Phytoplankton Biovolume Research Articles

Discharge-driven flood and seasonal patterns of phytoplankton biomass and composition of an Australian tropical savannah river

Discharge is a primary determinant of river phytoplankton, but its influence can be mediated by climate, water quality and catchment development. The relationship between discharge and phytoplankton over seasonal and flood temporal scales was examined for the Daly River in the Australian tropical savannah. Phytoplankton, water quality and hydrographic data were collected over the high-discharge wet season and lower-discharge dry season. Wet season main channel river conditions were unfavourable for phytoplankton growth. Floods, however, connected the main channel to off-channel water bodies that supplied phytoplankton, predominately Cryptomonas, to the river. Wet season phytoplankton biovolume and cell concentrations were higher than in the dry season and comprised the majority of the annual phytoplankton biomass load. High discharges served to both temporally connect the river to off-channel phytoplankton sources as well as dilute these sources. In the dry season, the Daly River was groundwater-fed and disconnected from off-channel phytoplankton sources and dominated by a potamoplanktonic population of Cryptomonas and Peridinium. River phytoplankton were determined by the seasonal discharge regime which drove water quality and underpinned a shift from highly productive, spatially extensive off-channel sources in the wet season to less productive more spatially confined in-channel sources in the dry season.

Ecology under lake ice.

Winter conditions are rapidly changing in temperate ecosystems, particularly for those that experience periods of snow and ice cover. Relatively little is known of winter ecology in these systems, due to a historical research focus on summer 'growing seasons'. We executed the first global quantitative synthesis on under-ice lake ecology, including 36 abiotic and biotic variables from 42 research groups and 101 lakes, examining seasonal differences and connections as well as how seasonal differences vary with geophysical factors. Plankton were more abundant under ice than expected; mean winter values were 43.2% of summer values for chlorophyll a, 15.8% of summer phytoplankton biovolume and 25.3% of summer zooplankton density. Dissolved nitrogen concentrations were typically higher during winter, and these differences were exaggerated in smaller lakes. Lake size also influenced winter-summer patterns for dissolved organic carbon (DOC), with higher winter DOC in smaller lakes. At coarse levels of taxonomic aggregation, phytoplankton and zooplankton community composition showed few systematic differences between seasons, although literature suggests that seasonal differences are frequently lake-specific, species-specific, or occur at the level of functional group. Within the subset of lakes that had longer time series, winter influenced the subsequent summer for some nutrient variables and zooplankton biomass.

The effect of increased nitrogen load on phytoplankton in a phosphorus‐limited lake

Summary Widespread use of artificial fertilisers and the burning of fossil fuels and/or biomass release a large amount of reactive nitrogen into the atmosphere. So far, the effects of increasing nitrogen deposition from the atmosphere have mainly been studied in nitrogen‐limited limnic and marine systems. Interestingly, in phosphorus‐limited lakes, additional nitrogen input might not affect phytoplankton biomass, but rather increase mainly the degree of phosphorus limitation. The resulting effects on plankton communities are difficult to predict and quantify. To estimate the effects of increasing nitrogen load on a spring phytoplankton community in a primarily phosphorus‐limited system, a mesocosm experiment was performed in an oligotrophic lake, in which a gradient of six increasing nitrogen enrichment levels was applied. During the initial phytoplankton growth phase (spring bloom), molar, seston nitrogen:phosphorus ratios increased from 43 to 72 and carbon:phosphorus ratios from 328 to 542 with increasing nitrogen enrichment, indicating increased phosphorus limitation. Three commonly used phytoplankton biomass proxies (phytoplankton biovolume, chlorophyll a and particulate organic carbon) showed only minor responses to nitrogen enrichment. Different groups and species of phytoplankton varied in their responses to the nitrogen enrichment in both the growth phase (spring bloom) and the descending phase (clear water phase). Overall, we detected an effect of nitrogen enrichment on phytoplankton stoichiometry and community composition. The observed changes in the phytoplankton community combined with changes in abundances of heterotrophic nanoflagellates and ciliates indicate bottom‐up driven alterations of the basal food web due to increased nitrogen loads.

