at several rivers inflowing to the northeastern part of the Black Sea. We describe the main characteristics of registered marine litter, including the distribution of its type and size. Based on the obtained results, we reveal the relation between river discharge rate and the litter flux for the considered rivers. Using this relation extended to all rivers of the study area, we assess the total annual flux of riverine litter to the northeastern part of the Black Sea.

Investigating the potential of liquefaction issue of some Turkish dams during earthquakes

This research is carried out to investigate and assess the critical role of soil properties and their content in influencing the soil liquefaction phenomenon that takes place when an earthquake happens. A case study is taken into account in this work, representing the Karakaya Dam. Two research approaches were implemented to achieve the research goal, including extrapolation in Excel and numerical optimization using linear regression. The outputs revealed that the annual temperature in the future of zones around the Karakaya Dam, including Azami, Ortalama, and Asgari, would witness a moderate increase of about 3 to 6 degrees Celsius next decade. Moreover, the research confirmed that the Euphrates River discharge rate at the Karakaya Dam would witness a significant increase from (100-350 m3) to (2,590-2,640 m3) in 2029, explaining that temperature and discharge rate may influence the liquefaction. Meanwhile, the research outputs indicated that soil temperature under the Karakaya Dam and chemical elements would not variate significantly next decade. Notwithstanding, the pH number will change widely from 4.14 to 9.74 in 2029. Besides, the most significant chemical molecule concentration in the soil under the Karakaya Dam is the phosphite anion, corresponding to a minimum and maximum concentration of 1 and 2 μg/m2, respectively.

Revised monthly energy generation estimates for 1,500 hydroelectric power plants in the United States

The U.S. Energy Information Administration (EIA) conducts a regular survey (form EIA-923) to collect annual and monthly net generation for more than ten thousand U.S. power plants. Approximately 90% of the ~1,500 hydroelectric plants included in this data release are surveyed at annual resolution only and thus lack actual observations of monthly generation. For each of these plants, EIA imputes monthly generation values using the combined monthly generating pattern of other hydropower plants within the corresponding census division. The imputation method neglects local hydrology and reservoir operations, rendering the monthly data unsuitable for various research applications. Here we present an alternative approach to disaggregate each unobserved plant’s reported annual generation using proxies of monthly generation—namely historical monthly reservoir releases and average river discharge rates recorded downstream of each dam. Evaluation of the new dataset demonstrates substantial and robust improvement over the current imputation method, particularly if reservoir release data are available. The new dataset—named RectifHyd—provides an alternative to EIA-923 for U.S. scale, plant-level, monthly hydropower net generation (2001–2020). RectifHyd may be used to support power system studies or analyze within-year hydropower generation behavior at various spatial scales.

Experimental assessment of downstream environmental DNA patterns under variable fish biomass and river discharge rates

AbstractThe development of environmental DNA (eDNA) methods toward implementation as a cost‐effective, nonlethal tool for fish biomonitoring in lotic environments requires insights on the temporal and spatial distribution of eDNA in river systems. Yet, little is known on how downstream eDNA dispersal is affected by the combination of river discharge and source biomass effects. In this study, we aimed at unraveling the effect of source‐ and system‐specific processes on the stream reach of eDNA. We used a longitudinal cage study in two river sections characterized by a significantly different discharge rate, where two invasive and two native fish species were introduced under two contrasting biomass treatments. Using droplet digital PCR (ddPCR) analyses, we found that eDNA concentrations become strongly reduced 2 km downstream from the source, an effect that is strengthened with increasing river discharge and coinciding dilution effects. Higher discharge rates resulted in equal or even higher detection probabilities at increasing distance from the source. The introduction of high fish stock biomass resulted in an increase of eDNA concentrations, as well as detection probabilities and in parallel reduced the stochasticity of the measurements. A peak in eDNA concentrations at a downstream distance ranging between 300 m and 2 km confirms the complexity of plume‐shaped downstream eDNA patterns. Our results showed interspecific variation in eDNA emission and suggest species‐specific differences in eDNA persistence. This study underlines the impact of both river discharge rate and source biomass on downstream eDNA detection and dispersal patterns.

Lake Sturgeon (Acipenser fulvescens) in Goulais Bay, Lake Superior: Cohort strength determinants and population viability

Lake Sturgeon (Acipenser fulvescens) is a species of conservation concern throughout North America, and healthy populations are rare. Earlier sampling efforts identified the Goulais Bay population in Lake Superior as a potentially healthy population after three years of sampling. With seven additional years of sampling, we updated the earlier analysis and developed a matrix population model to conduct a population viability analysis (PVA). We identified a non-linear relationship between cohort strength and May river discharge rate which was incorporated into the population model to evaluate the influence of future discharge scenarios on population persistence. Population size was estimated, with an open-population mark-recapture model, at approximately 5,200 juvenile Lake Sturgeon. This estimate equates to approximately 440 mature females and 625 mature males in the population. A population of this size has a probability of extinction of 4 % and 18 % over 250 and 1000 years under status quo conditions. If the May river discharge were to decrease in the future, which may represent the most likely scenario under future climate conditions, our model predicts an increased risk of population extirpation. This indicates that increased management actions may be required to ensure this population remains resilient.

