Planktonic Primary Production Research Articles

Primary Production of Plankton in the Volga Reservoirs

Primary Production of Plankton in the Volga Reservoirs

Effects of different nutrient loadings on planktonic primary production in embayments of Indonesia

A study on planktonic primary production was conducted in three Indonesian embayments subjected to different levels of eutrophication. The three embayments are Jakarta, Lampung and Semangka Bay. A previous study revealed that Jakarta Bay is heavily eutrophied while Lampung Bay is moderately eutrophied and Semangka Bay is close to pristine conditions. The eutrophication state in the three bays studied was closely related with respective nutrient loading of the embayments. Annual primary production in Jakarta Bay ranged from 47 to 503 g C m-2 y-1, in Lampung Bay from 31 to 196 g C m-2 y-1 and in Semangka Bay from 14 to 40 g C m-2 y-1. Spatial gradients in primary productivity were closely related to spatial nutrient gradients in the bays, except in Semangka Bay, due to the high turbidity of the river mouth. Temporal variability in primary productivity was small, consistent with small changes in environmental parameters across seasons. Jakarta Bay which has the most eutrophied waters was the highest in terms of primary productivity, followed by Lampung Bay and Semangka Bay. The primary productivity levels in the three bays was closely related with levels of nutrient loadings. This research is of importance for the development of primary production measurement in Indonesia since it is among that uses the radiocarbon technique.

Diel variations in dissolved oxygen concentration and algal growth in the Laver pit lake, northern Sweden

The diel oxygen technique relying on automated in-situ measurements of dissolved oxygen was used as an indicator of seasonal and diurnal variations of photosynthesis in the circumneutral Laver pit lake in northern Sweden. From July to September 2017, surface water temperature, electrical conductivity, pH, and dissolved oxygen were continuously measured at a time resolution of 30 min using sensors mounted on a floating buoy. The data could be monitored in real-time using a browser-based software and permitted calculation of gross primary production (GPP), net ecosystem production (NEP), and respiration (R) in the lake. The dissolved O2 concentration showed a consistent pattern of diel variations that reached up to 0.5 mg L−1 during the warmer summer period (July–August). Towards the end of August these variations decreased in magnitude and remained at ∼0.1 mg L−1 throughout September. pH showed diel variations that mimicked those of dissolved O2, with maximum daily variations of 0.4–0.5 pH units during July and August. A seven-day moving average of GPP showed a peak during July to mid-August, and the maximum GPP value of 0.55 mg O2 L−1 day−1 is similar to those found in natural oligotrophic lakes. A phytoplankton sample showed a total biomass concentration of 24 μg L−1, with the species Chrysophyceae, Chlorophyta, and Bacillariophyta occurring in the water. Diel oxygen data indicated that respiration by autotrophs and respiration of autochthonous labile organic matter by heterotrophs dominated in the lake, as is often the case in lakes where planktonic primary production is the main supplier of labile organic carbon. A close coupling between R and GPP suggests that nearly all GPP was respired in the epilimnion. The study shows that the diel oxygen technique can be used for real-time monitoring of seasonal and diurnal variations of dissolved oxygen and pH in pit lakes. This would be a useful technique in pit lake remediation projects where fertilization is used to stimulate algal growth and metal sequestering by algae.

Diverse nature of the seasonally coastal eutrophication dominated by oceanic nutrients: An eco-system based analysis characterized by salmon migration and aquaculture

Previously, studies of coastal eutrophication have usually focused on the nutrients input from adjacent land sectors, such as rivers, submarine-ground discharges, and atmospheric depositions. Here we report two examples of well-managed seasonal eutrophication phenomena in coastal marine environments, where nutrients come predominantly from offshore: one by humans and the other by nature (higher trophic animals). In the Sanggou Bay of North China, the total amount of incoming nutrients from the open Yellow Sea is taken up by seaweeds. Seaweed, in turn, supports bivalves culture activities and absorbs nutrients emitted by finfish. In the Academy Bay of Russian Far East, a relatively high plankton primary production sustains throughout the salmon-returning season when nutrients are released from the massive carcasses of dead fish after return from the ocean to their natal streams to spawn and die. This high plankton productivity, in turn, fuels higher trophic ecosystem constituents, including whale populations of global importance. In the future, dominance of nutrients from marine sources needs to be seriously considered in studies of coastal eutrophication.