Assessment of the cell biovolume of phytoplankton widespread in coastal and inland water bodies

The biovolume of phytoplankton must be assessed accurately in order to identify the ecological status of water bodies in line with the WFD requirements. Hence, the current study has been carried out to verify and improve the precision of as well as to facilitate and accelerate estimations of phytoplankton biovolume by reviewing and rearranging the basic geometrical shapes of these organisms applied in such evaluations. The latest standards comprise 17 geometric shapes and equations suitable for estimations of cell/filament/colony biovolume and additionally include taxa-specific ‘geometric correction factors’ to fit real shapes and ‘hidden dimension factors’ to achieve data on hardly measureable dimensions. This paper also discusses possible obstacles to making correct biovolume assessments, especially when analyzing taxa of special concern, e.g. Ceratium hirundinella, C. furcoides or Pediastrum duplex and Pseudopediastrum boryanum. Our comparison of two approaches, the previous and the new one, revealed that they yield statistically significantly different biovolume results of these species. Some recommendations how to deal with the new and old methods of biovolume estimations and how to reduce the possibility of errors with overestimation and underestimation were also given. The more recent method can be said to give more precise estimates of phytoplankton biovolume. Besides, it facilitates more rapid phytoplankton analyses in most cases, which is very useful when assessing the ecological status of lakes during routine monitoring programs.

Phytoplankton response to short-term temperature and nutrient changes

Meteorological extreme events (heavy rainfall, heat waves) may lead to fast changes in nutrient load and water temperature in temperate lakes. We conducted laboratory experiments with an artificial phytoplankton community to mimic a rapid temperature increase (from 21 °C to 29 °C) at low nutrient levels (‘heat wave scenario’), respectively temperature decrease (from 21 °C to 16 °C) and increased nutrient load (‘heavy rainfall scenario’). We hypothesised that there is a taxon specific nutrient x temperature interaction, leading to significant shifts in the phytoplankton community composition when both variables change. To separate the temperature effect from the nutrient effect, we performed another experimental series at a reduced temperature but without addition of nutrients. As expected, the nutrient effect was overall more important than temperature and significantly affected all five taxa tested that represented different algal classes. However, temperature also played an important role for community composition, because the cryptophyte Cryptomonas sp. and the dinoflagellate Peridinium sp. reached significantly higher biovolumes at lower temperatures. The nutrient x temperature interaction was significant in the green alga Scenedesmus obliquus . These findings suggest that our experimental results cannot be interpreted primarily by species competition for nutrients. Heterotrophic bacteria were present in all experiments. Bacterial biomass was significantly positively related to temperature and nutrients. However, relative to phytoplankton biovolume, bacterial biovolume decreased under nutrient replete conditions. In conclusion, our results demonstrate that short-term environmental change may significantly affect both the phytoplankton community (in terms of species dominance and total biomass) and the ratio between autotrophs and heterotrophs in temperate lakes.

Response of phytoplankton to an experimental fish culture in net cages in a subtropical reservoir.

This study aimed to evaluate nutrients concentration and spatial-temporal changes in phytoplankton biovolume during an experimental fish culture in net cages in a lateral arm of Salto Caxias reservoir, Brazil. Two sampling stations were placed in the affected lateral arm and other two in a cageless lateral arm. Neither abiotic variables nor phytoplankton biovolume presented significant differences between the treatments. Only temporal changes were confirmed by the analysis performed. Both lateral arms were classified as oligotrophic, reflecting low influence of the net cages. Phytoplankton growth seems to be limited by nitrogen. Biovolume values were, in general, low and five major functional groups were recognized (E, F, G, K and P). In summer higher biovolume values were observed and representatives of Chlorophyceae and Cyanobacteria belonging to the functional groups F and K, respectively, were the most important. In winter phytoplankton was mainly composed by Bacillariophyceae taxa from P group. G group was also restricted to winter and E group occurred in winter and summer. The variations recorded in phytoplankton structure appear to have been mainly influenced by seasonal changes in temperature, precipitation and nutrients availability. The effects of net cages on the abiotic variables and phytoplankton biovolume appear to have been small, probably due to the small number of net cages employed and the system dilution capacity. However, a permanent monitoring of phytoplankton is recommended, since this environment has a carrying capacity, from which the trophic state may increase.

