Long-term Changes In Phytoplankton Research Articles

Visualizing Oceanographic Data to Depict Long-term Changes in Phytoplankton.

Oceanographic time series providean important perspective on environmental processes in ecosystems. The Narragansett Bay Long-Term Plankton Time Series (NBPTS) in Narragansett Bay, Rhode Island, USA, represents one of the longest plankton time series (1959-present) of its kind in the world and presents a unique opportunity to visualize long-term change within an aquatic ecosystem. Phytoplankton representthe base of the food web in most marine systems, including Narragansett Bay. Therefore, communicating their importance to the 2.4 billion people who live within the coastal ocean is critical. We developed a protocol with the goal of visualizing the diversity and magnitude of phytoplankton by utilizing Adobe Illustrator to convert microscopic images of phytoplankton collected from the NBPTS into vector graphics that could be conformed into repetitive visual patterns through time. Numerically abundant taxa or those that posed economic and health threats, such as the harmful algal bloom taxa, Pseudo-nitzschia spp., were selected for image conversion. Patterns of various phytoplankton images were then created based on their relative abundance for select decades of data collected (1970s, 1990s, and 2010s). Decadal patterns of phytoplankton biomass informed the outline of each decade while a background color gradient from blue to red was used to reveal a long-term temperature increase observed in Narragansett Bay. Finally, large, 96-inch by 34-inch panels were printed with repeating phytoplankton patterns to illustrate potential changes in phytoplankton abundance over time. This project enables visualization of literal shifts in phytoplankton biomass, that are typically invisible to the naked eye while leveraging real-time series data (e.g., phytoplankton biomass and abundance) within the art piece itself. It represents an approach that can be utilized for many other plankton time series for data visualization, communication, education, and outreach efforts.

Long-term changes in phytoplankton and macrophyte communities in an eutrophic shallow reservoir and prospects for its restoration

Abstract Long-term changes in hydrochemistry and community structure of phytoplankton and macrophytes were analyzed in the Sestroretskiy Razliv reservoir (northwestern Russia). The average content of total phosphorus (TP) in May–October increased from 73 μg P l−1 in 1980 to 163 μg P l−1 in 2000. A significant increase in average chlorophyll a content from 16.6 μg l−1 in 1980 to 84.7 μg l−1 in 2000 and a shift in phytoplankton composition to the dominance of cyanobacteria over diatoms indicated a change in the trophic status of the reservoir from meso-eutrophic to hypertrophic. In 2016 and 2018, average TP was 96 and 101 μg P l−1, respectively. The average content of chlorophyll a was 43.6 μg l−1 in 2016 and 66.6 μg l−1 in warmer 2018, indicating persistent eutrophic conditions. Diatoms dominated both in 2016 and 2018, especially in 2016 characterized by unfavorable weather conditions. Cyanobacteria were more abundant in 2018 with higher summer temperatures. The decline of the total area covered by aquatic vegetation from 157 ha in 1980 to 76 ha in 2016 likely resulted from an increase in phytoplankton biomass and water turbidity. Based on the results of our observations, in addition to further reduction in nutrient loading, biomanipulation by introducing predatory fish as a restoration measure was proposed to improve the ecological status of the reservoir.

An updated phytoplankton check-list for the Helgoland Roads time series station with eleven new records of diatoms and dinoflagellates

