Long-term Phytoplankton Dynamics Research Articles

Spatiotemporal distribution of phytoplankton community structure and its relationship with environmental factors in Hongze Lake, China

Hongze Lake, which ranks as the fourth-largest freshwater lake in China, has considerable importance as a water transfer reservoir under the South-to-North Water Transfer Project. The evaluation of the lake's health and nutritional status could be achieved by the analysis of the phytoplankton community. Nevertheless, the understanding of the long-term phytoplankton dynamics in Hongze Lake after the implementation of the South-to-North Water Diversion remains insufficient. In this study, an investigation was conducted to analyze the community structure, distribution patterns, and environmental factors influencing the abundance of phytoplankton in Hongze Lake. The results of the study revealed that Hongze Lake showed seasonal variations in both the structure and biomass of its phytoplankton population. In fall, winter, and spring, Chlorophyta dominates, while Cryptophyta dominates in summer. Algae predominantly inhabit Chengzi Lake and Lihewa during the summer season. According to the redundancy analysis, temperature is positively correlated with algal abundance in summer but negatively correlated in spring and winter. Furthermore, the mantel analysis indicated that the abundance of different algal species was significantly correlated with dissolved oxygen and nutrient levels. The generalized linear model further clarified the contribution of environmental factors to algal abundance: total nitrogen (weights = 30.67%) ranked second in importance after temperature (weights = 34.52%). The results of this study provide insight into the alterations in the phytoplankton community within Hongze Lake following the implementation of the water transfer project. In addition, these findings offer valuable guidance for the regulation of lake water resources and water quality.

Seasonal and Long-Term Phytoplankton Dynamics in the Middle Caspian According to Satellite Data and In Situ Observations in the First Decades of the 21st Century

Seasonal and long-term variability of phytoplankton in the Middle Caspian was studied based on remote sensing data of the sea by SeaWiFS and MODIS-Aqua scanners in 1998–2021 and the results of field observations in 2004–2021. The seasonal variability of chlorophyll “a” (CHL) calculated from satellite data using a regional algorithm indicated that the autumn and winter seasons were the main phytoplankton production periods of the year. In summer, a period of stagnation was observed in phytoplankton growth in the surface layer. However, according to satellite data in the first months of each year, winter blooms were observed recurrently in the Middle Caspian Sea, as confirmed by the results of field observations in 2004–2021. The phytoplankton biomass during the winter vegetation period reached 4.5–5.0 g/m3. In the first decade of the century (2004–2006), winter blooms were almost entirely (as much as 96%) formed through the mass growth of the alien diatom Cerataulina pelagica. In the modern period (2021), the winter bloom was formed both by three endemic diatom species Thalassionema nitzschioides, Cyclotella comta and Dactyliosolen fragilissimus and by two alien species Pseudo-nitzschia seriata and Cerataulina pelagica. In spring, the diatom Cyclotella caspia and the dinoflagellate Prorocentrum micans, both endemics, dominated. In summer, the phytoplankton biomass was composed of the mass growth of small flagellates and dinoflagellates in the seasonal thermocline layer, which current remote sensing methods cannot record. The diatoms’ contribution to the community’s total biomass in summer did not exceed 3%. In the autumn phytoplankton, the main role was played by a diatom component represented by alien species, mainly Chaetoceros peruvianus.

Long-term phytoplankton dynamics in the Zeeschelde estuary (Belgium) are driven by the interactive effects of de-eutrophication, altered hydrodynamics and extreme weather events