Winter–spring diatom production in Lake Erie is an important driver of summer hypoxia

Abstract Re-eutrophication and harmful algal blooms in Lake Erie have resulted in a renewed call for remedial measures such as reductions of phosphorus loads to the lake's western basin. The action of further nutrient reductions may also reduce the intensity of seasonal central basin hypolimnetic anoxia by reducing algal biomass. However, winter–spring blooms of diatoms have not been fully recognized as a source of algal biomass that might contribute significantly to summer hypoxia. We compared spring and summer phytoplankton abundance in central and western Lake Erie based on monitoring data to show that spring phytoplankton biovolume was 1.5- to 6-fold greater than summer biovolume and that most spring biovolume was composed of filamentous diatoms, primarily Aulacoseira islandica , that is likely supported by an increasing silica load from Lake Huron. The rise of silica export was attributed to the dreissenid mussel invasion and establishment that reduced diatom abundance in Lake Huron and thereby increased silica availability in the receiving water body of Lake Erie. The relationship between phosphorus and winter–spring diatom blooms was unclear, but diatoms probably contributed the majority of the algal biomass that accumulated annually in the hypolimnion of the central basin of Lake Erie. Remedial measures aimed at reducing hypoxia must consider the winter–spring phytoplankton bloom in Lake Erie as an important and reoccurring feature of the lake that delivers a considerable quantity of algal biomass to the profundal zone of the lake.

Lake‐type‐specific seasonal patterns of nutrient limitation in German lakes, with target nitrogen and phosphorus concentrations for good ecological status

Summary Eutrophication is a global environmental problem that leaves many lakes with impaired ecological status. Human activity has increased the total concentrations of both nitrogen and phosphorus in aquatic systems, but their relative influence on phytoplankton biomass is uncertain. Their action as alternative limiting resources complicates assessment of their relative influence and disagreement may be in part due to seasonal shifts and lake‐type‐specific differences in the prevalence of limitation by nitrogen versus phosphorus. Debate continues as to whether measures to reduce nitrogen would be beneficial in addition to controls placed on phosphorus. We used a piecewise model to test whether total nitrogen (TN) concentrations, in addition to total phosphorus (TP), influence phytoplankton biomass in 369 lowland German lakes. The piecewise model predicts biomass from TN for low N : P ratio lakes, and from TP for high N : P ratio lakes. We tested three N : P mass ratios to divide lakes: dissolved inorganic nitrogen to TP (DIN : TP), DIN to dissolved reactive phosphorus (DIN : DIP) and TN : TP. TN was a better predictor of biomass than TP when either the DIN : TP ratio was below 1.6, DIN : DIP was below 8.4, or TN : TP below 29; predictions were most accurate when using the DIN : TP ratio. To investigate seasonal and lake‐type‐specific patterns of N and P limitation, we used the DIN : TP ratio, together with absolute concentrations of DIN and DIP, to predict the limiting nutrient at each lake in each month of the vegetation period. N limitation was much more common in polymictic than stratified lakes. While a high proportion of both stratified and polymictic lakes were P limited in early spring (60–70%), for polymictic lakes, we found a strong shift from P limitation to N limitation in summer: more than 50% of polymictic lakes were N limited between June and September and only 15–30% were P limited. To obtain lake‐type‐specific nutrient targets we estimated the average TN and TP concentrations at which lakes of different types achieved good ecological status according to EU water framework directive criteria. Stratified lakes achieved good ecological status at concentrations of 400–500 μg L−1 TN or 20–35 μg L−1 TP, while for polymictic lakes values of 500–1000 μg L−1 TN, or 35–75 μg L−1 TP were required. We estimate that nitrogen has an important influence on phytoplankton biovolume, and thus ecological status, for many polymictic lakes in Germany. While there is some uncertainty in the nutrient targets required to achieve good ecological status, this uncertainty is small compared with the range of concentrations currently observed, and lakes with moderate or worse status have concentrations of both TN and TP that are far above these current target estimates.