The Helgoland Roads time series is one of the longest and most detailed time series in the world. It comprises daily phytoplankton counts accompanied by physico-chemical measurements. As such, it provides valuable long-term record of changes and their underlying causes in the phytoplankton community around Helgoland. This work provides an updated check-list of the phytoplankton species encountered at the Helgoland Roads LTER station with additional taxonomic assessments from live net samples and scanning electron microscope surveys. Since the last check-list was published 11 additional taxa have been recorded for the first time comprising 9 diatom and 2 dinoflagellate species. Of the 9 diatom species 3 were Chaetoceros species: Chaetoceros anastomosans, C. pseudocurvisetus and C. lorenzianus (the latter identified by their resting cysts) which were all first recognised in September 2009. The toxic dinoflagellate Dinophysis tripos, and the bipolar centric diatom Odontella longicruris both were first observed in September 2015. The latest new record is the potentially toxic dinoflagellate Alexandrium ostenfeldii, first recorded in August 2017. All of the first records (with the exception of Dinophysis tripos) were first observed in semi-quantitative surveys based on live samples and SEM demonstrating that adding less frequent but very detailed assessments can complement high frequency counts of fixed samples as long as these data of different origin are linked efficiently to the individual sampling event and all metadata including representative pictorial metadata are recorded in a consistent manner. In this manner the enhanced checklist serves as a baseline against which long-term changes in phytoplankton potentially related to ecosystem state can be addressed.

The relative importance of weather and nutrients determining phytoplankton assemblages differs between seasons in large Lake Taihu, China

Climate change affects seasonal weather patterns, but little is known about the consequent effects on phytoplankton assemblage variation. We studied the changes in phytoplankton assemblages, expressed as morpho-functional groups, during four seasons over the past two decades in large shallow eutrophic Lake Taihu, China. During this period, both climate and nutrient levels changed in the lake. Wind speed declined significantly from 1997 to 2016 in all seasons, while global radiation increased significantly in spring and winter. Phosphorus and chlorophyll a concentrations showed a significant increasing trend in all seasons, especially in summer and autumn. Diatoms, mainly Aulacoseira and Asterionella, increased during late winter and early spring. Multiple stepwise regression analysis and non-metric multidimensional scaling indicated that climatic variables (i.e., decreasing wind speed and increasing global radiation) were the main drivers of phytoplankton assemblage variance in winter and early spring. An increase in the dominance of cyanobacteria (mainly Microcystis spp.) in summer and autumn was mainly related to changes in phosphorus. Our results indicate that both nutrients and climatic variables were major drivers of the observed changes in phytoplankton assemblages, differing in importance between seasons. The differential response of phytoplankton community variation to future environmental change in the different seasons needs to be taken into account when evaluating the long-term changes in phytoplankton.

Long-term changes of phytoplankton in the lake, not affected by anthropogenic impact (Lake Krivoe, North Karelia)

First studies of the lake ecosystem were performed in 1968–1969 in framework of the International Biological Program, as on a model lake for the observations on the natural dynamic processes. Further work had continued in 1972 and annually from 2002 to 2014. During all study period Cyanobacteria and Chrysophyta have been permanent representatives in phytoplankton. Cyanobacteria were mostly represented by small-cell species from Chroococcales, so their share in the total biomass was low, despite the high abundance. Algae from genera Dinobryon and Uroglena, had dominated in Spring and remained in the plankton during entire season. A distinctive feature of the lake plankton was a low development of diatoms (less than 10% in abundance and biomass) and the absence of the spring outbreak of diatoms in both: under ice and in open water. Cryptomonads (Cryptopyta), which also had been represented throughout of season, became practically new, fairly widespread group in lake phytoplankton. Detailed studies carried out in 2002–2014, have shown that the spring maximum of phytoplankton rarely exceeded the summer one and reached in average 0.46 mg/L. The percentage of each size class of algae in the total biomass of the plankton was determined. Algae with size to 40 microns, which are the most consumed ones by filter feeding zooplankton, constituted a significant share in the Spring time. However the most favorable trophic conditions for zooplankton were during the summer. The development of single-celled Cryptomonad, which reached about 30% of the total biomass, has increased the trophic importance of phytoplankton. Species composition and abundance of phytoplankton in the lake may indicate a conservation of the lake as a clean oligotrophic reservoir.

