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We simulated the decomposition of 3 dominant hygrophytes (i.e., Artemisia selengensis Turcz, Carex cinerascens Kukenth, and Phalaris arundinacea Linn) in Lake Poyang under inundation. Plant decomposition significantly altered physical and chemical variables, such as increasing turbidity and nutrients. The species numbers of cyanobacteria, diatoms, chlorophytes, and total phytoplankton significantly decreased in the A. selengensis and P. arundinacea treatments. The diversity of phytoplankton, which is mirrored by the Margalef diversity index, significantly decreased due to A. selengensis and P. arundinacea decomposition. Furthermore, A. selengensis might have a negative effect on phytoplankton diversity measured by the Shannon H index. With a large increase in nutrients, the competition mode among species shifted to light competition, which was probably unfavorable to species weakly competitive for light, resulting in diversity loss. The total densities increased in all 3 treatments, and the cryptophyte and euglenophyte densities increased significantly due to A. selengensis and P. arundinacea decomposition. This phenomenon was likely caused by the direct (assimilation and utilization) and indirect effects of dissolved organic matter release. However, the effects of C. cinerea decomposition on phytoplankton were weaker. Therefore, more attention should be given to plant decomposition under inundation in Lake Poyang due to the established phytoplankton responses. [ABSTRACT FROM AUTHOR]

To explore the effects of eutrophic deep waters offshore on red-tide outbreaks, waters were collected from 0, 20, and 40 m depths at an offshore station in the South Sea of Korea, and the growth rate of each major red-tide dinoflagellate Prorocentrum donghaiense, Tripos furca, Alexandrium fraterculus, and Margalefidinium polykrikoides in the waters was measured. No species grew at dissolved inorganic nitrogen concentrations (DIN) of < 7.0–8.4 µM, but the growth rates of all four species rapidly increased and became saturated at 12–15 µM DIN. On July 31, 2020, the DIN was 4.1–4.6 µM in 0–10 m depth waters but 8.9–18.4 µM in 20–50 m depth waters. Under these circumstances, considering that calculated reachable depths of P. donghaiense, T. furca, A. fraterculus, and M. polykrikoides were 10, 15, 24, and 52 m, respectively, A. fraterculus and M. polykrikoides can reach the deep waters and grow, but P. donghaiense and T. furca cannot. However, if the deep waters intrude and ascend by 10–20 m relative to that on July 31, four species can reach deep waters and grow, whereas if the deep waters retreat and descend by 10–20 m, only M. polykrikoides can reach the deep waters and grow. Red-tide outbreaks by M. polykrikoides in the South Sea in 2014 occurred after the deep water retreat. Thus, the position of the eutrophic deep waters, affected by their intrusion and retreat and solar insolation, can affect outbreaks of harmful M. polykrikoides red tides. [ABSTRACT FROM AUTHOR]

Sampling was done over a year (December 2020–November 2021) to study the distribution and species composition of phytoplankton in the southwestern Caspian Sea. Sea water from various depths was collected along four transects: Lisar, Anzali, Sefidrood and Chaboksar, with a total of 12 stations. A comparison was then made with the data collected in 1996 to look at the long-term changes. The increase in sea water temperature and salinity, especially in summer, was observed in the present study, which was possibly due to global warming and climate change. Amongst 48 identified phytoplankton species, Bacillariophyta (80.0%) and Cyanophyta (11.0%) were dominant. Phytoplankton abundance was measured as 99,775 ± 30,200 cell L−1 on average. The highest abundance was a non-native species Pseudo-nitzschia seriata (H. Peragallo 1900) from Bacillariophyta with more than 17,000 cell L−1, followed by another toxic species Nodularia spumigena (Mertens ex Bornet and Flahault 1888) from Cyanophyta. The N. spumigena species had the highest abundance as 5,000,000 cell L−1 in July 2021 at the Anzali region. Nutrient increase of more than threefold in 2020–2021 has caused a sevenfold increase of chlorophyll-a as compared to that in 1996. The increases in nutrients levels, sea surface temperature (> 30 °C) and salinity are generally regarded as important factors to cause variations in phytoplankton abundance and composition. The sevenfold increase of phytoplankton abundance between 1996 and 2020–2021 and change of trophic state from oligotroph to mesotroph, indicated the increase of stress and pressure on the native phytoplankton community. [ABSTRACT FROM AUTHOR]

In this study, we investigated the hydrological and ecological impacts of heavy rainfall caused by the storm Rumbia and Typhoon Lekima on Laizhou Bay (LZB) through land‒sea synchronous field surveys, online remote sensors, and simulated enclosure experiments. Within two weeks of Rumbia, approximately 9% and 16% of the annual riverine total nitrogen (TN) and total phosphorus (TP) fluxes, respectively, were transported to the LZB and the proportions were 17% and 35%, respectively, for Lekima. The land use on the watersheds increased the rates of land-derived nutrient loading and altered their biogeochemical forms. Consequently, the average concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) in the LZB increased by 2.6 and 1.0 times post-Rumbia and by 3.5 and 1.3 times post-Lekima, respectively. Relatively lower salinity and temperature, sudden increases in DIN, and strengthened coastal currents stimulated the growth of highly adaptable and small diatoms, resulting in the first diatom blooms. Subsequently, a bloom of Noctiluca scintillans formed. • Hydrology controls riverine nutrient concentrations and transport. • Heavy rainfalls changed the coastal biogeochemical environment. • A succession of phytoplankton community dominant species occurred. [ABSTRACT FROM AUTHOR]

In the present study, phytoplankton composition in relation to mucilage and accompanied physicochemical conditions were investigated in the sea water samples collected from four stations in İzmit-Kocaeli, Fatih-İstanbul, Biga-Çanakkale (in the Marmara Sea), and Rivaİstanbul (in the Black Sea). Samplings were carried out before (i.e., during September 2020) and at the beginning stage of the mucilage formations (i.e., during April 2021) which was observed in the Marmara Sea during spring and summer months of 2021. Seawater temperature, salinity, pH, and dissolved oxygen levels were measured in situ. Inorganic nitrogen, orthophosphate, and chlorophyll-a concentrations were analyzed spectrophotometrically. In total 83 phytoplankton species (44 Bacillariophyceae-BAC, 36 Dinophyceae-DIN, 2 Dictyochophyceae-DIC, and 1 Chlorophyceae-CHL) were identified during the study. BAC species were generally dominant. Among the 83 phytoplankton taxa identified, Cerataulina pelagica, Cylindrotheca closterium, Pseudo-nitzschia sp., Skeletonema costatum, Thalassiosira rotula, Alexandrium tamarense, Dinophysis acuminata, Dinophysis caudata, Dinophysis fortii, Gonyaulax fragilis, Gonyaulax spinifera, Gymnodinium sp., Gyrodinium sp., and Prorocentrum micans are known as the species associated with mucilage formation. The highest number of species was determined at the Biga-Çanakkale station (MDG25) with 38 taxa in September 2020. [ABSTRACT FROM AUTHOR]

The "larval starvation hypothesis" proposed that the growing frequency of Crown-of-Thorns Starfish (CoTS) outbreaks could be attributed to increased availability of phytoplankton. However, comprehensive field investigation on the living environment of CoTS larvae and the availability of phytoplankton are still lacking. A cruise was conducted in June 2022 in Xisha Islands, South China Sea, to study the interaction between environmental conditions and phytoplankton communities during CoTS outbreak period. The average concentrations of dissolved inorganic phosphorus (0.05 ± 0.01 μmol L−1), dissolved inorganic nitrogen (0.66 ± 0.8 μmol L−1) and chlorophyll a (0.05 ± 0.05 μg L−1) suggested that phytoplankton may be limited for CoTS larvae in Xisha Islands. Microscopic observation and high-throughput sequencing were used to study the composition and structure of the phytoplankton communities. Bacillariophyta predominated in phytoplankton communities with the highest abundance and species richness. 29 dominant species, including 4 species with size-range preferred by CoTS larvae, were identified in Xisha Islands. The diversity index of all stations indicated a species-rich and structure-stable phytoplankton community in Xisha Islands during the period of CoTS outbreak, which may contribute to CoTS outbreak. These findings revealed the structure of phytoplankton community and environmental factors in the study area during CoTS outbreak, providing the groundwork for future research into the causes and processes of CoTS outbreak. • Bacillariophyta predominated in phytoplankton community during the outbreak. • Phytoplankton species diversity may potentially affect the outbreak. • Most size-range preferred species contributed modest to phytoplankton community. • Food level in outbreak region was low for the larvae. [ABSTRACT FROM AUTHOR]

