Phytoplankton Primary Production Research Articles

Primary Production in the Kara, Laptev, and East Siberian Seas.

Understanding of the primary production of phytoplankton in the Kara Sea (KS), the Laptev Sea (LS), and the East Siberian Sea (ESS) remains limited, despite the recognized importance of phytoplankton in the Arctic Ocean. To address this knowledge gap, we conducted three NABOS (Nansen and Amundsen Basins Observational System) expeditions in 2013, 2015, and 2018 to measure in situ primary production rates using a 13C-15N dual-tracer method and examine their major controlling factors. The main goals in this study were to investigate regional heterogeneity in primary production and derive its contemporary ranges in the KS, LS, and ESS. The daily primary production rates in this study (99 ± 62, 100 ± 77, and 56 ± 35 mg C m-2 d-1 in the KS, LS, and ESS, respectively) are rather different from the values previously reported in each sea mainly because of spatial and regional differences. Among the three seas, a significantly lower primary production rate was observed in the ESS in comparison to those in the KS and LS. This is likely mainly because of regional differences in freshwater content based on the noticeable relationship (Spearman, rs = -0.714, p < 0.05) between the freshwater content and the primary production rates observed in this study. The contemporary ranges of the annual primary production based on this and previous studies are 0.96-2.64, 0.72-50.52, and 1.68-16.68 g C m-2 in the KS, LS, and ESS, respectively. Further intensive field measurements are warranted to enhance our understanding of marine microorganisms and their community-level responses to the currently changing environmental conditions in these poorly studied regions of the Arctic Ocean.

Microbial food web changes induced by terrestrial organic matter and elevated temperature in the coastal northern Baltic Sea

Climate change has been projected to cause increased temperature and amplified inflows of terrestrial organic matter to coastal areas in northern Europe. Consequently, changes at the base of the food web favoring heterotrophic bacteria over phytoplankton are expected, affecting the food web structure. We tested this hypothesis using an outdoor shallow mesocosm system in the northern Baltic Sea in early summer, where the effects of increased temperature (+ 3°C) and terrestrial matter inputs were studied following the system dynamics and conducting grazing experiments. Juvenile perch constituted the highest trophic level in the system, which exerted strong predation on the zooplankton community. Perch subsequently released the microbial food web from heavy grazing by mesozooplankton. Addition of terrestrial matter had a stronger effect on the microbial food web than the temperature increase, because terrestrial organic matter and accompanying nutrients promoted both heterotrophic bacterial production and phytoplankton primary production. Moreover, due to the shallow water column in the experiment, terrestrial matter addition did not reduce the light below the photosynthesis saturation level, and in these conditions, the net-autotrophy was strengthened by terrestrial matter enrichment. In combination with elevated temperature, the terrestrial matter addition effects were intensified, further shifting the size distribution of the microbial food web base from picoplankton to microphytoplankton. These changes up the food web led to increase in the biomass and proportion of large-sized ciliates (&amp;gt;60 µm) and rotifers. Despite the shifts in the microbial food web size structure, grazing experiments suggested that the pathway from picoplankton to nano- and microzooplankton constituted the major energy flow in all treatments. The study implies that the microbial food web compartments in shallow coastal waters will adjust to climate induced increased inputs of terrestrial matter and elevated temperature, and that the major energy path will flow from picoplankton to large-sized ciliates during the summer period.

Regulation of a surface chlorophyll hotspot by wind-driven upwelling and eddy circulation in the Santa Barbara Channel, Southern California