Diatom responses to warming, heavy rains and human impact in a Mediterranean lake since the preindustrial period

In the Mediterranean region, annual mean air temperature will continue to increase during the 21st century, while seasonal precipitation is expected to decrease and extreme events to be more frequent. Human-induced climate change will severely impact aquatic ecosystems. A subdecadal stratigraphic diatom record of Lake Montcortès (central Pyrenees) was investigated, focusing on the potential responses of diatoms to anthropogenic warming and catchment alteration. The study includes the end of the Little Ice Age (LIA), the transition to the industrial and postindustrial eras, and the recent global warming and its current acceleration. Sediment samples were treated and diatoms taxonomically identified. Relationships between diatom taxa abundances and climatic (temperature and precipitation) and environmental (land use, soil erosion, and eutrophication) variables were investigated using multivariate statistical methods. The results indicate that, from ca. 1716 to 1971 CE, the diatom community was dominated by Cyclotella cyclopuncta and showed small perturbations, despite the pressure of important stressors such as strong cooling episodes, droughts and an intense use of the lake for hemp retting during the 18th and 19th centuries. However, during the 20th century, other centric species gained relevance, and from the 1970s on, Cyclotella ocellata competed with C. cyclopuncta for dominance. These changes coincided with pulse-like disturbances in the form of extreme rainfall events along with the gradual 20th century increase in global temperature. These perturbations affected the planktonic diatom community and led to instability dynamics. The benthic diatom community did not reflect any comparable shifts under the effect of the same climatic and environmental variables. Because heavy rainfall episodes are likely to intensify with current climate change in the Mediterranean region, their importance as stressors of planktonic primary producers should be taken into account as potential disrupters of biogeochemical cycles and trophic networks of lakes and ponds.

Ecosystem changes through the Permian–Triassic and Triassic–Jurassic critical intervals: Evidence from sedimentology, palaeontology and geochemistry

ABSTRACTThe Permian–Triassic and Triassic–Jurassic critical intervals are among the most significant ecological upheavals in the Phanerozoic. Both evolutionary junctures are characterized by environmental deterioration associated with a marked biodiversity decline. In this study, Permian–Triassic and Triassic–Jurassic boundary sections from South China and the Northern Calcareous Alps were investigated. In order to reconstruct the interplay between biotic and abiotic processes, a multifaceted approach that included optical microscopy, X‐ray diffraction, Raman spectroscopy, stable carbon isotopes and lipid biomarkers was employed. The lower parts of these two sections are similar as both consist of limestone with abundant fossils of eukaryotic organisms. However, the Permian–Triassic record is dominated by dasyclad green algae and fusulinid foraminifera, while the Triassic–Jurassic record is typified by corals and coralline sponges. Moving upward, both sections consist mainly of micrite and marl. Concerning the Permian–Triassic section, it transits to volcanic ash intercalated by a distinct limestone bed with abundant calcispheres (tentatively attributed to ancestors of dinoflagellates). The Triassic–Jurassic section does not provide direct evidence for volcanic activity, but also becomes rich in calcisphere‐type cysts towards the top. Additionally, the section preserves abundant 4‐methyl sterenes (diagnostic for dinoflagellates) and C37–39 n‐alkanes (indicative for haptophytes). Hence, both critical intervals were associated with marked blooms of (ancestral) dinoflagellates and haptophytes (for example, coccolithophorids). These blooms were followed by ecological lag‐phases, as indicated by low carbonate contents and scarce fossils which only increased further up the sections. For both critical intervals, it is commonly assumed that the formation of voluminous volcanic provinces (Siberian Traps and Central Atlantic Magmatic Province, respectively), as well as associated processes (for example, burning of organic‐rich sediments such as coal), resulted in ecological devastation. However, results suggest that volcanism also had a positive effect on certain planktonic primary producers such as dinoflagellates and haptophytes, perhaps by delivering essential nutrients.