Despite their ecological and economic importance, coastal biological communities and ecosystem processes in large lakes have been understudied compared to those offshore. We investigated temporal variability in the abundance and assemblage composition of coastal organisms in northern Lake Michigan. We sampled nutrients, phytoplankton, zooplankton, periphyton, benthic invertebrates, and fish along the east coast of Beaver Island, Michigan, USA, with high temporal frequency (every d to every 2 wk) over 2 summers. We also examined connectivity between coastal and offshore habitats with both hourly water current data from the Great Lakes Coastal Forecasting System and sampling offshore 2 to 3× per summer. The abundance of littoral zone organisms varied markedly on daily to weekly timescales for both benthic invertebrates and water-column organisms (phytoplankton, zooplankton, fish). For example, zooplankton abundance changed by a mean of 297% between sampling dates at the same location. Within-season peaks in plankton abundance also differed among years. Specifically, peak chlorophyll a (Chl a) concentrations were observed 1 mo earlier in 2016 than 2015, and early summer (Jun) zooplankton abundance was 333% higher in 2016 than 2015. Furthermore, our data suggest that water currents may influence the abundance and assemblage composition of plankton, possibly by altering the flux of nutrients and organisms from offshore to coastal habitats. Specifically, zooplankton abundance increased by a mean of 194% when surface currents moved eastward before we sampled, and eastward surface velocity significantly altered zooplankton assemblage composition. Chl a concentration increased by a mean of 106% when surface currents moved northward prior to sampling. In contrast, the abundance and composition of benthic invertebrates and fish differed among sites and was not significantly related to water currents. The abundance of these organisms also declined throughout the summer. Therefore, benthic and water-column organisms are controlled by different processes, so patterns in their local abundance are out of sync. Understanding variability in coastal communities may enhance monitoring and design of effective protocols for investigating large lake ecology. Further, understanding the importance of regional movement of nutrients and organisms may be key to understanding community and ecosystem structure in coastal areas. [ABSTRACT FROM AUTHOR]

Highlights • Four temperatures and two nutrient conditions in 8 months were combined. • Under non-enriched conditions, warming affected positively, negatively, or negligibly. • Under the enriched conditions, warming in all months except one affected positively. • Thus, nutrient conditions can alter warming effects on phytoplankton production. • Ratio of initial nitrate to chlorophyll-a concentration was a critical factor. Abstract Phytoplankton production in coastal waters influences seafood production and human health and can lead to harmful algal blooms. Water temperature and eutrophication are critical factors affecting phytoplankton production, although the combined effects of warming and nutrient changes on phytoplankton production in coastal waters are not well understood. To address this, phytoplankton production changes in natural waters were investigated using samples collected over eight months, and under 64 different initial conditions, established by combining four different water temperatures (i.e., ambient T, +2, +4, and + 6 °C), and two different nutrient conditions (i.e., non-enriched and enriched). Under the non-enriched conditions, the effect of warming on phytoplankton production was significantly positive in some months, significantly negative in others, or had no effect. However, under enriched conditions, warming affected phytoplankton production positively in all months except one, when the salinity was as low as 6.5. These results suggest that nutrient conditions can alter the effects of warming on phytoplankton production. Of several parameters, the ratio of initial nitrate concentration to chlorophyll a concentration [NCCA, μM (μg L−1)−1] was one of the most critical factors determining the directionality of the warming effects. In laboratory experiments, when NCCA in the ambient or nutrient-enriched waters was ≥1.2, warming increased or did not change phytoplankton production with one exception; however, when NCCA was <1.2, warming did not change or decreased production. In the time series data obtained from the coastal waters of four target countries, when NCCA was 1.5 or more, warming increased phytoplankton production, whereas when NCCA was lower than 1.5, warming lowered phytoplankton production, Thus, it is suggested that NCCA could be used as an index for predicting future phytoplankton production changes in coastal waters. [ABSTRACT FROM AUTHOR]

To increase the efficiency of computing phytoplankton growth rate ( μ ), chlorophyll-to-carbon ( θ ) and nitrogen-to-carbon ratios ( Q N ) in three-dimensional ocean circulation models, it is preferable to directly calculate θ and Q N from ambient environmental factors instead of treating them as independent tracers. Optimality-based modeling has emerged as a novel and efficient approach to fulfill this task. However, it is still unclear precisely how the response of optimality-based models differs from conventional models. We compare a recent optimality-based phytoplankton model (PAHLOW model), based on which the familiar Droop function can be derived, to a commonly used Monod-type (MONOD) model. The two models generate similar patterns of μ with some important differences. Compared to the MONOD model, the PAHLOW model predicts higher μ under light limitation. The PAHLOW model also predicts that θ decreases with decreasing light under dim light and predicts decreasing Q N with increasing light even at constant nutrient levels. Compared to the MONOD model, these features of the PAHLOW model qualitatively agree better with laboratory data. The PAHLOW model also suffers from a few shortcomings including the underestimation of θ under very low light and two times of computation time compared to the MONOD model. The two models generate striking differences of Q N and θ in a one-dimensional implementation. Validation of such patterns will require more direct in situ measurements of μ , θ and Q N . [ABSTRACT FROM AUTHOR]

Invasive dreissenid mussels have altered plankton abundance and nutrient cycling in the Great Lakes. In this study, a 1-D hydrodynamic-biogeochemical coupled model is developed to investigate their effects at a mid-depth offshore site in Lake Michigan. Model simulation shows that water surface temperature and vertical thermal structure can be well reproduced. Driven by the simulated vertical mixing, the biological model solves the transport and transformation of nutrients, plankton and detritus in the water column. Mussel grazing and excretion are added at the bottom boundary. The biological model predicts a notable decline of phytoplankton biomass and considerable increase of dissolved phosphorus (DP) in the entire water column at the end of spring. However, the reduction of phytoplankton and the increase of DP are limited to the bottom 20 m in summer as a result of the strong stratification. Model results also show that mussels can maximize particle delivery to the benthos, as the modeled benthic diffusive flux of particulate phosphorus exceeds the passive settling rate by 4.2× on average. Model simulation over a 10-month period indicates that profundal mussels have the potential to significantly change the distribution of energy and nutrients in the water column, even in a deep and stratified environment. [ABSTRACT FROM AUTHOR]

The present study was carried out in Luoma Lake, a shallow lake in temperate eastern China. Based on a two-year study, the dynamics of phytoplankton functional groups and influencing factors were analyzed. A total of 178 taxa were identified and sorted into 20 codons, according to the phytoplankton functional group classification. In order to find the environmental factors driving phytoplankton variations, fifteen groups were analyzed in detail using redundancy analysis. Groups P (Fragilaria crotonensis), X2 (Chlamydomonas globosa, C. microsphaera and Chroomonas acuta), and MP (Navicula rotaeana) were dominant during low temperature periods, whereas groups X2, S1 (Pseudanabaena limnetica), and W1 (Euglena sp.) were dominant during high temperature periods. Water temperature, total phosphorus, and ammonium were the significant driving factors explaining phytoplankton succession. Furthermore, total phosphorus and ammonium could be broadly used in risk management for potential algal blooms in Luoma Lake. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) is one of the many severe ongoing environmental changes resulting from the increase in anthropogenic CO2. Many studies have reported that OA can affect marine organisms such as calcifying algae and animals. However, the interactive impacts of OA and other environmental stressors on marine phytoplankton remain poorly understood. First, we investigated the interactive effect of OA and iron availability on Bering Sea phytoplankton community. Second, we developed new culture media that allow for the independent manipulation of carbonate chemistry and iron availability. Third, we conducted unialgal culture experiments to examine the interactive effect of OA and iron availability using the new culture media. Through these above studies, we demonstrated that (i) iron availability could change as a result of OA in the iron-limited region of the Bering Sea, and (ii) CO2 and iron availability can independently affect individual bioelements in different ways. This paper presents a brief summary of our previous studies, recent trends in OA research worldwide and the agendas of OA-related studies. [ABSTRACT FROM AUTHOR]