While most of the U.S. Pacific coast is dominated by strong wind-driven upwelling in the spring and regular seasonal cycles of phytoplankton primary production, the Southern California Bight has weak intermittent wind-driven upwelling and low phytoplankton concentrations due to its irregular sheltered coastline. However, the Santa Barbara Channel (SBC), located in the northern Southern California Bight, contains an anomalous hotspot of phytoplankton biomass. We use 3D ocean circulation and particle tracking models, an empirical temperature-nitrate relationship, and satellite observations of surface chlorophyll from 1998 to 2007 to determine how wind-driven upwelling and cyclonic eddy circulation govern phytoplankton dynamics in the SBC. Our findings show that elevated surface chlorophyll in the spring is driven by the coupling of wind-driven upwelling and cyclonic eddy circulation and requires the presence of both high nitrate from wind-driven upwelling and prolonged residence times from eddy circulation. Long residence times, created by persistent cyclonic eddy circulation, allow nitrate transported into the surface layer by wind-driven upwelling to be retained in the SBC long enough to meet the required timescales for phytoplankton nutrient uptake and accumulation, overcoming the typically weak wind-driven upwelling of the Southern California Bight. Typical spring upwelling periods (SUPs) have high levels of surface chlorophyll, which are produced by the balanced coupling of upwelling strength and cyclonic eddy circulation. For two years of our study, 1998 and 1999, the SUP did not correlate with elevated surface chlorophyll. Corresponding to a strong El Niño event, the 1998 SUP had exceptionally weak wind-driven upwelling, which did not produce sufficient levels of nitrate to stimulate elevated surface chlorophyll. For the 1999 SUP, a strong La Niña event produced unusually strong wind-driven upwelling, which resulted in very high levels of nitrate, but suppressed eddy circulation and residence times to the point where phytoplankton biomass could not accumulate in the SBC. These anomalous SUPs illustrate that when wind-driven upwelling is too strong or too weak, the balance between wind-driven upwelling and cyclonic eddy circulation is disrupted, resulting in a dramatic reduction of surface chlorophyll, which may become more frequent with climate-driven upwelling changes in the future.

Increased sea ice melt as a driver of enhanced Arctic phytoplankton blooming.

Phytoplankton primary production in the Arctic Ocean has been increasing over the last two decades. In 2019, a record spring bloom occurred in Fram Strait, characterized by a peak in chlorophyll that was reached weeks earlier than in other years and was larger than any previously recorded May bloom. Here, we consider the conditions that led to this event and examine drivers of spring phytoplankton blooms in Fram Strait using in situ, remote sensing, and data assimilation methods. From samples collected during the May 2019 bloom, we observe a direct relationship between sea ice meltwater in the upper water column and chlorophyll a pigment concentrations. We place the 2019 spring dynamics in context of the past 20 years, a period marked by rapid change in climatic conditions. Our findings suggest that increased advection of sea ice into the region and warmer surface temperatures led to a rise in meltwater input and stronger near-surface stratification. Over this time period, we identify large-scale spatial correlations in Fram Strait between increased chlorophyll a concentrations and increased freshwater flux from sea ice melt.

The influence of biochemical parameters on primary production in the Gulf of Gdańsk region: A model study

Understanding the changing levels of biochemical parameters and the factors that influence them throughout the seasons is crucial for comprehending the dynamics of marine ecosystems. It also helps us identify potential threats that could harm their condition, aiding decision-making processes related to their protection. This study focuses on examining the variations in nutrients (such as nitrates, phosphates, and silicates), dissolved oxygen, and phytoplankton within the Gulf of Gdańsk. Additionally, we analyze the primary production process at three representative locations. To achieve this, we used data from the EcoFish biochemical numerical model. To ensure the model's accuracy, we compared its results with in situ data from the ICES database. The comparison revealed high correlations and minimal errors. Furthermore, we investigated how limiting factors impact primary phytoplankton production and demonstrated how the intensity of spring diatom blooms influences the nature of cyanobacterial blooms in the summer.

THE RELATIONSHIP OF PRIMARY PRODUCTIVITY OF PHYTOPLANKTON WITH OCEANOGRAPHIC PARAMETERS IN THE WATERS OF LUBUK GAUNG SUB-DISTRICT, SUNGAI SENIN DISTRICT, DUMAI