Glacial meltwater determines the balance between autotrophic and heterotrophic processes in a Greenland fjord

Global warming accelerates melting of glaciers and increases the supply of meltwater and associated inorganic particles, nutrients, and organic matter to adjacent coastal seas, but the ecosystem impact is poorly resolved and quantified. When meltwater is delivered by glacial rivers, the potential impact could be a reduction in light and nutrient availability for primary producers while supplying allochthonous carbon for heterotrophic processes, thereby tipping the net community metabolism toward heterotrophy. To test this hypothesis, we determined physical and biogeochemical parameters along a 110-km fjord transect in NE Greenland fjord, impacted by glacial meltwater from the Greenland Ice Sheet. The meltwater is delivered from glacier-fed river outlets in the inner parts of the fjord, creating a gradient in salinity and turbidity. The planktonic primary production was low, 20-45 mg C m-2 d-1, in the more turbid inner half of the fjord, increasing 10-fold to around 350 mg C m-2 d-1 in the shelf waters outside the fjord. Plankton community metabolism was measured at three stations, which displayed a transition from net heterotrophy in the inner fjord to net autotrophy in the coastal shelf waters. Respiration was significantly correlated to turbidity, with a 10-fold increase in the inner turbid part of the fjord. We estimated the changes in meltwater input and sea ice coverage in the area for the last 60 y. The long-term trend and the observed effects demonstrated the importance of freshwater runoff as a key driver of coastal ecosystem change in the Arctic with potential negative consequences for coastal productivity.

Linking variation in planktonic primary production to coral reef fish growth and condition.

Within low-nutrient tropical oceans, islands and atolls with higher primary production support higher fish biomass and reef organism abundance. External energy subsidies can be delivered onto reefs via a range of physical mechanisms. However, the influence of spatial variation in primary production on reef fish growth and condition is largely unknown. It is not yet clear how energy subsidies interact with reef depth and slope. Here we test the hypothesis that with increased proximity to deep-water oceanic nutrient sources, or at sites with shallower reef slopes, parameters of fish growth and condition will be higher. Contrary to expectations, we found no association between fish growth rate and sites with higher mean chlorophyll-a values. There were no differences in fish δ15N or δ13C values between depths. The relationship between fish condition and primary production was influenced by depth, driven by increased fish condition at shallow depths within a primary production ‘hotspot’ site. Carbon δ13C was depleted with increasing primary production, and interacted with reef slope. Our results indicate that variable primary production did not influence growth rates in planktivorous Chromis fieldi within 10–17.5 m depth, but show site-specific variation in reef physical characteristics influencing fish carbon isotopic composition.

Impact of Depuration Plants on Nutrient Levels in the North Adriatic Sea

Macronutrients (nitrogen—N; phosphorus—P; silicon—Si) play a crucial role in ocean surface waters stimulating the planktonic primary production; in fact, their concentrations are fundamental for the evaluation of the trophic status of the water body and eutrophication phenomena. Loads of nutrients into the sea are mainly represented by river runoff and depuration plant outflows. For this purpose, in the framework of the AdSWiM project, “Managed use of treated urban wastewater for the quality of the Adriatic Sea” levels of N-NO3, N-NO2, N-NH4, Si-Si(OH)4, P-PO4 (dissolved inorganic phosphorus—DIP) and total dissolved phosphorus (TDP) were determined colorimetrically at two sites in the Gulf of Trieste: Lignano Sabbiadoro and San Giorgio di Nogaro. For each site, during the bathing seasons of 2019 and 2020, a sample from the depuration plant (DP) outflow and another one in the bottom seawater near the discharging pipelines were collected. Results showed a strong dilution effect on nutrient levels passing from DPs to the sea, from one to three orders of magnitude and a low and not harmful concentration in seawater. The outflow composition of the two DPs showed that the main fraction of dissolved inorganic nitrogen (DIN) was represented by N-NO3 for Lignano, while in San Giorgio the major contribution came from N-NH4. Concerning phosphorus, Lignano showed a higher content (about 3 times) of P levels than San Giorgio, but a similar percentage composition, DIP:DOP (77:23), compared to the seawater site one DIP:DOP (2:98). Despite the difference between the DPs, no substantial differences were found in the sea sites, demonstrating the negligible effect of the DP outflows in the nutrient levels in the study area.

Insights into the farming-season carbon budget of coastal earthen aquaculture ponds in southeastern China