We studied how changing human impacts affected phytoplankton dynamics in the freshwater and brackish tidal reaches of the Zeeschelde estuary (Belgium) between 2002 and 2018. Until the early 2000s, the Zeeschelde was heavily polluted due to high wastewater discharges. By 2008, water quality had improved, resulting in lower nutrient concentrations and higher oxygen levels. Since 2009, however, increased dredging activities resulted in altered hydrodynamics and increased suspended sediment concentration. The combined effects of these environmental changes were reflected in three marked transitions in phytoplankton community composition. Assemblages were dominated by Thalassiosirales and green algae (especially Scenedesmaceae) until 2003. The period 2003–2011 was characterized by the wax and wane of the centric diatoms Actinocyclus and Aulacoseira, while in the period 2012–2018 Thalassiosirales and Cyanobacteria became dominant, the latter mainly imported from the tributaries. Phytoplankton biomass increased sharply in 2003, after which there was a gradual decline until 2018. By 2018, the timing of the growing season had advanced with about one month compared to the start of the study, probably as a consequence of climate warming and intensified zooplankton grazing pressure. Our study shows that de-eutrophication (during the 2000s) and morphological interventions in the estuary (in the 2010s) were dominant drivers of phytoplankton dynamics but that the main shifts in community composition were triggered by extreme weather events, suggesting significant resistance of autochthonous communities to gradual changes in the environment.

Long-Term Phytoplankton Dynamics in the Zeeschelde Estuary (Belgium) are Driven by the Interactive Effects of De-Eutrophication, Altered Hydrodynamics, and Extreme Weather Events

Long-Term Phytoplankton Dynamics in the Zeeschelde Estuary (Belgium) are Driven by the Interactive Effects of De-Eutrophication, Altered Hydrodynamics, and Extreme Weather Events

Long-term dynamics of phytoplankton and chlorophyll a concentration in the surface layer of the coastal waters of the Black Sea (Sevastopol region)

In the surface layer of the Sevastopol and Quarantine bays, during 2000–2014 in summer and in autumn, the average values of the concentration of chlorophyll a and phytoplankton biomass are reduced by a factor of 2–5. This is due to a decrease in the content of nitrates and silicon compounds in water, as well as the relative proportion of diatoms in the total biomass of phytoplankton. Regression analysis showed that in the summer period the long-term negative trend in the change in the relative biomass of diatoms was determined mainly by the nitrate content in the water and its temperature, while in the autumn – by the content of nitrates and silicon. The share of dinoflagellates and coccolithophores increased over the entire observation period. In winter and spring in bays, and in the open coast during all seasons, unidirectional changes in the concentration of chlorophyll and the total biomass of phytoplankton were not detected.

Long-Term Phytoplankton Dynamics in a Complex Temporal Realm

Faced with an environment of accelerated change, the long-term dynamics of biotic communities can be approached to build a consistent and causal picture of the communities’ life. We have undertaken a 25-year monthly-sampling study on the phytoplankton of a meso-oligotrophic lake, paying attention to controlling factors of overall biomass (TB) and taxonomical group biomass (TGBs). Long-term series included decreased trends of TB and TGBs, and multi-scale periodicity. A decadal TB periodicity emerged related to nitrogen concentration and Cryptophytes. Annual periodicities were mainly related to air and water temperature controlling the abundance of Chlorophytes or Dinoflagellates. Intra-annual cycles could arise from autogenic processes. The analysis by periods revealed relevant dynamics (for example, Diatom periodicities), hidden in the analysis of the complete series. These results allow us to establish that: i) two organizational levels of phytoplankton change differently in time scales from months to decades; ii) controlling factors (climate, water physics and chemistry) act at different time scales and on different TGBs, and iii) different combinations of the “taxonomical group-control factor-trend and periodicity” set throughout the studied time explain total biomass dynamics. A holistic approach (multiple complementary analyses) is necessary to disentangle the different actors and relationships that explain non-stationary long-term phytoplankton dynamics.

Analysis of Long-Term Phytoplankton Dynamics with Environmental Factors in Harima-Nada, Eastern Seto Inland Sea, Japan

Analysis of Long-Term Phytoplankton Dynamics with Environmental Factors in Harima-Nada, Eastern Seto Inland Sea, Japan

Temporal variation in zooplankton and phytoplankton community species composition and the affecting factors in Lake Taihu—a large freshwater lake in China

