Phytoplankton Populations Research Articles

Southern Ocean Biogeochemical Argo detect under-ice phytoplankton growth before sea ice retreat

Abstract. The seasonality of sea ice in the Southern Ocean has profound effects on the life cycle (phenology) of phytoplankton residing under the ice. The current literature investigating this relationship is primarily based on remote sensing, which often lacks data for half of the year or more. One prominent hypothesis holds that, following ice retreat in spring, buoyant meltwaters enhance available irradiance, triggering a bloom which follows the ice edge. However, an analysis of Biogeochemical Argo (BGC-Argo) data sampling under Antarctic sea ice suggests that this is not necessarily the case. Rather than precipitating rapid accumulation, we show that meltwaters enhance growth in an already highly active phytoplankton population. Blooms observed in the wake of the receding ice edge can then be understood as the emergence of a growth process that started earlier under sea ice. Indeed, we estimate that growth initiation occurs, on average, 4–5 weeks before ice retreat, typically starting in August and September. Novel techniques using on-board data to detect the timing of ice melt were used. Furthermore, such growth is shown to occur under conditions of substantial ice cover (>90 % satellite ice concentration) and deep mixed layers (>100 m), conditions previously thought to be inimical to growth. This led to the development of several box model experiments (with varying vertical depth) in which we sought to investigate the mechanisms responsible for such early growth. The results of these experiments suggest that a combination of higher light transfer (penetration) through sea ice cover and extreme low light adaptation by phytoplankton can account for the observed phenology.

Ecological assessment of Hooghly River considering a few of the more perturbed sites based on some relevant physico-chemical and biological variables—A part of the AVIRIS-NG (NASA-ISRO) ground truth verification

A study was performed on a 32 Km stretch of the River Hooghly as part of a project under the Airborne Visible Infrared Imaging Spectrometer - Next Generation (AVIRIS-NG) scheme between Indian Space Research Organization (ISRO) and National Aeronautics and Space Administration (NASA). It was governed by 33 water quality variables comprising physical, chemical, biological and ecological ones. The selected stations were within the tidal realm of the estuary, constituting the lower-middle stretch of the river that was severely affected by anthropogenic perturbations. Chief biotic components studied were phytoplankton population density, primary and auxiliary phytopigments, and productivity in addition to chromophoric dissolved organic matter (CDOM). Majority of the study sites were observed with very low concentrations of dissolved oxygen along with significant shifts in primary production. Overall prevalence of Cyanophyceae and Bacillariophyceae was indicative of significant eutrophication. Reverse phase high performance liquid chromatography (HPLC) and radiometry revealed the presence of a large array of algal taxonomic groups through the detection of various primary and auxiliary phytopigments. The data and the study itself is of paramount importance being part of the ground truth verification initiative which will be used to render remote sensing techniques more precise in the future to better monitor the estuarine system.

Modeling biogeochemical processes in the Azov Sea using statistically processed data on river flow

Introduction. This work is aimed at solving the problem of phytoplankton dynamics in the coastal environments using the example of the Azov Sea. This takes into account the transformation of forms of phosphorus, nitrogen and silicon, as well as the aquatic medium motion, the distribution of temperatures and salinities over the sea area. River flow, varying in volume and chemical composition, affects significantly the variability of hydrophysical and biogeochemical parameters of the processes occurring in the coastal environment. This explains the need for statistical processing of the data from long-term observations over the river flow characteristics. Materials and Methods. The mathematical model of biogeochemical cycles is based on a system of non-stationary equations of the convection-diffusion-reaction of parabolic type with nonlinear functions of sources and lower-order derivatives, to which the corresponding initial and boundary conditions are added. In the course of statistical analysis of the series of long-term observations over river flows, the values of the following indicators were found: skewness coefficient, degree of kurtosis, variance and standard deviation, coefficient of variation, autocorrelation coefficient, Neumann ratio, and Anderson criterion. Results. The statistical analysis of the series of long-term observations over the hydrochemical indicators of the Don river suggests heterogeneity of the field data. This is due to the stochasticity of nutrient inputs and the volume of freshwater flow to the sea as a result of natural and anthropogenic factors. Field data should be correlated with seasonal changes in the aquatic environment temperature. This paper presents the results of a computational experiment to model the dynamics of phytoplankton populations in summer season, when temperatures are favorable for their reproduction and growth. The proposed mathematical model considers the spatially inhomogeneous distribution and transformation of forms of phosphorus, nitrogen, and silicon, as well as changes in salinity, temperature, and motion of the aquatic environment. Discussion and Conclusions. The multispecies mathematical model of the dynamics of phytoplankton populations is considered with account for the transformation of forms of phosphorus, nitrogen, and silicon in the coastal environments. The analysis of data from field observations, for which its major statistical parameters are calculated, is carried out. As a result, it is concluded that data of the long-term observations are significantly variable. This is due to two reasons. Random nature of the input of nutrients and the volume of river flow as a result of anthropogenic factors is the first reason. The second reason includes the alternation of relatively high-water and low-water periods for fresh flow over the last 12-15 years. The hydrological regime is changing mainly due to the reduction of the average annual freshwater flow of the Don and partly of the Kuban. This trend is likely to increase due to climate changes, as well as with further regulation of the Don river flow after the Bagaevsky hydroelectric installation start-up. Numerical experiments based on the field data confirmed the predictive validity of the developed models and programs. They can be used to predict change in the composition and abundance (concentrations) in the Azov sea core planktonic populations, which define, on the one hand, food resources, and, on the other hand, the aquatic environment in terms of the ongoing sea salinization.