Small-hold aquaculture ponds are widespread globally, but their carbon greenhouse gas emissions are poorly quantified. In this study, we used a carbon budget approach to assess the climate footprint of three earthen aquaculture ponds in southeastern China with the whiteleg shrimp (Litopenaeus vannamei) during the farming period. The main carbon inputs to the ponds were planktonic primary production (58.5–61.8%), followed by commercial feeds (31.9–35.3%), while the major carbon outputs occurred through planktonic respiration (44.0–53.6%) and sedimentation (18.0–21.7%). Water-to-air emissions of carbon greenhouse gases (CO2 and CH4) represented only a small fraction of the carbon flow (0.8–1.6%), with a combined CO2-equivalent emission of 528.4 ± 193.3 mg CO2-eq m−2 h−1 based on GWP20. We also observed significant spatio-temporal variation in carbon greenhouse gases among the three ponds, which could be attributed to the variation in Chl-a and carbon substrate supply. Nevertheless, the magnitude of CH4 emission from these ponds was still higher than some other agro-ecosystems. Moreover, we found that only 21% of the excess organic carbon was converted to shrimp biomass, while another 20% ended up in the sediment. Our findings suggested that lowering the feed conversion ratio and removing the bottom sediments regularly could help improve production efficiency, reduce the excessive accumulation of carbon-rich detritus and minimize the climatic warming impacts of aquaculture production.

Modeling Carbon Budgets and Acidification in the Mediterranean Sea Ecosystem Under Contemporary and Future Climate

We simulate and analyze the effects of a high CO2 emission scenario on the Mediterranean Sea biogeochemical state at the end of the XXI century, with a focus on carbon cycling, budgets and fluxes, within and between the Mediterranean sub-basins, and on ocean acidification. As a result of the overall warming of surface water and exchanges at the boundaries, the model results project an increment in both the plankton primary production and the system total respiration. However, productivity increases less than respiration, so these changes yield to a decreament in the concentrations of total living carbon, chlorophyll, particulate organic carbon and oxygen in the epipelagic layer, and to an increment in the DIC pool all over the basin. In terms of mass budgets, the large increment in the dissolution of atmospheric CO2 results in an increment of most carbon fluxes, including the horizontal exchanges between eastern and western sub-basins, in a reduction of the organic carbon component, and in an increament of the inorganic one. The eastern sub-basin accumulates more than 85% of the absorbed atmospheric CO2. A clear ocean acidification signal is observed all over the basin, quantitatively similar to those projected in most oceans, and well detectable also down to the mesopelagic and bathypelagic layers.

Discovery of nondiazotrophic Trichodesmium species abundant and widespread in the open ocean

Filamentous and colony-forming cells within the cyanobacterial genus Trichodesmium might account for nearly half of nitrogen fixation in the sunlit ocean, a critical mechanism that sustains plankton's primary productivity. Trichodesmium has long been portrayed as a diazotrophic genus. By means of genome-resolved metagenomics, here we reveal that nondiazotrophic Trichodesmium species not only exist but also are abundant and widespread in the open ocean, benefiting from a previously overlooked functional lifestyle to expand the biogeography of this prominent marine genus. Near-complete environmental genomes for those closely related candidate species reproducibly shared functional features including a lack of genes related to nitrogen fixation, hydrogen recycling, and hopanoid lipid production concomitant with the enrichment of nitrogen assimilation genes. Our results elucidate fieldwork observations of Trichodesmium cells fixing carbon but not nitrogen. The Black Queen hypothesis and burden of low-oxygen concentration requirements provide a rationale to explain gene loss linked to nitrogen fixation among Trichodesmium species. Disconnecting taxonomic signal for this genus from a microbial community's ability to fix nitrogen will help refine our understanding of the marine nitrogen balance. Finally, we are reminded that established links between taxonomic lineages and functional traits do not always hold true.

Relationships Between Northern Hemisphere Teleconnection Patterns and Phytoplankton Productivity in the Neva Estuary (Northeastern Baltic Sea)

Teleconnection patterns can be an important tool for investigating the impact of climate change on biological communities. The aim of the study was, using 2003–2020 data on chlorophyll a concentrations (CHL) and plankton primary production (PP) in midsummer, to determine which of the teleconnection patterns have most pronounced effects on phytoplankton productivity in the estuary located on the border between western and eastern Europe. CHL correlated significantly with the winter values of the North Atlantic Oscillation (NAOw) and Scandinavia (SCANDw) indices, as well as with the values of the annual Polar/Eurasian (POLy) and annual Arctic Oscillation (AOy) indices. PP was significantly correlated with the values of POLy. East Atlantic/Western Russia pattern showed no significant correlation with both phytoplankton indicators. Stepwise multiple linear regressions were performed to determine the most influential indices affecting CHL and PP in the Neva Estuary. POLy, SCANDw, and NAOw appeared to be the main predictors in CHL multiple regression model, while the values of POLy and the July NAO and SCAND values were the main predictors in the PP model. According to our research, the productivity of phytoplankton in the Neva Estuary, located in the most northeastern part of the Baltic Sea, showed a significant relationship with the POL, which determines weather conditions in the northeastern regions of Eurasia. Possible mechanisms of the influence of these teleconnection patterns on phytoplankton productivity are discussed. Using the obtained multi-regression equations and the values of climatic indices, we calculated the values of CHL and PP for 1951–2002 and compared them with the results of field observations. The calculated and measured values of CHL and PP showed a significant increase in phytoplankton productivity in the Neva Estuary in the second half of the 2010s compared to earlier periods. In some years of the 1950s, 1980s, and late 1990s, CHL could also be above average and the low phytoplankton productivity should have been observed in the 1960s–1970s. This indicates a significant contribution of current climate change to fluctuation in phytoplankton productivity observed in recent decades, which should be taken into account when developing measures to protect aquatic ecosystems from eutrophication.