The waters of Lubuk Gaung Village, Sungai Sembilan District are areas that are widely used as transportation routes. Activities in these waters will cause environmental pollution, which affects the life of phytoplankton. The purpose of this study was to determine the relationship between the primary productivity of phytoplankton with oceanographic parameters in the waters of Lubuk Gaung Village, Sungai Sembilan District, Dumai. The method used is the survey method to determine the research station and the in situ method for measurement and sampling of oceanographic parameters. The results obtained are Oceanographic parameters from the three research stations, namely Brightness = 30 – 49 cm, Turbidity = 47.4 – 58.4 FTU, TSS = 124 – 209 mg/L, and BOD = 0.408 – 1.224 mg/L. The average value of primary productivity of the waters ranged from 48.07 to 79.69 mgC/m3/day. The value of primary productivity at station II is categorized into Oligotrophic, namely low waters. Stations I and III are categorized into mesotrophic waters, namely medium waters. The relationship between brightness, turbidity, and TSS with primary productivity has a very strong and positive (unidirectional) correlation value. The relationship between BOD and primary productivity has a very strong and negative (opposite) correlation.

Lateral Advection of Particulate Organic Matter in the Eastern Indian Ocean

AbstractThe Argo Abyssal Plain (AAP), south of Java and northwest of Australia in the tropical eastern Indian Ocean, is an oligotrophic region (low in chlorophyll and nutrients), downstream of the Indonesian throughflow. The processes that supply nitrogen to the AAP and support ecosystem production are unknown. Here we quantified lateral advection of particulate organic matter (POM) and the role of this advected POM in supplying new nitrogen (i.e., allochthonous nitrogen supply) to the mixed layer of the AAP using 14 yr of remotely sensed data, combined with sampling undertaken on a research cruise in February 2022. Our results indicate that the average net primary productivity of phytoplankton in this offshore oligotrophic region is 98.5 Gg C d−1 and that lateral advection transports 1.21 Gg C d−1 of particulate organic carbon (POC) into the region. We find that lateral advection of POM within the mixed layer supplies an annual average of 12% (95% C.I. = 5.2%–49%) of allochthonous “new” nitrogen supporting phytoplankton productivity, if regenerated to nutrients through microbial processes. Accounting for lateral transport in the deep euphotic zone, lateral transport supplies an average of 32% (10%–&gt;100%) of new nitrogen, although this calculation is less certain due to inability to constrain subsurface POM fields. Our data suggest that lateral advection is a quantitatively important but not dominant source of nitrogen supporting new production. Overall, approximately half of the lateral transport is driven by transient eddies (mostly during winter) highlighting the importance of mesoscale circulation.

Chlorophyll response to wind and terrestrial nitrate in the western and southern continental shelves of the Gulf of Mexico

In Mexico, 16 rivers directly discharge into the Gulf of Mexico. The Mexican rivers and those coming from the United States generate large regions in which phytoplanktonic primary production possesses a seasonal component that is linked to these nutrient-rich freshwater inputs. In the present study, new simulated flow and daily nutrient data were obtained for the largest Mexican rivers. These data were integrated as forcings in a configuration of the hydrodynamic Coastal and Regional Ocean COmmunity model coupled to an N2PZD2 biogeochemical model. We present a 21 year simulation using two different configurations. The first included river forcing, and the second did not consider their influence. The results were validated with satellite images of the surface chlorophyll concentration and discussed with data presented in previous studies. The model was able to realistically reproduce the seasonal dynamics of primary production in the Gulf of Mexico based on the concentration and distribution of chlorophyll, both at the surface and in the water column. We found significant differences in the response of chlorophyll to the input of nitrate from the rivers between both model configurations. The largest and most evident in the northern region of the continental shelf followed by the Bay of Campeche and Tamaulipas-Veracruz shelves. Finally, using the configuration with the river forcing, the physical processes that influence the dynamics of chlorophyll concentration in the deep region and continental shelf of the gulf were determined. In the deep region, primary production was driven by vertical mixing induced by the passage of cold fronts during winter and mesoscale structures. On the continental shelf, such dynamics were driven by coastal upwelling and fluvial nutrient contributions.