Morphology-based functional groups as effective indicators of phytoplankton dynamics in a tropical cyanobacteria-dominated transitional river–reservoir system

Cyanobacteria dominance is often associated with economic, ecological and health problems. The potential production of toxic compounds calls for frequent monitoring of cyanobacteria and their toxin production in many aquatic systems. Methods to simplify this process and facilitate management responses to sudden environmental changes are needed to improve the capability of risk-assessment. We tested the effectiveness of two different functional approaches (Functional Groups – FG, Reynolds et al., 2002; and Morphology-Based Functional Groups – MBFG, Kruk et al., 2010) as well as single species and taxonomic classifications as the best proxy of spatio-temporal phytoplankton dynamics and dominance of toxic algae in an impacted transitional river–reservoir system in the tropics. The Paraíba do Sul River and Funil Reservoir are located in one of the most heavily impacted regions of Brazil, and the latter system has a history of intense, long-lasting toxic cyanobacteria blooms. Sampling was conducted over the two climatological periods of the region: warm-rainy (October/2011 and January/2012) and cold-dry (July/2011 and May/2012), with stations in the following areas: tributary, reservoir and river (downstream from the dam). Our results showed that the MBFG classification was the most effective approach, i.e., best explained the response of the phytoplankton community to environmental variations. Environmental factors including light, nutrients, water temperature and hydrology increased the occurrence of different MBFGs on both spatial and temporal scales. The lotic areas showed a more diverse composition of MBFGs, including species with high to moderate tolerance to light limitation and flushing conditions (MBFGs I, III, IV, V and VI). In Funil Reservoir, phytoplankton biovolume was dominated by bloom-forming cyanobacteria (MBFGs III and VII) and remained high throughout the study. This dominance was related to the overall eutrophic conditions, low light availability and increased water-column stability of the reservoir. The seasonal dynamics in the reservoir was mainly related to changes in temperature and hydrology. Our results show for the first time that morphology captures efficiently eco-strategies of bloom-forming cyanobacteria and the MBFG approach can be used to predict and monitor the development of cyanobacteria HABs in temporal and spatial scales.

Endogenous origin of foams in lakes: a long-term analysis for Lake Maggiore (northern Italy)

The formation of foams on lakes is a complex phenomenon whose origin is often hardly identifiable. Recently (2007, 2008, and 2010) foam episodes started to occur in Lake Maggiore, northern Italy. The present work aimed to verify the hypothesis of an endogenous-natural origin of these foams, driven by trophic or climatic changes. To this purpose, a long-term (2000–2013) analysis of phytoplankton biovolumes, meteorological, and hydrological data has been performed together with the chemical characterization of foams. Foams resulted of endogenous origin and likely related to phytoplankton biomass degradation. Data analysis highlighted atypical warm temperature and residual lake stratification in winter in two of the three years of foam events, coupled with exceptional Bacyllariophyceae blooms in spring. Tabellaria flocculosa mostly contributed in terms of biomass in 2007 and 2008, but not in 2010; thus overall algal biomass seemed a better predictor of the risk of foam formation. Foam events occurred from July to December, driven by atypically windy conditions, and congruently with the time needed to degrade biomass into surface-active compounds. A co-occurrence of different factors resulted essential to generate foams, and climate changes likely contribute to enhance their occurrence in Lake Maggiore.

Phytoplankton biovolume is independent from the slope of the size spectrum in the oligotrophic Atlantic Ocean

Modelling the size-abundance spectrum of phytoplankton has proven to be a very useful tool for the analysis of physical–biological coupling and the vertical flux of carbon in oceanic ecosystems at different scales. A frequent observation relates high phytoplankton biovolume in productive regions with flatter spectrum slope and the opposite in oligotrophic ecosystems. Rather than this, the relationship between high biovolume phytoplankton assemblages and flatter size-abundance spectra does not correspond with measurements of the phytoplankton community in the Atlantic Ocean open waters. As part of the Malaspina Circunnavegation Expedition, sixty seven sampling stations within the Atlantic Ocean covering six oceanographic provinces, at different seasons, produced a complete set of phytoplankton size-spectra whose slope and biovolume did not show any obvious interrelation. In these oligotrophic sites, small (procaryotes) and medium-size (nanoplankton) cells are responsible for the most part of biovolume, and their response to environmental conditions does not apply to changes in the size-abundance spectrum slope as expected in richer, large-cell dominated ecosystems.