Red Sea MODIS Estimates of Chlorophyll a and Phytoplankton Biomass Risks to Saudi Arabian Coastal Desalination Plants

Harmful algal blooms (HABs) and the high biomass associated with them have afflicted marine desalination plants along coastal regions around the world. Few studies of HABs have been conducted in the Red Sea, where desalination plants along the Saudi Arabian Red Sea coast provide drinking water for millions of people. This study was conducted along the Saudi Arabian Red Sea coast from 2014 to 2015 to assess the potential for using Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing of chlorophyll a (Chl a) or fluorescence line height (FLH) to identify risks for biofouling at these desalination plants. Ship-based surveys of phytoplankton were conducted along the Saudi Arabian coastline offshore of desalination plants at Jeddah, Al Shoaibah and Al Qunfudhuh to assess the density of phytoplankton populations and identify any potential HAB species. Ship-based surveys showed low to moderate concentrations of phytoplankton, averaging from 1800–10,000 cells L−1 at Jeddah, 2000–11,000 cells L−1 at Al Shoaibah and 1000–20,500 cells L−1 at Al Qunfudhuh. Sixteen different species of potentially toxigenic HABs were identified through these surveys. There was a good relationship between ship-based total phytoplankton counts and monthly averaged coastal MODIS Chl a (R2 = 0.49, root mean square error (RMSE) = 0.27 mg m−3) or FLH (R2 = 0.47, RMSE = 0.04 mW m−2 µm−1 sr−1) values. Monthly average near shore Chl a concentrations obtained using MODIS satellite imagery were much higher in the Red Sea coastal areas at Al Qunfudhuh (maximum of about 1.3 mg m−3) than at Jeddah or Al Shoaibah (maximum of about 0.4 and 0.5 mg m−3, respectively). Chlorophyll a concentrations were generally highest from the months of December to March, producing higher risks of biofouling desalination plants than in other months. Concentrations decreased significantly, on average, from April to September. Long-term (2005–2016) monthly averaged MODIS Chl a values were used to delineate four statistically distinct zones of differing HAB biomass across the entire Red Sea. Sinusoidal functions representing monthly variability were fit to satellite Chl a values in each zone (RMSE values from 0.691 to 0.07 mg m−3, from Zone 1 to 4). December to January mean values and annual amplitudes for Chl a in these four sinusoidal functions decreased from Zones 1–4. In general, the greatest risk of HABs to desalination occurs during winter months in Zone 1 (Southern Red Sea), while HAB risks to desalination plants in winter months are low to moderate in Zone 2 (South Central Red Sea), and negligible in Zones 3 (North Central) and 4 (Northern).

Elevated co2 has Differential Effects on Five Species of Microalgae from a Subtropical Freshwater Lake: Possible Implications for Phytoplankton Species Composition.