Eutrophication and undesired algal blooms in surface water are common and have been linked to increasing nutrient loading. Effects of extreme events such as storms on reservoir nutrient and phytoplankton remain unclear. Here we carried out continuous high-frequency measurements in a long and narrow dam reservoir in southeast China during a storm period in June–July 2015. Our results show a strong nutrient-phytoplankton relationship as well as a very rapid response to storm runoff. We observed an increase in total suspended matter (TSM), ammonium (NH 4 -N), and dissolved reactive phosphate (DRP), with a sharp decline in chlorophyll- a (Chl- a ) in the high flow periods. Afterward, Chl- a , total phytoplankton abundance and Cyanophyta fraction elevated gradually. Nitrate was diluted at first with increasing discharge before concentration increased, likely following a delayed input of groundwater. Physiochemical parameters and Chl- a were evenly distributed in the water column during the flooding period. However, 10% of NH 4 -N and 25% of DRP were removed in surface water (0–1 m) when an algal bloom (Chl- a > 30 μg L − 1 ) occurred 10 days after peak discharge. Conversely, total particulate P (TPP) of surface water was 58% higher than in the deeper water. Dynamic factor analysis (DFA) revealed that TSM, NH 4 -N, DRP, total P and discharge significantly explain Chl- a variations following storms ( C eff = 0.89). These findings highlight that the reservoir ecosystem was vulnerable to pulse input from storm runoff and the Cyanophyta bloom was likely fueled by phosphate and ammonium rather than nitrate. [ABSTRACT FROM AUTHOR]

A field study was carried out during the summer of 2013 in Liaodong Bay, China to determine the dynamics of the phytoplankton in the bay and the extent to which primary production in the bay was constrained by environmental factors. There was little or no evidence of limitation of phytoplankton production by nutrient concentrations at any of the sampling stations, with the possible exception of a few offshore stations where phosphate concentrations were less than 30 nM. This assessment was consistent with the results of nutrient enrichment experiments and the values of light-saturated photosynthetic rates and areal photosynthetic rates. To examine the effects of irradiance and temperature on light-saturated photosynthetic rates normalized to chlorophyll a concentrations ( P o p t b ) at twelve stations where photosynthetic rates were measured by 14 C method, light-conditioned values were modeled as a function of the temperature with a satisfactory fit to our field data ( R 2  = 0.60, p  = 0.003). According to this model, the light-conditioned P o p t b values increased with temperatures from 22 °C to roughly 25 °C but declined precipitously at higher temperatures, and P o p t b values and corresponding areal photosynthetic rates at all 66 stations were estimated to be 7.6 ± 2.4 g C g −1 Chl a h −1 and 532 ± 429 gC m −2  d −1 in average, respectively. The quanta absorbed per carbon atom fixed averaged 14 ± 2 and 37 ± 10 at six coastal stations and six estuarine stations, respectively. The relatively high P o p t b values and low quantum requirements at the coastal stations implied the highly efficient usage of absorbed light by phytoplankton under nutrient-replete conditions and favorable temperatures. Comparatively, the low P o p t b values and high quantum requirements at the estuarine stations suggested rather extreme light limitation and lowly efficient usage of absorbed light in photosynthesis in the Liaohe River estuary. Areal production in Liaodong Bay appears to be controlled by a combination of temperature and light limitation. [ABSTRACT FROM AUTHOR]

Mathematical modeling is an important tool to study planktonic ecosystem dynamics and various mechanisms involved in its interaction with hydrological regime. The difficulty arises when describing plankton dynamics under wide range of estuarine environmental conditions due to inadequate knowledge to interpret the mechanism to which the environmental nature of a given situation force the model condition towards the observation and the extent to which the details of the model implementations do. We present a model of the phytoplankton dynamics and nitrogen cycling in the estuarine environment of Sundarbans. We have tested the sensitivity of each model parameter in turn by running the model to a steady-state within a certain range of value satisfying the trend of phytoplankton and nutrient distribution. In this way, it is possible to determine which parameters had the most influence on which variables and the possible mechanism underlying the ecological processes in estuarine environment. The model exhibits stable behavior for the state variables over the tidal cycle and follows the trend of phytoplankton and nutrient distribution along the river channel. This exercise will obviously set a background to have some knowledge of the tuning of the ecological model to the parameter values. [ABSTRACT FROM AUTHOR]

The ongoing restoration of the Florida Everglades has changed the hydrology in south Florida and increasing freshwater discharge has contributed to a shift in nutrients and phytoplankton in northern Florida Bay. To understand the effect of the changing nitrogen (N) forms and nitrogen:phosphorus (N:P) ratios on phytoplankton biomass and assemblage composition, five mesocosm experiments were conducted. Nutrient additions included a matrix of different forms of N (NO 3 − , NH 4 + , and DON) and P (as sodium β-glycerophosphate pentahydrate) in differing N:P molar ratios (4, 16, 32), a P alone addition, and a control. In general, chlorophyll a increased three-fold in the + P treatments and ten-fold in the + N + P treatments, while it did not increase in the + N treatments. Typically the + N + P treatments, particularly the + NO 3 − +P at the N:P molar ratio of 32, promoted high concentrations of fucoxanthin (generally indicative of diatoms) relative to chlorophyll a . While chlorophyll a did not increase significantly in the + N alone treatments, there was a change in the phytoplankton assemblage. The + N treatments, when N was in the form of + NH 4 + yielded proportionally higher zeaxanthin (generally indicative of picocyanobacteria). When the + N:P ratio increased, the relative concentrations of fucoxanthin and alloxanthin (generally indicative of cryptophytes) to chlorophyll a increased, whereas the relative concentrations of zeaxanthin and dinoflagellates (generally indicative of photosynthetic dinoflagellates) declined. This study highlights the importance of dual P and N control, particularly N in the forms of NH 4 + and DON if picocyanobacterial blooms are to be controlled. [ABSTRACT FROM AUTHOR]

Along the French Mediterranean coast, a complex of eight lagoons underwent intensive eutrophication over four decades, mainly related to nutrient over-enrichment from continuous sewage discharges. The lagoon complex displayed a wide trophic gradient from mesotrophy to hypertrophy and primary production was dominated by phytoplankton communities. In 2005, the implementation of an 11 km offshore outfall system diverted the treated sewage effluents leading to a drastic reduction of anthropogenic inputs of nitrogen and phosphorus into the lagoons. Time series data have been examined from 2000 to 2013 for physical, chemical and biological (phytoplankton) variables of the water column during the summer period. Since 2006, total nitrogen and phosphorus concentrations as well as chlorophyll biomass strongly decreased revealing an improvement in lagoon water quality. In summertime, the decline in phytoplankton biomass was accompanied by shifts in community structure and composition that could be explained by adopting a functional approach by considering the common functional traits of the main algal groups. These phytoplankton communities were dominated by functional groups of small-sized and fast-growing algae (diatoms, cryptophytes and green algae). The trajectories of summer phytoplankton communities displayed a complex response to changing nutrient loads over time. While diatoms were the major group in 2006 in all the lagoons, the summer phytoplankton composition in hypertrophic lagoons has shifted towards green algae, which are particularly well adapted to summertime conditions. All lagoons showed increasing proportion and occurrence of peridinin-rich dinophytes over time, probably related to their capacity for mixotrophy. The diversity patterns were marked by a strong variability in eutrophic and hypertrophic lagoons whereas phytoplankton community structure reached the highest diversity and stability in mesotrophic lagoons. We observe that during the re-oligotrophication process in coastal lagoons, phytoplankton shows complex trajectories with similarities with those observed in freshwater lake systems. [ABSTRACT FROM AUTHOR]

We discuss a mathematical model of growth of two types of phytoplankton, non-nitrogen-fixing and nitrogen-fixing, that both require light in order to grow. We use general functional responses to represent the inhibitory effect their biomass has on the exposure to light. We give conditions for the existence and local stability of all of the possible steady-states (die out, single species survival, and coexistence). We derive conditions for global stability of the die out and single-species steady-states and for persistence of both species when the coexistence steady-state exists. Numerical investigation illustrates the qualitative dynamics demonstrating that even under constant environmental conditions, both stable intrinsic oscillatory behavior and a period doubling route to chaotic dynamics are possible. We also show that competitor-mediated coexistence can occur due to the positive feedback resulting from recycling by the nitrogen-fixing phytoplankton. To show the impact of seasonal change in water depth, we also allow the water depth to vary in an annual cycle and discuss echo blooms in this context. [ABSTRACT FROM AUTHOR]