The ecological history of Lake Ontario according to phytoplankton

Abstract Lake Ontario's condition has fluctuated since European settlement, and our understanding of the linkages between observed ecosystem shifts and stressors is improving. Changes in the physical and chemical environment of the lake due to non-indigenous species, pollution, sedimentation, turbidity, and climate change altered the pelagic primary producers, so algal assessments have been valuable for tracking long-term conditions. We present a chronological account of algal assessments to summarize past and present environmental conditions in Lake Ontario. This review particularly focuses on pelagic, diatom-based assessments as their fossils in sediments have revealed the combined effects of environmental insults and recovery. This review recaps the long-term trends according to three unique regions: Hamilton Harbour, the main lake basin, and the Bay of Quinte. We summarize pre-European impact settlement; eutrophication throughout most of the 20th century; subsequent water quality changes due to nutrient reductions; and filter-feeding dreissenid colonization and contemporary pelagic, shoreline, and embayment impairments. Recent data suggest that although phytoplankton biovolume is stable, species composition has shifted to an increase in densities of spring eutrophic diatoms and summer cyanobacteria. Continued monitoring and evaluation of historical data will assist in understanding and responding to the natural and anthropogenic drivers of Lake Ontario's environmental conditions.

Cell volumes of marine phytoplankton from globally distributed coastal data sets

Globally there are numerous long-term time series measuring phytoplanton abundance. With appropriate conversion factors, numerical species abundance can be expressed as biovolume and then converted to phytoplankton carbon. To-date there has been no attempt to analyze globally distributed phytoplankton data sets to determine the most appropriate species-specific mean cell volume. We have determined phytoplankton cell volumes for 214 of the most common species found in globally distributed coastal time series. The cell volume, carbon/cell and cell density of large diatoms is 200,000, 20,000 and 0.1 times respectively, compared to small diatoms. The cell volume, carbon/cell and cell density of large dinoflagellates is 1500, 1000 and 0.7 times respectively, compared to small dinoflagellates. The range in diatom biovolumes is 100 times greater than across dinoflagellates (i.e. >200,000 vs. 1500 times) and within any diatom species, the range in biovolume is up to 10-fold. Variation in diatom cell volumes are the single largest source of uncertainty in community phytoplankton carbon estimates and greatly exceeds the uncertainty associated with the different volume to carbon estimates. Small diatoms have 10 times more carbon density than large diatoms and small dinoflagellates have 1.5 times more carbon density than large cells. However, carbon density varies relatively little compared to biovolume. We recommend that monthly biovolumes should be determined on field samples, at least for the most important species in each study area, since these measurements will incorporate the effects of variations in light, temperature, nutrients and life cycles. Since biovolumes of diatoms are particularly variable, the use of size classes will help to capture the percentage of large and small cells for each species at certain times of the year. This summary of global datasets of phytoplankton biovolumes is useful in order to evaluate where locally determined biovolumes lie within the global spectrum of spatial and temporal variations and may be used as a species cell volume reference where no locally determined volume estimates are available. There is a need to adopt standard protocols for measuring biovolumes and documenting the accompanying metadata which would improve inter-comparability among time series data sets.

Biomonitoring ecological status of two reservoirs of the Brazilian semi-arid using phytoplankton assemblages (Q index)

AimAssess whether the assembly index is a suitable tool for biomonitoring of aquatic ecosystems of semi-arid environment.MethodsMonthly, samples were collected between October 2011 and May 2012 in Santa Cruz do Apodi (5°43'59"S; 46" 00 119 "W) and Pau dos Ferros (6°08'30.12" S; 038°10'59 880"W) reservoirs.ResultsThe Pau dos Ferros reservoir, shallow, turbid and eutrophic showed dominance of the functional group SN throughout the sample period. Total phytoplankton biovolume ranged between 20 and 70 mm³.L–1, the lowest values coincided with the increase of the mixing zone and transparency, which occasioned a change in composition of the phytoplankton community. Pau dos Ferros reservoir was categorized as poor for most of the sample period. The Santa Cruz do Apodi reservoir was characterized as meso-eutrophic, exhibiting low total phytoplankton biovolume (0.04 to 0,4 mm³.L–1) and greater diversity in the phytoplankton composition. It showed moderate condition during most of the period.ConclusionIn summary, the index Q reflected well the changes in phytoplankton composition, being a good indicator for biomonitoring of these systems.