Rising atmospheric CO2 concentrations are predicted to have a significant impact on global phytoplankton populations. Of particular interest in freshwater systems are those species that produce toxins or impact water quality, though evidence for how these species, and many others, will respond is limited. This study investigated the effects of elevated CO2 (1,000ppm) relative to current atmospheric CO2 partial pressures (400ppm), on growth, cell size, carbon acquisition, and photophysiology of five freshwater phytoplankton species including a toxic cyanophyte, Raphidiopsis raciborskii, from Lake Wivenhoe, Australia. Effects of elevated CO2 on growth rate varied between species; notably growth rate was considerably higher for Staurastrum sp. and significantly lower for Stichococcus sp. with a trend to lower growth rate for R.raciborskii. Surface area to volume ratio was significantly lower with elevated CO2 , for all species except Cyclotella sp. Timing of maximum cell concentrations of those genera studied in monoculture occurred in the lake in order of CO2 affinity when free CO2 concentrations dropped below air equilibrium. The results presented here suggest that as atmospheric levels of CO2 rise, R.raciborskii may become less of a problem to water quality, while some species of chlorophytes may become more dominant. This has implications for stakeholders of many freshwater systems.

Effect of the microorganism-adherent carrier for Nitzschia palea to control the cyanobacterial blooms

To evaluate the effect of microorganism adherent carrier for Nitzschia palea on the control of Cyanobacterial blooms, the changes of phytoplankton population structure and the chlorophyll a concentration after carrier installation were compared with those without carrier installation in field and laboratory experiments. The results showed that the installation of the carrier could control the growth of Microcystis spp., effectively. In the field investigation, the cell number of Microcystis spp. can decrease to 54,800 cells/mL after 5 d treatment comparing to 464,000 cells/mL in water without treatment, but the installation of adherent carrier did not influence the growth of other phytoplanktons including Chlorophyta. Through the observation by a microscope, the adhesion of the Nitzschia palea to this carrier was observed as well as the gliding movement of the Nitzschia palea onto the colonies of Microcystis, indicating that the adhesion, invasion and sliding movement of Nitzschia palea induced the physical destruction and effective control of Microcystis colony. Overall, the installation of this carrier can promote the growth of Nitzschia palea near carrier fiber, and control cyanobacterial blooms by the invasion of Nitzschia palea onto Microcystis colony, which can be used as one of energy-saving and sustainable eco-engineered blue-grass control methods in closed water areas such as lakes and reservoirs.

Spatial distribution of nutrients and chlorophyll a across the Persian Gulf and the Gulf of Oman

Despite the economic and political importance of the Persian Gulf and the vast amount of marine trade carried on, mainly in tanker traffic, chemical oceanographic properties of the area, particularly nutrients and chlorophyll a had been measured only a few times in the past (expeditions of the Research Vessels Meteor (1965), Atlantis II (1977), Umitaka-Maru (1993–1994), ROPME (2000, 2001 and 2006)) and no observations after 2006 (ROPME cruise) were taken. The present study aims to investigate the hydrographic characteristics, nutrients and chlorophyll a on 20 stations between 25° N and 27°N across the Persian Gulf and the Gulf of Oman during the PGE 1801 cruise in January 2018. Seawater samples were collected at the surface, 10 m, 25 m, 50 m, 75 m and upper depths, depending on each station's total depth (the deepest sample was taken at 180 m). The results showed that chlorophyll a is concentrated in the surface layer and decreases with increasing depth, which may be associated with a decrease in the phytoplankton population in the lower layers. The inflowing surface water is high in phosphate (0.74–1.10 μM) due to the north-east monsoon's upwelling. The N/P ratio was lower than the standard Redfield ratio of 16/1 suggesting nitrogenous nutrients as limiting elements. In nearly-enclosed basins with minimal exchanges with open oceans similar to the Persian Gulf, the primary production generally is limited by nitrogen. Nitrate was the highest and ammonium was the lowest in the Persian Gulf and Gulf of Oman waters. The results show the penetration of surface water with a salinity of 36.7 psu into the Persian Gulf which is carried along the Iranian Coast, gradually increasing in salinity to more than 38.2 psu.

COMPOSICIÓN DE LA DIETA DE Asplanchna girodi (PLOIMA, ASPLANCHNIDAE) EN UN EMBALSE ALTOANDINO ECUATORIAL EN COLOMBIA BASADO EN OBSERVACIONES DE CAMPO