Long-term changes of the phytoplankton community and biomass in the subtropical shallow Patos Lagoon Estuary, Brazil

Seasonal and interannual changes (1993–2012) of water temperature and transparency, river discharge, salinity, water quality properties, chlorophyll a (chl-a) and the carbon biomass of the main taxonomical phytoplankton groups were evaluated at a shallow station (∼2 m) in the subtropical Patos Lagoon Estuary (PLE), Brazil. Large variations in salinity (0–35), due to a complex balance between Patos Lagoon outflow and oceanic inflows, affected significantly other water quality variables and phytoplankton dynamics, masking seasonal and interannual variability. Therefore, salinity effect was filtered out by means of a Generalized Additive Model (GAM). River discharge and salinity had a significant negative relation, with river discharge being highest and salinity lowest during July to October. Diatoms comprised the dominant phytoplankton group, contributing substantially to the seasonal cycle of chl-a showing higher values in austral spring/summer (September to April) and lowest in autumn/winter (May to August). PLE is a nutrient-rich estuary and the phytoplankton seasonal cycle was largely driven by light availability, with few exceptions in winter. Most variables exhibited large interannual variability. When varying salinity effect was accounted for, chl-a concentration and diatom biomass showed less irregularity over time, and significant increasing trends emerged for dinoflagellates and cyanobacteria. Long-term changes in phytoplankton and water quality were strongly related to variations in salinity, largely driven by freshwater discharge influenced by climatic variability, most pronounced for ENSO events. However, the significant increasing trend of the N:P ratio indicates that important environmental changes related to anthropogenic effects are undergoing, in addition to the hydrology in the PLE.

Long-term changes in phytoplankton in a humic lake in response to the water level rising: the effects of beaver engineering on a freshwater ecosystem

Although water level changes are supposed to be a key factor affecting the functioning of lake ecosystems, knowledge on this topic is scarce, particularly for humic lakes. This paper presents the results of 18 years’ research on a small humic lake exposed to hydrological change (rising of the water level), which was induced by spontaneous colonization of the lake by the European beaver (Castor fiber L.). We put forward a hypothesis that this change will be reflected in the quantity and structure of summer phytoplankton due to expected changes in the water chemistry. We noted a statistically significant decrease in total phosphorus and calcium concentrations, electrolytic conductivity, and Secchi disc transparency, and an increase in water color. The phytoplankton structure changed, with cyanoprocaryota and greens decreasing and flagellates increasing. The alteration was observed in a lake which had previously been drained by ditches, so beaver damming appeared to cause the return of the lake to its original endorheic conditions as well as to a water chemistry and phytoplankton structure more typical of undisturbed humic lakes.

Long-term changes in phytoplankton in the Kattegat, the Belt Sea, the Sound and the western Baltic Sea

The development in biomass and dominant groups and species of phytoplankton was examined at six monitoring stations in the Kattegat, the Belt Sea, the Sound and the western Baltic Sea. Since the initiation of the monitoring in 1979 the biomass of phytoplankton has decreased significantly. The decrease correlated with Danish nitrogen loads to the Danish Straits but also with increases in surface water temperature. The decline in biomass was mainly due to less pronounced spring blooms in the Kattegat and the Belt Sea and reduced biomass during late summer–autumn on all stations. Diatoms have been the overall dominant phytoplankton group on all stations but the western Baltic Sea. However, their contribution to the total biomass has varied considerably throughout the monitoring period as during the years 1987–1989 phytoplankton was dominated by an unusually high dinoflagellate biomass. A qualitative comparison showed that the dominant species (diatoms and dinoflagellates) found in plankton net tows taken during spring and autumn around year 1900 were still among the dominant species during the monitoring period 1979–2006. However, several of the dominant species found during the latter period were not present in the samples taken around year 1900 despite that they should have been captured by the methods used.