Photophysiological effects of Fe concentration gradients on diatom-dominated phytoplankton assemblages in the Antarctic Peninsula region

The Southern Ocean is generally a high-nutrient and low-chlorophyll (HNLC) area, primarily due to the limitation of micronutrients, such as iron (Fe). Nevertheless, microphytoplankton may bloom if Fe is available and if light and mixing conditions are suitable. This study aimed to investigate the ecological and photophysiological responses of the phytoplankton, such as size, community composition, nutrient usage and photosynthetic potential, under high irradiance levels and over an iron concentration gradient. A 6-day deck incubation experiment was conducted during the austral summer of 2013, using phytoplankton populations from the upper mixed layer in the Bransfield Strait waters. After sampling the water (Fe clean protocol), experimental units were maintained in on-deck incubation in triplicate for 6days with 3 treatments (Control: natural sea water; +Fe: Fe addition; +DFA: Fe less available). +Fe treatment samples were inoculated with FeCl2 (1nM), while in the +DFA treatment, a Fe-binding agent (desferrioxamine) was added which reduces Fe availability tenfold. Values of chlorophyll a, phytoplankton biovolume, PSII maximum quantum efficiency (Fv/Fm) and the relative electron transport rate (rETR) were measured in all treatments. After six days of experimentation, chlorophyll a in the +DFA treatment increased by a lower proportion (6.4mgm−3, compared with the +Fe treatment, which increased to 10.2mgm−3) and presented Fv/Fm values of 0.55±0.02 (compared with the +Fe treatment, with a value of 0.62±0.02). Microscopic analysis showed the preponderance of larger diatoms in the +Fe treatment, while smaller diatoms dominated in the +DFA, in particular the Pseudo-nitzschia species. Although desferrioxamine might have inhibited biogenic Fe uptake in the +DFA treatment, phytoplankton continued to grow, however with lower responses within the measured physiological parameters, indicating the first signs of Fe limitation. Considerable phytoplankton growth, represented by a doubling of chlorophyll a concentration and a massive biovolume increase after 6days in all three treatments, indicates that the waters of the study region in the Bransfield Strait were not limited by the microelement Fe.

Phytoplankton composition and microcystin concentrations in open and closed bays of Lake Victoria, Tanzania

This study was carried out in order to investigate the spatial variation of algal toxin (microcystin) concentrations along the shoreline of Lake Victoria. A total of 16 nearshore stations differing in connectivity to the main lake basin were categorized as either closed bays (ratio of bay area to bay opening < 1) or open bays (ratio ≥ 1) and sampled during November and December 2009. Water samples were analyzed for total phosphorus (TP), chlorophyll a, phytoplankton community composition and concentrations of microcystin (MC). Open and closed bays were significantly different for phytoplankton abundance and composition: Average phytoplankton biovolume was higher for closed bays (45 mm3 L-1 ± 11 SE) than open bays (5 ± 2 mm3 L-1). Cyanobacterial biovolume (mainly Microcystis spp., Anabaena spp. and Planktolyngbya spp.) also was significantly higher in closed bays (82 ± 9% of total biovolume) than in open bays (44 ± 5%). In contrast, diatom biovolume was lower in closed bays (7 ± 1%) than in open bays (36 ± 6%). MCs were found only among sites from closed bays and concentrations ranged from 0.4 to 13 μg L-1 MC-LR equiv. and coincided with high abundance of Microcystis spp. It is concluded that the level of water exchange from individual bays to the main basin is an important factor influencing eutrophication and microcystin production in nearshore habitats of Lake Victoria.

Phytoplankton communities in rock pools on the Åland Islands, SW Finland – environmental variables, functional groups and strategies

Studies of rock pools tend to focus on the surrounding emergent habitat. Moreover, research on phytoplankton in small, nutrient-rich water bodies is limited. Summer phytoplankton species, functional groups and life strategies, as well as physicochemical variables potentially influencing the phytoplankton, were surveyed in 34 brackish rock pools. Except from total nitrogen and total phosphorus, the pools were chemically quite similar. Phytoplankton abundance and biovolume consisted mainly of charophytes (Zygnematales), unidentified small flagellates, cyanobacteria, chlorophytes and dinoflagellates. Many of the phytoplankton functional groups were representative of shallow, nutrient-rich and light-abundant environments. The majority of the common and abundant species were classified as C-strategists (invasive opportunists). Total nitrogen, total phosphorus and phytoplankton biomass varied greatly between the rock pools, and were positively related. The rock pool depth and macrovegetation presence–absence played a central role in shaping the phytoplankton species distribution. Frequently occurring species, present in the majority of the rock pools, seldom dominated the phytoplankton. Species dominating the phytoplankton rock pool assemblages were not common components of the phytoplankton flora.