Seasonal distribution of dissolved nutrients (,,,,) was measured in the Sanggou Bay (SGB), China. In order to understand the impact of rivers and of the Yellow Sea (YS) and the role of integrated multi-trophic aquaculture (IMTA) in nutrient reduction and dynamics. Seasonal surveys were conducted in spring (April), summer (August), autumn (October) and winter (January) in 2011–2012 along 19 stations covering culture areas. The summer was highly impacted by excess water discharge and aquaculture activities than benthic sediments source; however other seasons were mostly influenced by the YS. Results showed that nutrients were vertically mixed and IMTA helped in reducing the elevated nutrient concentration generated by water discharge and the mixing process. The N/P ratio indicated phosphate as a limiting nutrient. Historical values of nutrient data showed that the concentration of,andincreased whiledecreased with slightly higher uptake rate ofin the bay during the last decade. A simple mass-balance model was employed to determine the nutrient budget which showed that nutrients were mostly from the river input. This implies an increase in the anthropogenic activities and assimilation ofin the SGB. Such increasing trends in nutrient concentration could cause eutrophication in the bay. [ABSTRACT FROM AUTHOR]

The Bisan Strait is a vertically well-mixed, shallow area (mean depth 13.9 m) in the Seto Inland Sea. The strait has the lowest Secchi transparency (mean 4.5 m) within the Inland Sea because of active sediment re-suspension. Therefore, in comparison with adjacent areas, phytoplankton production in the strait may be strongly affected by light availability in addition to nutrient availability. In this study, we examined environmental variables, photosynthesis–irradiance (P–I) curves and phytoplankton production in the Bisan Strait over 1 year. There were temporal variations in the light-saturated photosynthesis rate (P B m ) and initial slope of P–I curve (α B ), with maxima in autumn and minima in spring. Most of the variability in P B m and α B was explained by variations in nutrient concentrations (dissolved inorganic nitrogen) and water temperature. Meanwhile, phytoplankton production reached a peak in summer and a nadir in spring, but an autumn peak in production was not observed. Diagnostic analysis suggested that, for almost all of the year, nutrients were more important for phytoplankton growth than light limitation. However, light limitation became more important in autumn when underwater irradiance reached low levels. Therefore, the lack of an autumn peak in production is likely to be related to light limitation. We suggest that low light availability during the autumn depresses the annual rate of phytoplankton production in the Bisan Strait, in comparison with adjacent areas where seasonal stratification is established and phytoplankton blooms frequently occur in early autumn. [ABSTRACT FROM AUTHOR]

Atelomixis influences phytoplankton composition in regions where day-night temperature variations are high. Although this physical process is shown as the most important driver in a number of tropical-subtropical lake systems, information on tropical high-mountain lakes is largely lacking. We therefore studied the phytoplankton community composition and the underlying limnological variables of the atelomictic tropical high-mountain Lake Wonchi (Ethiopia) for 13 months. Nutrient levels indicated oligotrophic conditions with ammonium being the primary nitrogen form. The phytoplankton community comprised 53 taxa distributed in five taxonomic divisions, which could be assigned to 15 codas based on phytoplankton functional group classification. Partial atelomixis and low nutrient concentrations seemed to be key variables in structuring phytoplankton community composition, which was quite stable and characterized by high diversity of heavy, immobile and fast-sinking planktonic desmids of the N codon during mixing followed by diatoms ( MP codon). A near-monospecific bloom of Peridinium cinctum ( Lo codon) prevailed before the onset of lake turnover in December 2011 with conditions of nutrient depletion, which was later followed by the functional groups F- J during the episode of complete mixing and then replaced by the N codon. Non-metric multidimensional scaling resulted in a 2-dimensional solution, which revealed clear segregation of phytoplankton community to five groups. Mixing regime of the water column, conductivity, total phosphorus, ammonium and zooplankton had significant influence on the observed seasonal pattern. [ABSTRACT FROM AUTHOR]

The global environmental changes owing to natural and anthropogenic influences are challenging the structure and functioning of the ocean ecosystem. The complex processes interacting within the physical, chemical, and biological environment at different spatio-temporal scales and their impact on the ocean ecosystem processes are yet to be investigated. A long term trend on phytoplankton biomass in terms of Chlorophyll- a concentration (Chl- a), phytoplankton compositions and the processes that control the variability is required for understanding the ocean ecosystem. This study investigated decadal trends (2002–2015) of phytoplankton composition and biogeochemical parameters over the Global Ocean (GO), Southern Ocean (SO), and the Arctic Ocean (AO) using ocean color remote sensing and assimilated data from the National Aeronautics and Space Administration (NASA) Ocean biogeochemical model. The results revealed the dominance of larger cell phytoplankton mainly diatoms throughout the SO and AO; however, the coccolithophores dominate in the remaining part of the GO. Analysis of nutrients showed that nitrate is not a limiting factor for the variability of phytoplankton biomass in the SO and AO. The low nitrate concentration influenced in the rest of the GO. The photosynthetically available radiation (PAR) limiting the phytoplankton biomass and composition in the SO and AO. Although the SO is known as the high nutrient low chlorophyll (HNLC) region of the GO, the low iron concentration along with the PAR co-limits the growth of phytoplankton biomass. Trend analysis showed that an increase in Chl- a and diatoms in the SO and AO. In contrast, it declined significantly in the other regions of the GO, in response to the consistent increase in sea surface temperature. The results indicated that, shifting of phytoplankton community from regional to global scale have a greater implication for climate change and marine ecosystem. [ABSTRACT FROM AUTHOR]

This study investigates whether ecosystem alteration occurred in a shallow, lowland lake following establishment of the alien zebra mussel, Dreissena polymorpha (Pallas). Measurements of total phosphorus (TP) loads, lake TP concentrations, phytoplankton (chlorophyll a) and transparency levels for the period 1990-2008 were examined to determine the water quality effects of D. polymorpha. The period of time also included the implementation of catchment measures aimed at reducing phosphorus (P) loading to the lake. A range of loading-response models was tested to explore changes in the net sedimentation rate for P. Results show that while high TP loads from the catchment were reduced, TP concentrations in the lake remained high after D. polymorpha invasion. Decoupling of the previous chlorophyll a-TP relationship also occurred. Results from a TP loading-response model that closely simulated observed concentrations in the lake prior to establishment of D. polymorpha indicated that measured TP post establishment was statistically higher than predicted for the same conditions but without the presence of D. polymorpha. Data presented in the paper highlight the need to consider the potential impacts of invasive species in evaluations of the effectiveness of measures aimed at mitigating aquatic pollution. [ABSTRACT FROM AUTHOR]

Coupled physical–biological modelling experiments were made for the period of 1995–2009 to analyse the spatial and interannual variability of nutrients and phytoplankton production in the Gulf of Maine (GOM). The physical model was the Finite-Volume Community Ocean Model (FVCOM) and the biological model was a Nitrogen, Phytoplankton, Zooplankton, and Detritus (NPZD) model. The simulation was carried out with realistic meteorological surface forcing, five major tidal constituents, river discharge, and observation-based open boundary conditions. The results were robust with comparison to SeaWiFS chlorophyll data and historical data of nitrogen. An Empirical Orthogonal Function analysis clearly identified two dominant modes in nutrient and phytoplankton dynamics: (1) sustained nutrient supply and phytoplankton production from spring through autumn, and (2) a dominating phytoplankton bloom in spring, relatively low production in summer, and a noticeable bloom in autumn. Mode 1 was a dominant feature in strong tidal energy dissipation regions such as the southwestern shelf of Nova Scotia, Georges Bank, Nantucket Shoals, the Bay of Fundy, and the coastal regions of GOM, where tidal pumping and mixing were the major drivers for the sustained nutrient supply, and primary production showed certain resilience with less interannual variability. Mode 2 was a characteristic in the deep Gulf, the offshore region of the Scotian Shelf, and in the open sea area, where the timing and amplitude of the spring phytoplankton bloom is essentially controlled by the salinity regime, and its interannual variability was significantly influenced by freshening events controlled by local and remote forcing. [ABSTRACT FROM PUBLISHER]