Monitoring diverse components of aquatic ecosystems is vital for elucidation of diversity dynamics and processes, which alter freshwater ecosystems, but such studies are seldom conducted. Phytoplankton and zooplankton are integral components which play indispensable parts in the structure and ecological service function of water bodies. However, few studies were made on how zooplankton and phytoplankton community may respond simultaneously to change of circumstance and their mutual relationship. Therefore, we researched synchronously the phytoplankton communities as well as zooplankton communities based on monthly monitoring data from September 2011 to August 2012 in heavily polluted areas and researched their responses to variation in environmental parameters and their mutual relationship. As indicated by Time-lag analysis (TLA), the long-term dynamics of phytoplankton and zooplankton were undergoing directional variations, what's more, there exists significant seasonal variations of phytoplankton and zooplankton communities as indicated by Non-Metric Multidimensional scaling (NMDS) methods. Also, Redundancy Analysis (RDA) demonstrated that environmental indicators together accounted for 25.6% and 50.1% variance of phytoplankton and zooplankton, respectively, indicating that environmental variations affected significantly on the temporal dynamics of phytoplankton as well as zooplankton communities. What's more, variance partioning suggested that the major environmental factors influencing variation structures of zooplankton communities were water temperature, concentration of nitrogen, revealing the dominating driving mechanism which shaped the communities of zooplankton. It was also found that there was significant synchronization between zooplankton biomass and phytoplankton biomass (expressed as Chl-a concentration), which suggested that zooplankton respond to changes in dynamic structure of phytoplankton community and can initiate a decrease in phytoplankton biomass through grazing in a few months.

Long-Term Phytoplankton Dynamics in the Denishi Reservoir (Ukraine)

Long-Term Phytoplankton Dynamics in the Denishi Reservoir (Ukraine)

Functional approach based on morphology as a model of phytoplankton variability in a subtropical floodplain lake: a long-term study

Long-term phytoplankton dynamics in a floodplain lake, between periods of limnophase and potamophase was studied using the morphology-based functional classification (MBFG). The work was carried out to test the hypothesis that the temporal distribution of MBFGs is influenced by the hydrosedimentological regime of the Parana River, and that these differences can be registered by analyzing the dominant MBFGs in the two periods. Samples were taken in an isolated floodplain lake on the Upper Parana River floodplain, Brazil, from 2000 to 2012, and water level, water temperature, conductivity, pH, dissolved-oxygen, euphotic zone, maximum depth, and nutrients were used to explain the distribution of MBFGs. 478 taxa were identified and distributed in seven MBFGs (I–VII). MBFG V (flagellates algae) and VI (diatoms) showed 100% frequency of occurrence. MBFG II was associated exclusively with the limnophase; MBFG IV and VII were associated with limnophase periods with higher pH and dissolved-oxygen content; and MBFG I, III, V, and VI were associated with limnophase and potamophase, mainly associated with transparency, nutrients, and conductivity. The MBFG approach represented the trends of each group in terms of its occurrence and biovolume, according to the hydrosedimentological regime, providing broad-scale information on changes in the phytoplankton.

Contrasting long-term trends and shifts in phytoplankton dynamics in two large rivers

Knowledge about long-term dynamics of phytoplankton in river ecosystems as well as the physical and chemical drivers that potentially control the plankton is essential for predicting future developments, e.g. in response to global climate change. The present study analyzes long-term trends in phytoplankton biomass and shifts in the timing of phytoplankton spring blooms observed in the large rivers Rhine and Elbe from 1990–2009 and 1994–2009, respectively, and analyzes the factors potentially regulating phytoplankton biomass. While phytoplankton biomass in the Elbe was high (seasonal mean chlorophyll-a concentration: 62 µg/L) and showed an increasing tendency, it was much lower in the Rhine (seasonal mean chlorophylla concentration: 10 µg/L) where it decreased significantly during the study period. This decrease coincided with an earlier occurrence of the phytoplankton spring maximum. In the Elbe, the timing of low discharge conditions was crucial for the occurrence of the spring bloom, i.e. an earlier end of the discharge maximum was connected with an earlier spring bloom. In the Rhine, we found a positive correlation between the timing of the spring bloom and the end of winter flood flow. The maximum chlorophylla values during the bloom correlated with the timing of maximum light availability in the Rhine. The findings indicate that climate related factors, like discharge or light conditions, have a high potential to regulate phytoplankton spring bloom dynamics in large rivers. Such dependence could be relevant for predicting phytoplankton development under climate change.