Horizontal Heterogeneities of Functioning of Phyto- and Zooplankton in a Lake With Wind Currents

A hypothesis about the formation of horizontal heterogeneities of zooplankton and phytoplankton for the lake subjected to regular daily changes in wind currents has been tested. Formation of horizontal heterogeneities is based on a combination of low-amplitude vertical migration of zooplankton and epilimnion wind currents: surface currents, which bring water depleted in zooplankton to the downwind shore (in the direction in which the wind is blowing), and compensatory above-thermocline ones, which bring zooplankton-enriched water to the upwind shore (against the wind). The spatial separation of phytoplankton and zooplankton may result in the weakening of trophic links between these trophic levels. The hypothesis was tested in 2020 in the pelagic zone of Lake Shira (Khakassia, Russia), a brackish meromictic water body with simple bathymetry and a simple food web. The epilimnion horizontal heterogeneities were assessed using a survey across the lake by measuring biological and physical parameters with a submersible fluorimeter probe and a plankton net at 11 stations and recording the dynamics of wind speed and direction. Differences in the values of primary production, plankton destruction, and intensity of phytoplankton grazing by zooplankton near the downwind and upwind shores were estimated using the bottle method in 3 experiments. The experiments confirmed the expected differences in the functioning of the trophic cascade near the northeastern (more often upwind during the day and downwind at night) and south-southwestern (downwind during the day and upwind at night) shores. Namely, the concentration of chlorophyll a, the gross and net primary production of phytoplankton (estimated by bottle and fluorescent methods), and the daily intensity of zooplankton feeding (based on chlorophyll) were higher near the southern coast, while the biomass of net zooplankton and the respiration rate of the plankton community were higher near the northeastern shore, which coincided with the pattern of phyto- and zooplankton distribution over the lake according to the sampling data under similar weather conditions. The hypothesis was confirmed and supplemented by the data on the evening-night vertical migrations of zooplankton.

Environmental factors drive phytoplankton primary productivity in a shallow Lake

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Spatial and daily variability of oxygen balance and chlorophyll content in the Bay Sivash ecosystem, the world’s largest hypersaline lagoon

Oxygen concentration, salinity, temperature, total suspended solids, chlorophyll a content as well as wind direction and speed were measured in 13 sites of Bay Sivash, the largest hypersaline water body in the world, in August 2021. The oxygen concentration and oxygen saturation of water increased significantly after sunrise between 6.30 and 14.00 h, from 1.2–1.3 mgO L−1 to 5.0–6.0 mgO L−1 and from 25%–28% to 112%–142%, respectively. Between about 11 am and 4 pm, the flow of oxygen was from the lagoon to the atmosphere, averaging 0.1 mgO L−1 h−1. The rest of the time, the flow of oxygen was from the atmosphere to the lagoon, on average 0.13 mgO L−1 h−1. There was a significant negative correlation between salinity and oxygen concentration in the lagoon. Chlorophyll a concentration varied significantly during the daytime negatively depending on the oxygen concentration and temperature. The primary production of phytoplankton averaged 5–7 mgC L−1 h−1. New data indicate that in summer at night, anoxic conditions also can form in places where there are no algal mats.

Ocean dynamics and biological feedbacks limit the potential of macroalgae carbon dioxide removal

In combination with drastic emission reduction cuts, limiting global warming below 1.5 °C or 2 °C requires atmospheric carbon dioxide removal (CDR) of up to 16 GtCO2 yr−1 by 2050. Among CDR solutions, ocean afforestation through macroalgae cultivation is considered promising due to high rates of productivity and environmental co-benefits. We modify a high-resolution ocean biogeochemical model to simulate the consumption of dissolved inorganic carbon and macronutrients by idealised macroalgal cultivation in Exclusive Economic Zones. Under imposed macroalgal production of 0.5 PgC yr−1 with no nutrient feedbacks, physicochemical processes are found to limit the enhancement in the ocean carbon sink to 0.39 PgC yr−1 (1.43 GtCO2 yr−1), corresponding to CDR efficiency of 79%. Only 0.22 PgC yr−1 (56%) of this air–sea carbon flux occurs in the regions of macroalgae cultivation, posing potential issues for measurement, reporting, and verification. When additional macronutrient limitations and feedbacks are simulated, the realised macroalgal production rate drops to 0.37 PgC yr−1 and the enhancement in the air–sea carbon flux to 0.21 PgC yr−1 (0.79 GtCO yr−1), or 58% of the macroalgal net production. This decrease in CDR efficiency is a consequence of a deepening in the optimum depth of macroalgal production and a reduction in phytoplankton production due to reduced nitrate and phosphate availability. At regional scales, the decrease of phytoplankton productivity can even cause a net reduction in the oceanic carbon sink. Although additional modelling efforts are required, Eastern boundary upwelling systems and regions of the Northeast Pacific and the Southern Ocean are revealed as potentially promising locations for efficient macroalgae-based CDR. Despite the CDR potential of ocean afforestation, our simulations indicate potential negative impacts on marine food webs with reductions in phytoplankton primary production of up to −40 gC m−2 yr−1 in the eastern tropical Pacific.