Species-level associations of phytoplankton with environmental variability in the Neva Estuary (Baltic Sea)

Changes in phytoplankton communities due to anthropogenic nutrient load and climate change often lead to eutrophication and harmful algal blooms that can affect biogeochemical cycling. However, little is known about the specific responses of various species to environmental variables. 17-year long data on the midsummer phytoplankton biomass in the Neva Estuary were analyzed to show the changes in the composition of phytoplankton in relation to water depth, transparence, salinity, temperature, concentrations of total phosphorus and chlorophyll a, and plankton primary production. One hundred seventy-four species and forms from eight taxonomic classes were found in phytoplankton. Fifteen species were potentially harmful. The most diverse and abundant groups were cyanobacteria, green algae and diatoms. Canonical Correspondence Analysis showed that the biomass of various species from each phytoplankton group correlated differently with environmental factors. However, within each group, there were some predominant trends in the correlative response to changes in environmental variables. The biomass of cyanobacteria was high in the middle and lower reaches of the estuary and, in general, positively correlated with water salinity. The biomass of most species of green algae and diatoms correlated negatively with it. These algae showed a positive trend in biomass in the upper and middle reaches of the estuary during the last decades that may be explained by changes in weather conditions. Taking into account that climate models predict future increases in precipitation and temperature in the northern Baltic, the future expansion of freshwater phytoplankton species in estuaries of the northern Baltic Sea is very likely.

High nitrogen to phosphorus ratio in a Texas coastal river: origins and implications for nutrient pollution sources and exports

Inorganic forms of nitrogen and phosphorus, oxygen levels, suspended solids, and planktonic primary productivity were monitored in Guadalupe River, a major waterway in southeast Texas. Our measurements have shown elevated levels of inorganic nutrients, with soluble reactive phosphorus reaching into 30 μg/L. Curiously, those elevated levels of nutrients combined with unexpectedly high nitrogen to phosphorus (N:P) ratio and low planktonic primary productivity. We attribute those phenomena to suspended solids acting as a selective sink for phosphorus while preventing effective photosynthesis in planktonic algae. At the same time, the potential for nitrogen removal is limited by abundant oxygen present in the water. This combination of low light, selective phosphorus removal, and high oxygen levels suggest that the Guadalupe River is likely to effectively export nitrogen, but not phosphorus into the estuary.

Planktonic primary production in the western Dutch Wadden Sea

Pelagic primary production measurements provide fundamental information about the trophic status of a marine ecosystem. Measured carbon fixation rates generally have a limited temporal and spatial resolution, but can be combined with Earth Observation data to extrapolate the measurements. Here,P-Ecurves were fitted for 3 yr of14C incubation data from the western Wadden Sea, using 4 different models; 2 with and 2 without photo-inhibition. The curve-fit model by Jassby & Platt (1976) best fit the data. Applying this model showed that the photosynthetic parameters, normalised for chlorophyllaconcentration, of maximum production (PBmax) and initial slope of theP-Ecurve (αB) were correlated. Seasonality in photosynthetic parameters of this model and the relationship with environmental variables were explored, with a focus on variables that can be inferred from satellite algorithms. There were no significant correlations between αBand any of the environmental variables measured. WhilePBmaxcorrelated with sea surface temperature (SST), the vertical light attenuation coefficient, silicate and nitrate + nitrite concentration, the multivariate model that best explained the variation in estimates ofPBmaxwas a model that included SST and year. In the period from 2012-2014, daily and annual production ranged between 3.4 and 3800 mg C d-1and between 131 and 239 g C m-2yr-1, respectively. Comparison of these results with historical data (1990-2003) indicates that the decline in planktonic primary production that has been happening since the 1990s has halted. Although not tested, we believe that our approach is generally applicable to coastal waters.