Dissolved Trace Metals and Organic Matter Distribution in the Northern Adriatic, an Increasingly Oligotrophic Shallow Sea

We report a monthly distribution of Zn, Cd, Pb, Cu, Ni and Co, biologically relevant trace metals (TMs), within one year, in the productive surface layer at two stations with different trophic characters in the northern Adriatic (NA). The TM data was accompanied by a multivariable dataset, including dissolved organic carbon (DOC), surface-active organic substances (SAS), nitrogen-containing polymeric organic material (N-POM), nutrients, pH, dissolved O2, chlorophyll a (Chl a), seawater temperature, and the Po River discharge rate. At the eu- to mesotrophic station 108, the concentrations of dissolved TMs were 5–116 nM for Zn, 0.04–0.18 nM for Cd, 0.05–0.63 nM for Pb, 3–17 nM for Cu, 4–11 nM for Ni, and 0.2–1.2 nM for Co, while at the oligotrophic station 107, they were 6–224 nM for Zn, 0.03–0.16 nM for Cd, 0.05–1.25 nM for Pb, 3–17 nM for Cu, 4–19 nM for Ni, and 0.1–0.7 nM for Co. The characterization of organic matter (OM) in conjunction with the analysis of correlations with TMs indicated that the OM–TMs interactions differed between the two stations; namely, the freshly produced OM detected at station 108 was probably involved in the complexation of Cu, Co, Cd, and Ni, whereas at station 107, such complexation processes were not present. Accumulation of DOC was observed during the summer months at both stations. Our results present a significant contribution to biogeochemical studies in the NA by focusing on the complexity of TM–OM interactions, which is a prerequisite for interpretation of their responses to local and global changes.

Spreading and accumulation of river-borne sediments in the coastal ocean after the environmental disaster at the Doce River in Brazil

This study is focused on the fate of a large volume of mine slurry discharged from the Doce River (DR) to the coastal ocean after the worst environmental disaster in Brazilian which occurred in November 2015. We used Eulerian (ROMS) and Lagrangian (STRiPE) numerical models, as well as satellite remote sensing data, to study the spreading and seafloor accumulation of fine river-borne sediments during the initial six months following the disaster. We show that the regions of intense sediment accumulation were determined by spreading patterns of the surface-advected DR plume. The river discharge rate governed the plume surface area, while its position depended on local wind forcing conditions. The spreading of sediments carried by the DR plume was dominated by southward transport caused by prevailing upwelling-favorable northeasterly winds during the study period. Under high discharge conditions, river-borne sediments were transported over 100 km southward from the DR mouth and reached the outer shelf. In contrast, sediments were arrested near the mouth during drought periods and remained on the inner shelf. As a result, fine river-borne sediments accumulated on the seafloor, mainly in the large shallow shelf area southward from the DR mouth. Conversely, only a small fraction of residue was deposited northward. Thus, the Environmental Protection Area (EPA) of Costa das Algas, located 40 km southward from the DR, potentially exhibited more susceptibility to sediment arrival. On the other hand, their influence on Abrolhos Marine National Park, located 200 km northeastward from the DR mouth, was presumably minimal.

Water Exchange Between the Gulf of Ob and the Kara Sea During Ice-Free Seasons: The Roles of River Discharge and Wind Forcing

The Gulf of Ob is among the largest estuaries in the World Ocean in terms of area, watershed basin, and freshwater discharge. In this work, we describe the roles of river discharge and wind forcing on the water exchange between the Gulf of Ob and the Kara Sea during ice-free seasons. This work is based on the extensive in situ measurements performed during 10 oceanographic surveys in 2007–2019. Due to large river runoff (∼530 km3 annually) and low tidal forcing (&amp;lt;0.5 m/s), the estuarine processes in the Gulf of Ob during the ice-free season are generally governed by gravitational circulation. Local wind forcing significantly affects general estuarine circulation and mixing only in rare cases of strong winds (∼10 m/s). On the other hand, remote wind forcing over the central part of the Kara Sea regularly intensifies estuarine—sea water exchange. Eastern winds in the central part of the Kara Sea induce upwelling in the area adjacent to the Gulf of Ob, which increases the barotropic pressure gradient between the gulf and the open sea. As a result, intense and distant (120–170 km) inflows of saline water to the gulf occur as compared to the average conditions (50–70 km). Remote wind forcing has a far stronger impact on saltwater intrusion into the Gulf of Ob than the highly variable river discharge rate. In particular, saltwater reaches the shallow central part of the gulf only during upwelling-induced intense inflows. In the other periods (even under low discharge conditions), fresh river water occupies this area from surface to bottom. The upwelling-induced intense inflows occur on average during a quarter of days (July to October) when the gulf is free of ice. They substantially increase the productivity of phytoplankton communities in the gulf and modify the taxa ratio toward the increase of brackish water species and the decrease of freshwater species.