Asplanchna girodi (de Guerne, 1888) is a predatory rotifer of wide distribution in temperate and tropical freshwater ecosystems. Of this species, little is known about its diet and its food preferences under natural conditions, since most of the work related to this aspect has been carried out under laboratory conditions. During a short monitoring program at La García Reservoir, a high Andean equatorial reservoir located in the central region of the department of Antioquia (Colombia), in which this species reached a total density of 2.296,2 ind.L-1, studied the composition of the A. girodi diet based only on the direct observation, under the microscope, of the organisms contained in the stomachs of all the individuals present in the simples. Between June and September 2014, integrated samples composed of five depths were taken monthly at three monitoring stations in the entire water column, with a sampling bottle of 10 L capacity. The collected material was filtered through a 30µm plankton net of mesh eye. It was found that A. girodi, presented a wide trophic preference that included the foraging of a dinoflagellate (Ceratium, Schrank), five species of rotifers and a cladoceran. These results lead to the conclusion that A. girodi is possibly an opportunistic species, since consumption is directed at the species with the highest availability (in this case Ceratium) and with the greatest energy savings, since no investment is made in the search for specific prey and in turn would become an important factor in controlling phytoplankton populations.

Hydrocarbon-Degrading Bacteria Found Tightly Associated with the 50–70 μm Cell-Size Population of Eukaryotic Phytoplankton in Surface Waters of a Northeast Atlantic Region

The surface of marine eukaryotic phytoplankton can harbour communities of hydrocarbon-degrading bacteria; however, this algal–bacterial association has, hitherto, been only examined with non-axenic laboratory cultures of micro-algae. In this study, we isolated an operationally-defined community of phytoplankton, of cell size 50–70 μm, from a natural community in sea surface waters of a subarctic region in the northeast Atlantic. Using MiSeq 16S rRNA sequencing, we identified several recognized (Alcanivorax, Marinobacter, Oleispira, Porticoccus, Thalassospira) and putative hydrocarbon degraders (Colwelliaceae, Vibrionaceae) tightly associated with the phytoplankton population. We combined fluorescence in situ hybridisation with flow-cytometry (FISH-Flow) to examine the association of Marinobacter with this natural eukaryotic phytoplankton population. About 1.5% of the phytoplankton population contained tightly associated Marinobacter. The remaining Marinobacter population were loosely associated with either eukaryotic phytoplankton cells or non-chlorophyll particulate material. This work is the first to show the presence of obligate, generalist and putative hydrocarbonoclastic bacteria associated with natural populations of eukaryotic phytoplankton directly from sea surface water samples. It also highlights the suitability of FISH-Flow for future studies to examine the spatial and temporal structure and dynamics of these and other algal–bacterial associations in natural seawater samples.

Seasonal variation in Population dynamics of phytoplankton in Guthia Taal, Wetland of Bahraich (U. P.) India

Guthia taal is a large, shallow and horse shoe shaped wetland of tarai region of eastern U.P. The seasonal variation of phytoplankton density and diversity were studied for a period of one year. In the present study total 31 genera of phytoplankton were identified. Out of 31, thirteen belong to Chlorophyceae, 10 Bascillariophyceae, 6 Cyanophyceae and 2 Euglenophyceae. The annual density shows that Chlorophyceae dominates and constituted 51.57% of the total phytoplankton population was followed by Bascillariophyceae (27.37%), Cyanophyceae (16.45%) and Euglenophyceae (4.61%). However, the overall phytoplankton was found maximum in summer, medium in winter and lowest in monsoon season.

Intense bloom of the diatom Hemidiscus hardmanianus (Greville) in relation to water quality and plankton communities in Tuticorin coast, Gulf of Mannar, India

The present study reports a dense bloom of the marine-diatom Hemidiscus hardmanianus observed off the Tuticorin coast in the Gulf of Mannar (GoM), India. The surface water discoloration (pale green) was observed during a coastal survey conducted in the initial period of the northeast monsoon (October 2018). The bloom extended over an area of approximately 5 km2 around the Tuticorin harbor. Distribution and relative abundance of the phytoplankton and zooplankton species together with the water quality and Chlorophyll-a were studied in the area of bloom. H. hardmanianus density was maximum (10.57 × 104 cells L−1) in the bloom site, which was almost 97% of the total phytoplankton population. The present report is the first record of H. hardmanianus bloom in the Gulf of Mannar. The chain-forming diatom Biddulphia biddulphiana was also observed in strong numbers (802 and 432 cells L−1), which has been rarely reported from the Indian coastal waters.