Abstract: Species composition and biomass of phytoplankton assemblages of a heavily impacted lake (Lake Illawarra) and a less impacted lake (Burrill Lake) in the South-Eastern region of Australia were compared based on bimonthly samples from three sites in each lake collected between April 2005 and April 2007. Lake Illawarra was generally characterized by higher nutrient concentrations and lower salinity than Burrill Lake. Phytoplankton assemblages displayed significant differences between the two lakes in terms of the dominant species composition and patterns of seasonal change rather than biomass. Diatoms were the dominant species in Lake Illawarra on most sampling occasions. In contrast, dinoflagellates (including toxic species) dominated in Burrill Lake during most seasons. Seasonal succession of phytoplankton in the two lakes did not follow the strict spring maximum that is generally observed in temperate waters. In Burrill Lake, maximum phytoplankton biomass often occurred in winter, while the maximum biomasses in Lake Illawarra occurred in autumn, winter and spring. The significant difference of nutrient structure between two lakes and warm temperate regime was regarded as important factors to affect these results. The results suggested care should be taken when relying on estuary health “indicators”, such as chlorophyll a, rather than more detailed investigations of phytoplankton species compositions. [Copyright &y& Elsevier]

We consider a phytoplankton-zooplankton interaction model which depends on two complementary nutrients. For a realistic representation in chemostat plankton ecosystem, we have incorporated various natural phenomena such as dissolved limiting nutrients with nutrient uptake functions and yield constants. For the model with two different constant nutrient inputs with same constant washout rate, existence and stability of non-negative equilibria as well as persistence are given. We analyze the behavior of solution of model in order to answer the biological question and seek to determine the limiting behavior of the surviving organisms and the nutrients. It is observed that the constant nutrient inputs of two complementary nutrients play an important role to change steady state behavior of the system. Further it is observed that if the dilution rate of chemostat crosses certain critical value, the system enters into Hopf-bifurcation. Finally, we have derived the explicit algorithm which determines the direction of Hopf-bifurcation. Computer simulations have been carried out to illustrate different analytical results. [ABSTRACT FROM AUTHOR]

Water samples were collected at 20 sites on 4 occasions in 2009 (twice in May, and once in both August and November) along the Jiulong River, South China to examine how nutrient inputs from the Jiulong River could affect the nutrient status of the Xiamen Water. Samples were analyzed for nitrite (NO-N), nitrate (NO-N), ammonium (NH-N), phosphate (PO-P), silicate (SiO-Si), salinity, and temperature, to determine the nutrient and trophic status of the river. The results indicate that nutrients are derived mainly from river runoff. NO-N was the main form of DIN in most parts of the river. In addition, NO-N, DIN, and SiO-Si behave conservatively. There is a surplus of DIN and SiO-Si in the river, and PO-P is a limitation on phytoplankton growth. The concentration of DIN is typically above 0.60 mg/dm, and higher than 1.00 mg/dm in most parts of the river. The concentration of PO-P is typically above 0.02 mg/dm, while the concentration of SiO-Si is higher than 1.00 mg/dm. Between 2003 and 2008, samples were collected 3 times per year (May, August and November) at 27 sites in the Xiamen Water and analyzed for NO-N, NO-N, NH-N, PO-P, salinity, and temperature. We discovered that the Jiulong River was the key source of DIN into the Xiamen Water, but not PO-P, indicating the reason of the N/P molar ratio imbalance in the Xiamen Water. In the future, the effects of high DIN concentrations on the phytoplankton communities and marine ecosystems of the Xiamen Water shall be studied. [ABSTRACT FROM AUTHOR]

Field studies, experiments, and mathematical modeling showed that seasonal cycle of the Black Sea phytoplankton is regulated by three major physiological mechanisms. The first mechanism is a high specific growth rate, high values of the uptake rate and the half-saturation constant of the uptake of the limiting nutrient. It operates in spring when small-cell diatoms Pseudo-nitzschia pseudodelicatissima and Chaetoceros curvisetus grow actively. The second mechanism is notable for relatively low rates of growth, the uptake rate, and half-saturation constant; it operates mainly at the end of spring and in the beginning of summer when coccolithophore Emiliania huxleyi is in abundance. The third mechanism prevails in summer and autumn when the mass of water is regularly agitated by wind and waves with domination of macrocellular diatoms Proboscia alata and Pseudosolenia calcar-avis. The cells of these algae can accumulate nutrient ensuring numerous divisions. [ABSTRACT FROM AUTHOR]

• Prominent seasonality in spatial variation of hydro-biological parameters. • Cold-core eddy fuelled higher pre-southwest monsoon chlorophyll- a levels. • Lower surface chlorophyll- a levels despite higher nutrient during post-southwest monsoon. • Potential role of nutrient stoichiometry in determining chlorophyll- a seasonality. • Post-southwest monsoon phosphate-limitation induced lower chlorophyll- a levels off Godavari. The hydro-biological parameters such as thermohaline structure, nutrients, and chlorophyll- a (chl- a) during pre-southwest monsoon (PRSWM) and post-southwest monsoon (POSWM) periods of 2017, was investigated and compared along a coastal transect in the western Bay of Bengal (BoB). The impact of cold-core and warm-core eddies on chl- a in the very near coastal waters of the western BoB was analyzed. During PRSWM period, the water column was recharged with phytoplankton growth-promoting nutrients entrained by cold-core eddies that resulted in an increment in chl- a concentration. A three-times increase in chl- a concentration was observed due to the cold-core eddy, whereas the presence of warm-core eddy reduced the chl- a concentration by 87%. However, during POSWM period, despite having higher nitrate concentration and adequate light in the water column, the surface chl- a was substantially lesser than PRSWM. The molar ratio of ambient inorganic macronutrients during POSWM period played a significant role resulting in lower chl- a concentration. Nitrogen to phosphate (N:P) and nitrogen to silicate (N:Si) ratios were less than the Redfield values. The chl- a concentration off Godavari, a biological hotspot, was the lowest during POSWM period. This study highlights phosphate limitation off Godavari during the high river discharge period. [ABSTRACT FROM AUTHOR]

Abstract: The Júcar River, characterized by a very irregular freshwater flow, discharges into the Spanish Mediterranean coastal waters. However, the flow at its mouth is usually insignificant due to the overexploitation of upstream waters, except during intense rain periods. The presence or absence of freshwater generates two different scenarios/conditions in this ecosystem. The vertical gradient of salinity due to freshwater flows generates differences in nutrient content and phytoplankton composition and abundance along the water column. Nutrients, in general, increase their concentration in the superficial layers due to the river inputs. However, orthosilicic acid, nitrite and nitrate decrease with depth and when getting closer to the river mouth. The main freshwater phytoplankton groups are Bacillariophyceae, Chlorophyceae and Cyanobacteria. Whether or not freshwater flow reaches the estuary, the water column is almost entirely formed by marine water. Under this condition, nutrient concentrations are lower, and Cryptophyceae, Prymnesiophyceae, Dinophyceae and picocyanobacteria dominate phytoplankton composition. This paper presents the results of two campaigns with different environmental conditions (with and without freshwater flow respectively). Physicochemical and biological variables were studied at three stations placed along the estuary. [Copyright &y& Elsevier]

Eutrophication is the most widespread pressure impacting on lakes worldwide and, in general, its control is underpinned by the premise that algal biomass is regulated by phosphorus availability. This paper aims to demonstrate that not all lakes will conform to the underlying principle of the Chl:TP relationships using variables collected widely in lake monitoring programmes across the world (i.e. total phosphorus (TP) and chlorophyll a (Chl) concentrations). The ratio of annual mean Chl and TP concentrations in 94 lakes (2007 and 2008) was used as a measure of the efficiency with which TP is transferred into algal biomass (i.e. as an indicator of P limitation) to investigate the validity of the phosphorus reduction approach. Chl:TP ratios ranged from 0.02 to 0.84 in 2007 and from 0.03 to 0.96 in 2008. Chl and TP values were positively correlated (p < 0.05) with alkalinity, and negatively correlated with depth and surface area, in both years. In general, mean annual Chl and TP concentrations increased as alkalinity increased and depth decreased. However, Chl:TP ratio was highest in high alkalinity lakes in 2007, and moderate alkalinity lakes in 2008. Our results indicate that the use of TP water quality targets alone is insufficient to accurately manage eutrophication pressures at the lake specific scale, and that a wider range of ecological and ecosystem service evaluation targets would provide a more comprehensive assessment of management needs. The wide range of Chl:TP ratio values reported in this study suggests that, although reducing TP concentrations in lakes is undoubtedly a sensible approach to eutrophication management in many cases, TP reductions alone may not result in the expected reductions in phytoplankton biomass in all lakes. [Copyright &y& Elsevier]