Phytoplankton fuels Delta food web

Populations of certain fishes and invertebrates in the Sacramento-San Joaquin Delta have declined in abundance in recent decades and there is evidence that food supply is partly responsible. While many sources of organic matter in the Delta could be supporting fish populations indirectly through the food web (including aquatic vegetation and decaying organic matter from agricultural drainage), a careful accounting shows that phytoplankton is the dominant food source. Phytoplankton, communities of microscopic free-floating algae, are the most important food source on a Delta-wide scale when both food quantity and quality are taken into account. These microscopic algae have declined since the late 1960s. Fertilizer and pesticide runoff do not appear to be playing a direct role in long-term phytoplankton changes; rather, species invasions, increasing water transparency and fluctuations in water transport are responsible. Although the potential toxicity of herbicides and pesticides to plankton in the Delta is well documented, the ecological significance remains speculative. Nutrient inputs from agricultural runoff at current levels, in combination with increasing transparency, could result in harmful algal blooms.

Trend and noise: long-term changes of phytoplankton in the Keszthely Basin of Lake Balaton, Hungary

(2002). Trend and noise: long-term changes of phytoplankton in the Keszthely Basin of Lake Balaton, Hungary. SIL Proceedings, 1922-2010: Vol. 28, No. 1, pp. 194-203.

Long-term phytoplankton changes in an artificially divided, top-down manipulated humic lake

Lake Grose Fuchskuhle (Brandenburg, Germany) is a naturally acidic bog lake that was artificially divided into four basins by large plastic curtains for biomanipulation experiments in 1990. Different numbers of perch were added to each compartment beginning in the spring of 1993. The species composition and abundance of phytoplankton, pH, nutrient concentrations, dissolved organic carbon (DOC) and chlorophyll a content were analyzed at regular intervals during 1991 and 1998. The division of the lake resulted in divergent developments in the physical and chemical environment of the compartments. This study compared the phytoplankton assemblages of the Northeast- (NE) and Southwest- (SW) basins which differed strongly in chemistry during the investigation period. Divergent developments in phytoplankton species composition in both basins can be explained by changes in physical and chemical conditions (bottom-up effects). Increased pH values and DOC concentrations probably favoured mass developments of the dinoflagellate Gymnodinium uberrimum since 1993, while increased nutrients (dissolved inorganic carbon, total nitrogen and especially total phosphorus) as well as further changes in pH and DOC led to the dominance of the raphidophyte Gonyostomum semen in 1998. This bloom was characterized by extreme biomasses of up to 143 mg l−1 wet weight, corresponding with high chlorophyll a concentrations of up to 413 μg l−1 at the same time. In contrast, no significant relationship between experimental manipulations by piscivorous fish stocking (top-down effects) and phytoplankton biomass were observed.

Long-term Changes in Phytoplankton of the Upper Reaches of the Dnieper River

Long-term Changes in Phytoplankton of the Upper Reaches of the Dnieper River

Long-term changes of phytoplankton in a eutrophicated boreal lake during the past one hundred years (1893-1998)

Long-term changes of phytoplankton in a eutrophicated boreal lake during the past one hundred years (1893-1998)

Long-term phytoplankton changes in acid and limed lakes in SW Sweden

Phytoplankton development in the acidified Lakes Ostra Nedsjon and Ommern, situated in SW Sweden, was followed during 1973–92. The former lake was first limed in 1971–73 which increased the pH value from ca 5.3 to 6, without affecting the plankton markedly. In Lake Ommern, acidification lowered the pH value from ca 6 to 5.3 during 1976–1981, which caused oligotrophication and reduced number of species. In 1981/82 both lakes were limed, and during the following period treatments were regularly made, resulting in average pH levels of 7.2 and 6.9, respectively. The concentrations of humic compounds and phosphorus increased and the distribution of the major plankton groups was markedly changed. In both lakes the cyanophycean volume decreased, whereas diatoms became quantitatively important. Especially in relation to the acidic period 1979–81, there was increased species richness in both lakes. However, in contrast to the development in Lake Ommern, the desmids were eliminated in Lake O.Nedsjon, where the pre-acidification phytoplankton was not restored.