Biomarker evidence of the water mass structure and primary productivity changes in the Chukchi Sea over the past 70 years

The Chukchi Sea has experienced significant changes under global warming in the Common Era, including the shift of primary productivity. However, modern observations are too short to fully investigate the effects of environmental changes in this area. Here, we analyzed lipid biomarkers (e.g. long-chain n-alkanes, n-alkanols, n-alkanoic acids, diols, and sterols) from a sediment core (R07) collected from the Chukchi Sea shelf to determine phytoplankton primary productivity variations and factors influencing these changes over the past 70 years. Similar trends of the abundance of terrestrial ecosystem-derived compounds (e.g. long-chain n-alkanes, n-alkanols, n-alkanoic acids, and C32 1,15-diol) indicate that terrigenous input increased from ca. 1946 towards ca. 1983 and then decreased thereafter. In comparison, biomarkers with marine origin indicate that the ratio of diatoms to dinoflagellates increased after ca. 1983 towards the core-top (ca. 2011). Concurrent changes in terrigenous input and phytoplankton community indicated a shift in water mass structure at ca. 1983 (i.e. the Alaska Coastal Water decreased and the Bering Sea Water increased), which may be attributed to the phase shift of the Arctic Oscillation and/or unsynchronized flow changes in different water masses. Owing to the different water mass properties, the change of water mass structure caused intense water mixing and the resulting high turbidity in the study area, which led to light limitation for phytoplankton growth. These conditions probably account for the reduced phytoplankton primary productivity from ca. 1983 to ca. 2000 in the general trend of increasing. The results indicate that, in addition to global warming and sea ice retreat, other factors, such as change in regional water mass structure (i.e. different water masses), may also have a significant influence on the primary productivity and the phytoplankton community in the Chukchi Sea shelf.

Relationships between biomass of phytoplankton and submerged macrophytes and physicochemical variables of water in Lake Caohai, China: Implication for mitigation of cyanobacteria blooms by CO2 fertilization

Reducing nutrient input in aquatic ecosystems has been widely recognized as a way to mitigate eutrophication. The paradigm of nutrient limitation by N and P is pervasively accepted, without considering the possibility of C limitation. However, our assumption that C might affect the aquatic biological composition, lacks fieldwork support. We tested the co-limitation of C/N/P on the growth of submerged macrophytes and phytoplankton in the Caohai Lake, a typical shallow karst lake in southwestern China. This study documented the seasonal variations in the concentration and comparative availability of nutrients C/N/P, in addition to physicochemical parameters, submerged macrophytes biomass, and phytoplankton composition in the lake. Our results show that dissolved inorganic carbon plays a substantial role in enhancing the primary production of phytoplankton and macrophytes, which suggests that primary production can be suppressed not only by P and/or N (as generally believed) but also by C, owing to the unique physicochemical characteristics that prevail in typical karst regions. Additionally, submerged macrophytes have been found to inhibit phytoplankton growth. Further analysis showed that the proportion of Cyanobacteria over Chlorophyta and Bacillariophyta throughout the year was reduced at dissolved carbon dioxide/total nitrogen (CO2/TN) ratios (>0.2) and dissolved carbon dioxide/total phosphorus (CO2/TP) ratios (>10) in this study. Isotopic evidence further indicated that the abundance of Cyanobacteria was reduced when CO2 >30 µmol/L. In summary, the combined results suggest that when controlling N and P, CO2 fertilization may significantly affect both the growth and composition of phytoplankton communities/submerged macrophytes and carbon sequestration in karst surface water ecosystems. This implies a new “paradigm” in the mitigation of cyanobacteria blooms by adding more CO2 to aquatic ecosystems with low pCO2, during which carbon sequestration may also be enhanced.