İzmir Bay has been one of most polluted bays of the Mediterranean for a long time. When the "Big Channel Project" was completed in 2000, sewage flow into the bay ended. Hence, the influence of creeks, which are the only source of water transportation to the inner bay, was investigated in the current study. Monthly samples of creek water and seawater were taken. Basic water quality variables and nutrients were measured. In addition, the phytoplankton community was arrayed into size fractions to assess the contribution of each size fraction to biomass and pigment concentrations. Analyses showed that the creek waters had very high nutrient concentrations. Although decreasing nutrient concentrations of the sea as compared to past years were detected, results of the analyses showed that the phytoplankton biomass was increased. Minimum and maximum values of nutrient concentrations and chlorophyll-a were 0.23-22.28 µM for ammonium, 1.54-11.77 µM for nitrate, 0.00-3.51 µM for nitrite, 1.99-41.94 µM for silicate, 0.00-5.96 µM for phosphate, and 5.03-30.26 µg/L for chlorophyll-a. Nanoplankton was the dominant phytoplankton group in the inner bay. An increment in picoplankton was detected towards the outer part of the bay. The microplankton biomass was correlated with NH+4-N, [Si(OH) 4-Si], and o.PO4-P. [Si(OH) 4-Si], o.PO4-P, and microplankton were the most important constituents in the inner bay. Consequently, controlling nutrient concentrations in the creeks might contribute to the cleaning process in İzmir Bay. [ABSTRACT FROM AUTHOR]

Diel vertical migration (DVM) of zooplankton is commonly considered an adaptation for feeding in food-rich and warm surface waters at night and avoiding visual predators during the day. However, the critical assessment of migration patterns frequently suggests that: (i) zooplankton may leave deeper waters with rich, deep-chlorophyll layers and move into the epilimnion where food resources are lower and/or (ii) the night-time increase in epilimnetic plankton abundance is not matched by a density decrease in deeper strata. To study these discrepancies, we measured DVM of zooplankton in a 1.3-ha Spanish karst lake (Laguna del Tejo) where the phytoplankton in the deep chlorophyll layer had been labelled with the isotopic tracer 15N. There were only limited changes in the vertical distribution patterns of rotifers and copepods over the diel cycle, but night-time biomass (mg L−1) of the cladoceran, Diaphanosoma brachyurum in the water column of the oxic zone increased 168% in the central area of the lake but there was not a parallel reduction in their density in the metalimnion or hypolimnion. Additionally, the isotopic signatures of the zooplankton in the epilimnion stayed constant from day to night, suggesting that there was little vertical migration. The results suggest that horizontal movements rather than vertical migration explain the increasing abundance of zooplankton in the central epilimnion of Laguna del Tejo during the night and that low food resources in this layer provide no incentive for DVM. [ABSTRACT FROM AUTHOR]

Increased precipitation is one projected outcome of climate change that may enhance the discharge of freshwater to the coastal zone. The resulting lower salinity, and associated discharge of both nutrients and dissolved organic carbon, may influence food web functioning. The scope of this study was to determine the net outcome of increased freshwater discharge on the balance between auto- and heterotrophic processes in the coastal zone. By using long-term ecological time series data covering 13 years, we show that increased river discharge suppresses phytoplankton biomass production and shifts the carbon flow towards microbial heterotrophy. A 76% increase in freshwater discharge resulted in a 2.2 times higher ratio of bacterio- to phytoplankton production (Pb:Pp). The level of Pb:Pp is a function of riverine total organic carbon supply to the coastal zone. This is mainly due to the negative effect of freshwater and total organic carbon discharge on phytoplankton growth, despite a concomitant increase in discharge of nitrogen and phosphorus. With a time lag of 2 years the bacterial production recovered after an initial decline, further synergistically elevating the microbial heterotrophy. Current climate change projections suggesting increased precipitation may therefore lead to increased microbial heterotrophy, thereby decreasing the transfer efficiency of biomass to higher trophic levels. This prognosis would suggest reduced fish production and lower sedimentation rates of phytoplankton, a factor of detriment to benthic fauna. Our findings show that discharge of freshwater and total organic carbon significantly contributes to the balance of coastal processes at large spatial and temporal scales, and that model's would be greatly augmented by the inclusion of these environmental drivers as regulators of coastal productivity. [ABSTRACT FROM AUTHOR]

Phytoplankton biomass-nutrient relationship is widely used by lake managers to assess the eutrophication impact and to set the nutrient targets. Submerged vegetation and large zooplankton grazing have long been identified as factors weakening the relationship by decoupling phytoplankton from nutrients. Proving this decoupling unambiguously is difficult because, in natural systems, many factors act together, blurring each other's effect. In this article, we present the results of continuous monitoring of 13 ponds where the effects of submerged vegetation and zooplankton grazing were enhanced by biomanipulation (fish removal). The monitoring allowed these effects to be assessed and compared with the pre-biomanipulation situations when phytoplankton biomass was mainly nutrient driven. The comparison showed a strong weakening effect of submerged vegetation and large zooplankton grazing on the chlorophyll a-total phosphorus relationship suggesting that a considerable degree of ecological quality of ponds affected by eutrophication can be restored even when nutrient-loading reduction is not feasible. [ABSTRACT FROM AUTHOR]

Abstract: Chlorophyll-a and nutrient concentrations were monitored at weekly intervals across 21 river sites throughout the River Thames basin, southern England, between 2009 and 2011. Despite a 90% decrease in soluble reactive phosphorus (SRP) concentration of the lower River Thames since the 1990s, very large phytoplankton blooms still occur. Chlorophyll concentrations were highest in the mid and lower River Thames and the larger tributaries. Lowest chlorophyll concentrations were observed in the smaller tributaries, despite some having very high phosphorus concentrations of over 300μgl−1. There was a strong positive correlation between river length and mean chlorophyll concentration (R2 =0.82), and rivers connected to canals had ca. six times greater chlorophyll concentration than ‘natural’ rivers with similar phosphorus concentrations, indicating the importance that residence time has on determining phytoplankton biomass. Phosphorus concentration did have some influence, with phosphorus-enriched rivers having much larger phytoplankton blooms than nutrient-poor rivers of a similar length. Water quality improvements may now be capping chlorophyll peaks in the Rivers Thames and Kennet, due to SRP depletion during the spring/early summer phytoplankton bloom period. Dissolved reactive silicon was also depleted to potentially-limiting concentrations for diatom growth in the River Thames during these phytoplankton blooms, but nitrate remained in excess for all rivers throughout the study period. Other potential mitigation measures, such as increasing riparian shading and reducing residence times by removing impoundments may be needed, alongside phosphorus mitigation, to reduce the magnitude of phytoplankton blooms in the future. [Copyright &y& Elsevier]

Abstract: Recent characterizations of atmospheric conditions favorable to upwelling events in the Western Cantabrian Sea have stressed the need to analyze the significance of the orientation of the coast on the phenomenon of upwelling. Surface-wind fields for the northwestern Galician marine area were provided by the QuikSCAT satellite and an SST map was elaborated using the NASA GHRSST satellite data. A cruise was conducted aboard the RV Lura in June 2009 during northern prevailing winds. Data of thermohaline variables, concentration of dissolved oxygen, dissolved inorganic nitrogen, chlorophyll, dissolved and particulate organic carbon and nitrogen and phytoplankton abundances were obtained. When the upwelling developed west of the Cape Ortegal was strong, the Eastern North Atlantic Central Water mixed with coastal water eastward of the Cape and the upwelled seawater reached the westernmost of the Northern Galician Rias, the Ria of Ortigueira. Incoming seawater was poor in nitrate and chlorophyll concentrations when compared to that of the upwelling events in the Western Galician Rias. The phytoplankton assemblages were typical of summer upwelling blooms in the latter Rias but phytoplankton biomass was lower in the Ria of Ortigueira and the species were indicatives of initial (inner ria under continental influence) and advanced (outer ria under upwelling inputs) stages of phytoplankton succession. The observed process arose when the upwelling edge-zone reaches a change of coastal orientation as may also occur in other upwelling regions. [Copyright &y& Elsevier]