Meroplankton dynamics in a saline, turbulent, turbid shallow lake (Neusiedlersee, Austria and Hungary)

Phytoplankton species composition, horizontal distribution, seasonal- and long-term dynamics are investigated in relation to some environmental factors, based on about 700 samples taken between 1968 and 1992 in the shallow, turbid, turbulent, saline Neusiedlersee (Austria/Hungary). We deduced: 1. The phytoplankton is relatively poor in species which is attributable to high salinity and turbidity. Blue-green algae of picoalgal size, meroplanktonic diatoms, green algae either with gelee or elongated form are the most important groups in the plankton; 2. No consequent horizontal differences in the distribution of phytoplankton biomass were found; the high contribution of diatoms (69%) and green algae (22%) is characteristic; 3. Despite the low percentage contribution (0.54%) of phytoplankton dry weight in total seston, the two variables correlate closely because of simultaneous resuspension after wind actions. The prevalence of both low phytoplankton/seston ratio and significant correlation between these two variables is indicative to the presence of a meroplankton; 4. Phytoplankton biomass, especially that of diatoms, varies within wide limits in the short term as a combined effect of growth/loss, transport by horizontal water currents and periodic resuspension from the sediment surface. Diatoms like Fragilaria, Surirella and Campylodiscus are involved especially. Parameters of population dynamics (growth rate, annual cycles, length of stationary phases, standing crop) were estimated based on moving averages. Growth rates were smaller than those of ‘normal’ planktonic species; however, the similarities of seasonal pattern suggest that the carrying capacity of the lake is very constant; 5. Picoalgal biomass is very high in the lake; its contribution to total biomass can exceed 75%, especially in spring. The large cellular chlorophyll a content of Neusiedlersee’s phytoplankton can most probably be explained by this high picoalgal standing crop, which is not included in the routine biomass estimations; 6. Concerning long-term changes of phytoplankton, periodic appearances and disappearances are very characteristic. Annual average biomass of most species is growing for several (3–5) years, then declining with a similar rate and these periods are recurrent. Climatic drying-out periods, during which water level lowers, conductivity increases, nutrients and their ratios change following trend-like periodicities, and they are supposed to be responsible for the observed longterm periodicity of dominant species. An increased nutrient load in the seventies was superimposed on this cyclicity; 7. Most of the species can be found in smaller or larger amounts in the littoral microhabitats (canals, inner ponds) of the lake in periods when they are absent or very rare in the open water. Thus, these littoral microhabitats play a very important role in the survival and recruitment of planktonic populations to the open water.

Long-term phytoplankton changes in a shallow hypertrophic lake, Albufera of Valencia (Spain)

A long-term phytoplankton study was carried out in the Albufera of Valencia, a shallow hypertrophic lake (surface area 21 km2, mean depth 1 m, total inorganic nitrogen load 155 g m-2 y-1, total inorganic phosphate load 15 g m-2 y-1) from 1980 to 1988. The lake functions as a reservoir for the surrounding rice cultivation. From 1940's to 1988, its phytoplankton assemblage has been altered from a mesotrophic to a hypertrophic character, as consequence of the increasing pollution. For 1980–88, annual variations in the phytoplankton were less pronounced than seasonal changes. The hypertrophic and morphometric features of the lake favoured the stability of the phytoplankton assemblage and chlorophyll a levels during the study period. Seasonal and horizontal distribution of the total phytoplankton abundance and biomass were highly influenced by the hydrological cycle of the lagoon. Compared with other shallow nutrient rich lakes, the Albufera of Valencia is similar to the shallow hypertrophic lakes of the Netherlands.

Long-term phytoplankton changes in a tropical reservoir

Long-term phytoplankton changes in a tropical reservoir

Long-term phytoplankton changes in Lake Michigan: Cultural entrophication or biotic shifts

(1984). Long-term phytoplankton changes in Lake Michigan: Cultural entrophication or biotic shifts. SIL Proceedings, 1922-2010: Vol. 22, No. 1, pp. 452-459.