Response of predominant phytoplankton species to anthropogenic impacts in Lake Taihu

A year-long investigation of patterns in dominant phytoplankton species was conducted to reveal the response of the phytoplankton community to anthropogenic impacts in Lake Taihu. Microcystis spp. and Cyclotella meneghiniana were the predominant species throughout the lake. Another 14 taxa were codominant species in parts of the lake. In the northwest, the highest phytoplankton biovolume appeared and Microcystis spp. and C. meneghiniana alternately dominated. Aulacoseira granulata, Asterionella formosa and Synedra spp. codominated in succession with C. meneghiniana in winter and spring. Species diversity indices were highest in spring while lowest in summer and anthropogenic nutrient inputs were the key factors controlling the alternating dominance of phytoplankton species. In the Gonghu area (the northeast), Microcystis spp. and C. meneghiniana codominated all year long; the predominant species was determined by water transfer from the Yangtze River, where the codominant species took advantage of flushing and mixing. In the southwest and the lake center with weak anthropogenic impacts, internal nutrient release was the key factor affecting the codominance of Microcystis spp. and C. meneghiniana all year long as well as the codominance of A. granulata, Dolichospermum flos-aquae and Ceratium spp. in succession. It could be concluded that anthropogenic influences shaped the structure of the phytoplankton community and determined the composition of dominant species in Lake Taihu. Species diversity was significantly correlated with nutrient inputs. Not only exogenous P reduction, but also internal P source reduction should be undertaken to prevent harmful cyanobacterial bloom. Water transfer could be used as an emergency management for bloom control.

Multispectral remote sensing of harmful algal blooms in Lake Champlain, USA.

This study developed satellite remote sensing models to detect cyanobacterial blooms via chlorophyll a in Lake Champlain. Landsat Enhanced Thematic Mapper Plus data was used to retrieve chlorophyll a concentrations, phytoplankton, and cyanobacteria biovolume by calibrating and validating with coincident observation data. Correlation analysis results showed that band 2 (green band) and the band ratio of 2/1 (green/blue) were most highly correlated to chlorophyll a concentration (r = 0.76 and 0.82, respectively). Multiple regression results identified band 2 and 3 (red), and band ratio of 2/1 and 3/1 (red/blue) as critical information to estimate chlorophyll a concentrations. The regression models accounted for 72 to 83% of the variability in chlorophyll a observations, allowing for estimates of phytoplankton and cyanobacteria levels in the lake. Satellite image processing results successfully showed the temporal and spatial distribution of chlorophyll a, phytoplankton, and cyanobacteria in the lake. This information can be used to evaluate the effect of pollution sources and weather conditions, and assist decision making for water management.

Large contribution of small phytoplankton at Marian Cove, King George Island, Antarctica, based on long-term monitoring from 1996 to 2008

To detect and monitor coastal marine ecosystem responses to current environmental changes, the phytoplankton assemblage, salinity, and macro-nutrients were monitored daily at a fixed coastal site in Marian Cove, Antarctica, from 1996 to 2008. The monthly average water temperature at the site was highest (2.14 ± 0.36 °C) during the summer period (December–February) and lowest (−1.80 ± 0.22 °C) during the winter period (July–September). The salinity levels exhibited the opposite trend with the lowest values (30.9 ± 0.68 psu) during summer and the highest values (35.2 ± 1.15 psu) during winter. The concentrations of major nutrients were always high enough for phytoplankton growth, indicating the nutrients are not a main controlling factor for phytoplankton growth. Total chlorophyll-a generally started to increase from late November with a peak (1.14 ± 1.41 mg chl-a m−3) around January when the water temperature was the warmest during the year. Within the phytoplankton communities, the average contribution of small (nano- plus pico-) phytoplankton (<20 μm) to the total chl-a concentration was high (62.9 %) throughout the study period, which supports the observation that small phytoplankton contributed 85.7 % to the cell numbers and 56.4 % to the biovolume of the total phytoplankton. The high contribution of small phytoplankton is a general characteristic at Marian Cove and may be expected to increase under future warming conditions.