Seasonal Distributions of Phytoplankton and Environmental Factors Generate Algal Blooms in the Taehwa River, South Korea

Algal blooms have occurred in the Taehwa River estuary in South Korea despite the improvement of water quality since environmental renewal projects in the 1990s. In this study, we investigated the causes of algal blooms by measuring the water retention time using a floating buoy, water quality parameters, and phytoplankton distribution data from 2012. An algal bloom did not occur in February because of phosphate limitations in the Taehwa River estuary; however, the concentration of nutrients in the water inflow from the basin triggered a significant algal bloom in the upper estuary in the month of May. In this regard, the phytoplankton population was dominated by nano- and pico-sized flagellates. In August, the freshwater inflow into the estuary greatly increased due to heavy rainfall, resulting in a shorter retention time of the water bodies, which seemed to prevent an algal bloom. In November, a bloom of Cryptophyceae occurred at one of the sites (the U2 site) due to sufficient nutrients in the water and the long retention times of the water bodies. Our results indicate that a decrease in the nutrients (N and P) supplied from the basin is required for a reduction in algal blooms in the Taehwa River estuary. Additional studies are needed to further elucidate the effects of the land-based, nutrient-rich pollutants flowing into the Taehwa River estuary on algal bloom generation considering the fact that the streams have different environmental characteristics.

Fluorescence Quenching of Chlorophyll by Sea Water Components

Oceanic phytoplankton populations are actively monitored via satellite measurements coupled with local validation. Increasingly, chlorophyll fluorescence is used for such measurements, both from re...

A new approach to interspecific synchrony in population ecology using tail association.

Standard methods for studying the association between two ecologically important variables provide only a small slice of the information content of the association, but statistical approaches are available that provide comprehensive information. In particular, available approaches can reveal tail associations, that is, accentuated or reduced associations between the more extreme values of variables. We here study the nature and causes of tail associations between phenological or population‐density variables of co‐located species, and their ecological importance. We employ a simple method of measuring tail associations which we call the partial Spearman correlation. Using multidecadal, multi‐species spatiotemporal datasets on aphid first flights and marine phytoplankton population densities, we assess the potential for tail association to illuminate two major topics of study in community ecology: the stability or instability of aggregate community measures such as total community biomass and its relationship with the synchronous or compensatory dynamics of the community's constituent species; and the potential for fluctuations and trends in species phenology to result in trophic mismatches. We find that positively associated fluctuations in the population densities of co‐located species commonly show asymmetric tail associations; that is, it is common for two species’ densities to be more correlated when large than when small, or vice versa. Ordinary measures of association such as correlation do not take this asymmetry into account. Likewise, positively associated fluctuations in the phenology of co‐located species also commonly show asymmetric tail associations. We provide evidence that tail associations between two or more species’ population‐density or phenology time series can be inherited from mutual tail associations of these quantities with an environmental driver. We argue that our understanding of community dynamics and stability, and of phenologies of interacting species, can be meaningfully improved in future work by taking into account tail associations.

Genotype and host microbiome alter competitive interactions between Microcystis aeruginosa and Chlorella sorokiniana

Cyanobacterial harmful algal blooms (cyanoHABs) continue to increase in frequency and magnitude, threatening global freshwater ecosystems and services. In north-temperate lakes cyanobacteria appear in early summer, succeeding green algae as the dominant phytoplankton group, a pattern thought to be mediated by changes in temperature and bioavailable nutrients. To understand additional drivers of this successional pattern our study used reciprocal invasion experiments to examine the competitive interaction between Microcystis aeruginosa, a dominant contributor to cyanoHABs, and the green alga Chlorella sorokiniana. We considered two factors that may impact these interactions: (1) strain variation, with a specific emphasis on the presence or absence of the gene for the hepatotoxin microcystin, and (2) host-associated bacteria. We used toxic M. aeruginosa PCC 7806 (microcystin producing strain), a non-toxic mutant of PCC 7806, non-toxic M. aeruginosa PCC 9701 (non-microcystin producing strain), and C. sorokiniana. Each organism was available free of all bacteria (i.e., axenic) and with a re-introduced defined bacterial community to generate their xenic counterparts. Competitive interactions were assessed with reciprocal invasion experiments between paired xenic and paired axenic populations of C. sorokiniana and one of the two Microcystis strains, each assessed separately. Flow cytometry and random forest models were used to rapidly discriminate and quantify phytoplankton population densities with 99% accuracy. We found that M. aeruginosa PCC 7806, but not strain PCC 9701, could proliferate from low abundance in a steady-state population of C. sorokiniana. Further, the presence of bacteria allowed M. aeruginosa PCC 7806 to grow to a higher population density into an established C. sorokiniana population than when grown axenic. Conversely, when M. aeruginosa was dominant, C. sorokiniana was only able to proliferate from low density into the PCC 9701 strain, and only when axenic. The mutant of PCC 7806 lacking the ability to produce microcystin behaved similarly to the toxic wild-type, implying microcystin is not responsible for the difference in competitive abilities observed between the two wild-type strains. Quantification of microcystins (MCs) when PCC 7806 M. aeruginosa was introduced into the C. sorokiniana culture showed two-fold more MCs per cell when host-associated bacteria were absent compared to present in both species cultures. Our results show that the ability of M. aeruginosa to compete with C. sorokiniana is determined by genomic differences beyond genes involved in microcystin toxin generation and indicate an important role of host-associated bacteria in mediating phytoplankton interspecies interactions. These results expand our understanding of the key drivers of phytoplankton succession and the establishment and persistence of freshwater harmful cyanobacterial blooms.