Long-term phytoplankton dynamics in a Mediterranean eutrophic lagoon (Cabras Lagoon, Italy)

The temporal variations in phytoplankton abundance and diversity were analysed from 1999 to 2009 in Cabras Lagoon, a shallow eutrophic Mediterranean lagoon (west coast of Sardinia). It is one of the aquatic ecosystems listed in the “Marine Ecosystems of Sardinia” by the Italian Network of Long-Term Ecological Research (LTER Italy). The objectives of this work were to assess the general features of phytoplankton succession and its dynamics in relation to environmental factors along the decade 1999–2009, and to identify the main forces driving phytoplankton variability in terms of the general trends in Mediterranean transitional waters. Our results highlight several important aspects: a shift in the annual peak density from the summer–autumn season, observed in 1999–2002, to the winter–spring season in subsequent years; simultaneous reductions in chlorophyll a concentrations and cell size from 1999 to 2008; and the modification of the structure of the phytoplankton assemblages, from a more differentiated class composition in 1999–2002 to the subsequent dominance of the Cyanophyceae. Moreover, analysis of similarity on both abiotic and phytoplanktonic data shows significant differences among the hydrological years considered. Pearson's correlations indicate temperature, salinity and nutrients as the environmental parameters that most influenced the phytoplankton composition and dynamics.

An analysis of long-term phytoplankton dynamics in Muskegon Lake, a Great Lakes Area of Concern

Long-term monitoring of aquatic ecosystems is essential to distinguish the effects of human-induced stressors from natural patterns of ecologic variation, especially in Great Lakes Area of Concern such as Muskegon Lake. Samples collected between 2003–2009, as part of a continuing long-term monitoring study of the lake, were analyzed to: 1) detect spatial and temporal patterns in the phytoplankton biovolume and species composition; 2) evaluate the environmental variables that regulate phytoplankton community composition changes; and 3) determine the ecological conditions under which toxin-producing Microcystis species occur. Distinct patterns in Muskegon Lake phytoplankton were not evident among sites, which can be explained, at least in part, by the well-mixed waters in this drowned river mouth system. However, surface and bottom samples within sites had significantly different biovolume and species composition, suggesting that horizontal mixing did not extend throughout the water column. Surface samples had greater phytoplankton biovolume than bottom samples, possibly because of greater irradiance. Seasonally, the least biovolume was recorded in spring samples, which were dominated by diatoms. Phytoplankton biovolume was greatest in the summer when cyanobacteria were abundant. Environmental variables that correlated highly with the ordination space defined by species composition included sulfate, specific conductance, total dissolved solids, and chloride. Results from regression tree analysis predicted increasing biovolume of Microcystis aeruginosa with increasing concentrations of the total Kjeldahl nitrogen. The seven-year period of this study did not reveal major changes in the lake's environment and phytoplankton communities, but the presence of invasive and toxin-producing species warrants their continued monitoring.

Multiscale Variability of Twenty-Two Coastal Phytoplankton Time Series: a Global Scale Comparison

We provide an introduction and a foreword to the Special Issue “Phytoplankton Time Series in Estuaries and Coastal Ecosystems”. This issue includes long-term investigations (10–40 years) of 22 coastal ecosystems and a comparative analysis of chlorophyll a from 84 time series. The results and conclusions provided by these studies help to illuminate the disparities and similarities in long-term phytoplankton dynamics among a wide range of coastal systems and provide insight into the major driving factors responsible for short- and long-term trends in phytoplankton communities.