Trends in Changes in Primary Phytoplankton Production According to Remote Sensing Data in the Deep-Sea Region of the Black Sea for 1998–2015

The analysis of long-term seasonal changes in the concentration of chlorophyll, the maximum rate of phytoplankton photosynthesis and water temperature in the surface layer of the open waters Black Sea from 1998 to 2015 has been carried out. The trends of these indicators were assessed. For the research, we used the data of satellite observations SeaWiFS and MODIS-Aqua, MODIS-Terra. Typical positive temperature trends of 4 % in the deep-water western part of the sea. An annual temperature rise in deep-water areas was noted in the western cyclonic circulation by 0.038 °C. According to average annual data in other areas, no increase was found. The increase was mainly due to the winter season. Negative trends of primary phytoplankton production within 16.4–18.6 % of the initial level according to average annual values throughout the deep-water area. Significance level — p &lt; 0.1. A decrease in primary production was observed in the summer. There were no statistically significant directional changes in chlorophyll concentration based on averaged data over 18 years. In different parts of the deep-sea area, the direction of interannual and seasonal changes in all indicators was similar. The emerging trend towards a decrease in phytoplankton productivity in recent years may lead to a restructuring of the phytoplankton community.

Saline groundwater discharge accelerates phytoplankton primary production in a Sanriku ria coastal embayment, Japan

Nutrient supply through submarine groundwater discharge into coastal seas can be critical to primary production. However, the influence of recirculated saline groundwater on phytoplankton primary production has not been fully elucidated. Here, we assessed how saline groundwater discharge stimulates phytoplankton primary production in a semi-enclosed embayment (Kesennuma Bay, Japan). We contrasted offshore nutrient supply conditions during summer (stratified condition) and autumn (vertical mixed condition). First, we measured phytoplankton primary productivity in surface seawater using the stable carbon isotope tracer method and identified water sources based on radium isotopes. Then, bioassay incubation experiments were conducted to determine the nutrients limiting phytoplankton primary production and ascertain the effect of saline groundwater discharge. The results showed that nutrients derived from saline groundwater accounted for 19.3 to 38.3, 7.1 to 19.0, and 12.7 to 21.0% of dissolved inorganic nitrogen, phosphorus, and silica concentrations, respectively, in surface seawater. Furthermore, chl a-normalized primary productivity was higher in autumn when the relative contribution of saline groundwater in surface seawater increased. The bioassay experiment showed that phytoplankton growth was most stimulated by a combination of nitrogen and phosphorus, but nitrogen addition enhanced phytoplankton growth in most cases, even at low phosphate concentration (≤0.04 µmol l-1) in seawater. Our findings suggest that input of nitrogen-enriched saline groundwater could mitigate the nitrogen limitation of phytoplankton growth, and can be more effective in the vertically mixed season due to the high contribution of offshore phosphorus to surface water. Overall, saline groundwater discharge can stimulate phytoplankton primary production, and should be considered a significant nutrient source for sustaining biological production in coastal seas.

Primary production and destruction of organic matter in Lake Arakhley (Eastern Transbaikalia, Russia)