Abstract: We consider a plankton–nutrient interaction model consisting of phytoplankton, zooplankton and dissolved limiting nutrient with general nutrient uptake functions and instantaneous nutrient recycling. In this model, it is assumed that phytoplankton releases toxic chemical for self defense against their predators. The model system is studied analytically and the threshold values for the existence and stability of various steady states are worked out. It is observed that if the maximal zooplankton conversion rate crosses a certain critical value, the system enters into Hopf bifurcation. Finally it is observed that to control the planktonic bloom and to maintain stability around the coexistence equilibrium we have to control the nutrient input rate specially caused by artificial eutrophication. In case if it is not possible to control the nutrient input rate, one could use toxic phytoplankton to prevent the recurrence bloom. [Copyright &y& Elsevier]

An analysis is made on a three dimensional mathematical model for the interaction of nutrient, phytoplankton and their predator zooplankton population in an open marine system. For a realistic representation of the open marine plankton ecosystem, we have incorporated various natural phenomena such as dissolved limiting nutrient with general nutrient uptake function, nutrient recycling, interspecies competition and grazing at a higher level. For the model with constant nutrient input and different constant washout rates, conditions for boundedness of the solutions, existence and stability of non negative equilibria, as well as persistence are given. The model system is studied analytically and the threshold values for the existence and stability of various steady states are worked out. It is observed that if the dilution rate of nutrient crosses certain critical value, the system enters into Hopf-bifurcation. Finally, it is observed that planktonic bloom can be controlled and stability around the equilibrium of coexistence can be obtained if the dilution rate of phytoplankton population is increased. Computer simulations have been carried out to illustrate different analytical results. [ABSTRACT FROM AUTHOR]

Abstract: Iron [dissolved Fe (D-Fe) and total dissolvable Fe (T-Fe)] and nutrient concentrations in the surface water of the Oyashio region (northwestern North Pacific) were measured before and during spring phytoplankton bloom (March to May in 2007). During the pre-bloom period (middle of March), we observed vertically uniform concentrations of iron (0.3–0.5nM [D-Fe] and 3–5nM [T-Fe]), macronutrients (10–15μM NO3+NO2, 1.0–1.5μM PO4 and 20–30μM Si(OH)4) and chlorophyll a (Chl-a, 0.3–0.4μg l−1) throughout the upper 125 to 150m due to vertical mixing during winter. Water temperature and salinity before the bloom were also vertically uniform with >5°C and S>33.5, the conditions of a modified Kuroshio warm-water (MKW) ring, higher than those of the Coastal Oyashio Water (COW). The cold COW (<2°C, S<33.2) intruded a few times into the surface during the bloom period with high iron (0.4–0.6nM [D-Fe] and 10–25nM [T-Fe]) and Chl-a (10–23μg l−1) concentrations. The high Chl-a observed in the COW is due to the higher original concentrations of iron and macronutrients in the COW than in the MKW. An incubation experiment conducted during a COW intrusion in early April resulted in robust phytoplankton growth and complete exhaustion of nutrients, indicating an adequate supply of bioavailable iron. This result is also consistent with robust in situ phytoplankton growth and Chl-a production due to the presence of high iron levels in the COW. The most important mechanisms transporting iron to the surface water, which would regulate the primary production during spring bloom in the Oyashio region, are the surface intrusions of iron- and nutrient-rich COW derived from vertical and lateral mixing processes and vertical mixing in MKW during winter and spring. [Copyright &y& Elsevier]

Abstract: We investigated the nutrient and diatom dynamics during late winter and spring (9-March to 1-May 2007) in the Oyashio region as part of the OECOS-WEST research cruises. Macronutrients, iron, chlorophyll a (Chl-a) and biogenic silica (BSi) concentrations in the upper mixed layer varied remarkably ranges were 1.88–18.8μmolL−1 for NO3+NO2, 0.64–1.85μmolL−1 for PO4, 3.14–35.7μmolL−1 for Si(OH)4, 0.14–0.54nmolL−1 for D-Fe, 0.64–24.6nmolL−1 for T-Fe, 0.30–17.4μgL−1 for Chl-a, and 0.34–14.1μmolL−1 for BSi. Mixed-layer depth (MLD) varied from 8–190m during the cruises. The growth rate of in situ phytoplankton communities, dominated by centric diatoms, varied in shipboard culture experiments from 0.55d−1 for iron-replete to 0.14d−1 for iron-limited conditions. A relationship between BSi and Chl-a concentrations indicates that the in situ diatom community in the warmer water system (>4°C) was heavily silicified, probably due to iron-limitation. The in situ macronutrient and dissolved iron concentrations below the MLD and estimated macronutrient concentrations during winter were negatively correlated to temperature (1–6°C), that is to the relative proportion of warm modified Kuroshio Water mixed into the colder Oyashio water system. The rate of decrease in Si(OH)4 per °C increase was greater than the rates for NO3+NO2 and PO4 for both in situ and estimated winter values. These results suggest that the spring bloom in the cold-water system with high macronutrients and iron concentrations would progress rapidly and intensely, and then be terminated by nitrogenous nutrient depletion. However, the diatom bloom in warmer waters with lower macronutrients and iron concentrations would be terminated by Si- and/or iron-limitation of heavily-silicified diatoms. In the OECOS study, variation of macronutrients and iron due to the surface intrusions of several water masses and modification from different chemical conditions during winter were the most important factors regulating the progression, magnitude and probably fate of the spring phytoplankton bloom in the Oyashio region. [Copyright &y& Elsevier]

1. Grazing by invasive species can affect many aspects of an aquatic system, but most studies have focused on the direct effects on plants. We conducted mesocosm and laboratory experiments to examine the impact of the invasive apple snail Pomacea canaliculata on macrophytes, filamentous algae, nutrients and phytoplankton. 2. In a freshwater pond, we confined 500 g of Myriophyllum aquaticum or Eichhornia crassipes with 0, 2, 4 or 8 apple snails in 1 m × 1 m × 1 m enclosures for approximately 1 month. Apple snails grazed heavily on both species of macrophytes, with higher overall weight losses at higher snail densities. The damage patterns differed between the two macrophytes. In M. aquaticum, both leaves and stems suffered from substantial herbivory, whereas in E. crassipes, only the roots suffered significant weight reduction. 3. In addition to grazing on macrophytes, apple snails appeared to have controlled the growth of filamentous algae, as these did not develop in the snail treatments. The ability of P. canaliculata to control filamentous algae was supported by a laboratory experiment where the consumption was as high as 0.25 g g−1 snail DW d−1. Because of a lack of native herbivorous snails in the pond, the growth of filamentous algae (mainly Spirogyra sp.) reached 80.3 g m−2, forming a spongy pond scum in the no-apple snail control. Together with previous reports that apple snails could eat the juveniles and eggs of other freshwater snails, our results indicated that P. canaliculata could have out-competed native herbivorous snails from the pond by predation on their juveniles or eggs. Alternatively, P. canaliculata might have out-competed them by monopolisation of food resources. 4. Nitrogen and phosphorous concentrations remained low throughout both experiments and were not correlated with apple snail density. The treatment effects on chlorophyll a (Chl a) and phytoplankton composition varied in the two experiments. In the M. aquaticum experiment, with increasing snail density, Chl a increased, and the phytoplankton community became dominated by Cryptophyceae. In the E. crassipes experiment, Chl a level was independent of snail density, but with increasing snail density, the phytoplankton community became co-dominated by Cryptophyceae, Chlorophyceae and Bacillariophyceae. 5. Given the multiple effects of P. canaliculata on wetland biodiversity and function, management strategies should be developed to prevent its further spread. In invaded wetlands, strategies should be developed to eradicate the apple snail and re-introduce native snails which can control the development of filamentous algae. [ABSTRACT FROM AUTHOR]