Interactive effects of foundation species on ecosystem functioning and stability in response to disturbance.

A major challenge in ecology is to understand determinants of ecosystem functioning and stability in the face of disturbance. Some important species can strongly shape community structure and ecosystem functioning, but their impacts and interactions on ecosystem-level responses to disturbance are less well known. Shallow ponds provide a model system in which to study the effects of such species because some taxa mitigate transitions between alternative ecosystem states caused by eutrophication. We performed pond experiments to test how two foundation species (a macrophyte and a mussel) affected the biomass of planktonic primary producers and its stability in response to nutrient additions. Individually, each species reduced phytoplankton biomass and tended to increase rates of recovery from disturbance, but together the species reversed these effects, particularly with larger nutrient additions. This reversal was mediated by high cyanobacterial dominance of the community and a resulting loss of trait evenness. Effects of the foundation species on primary producer biomass were associated with effects on other ecosystem properties, including turbidity and dissolved oxygen. Our work highlights the important role of foundation species and their interactive effects in determining responses of ecosystem functioning to disturbance.

Rewiring and indirect effects underpin modularity reshuffling in a marine food web under environmental shifts.

Species are characterized by physiological and behavioral plasticity, which is part of their response to environmental shifts. Nonetheless, the collective response of ecological communities to environmental shifts cannot be predicted from the simple sum of individual species responses, since co‐existing species are deeply entangled in interaction networks, such as food webs. For these reasons, the relation between environmental forcing and the structure of food webs is an open problem in ecology. To this respect, one of the main problems in community ecology is defining the role each species plays in shaping community structure, such as by promoting the subdivision of food webs in modules—that is, aggregates composed of species that more frequently interact—which are reported as community stabilizers.In this study, we investigated the relationship between species roles and network modularity under environmental shifts in a highly resolved food web, that is, a “weighted” ecological network reproducing carbon flows among marine planktonic species. Measuring network properties and estimating weighted modularity, we show that species have distinct roles, which differentially affect modularity and mediate structural modifications, such as modules reconfiguration, induced by environmental shifts.Specifically, short‐term environmental changes impact the abundance of planktonic primary producers; this affects their consumers’ behavior and cascades into the overall rearrangement of trophic links. Food web re‐adjustments are both direct, through the rewiring of trophic‐interaction networks, and indirect, with the reconfiguration of trophic cascades. Through such “systemic behavior,” that is, the way the food web acts as a whole, defined by the interactions among its parts, the planktonic food web undergoes a substantial rewiring while keeping almost the same global flow to upper trophic levels, and energetic hierarchy is maintained despite environmental shifts. This behavior suggests the potentially high resilience of plankton networks, such as food webs, to dramatic environmental changes, such as those provoked by global change.

Eutrophication in the Neva Estuary (Baltic Sea): response to temperature and precipitation patterns

Estuaries provide valuable ecosystem services but are threatened by eutrophication caused by increasing nutrient concentrations and climatic factors. We tested the hypothesis that cool and rainy weather in midsummer has a stronger stimulatory effect on indicators of eutrophication in the Neva Estuary than warm weather. The analysis showed that the concentration of total phosphorus in the estuary was positively correlated with the amount of precipitation and the number of rainy days in the region. Significant positive relationships were found between precipitation in midsummer and chlorophyll concentrations and plankton primary production in the upper part of the estuary. Chlorophyll concentrations and plankton primary production were higher in years with a rainy and cool July than in years with warm and dry July. Such conditions could negate existing measures to improve water quality in the Neva Estuary, meaning that greater effort will be needed.

Seasonal and interannual fluctuations of phytoplankton primary production in the rybinsk water reservoir: effect of the weather and climatic changes

Seasonal and multi-annual dynamics of phytoplankton primary production were examined in the Rybinsk water reservoir (Upper Volga) in 2005–2014. Positive links were detected between the average values of plankton primary production during the vegetation period and abiotic factors of the water environment (temperature, solar irradiation, and concentration of biogenic elements), as well as between the primary production and the index of the North Atlantic Oscillation, excluding the data for the abnormally hot summer in 2010. Water temperature increase (up to 27.9°С) in summer 2010 caused a significant increase in phytoplankton production. Significant increase of phytoplankton primary production was noted in the Rybinsk water reservoir during the analysis period.