Influence of Ocean–Lagoon exchanges on spatio-temporal variations of phytoplankton assemblage in an Atlantic Lagoon ecosystem (Oualidia, Morocco)

The Oualidia Lagoon is a semi enclosed marine ecosystem connected to the Atlantic Ocean of Morocco and exposed to human activities, mainly agriculture and oyster farming. The present study aims to characterize the spatio-temporal variation of the phytoplankton assemblage and to highlight the effect of the main environmental parameters on this important planktonic component evolving in a vulnerable anthropized ecosystem. For this purpose, a field survey was carried out during four seasons in 2011 to determine the biotic (phytoplankton, chlorophyll a) and abiotic (temperature, salinity and nutrients) variables during low and high tide periods. Results highlight an established spatial variation of physico-chemical parameters especially at low tide, with contrasted environmental conditions between the upstream and downstream zones. The phytoplankton diversity and abundance were characterized by a pronounced seasonal pattern. The Oualidia Lagoon is a nutrient rich ecosystem, especially in its upstream part. We also showed that both planktonic diversity and abundance were maximum in autumn and summer. The phytoplankton richness is governed by two main factors: the seasonality of nutrient enrichment and the regular supply of Atlantic seawater. Nitrate and ammonium were the main environmental abiotic factors determining the development of phytoplankton populations. The dynamic of phytoplankton in the Oualidia Lagoon is highly influenced by marine waters incoming from the Atlantic Ocean especially during the upwelling season. Finally, potential harmful algal species belonging to different genera such as Pseudo-nitzschia, Alexandrium, Prorocentrum, Dinophysis, Ostreopsis, Karenia, Coolia, Gonyaulax, Gymnodinium, Dictyocha and Chattonella were encountered showing a potential in this ecosystem to develop noxious blooms.

Using empirical dynamic modeling to assess relationships between atmospheric trace gases and eukaryotic phytoplankton populations in coastal Southern California

Many different atmospheric trace gases have been directly and indirectly linked to biological sources and sinks. Here we assess how atmospheric mixing ratios of a range of halocarbons (CH3Br, CH2Br2, CHBr3, CH3Cl, CHCl3, and CH3I) and COS are causally connected to naturally occurring marine eukaryotic phytoplankton in coastal Southern California. We use a self-organizing map to characterize the abiotic environment and empirical dynamic modeling with convergent cross mapping to identify causal interactions between multiple in situ 8-year time-series, sampled at the Ellen Browning Scripps Pier at Scripps Institution of Oceanography. Our work supports previous findings that halocarbon production is found in a variety of marine phytoplankton taxa and suggests that local phytoplankton may have the ability to affect changes in the mixing ratios of halocarbons in nearshore environments. There were notable links between changes in CH3I and several different diatom taxa and between changes in CHCl3 and a group of phytoplankton during specific ecosystem states. Our results suggest that both seasonal and non-seasonal shifts in eukaryotic phytoplankton structure contribute to small fluctuations in atmospheric halocarbon mixing ratios that exhibit strong seasonality and may occasionally play a larger role in atmospheric mixing ratios of halocarbons that display reduced seasonality.