Long-term Dynamics of Phytoplankton in the Rhode River, Maryland (USA)

We analyzed interannual variability in a long-term record of chlorophyll concentration and phytoplankton species composition in the Rhode River, Maryland (USA). Over the approximately 30-year record, there was no long-term monotonic trend in phytoplankton chlorophyll concentration, though temporary directional trends related to precipitation patterns sometimes persisted for a decade before reversing. From counts on preserved samples, we estimated the dominance by different pigment-bearing groups and size classes. Diatoms, dinoflagellates, and cryptophytes comprised about 80–97% of the annual averaged class-specific biovolume. Cryptophytes dominated the first 2 years in the data set but displayed a long-term decline, after which diatoms dominated in all but four consecutive years in which there were large dinoflagellate blooms. There was a long-term increase in cells with equivalent spherical diameters from 4 to 10 µm, accompanied by declines in the proportion of cells in the 2- to 4- and 10- to 20-µm size classes. The main cause of these changes in size classes was a long-term increase in Chroomonas sp. and Apedinella radians and long-term decline in Microcystis sp. and an unidentified cryptophyte, respectively. These taxa were cosmopolitan in their seasonal and spatial distributions, and hence the long-term changes in taxa did not conform well with conceptual models based on succession of “life-forms.” The segregation of diatoms and dinoflagellates expected on the basis of “life-forms” applied to seasonal and spatial patterns. Characterizing the phytoplankton community in terms of diversity, size, and class-specific biovolume gave results that were consistent with one another and added insight to the broad-scale changes in chlorophyll concentration. Subtle changes in the size distribution of cryptophytes were not apparent from biovolume measures and would not have been apparent without microscopy. Though causes of such shifts may be difficult to identify, identifying the causes and predicting potential consequences cannot even be attempted without awareness of the phenomena.

Patternising phytoplankton dynamics of two shallow lakes in response to restoration measures by applying non-supervised artificial neural networks

Long-term time-series data sets of two shallow Dutch lakes, Lake Veluwemeer and Lake Wolderwijd were subjected to ordination and clustering by means of non-supervised artificial neural networks (ANN). Splitting of the data sets into sub-series corresponding with three different management periods have allowed a comparative analysis of both the short-term seasonal and long-term phytoplankton dynamics in relation to the restoration measures. The lakes were considered as hyper-eutrophic and have been managed both with bottom-up and top-down management approaches. Results of the study have demonstrated that non-supervised ANN allow to elucidate causal relationships of complex ecological processes (1) within the specific genus, Oscillatoria and Scenedesmus and (2) the combination of external nutrient control and in-lake food web manipulation of the two lakes achieved to control eutrophication.

Long-term dynamics of phytoplankton from a small shallow lake in central Japan

Long-term dynamics of phytoplankton from a small shallow lake in central Japan

Long-Term Dynamics of Phytoplankton in the Mozhaisk Reservoir and Its Production–Destruction Processes under Anthropogenic Effect

Data of observations made in 1967–1996 on the Mozhaisk Reservoir were used to examine the dynamics of primary production and destruction and their proportion. The species and size structure of the phytoplankton community was found to have changed significantly and the community biomass, to have increased in the course of long-term succession.

Multivariate analysis of phytoplankton and related environmental factors, in a shallow hypertrophic lake

Data on some relevant environmental variables and phytoplankton species composition, collected from the hypertrophic shallow lake Albufera of Valencia (Spain) during 1980–88, were examined using Redundancy Analysis (RDA). The hydrological cycle of the lake is manipulated for rice cultivation in the area. Seasonality and the particular hydrological cycle of the lake were the principal factors influencing long-term phytoplankton dynamics. Annual or horizontal differences were less important than the seasonal factor. However, a trend of phosphate increase and underwater illumination decrease was observed between 1980 and 1988. These changes might be related to some species year-to-year variations, although in general interannual phytoplankton changes were scarce. Spatial phytoplankton differences were much smaller than physical and chemical differences, which were mainly related to loading and residence times at the different sampling zones. Shallowness, hypertrophy and the regular hydrological cycle of the Albufera for rice yield, seem to contribute to the maintenance of an almost stable and homogeneous algal community, mainly composed of filamentous cyanophytes. RDA analysis has proved to be an efficient method in yielding valuable information on phytoplankton-environment interactions and trends over a long series of data. It seems also a feasible technique to monitor the results of lake management and restoration in the future.