Global climate changes affect water ecosystems. Long-term observations of climatic variables are indicative of cyclic climate changes. The fluctuations result in changes in water levels in lakes, which, in turn, alter primary production processes. Planktonic algae are the main drivers of primary production. This research continues long-term studies on hydroecology of Lake Arakhley. The lake is used for fishery and recreation. This work aims to estimate production and destruction processes in Lake Arakhley during the current transitional period between dry and wet years. To this end, we performed field studies on Lake Arakhley in August from 2016 to 2021, during the season of maximum precipitation, in the central and littoral zones of the lake. Primary production of phytoplankton in water was estimated by the oxygen light and dark bottle method. Sampling was carried out to assess physical and chemical parameters of water using a multiparameter water quality instrument. Lake Arakhley features the low level of mineralization under alkali conditions and relatively stable level of mineralization registered from 2016 to 2021. Macrophytes zone expanded after the massive flooding of the shore in 2021 hence alterating the values of such environmental factors as oxygen levels, total and mineral phosphorus, with destruction prevailing over organic matter production. Depth and transparency however contribute to significant production of organic matter in the lake. The findings can be used as the groundwork for the sustainable management of the lake.

Seasonal variation and driving factors of primary productivity of phytoplankton in Lake Changhu, Jianghan Plain

Seasonal variation and driving factors of primary productivity of phytoplankton in Lake Changhu, Jianghan Plain

Evaluation of Satellite-Derived Size-Fractionated Phytoplankton Primary Production in the South China Sea

Space-borne observations of primary production (PP) are essential for understanding the role of phytoplankton in the biogeochemical cycles on a global or regional scale. In this study, the vertically generalized production model (VGPM) and two size-fractionated PP algorithms (namely U10 and B17) were evaluated in the SCS. Comparison between estimated and in situ measured total PP showed the best performance of U10 with an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 0.65 and mean absolute percentage deviation (MAPD) of 31.11%. B17 produced better accuracy than U10 for PP from pico-phytoplankton (PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pico</sub> ) and micro-phytoplankton (PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">micro</sub> ), whereas U10-derived PP from nano-phytoplankton (PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nano</sub> ) agreed better with in situ measurements than B17-derived PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nano</sub> . Sensitivity analysis showed that PP estimation was most sensitive to chlorophyll-a (Chla), followed by euphotic zone depth (Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eu</sub> ), and photosynthetically available radiation (PAR), and physiological parameters. With regional optimization of Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eu</sub> , phytoplankton size class (PSC), photosynthesis-irradiance curve parameters, and Chla profile modelling, B17 was tuned for the SCS. Its accuracy was greatly improved, as indicated by slopes close to 1, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> s > 0.55, and MAPD < 145%, for all size classes and total PP. Application of the tuned algorithm to satellite produced data demonstrated a decreasing trend for the total PP, PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pico</sub> , and PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nano</sub> while no apparent trend for PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">micro</sub> . This study represents the feasibility of improving PP estimation from satellite observation for regional applications through retuning to local data. Our findings are useful for understanding the ecological response to climate change in the region and unveil the role of size-fractionated phytoplankton in biogeochemical and carbon cycles on a basin scale.

Distribution, Size-Morphological Structure and Production of Heterotrophic Bacterioplankton in Gorky Reservoir

The abundance, biomass, size-morphological structure, growth rate and production of bacterioplankton, the intensity of primary phytoplankton production and dark fixation of CO2, as well as the abundance and biomass of heterotrophic nanoflagellates were determined in a large plain eutrophic reservoir (Gorky Reservoir, Middle Volga). The abundance, biomass, and production of bacterioplankton were relatively high and averaged 7.6 × 106 cells/mL, 117.9 mg C/m3, and 59.2 mg C/(m3 × day), respectively. Heterotrophic nanoflagellates reached a high level of quantitative development – 6.9 × 103 cells/mL, 47.9 mg C/m3. Their biomass averaged 41.6 ± 18.4% of the bacterioplankton biomass, which indicates that, in addition to bacteria, nanoflagellates used other food sources. Small rods and cocci dominated among the size-morphological bacterioplankton groups and accounted for 36.3 and 33.3% of its total abundance, respectively. Small rods averaged more than a half (56.2%) of the total biomass and were the most stable component of the community. The growth rate and production of bacterioplankton increased in those parts of the reservoir where the medium-sized cocci and coccobacilli accounted for from 18.2 to 29.3% of the total abundance. The highest bacterial activity was recorded in the area affected by the warm waste waters of the Volgorechensk State District Power Plant. Based on the data obtained, the reservoir divided on the upper river section and the lower lake section.