Analysis of nonlinear stratified convective flow of Powell-Eyring fluid: Application of modern diffusion

The stratification phenomena have great importance in fishery management, insufficiency of dissolved oxygen in the lower parts of lakes, rivers and ponds, and phytoplankton populations. Thus the present article examines vital role of stratification phenomena in Powell-Eyring fluid flow due to inclined sheet which is stretched in a linear way. Collaboration of Cattaneo-Christov heat and mass flux model instead of Fourier Law of heat conduction is also accounted. Interpretation of heat transport is carried out with heat generation/absorption. Thermal stratification supports heat transport. Chemical reaction and solutal stratification also helped out mass transport. Non-linear governing equations with partial derivatives are converted into ordinary differential equation with the help of similarity transformations. Homotopic method is applied to solve arising dimensionless governing equations. Pertinent parameters and their physical behavior are displayed graphically. Drag force coefficient is also examined graphically. In culmination, substantial parameters of radiation and heat generation/absorption raised the temperature field while thermal relaxation time and solutal relaxation time parameters lower the temperature and concentration fields, respectively.

Algal blooms in a freshwater reservoir – A network community detection analysis of potential forcing parameters

Nutrient leakage due to modern agriculture and disposal of untreated urban wastewater results in the eutrophication of freshwater lakes and reservoirs, with elevated levels of cyanobacteria algal blooms often resulting in toxic conditions for animals and humans. A unique dataset of 22 coincident nutrient, phytoplankton, meteorological, and reservoir condition variables were recorded or calculated monthly for Hoover Reservoir near Columbus, Ohio, from February 1999 to December 2005. Network science was used in this study to visualize and differentiate selected nutrient and phytoplankton seasonality in Hoover Reservoir. Nutrient and phytoplankton concentrations in Hoover Reservoir respond independently to a number of external and internal environmental variables, but are also biochemically interdependent within the reservoir ecosystem. A number of forcing parameters can significantly alter seasonal phytoplankton growth and succession patterns. Chief among these are variability in the daily, seasonal, and/or yearly patterns and intensities of precipitation and the resultant surface runoff; duration and intensity of solar radiation; air and resultant water temperatures; and agricultural practices. The phytoplankton population in Hoover Reservoir is ecologically driven, with algal succession and nutrient levels constraining population concentrations. Complemented by selected statistical analyses, this limited network community detection study provides the hydrologist/ecologist with a dynamic and quantitative visualization of the complex hydrometeorological variable and biogeochemical process forcing parameters present in reservoirs and lakes.

The impact of temporal variability in light-climate on time-averaged primary production and a phytoplankton bloom in a well-mixed estuary

Phytoplankton primary production (PP) in turbid estuaries is often limited by light-availability. Two important factors altering light-climate are solar irradiance at the water surface and exponential light-extinction coefficient within the water column. Additionally, the depth of the water body changes the light-climate and corresponding PP by altering the ratio of the euphotic and mixing depth in a well-mixed estuary. These three parameters are highly variable yet are often assumed to be constant by both experimental scientists and modelers because of a lack of data or to reduce complexity. Because assuming constant parameters introduces an error, we utilize an idealized model of depth-integrated primary production to analyze the (individual) impact of temporal variability in these three parameters. We only consider the main tidal and solar constituents in temporal variability of the forcings and apply a second-order moment approximation to analyze the bias introduced to time-averaged PP estimates by neglecting temporal fluctuations. We demonstrate that the sign and magnitude of this bias are system-specific and depend on two non-dimensional parameters that characterize the system. The first is equivalent to the ratio of mixing and photic depth. The second accounts for typical incident irradiance and the photosynthetic parameters of the phytoplankton population present. To demonstrate the applicability of our approach, we apply the model to two cases in the Scheldt estuary (Belgium) in the brackish and freshwater part. In the first application, we study the impact of fluctuations on phytoplankton in dynamic equilibrium, where biomass is assumed to be constant. We show that variability in solar irradiance has the largest impact on time-averaged PP in dynamic equilibrium, resulting in a 30 percent decrease compared to time-invariant forcing. By comparing with a numerical integrator, we show that a second-order moment approximation correctly predicts the order of magnitude of the impact of temporal variability of the individual parameters. In the second application, we study the impact of fluctuations on unbounded exponential phytoplankton growth. Also here, fluctuations in solar irradiance have the largest impact and lead to a significant decrease in exponential growth. In this case study, we show that temporal fluctuations delay the onset of the biomass by two weeks and decrease the biomass by a factor 14 after two weeks compared to time invariant forcing. Additionally, we show that the temporal fluctuations induce low-frequency variability in phytoplankton biomass with similar periodicity as the spring-neap cycle, making it difficult to observe these phenomena in real-world time series.