This study was carried out to determine the diurnal distributions of phytoplankton density, bio-volume, and chlorophyll a in relation to nutrients and CTD measurements in surface waters of the coastal area in the Dardanelles during high density of phytoplankton, especially high diatom production (between 3 July and 4 August 2002). Ninety nine surface samples were collected for nutrient, chlorophyll a, and phytoplankton in 3 different time periods of the day (08:00, 13:00 and 18:00 hours) in the sampling period. Based on the sample analyses, average temperature, salinity, pH, DO, TDS, TSS, NO2-+NO3-, PO4-3, SiO4, chlorophyll a, N:P, and Si:P were calculated as 25 °C, 23.3 ppt, 8.42, 9.26 mg L-1, 23.9 g L-1, 36.1 mg L-1, 1.90 μM, 0.24 μM, 3.61 μM, 1.70 μg L-1, 12.5, and 25, respectively. Total phytoplankton density and biovolume varied from 2.86 × 105 to 1.5 × 107 cells L-1 and from 5.98 × 108 to 8.81 × 1010 μm³ L-1, respectively. Contribution rate of Bacillariophyceae (66.5%) to total phytoplankton bio-volume was higher than that of Dinophyceae (31.0%). Phytoplankton community structure was observed to be controlled by 6-7 species. Other species can be considered as insignificant species that do not cause important fluctuations in the phytoplankton density and bio-volume. It has been reported that there were 9-11 population growth slopes for different species at different times and densities. Therefore, life cycles of phytoplankton species were completed between 3 and 4 days. Diurnal variations of biological and physicochemical parameters in the time interval between 0800 and 18:00 were generally much higher than daily variations between 3 July and 4 August 2002 due to the 2 counter flows system of the Dardanelles and domestic inputs of Çanakkale city. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to investigate the cycling of dissolved inorganic and organic nutrients using moored instrumented buoys (SmartBuoys) during the spring bloom in the North Sea. The instrumentation on the buoys enabled high frequency measurements of water-column integrated irradiance and in situ chlorophyll to be made, and also preserved water sample collection which were used for dissolved inorganic and organic nutrient analyses. The SmartBuoys were located in the year-round well-mixed plume zone associated with the River Thames and in the summer stratified central North Sea. These site locations allowed comparison of nutrient concentrations and cycling, and spring bloom development at two contrasting sites. The spring bloom was expected to be initiated at both stations due to increasing insolation and decreasing suspended load leading to higher water-column integrated irradiance. Due to differences in suspended load between the sites, the spring bloom started ∼2 months earlier in the central North Sea. The spring bloom in the Thames plume also resulted in higher maximum phytoplankton biomass due to the higher pre-bloom nutrient concentrations associated with riverine input. The use of SmartBuoys is also shown to allow the cycling of dissolved organic nutrients to be examined over the critical, and often undersampled, spring bloom period. Dissolved Organic Nitrogen (DON) clearly increased during the spring bloom in the central North Sea compared to winter concentrations. DON also increased in the Thames plume although showing greater winter variability related to higher riverine and sedimentary dissolved organic matter input at this shallow (∼18 m) coastal site. DON increase during the spring bloom was therefore related to primary production at both sites probably due to active release by phytoplankton. At both stations DON decreased to pre-bloom concentrations as the bloom declined suggesting the released DON was bioavailable and removed due to heterotrophic uptake and production. The preserved nutrient samples from the central North Sea site were also suitable for Dissolved Organic Phosphorus (DOP) analysis due to their low suspended load with similar trends and cycling to DON, albeit at lower concentrations. This suggested similar processes controlling both DON and DOP. The variable timing of short term events such as the spring bloom makes sampling away from coastal regions difficult without the use of autonomous technology. This study demonstrates for the first time the applicability of using preserved samples from automated buoys for the measurement of dissolved organic nutrients. [Copyright &y& Elsevier]

An experiment was conducted with a natural freshwater phytoplankton community from a eutrophic pond to investigate the combined effects of phytoplankton community competitive interactions, nutrient enrichment and zooplankton on Microcystis bloom formation. The pond water initially had a very low concentration of Microcystis, but the total phytoplankton biomass as chlorophyll a reached ∼110 µg L−1 in summer. The pond water was incubated outdoors at natural temperature and light with a 2 × 2 factorial manipulation of nutrient (nutrient additions versus no additions) with and without zooplankton. The interaction of a two-phase nutrient addition (a net increase in concentrations of 250.0 µM N and 16.1 µM P each time) and the presence of zooplankton significantly altered phytoplankton community composition. When the water initially contained zooplankton, nitrogen and phosphorus enrichment promoted a surface Microcystis bloom. However, when the zooplankton was removed from the water at the start of the experiment, no surface Microcystis bloom formed, regardless of nutrient additions. Chlorophyta dominated in the absence of zooplankton, when the same nutrient was provided. Our results demonstrate that Microcystis bloom formation in this eutrophic water body at a mean temperature of about 36°C at 14:00 h was closely related to the initial presence of zooplankton and a sufficient supply of nitrogen and phosphorus. We believe this is one of the first demonstrations of zooplankton controlling Microcystis bloom formation in a water body previously free of surface cyanobacterial blooms. [ABSTRACT FROM PUBLISHER]

The Changjiang River is well-known to channel significant anthropogenic influences to the estuary. However, long-term changes in plankton community related to anthropogenic eutrophication in the estuarine water are not well documented. In this paper, data from a nine year study (1996, 1998-2005) on suspended matter, chemical oxygen demand, nutrients and plankton community were collected and analyzed by principal component analysis. These data reveal that N/P ratio was always much higher than 40 and Si/N ratio decreased from 1.35 to 0.94 between 1996 and 2005. As an ecological consequence to such nutrient balance changes, phytoplankton species diversity and the dominance of diatoms decreased, dinoflagellates increasingly dominated the phytoplankton population, and the frequency of harmful algal blooms caused by dinoflagellates also increased. Furthermore, due to the reduced diatom availability, the dominance of copepods decreased, zooplankton diversity increased, and medusae increasingly dominated the zooplankton population. Water column nutrient ratios, therefore, are also important factors affecting anthropogenic eutrophication, as are the contamination loadings from land. [ABSTRACT FROM AUTHOR]

This paper provides a synthesis of current knowledge on phytoplankton production, seasonality, and stratification in tropical African lakes and considers the effects of nutrient enrichment and the potential impacts of climate warming on phytoplankton production and composition. Tropical African lakes are especially sensitive to climate warming as they experience wide fluctuations in the thermocline over a narrow range of high water temperatures. Recent climate warming has reduced phytoplankton biomass and production in the lakes. A decline in the production of palatable chlorophytes and an increase in cyanobacteria has led to reduced zooplankton production and a consequent decline in fish stocks, all of which can be associated with the elevated water temperatures. This indicates that even moderate climate warming may destabilise phytoplankton dynamics in tropical African lakes, thereby reducing water quality and food resources for planktivorous fish, with consequent negative impacts on human livelihoods. [ABSTRACT FROM AUTHOR]

Abstract: During an iron-enrichment experiment in the western subarctic Pacific (SEEDS-II), concentrations of dissolved and acid-soluble rare earth elements (REEs) were determined in shallow waters. Detailed vertical profiles of dissolved REEs were compared with those of nutrients in a preliminary survey. The results showed good correlation, except for Ce and Y. Along with phytoplankton growth within the iron-enriched patch, dissolved REEs were decreased in surface waters. The changes in REE concentrations were small but systematic: light REEs were adsorbed preferentially over heavy REEs. This systematic trend is consistent with results of earlier studies of REE adsorption onto biogenic particle surfaces. However, we were unable to detect a decrease of acid-soluble REEs in surface waters. During the phytoplankton bloom decline phase, dissolved REEs were elevated to concentration levels at the preliminary survey, although nutrients were decreased. The liberation of REEs from the suspended particles might be related to disaggregation from large particles to colloid particles, desorption from the particulate phase, and remineralization from organic matter. Outside the Fe-patch, time variations of REEs were also observed during SEEDS-II, indicating that both artificially induced phytoplankton blooms and natural variation of biogenic particles can affect the biogeochemical cycles of REEs in shallow waters within a short time. [Copyright &y& Elsevier]