Combining a regional climate model with a phytoplankton community model to predict future changes in phytoplankton in lakes

1. Linking a regional climate model (RCM) configured for contemporary atmospheric greenhouse gas concentrations, with a phytoplankton community model (PROTECH) produced realistic simulations of 20 years of recent phytoplankton data from Bassenthwaite Lake, in the North‐West of England. 2. Meteorological drivers were derived from the RCM to represent a future climate scenario involving a 1% per annum compound increase in atmospheric CO₂ concentrations until 2100. Using these drivers, PROTECH was run for another 20 year period representing the last two decades of the 21st century. 3. Comparison of these present and future simulations revealed likely impacts on the current seasonal phytoplankton development. Under future climate conditions, the simulated spring bloom showed an increase in cyanobacteria dominance caused by greater success of Planktothrix. Also, the summer cyanobacteria bloom declined earlier because of nutrient limitation caused by the increased spring growth. Overall productivity in the lake did not change. 4. Analysis showed that these predicted changes were driven by changes in water temperature, which were in turn triggered by the higher air temperatures predicted by the RCM.     

The seasonal sensitivity of Cyanobacteria and other phytoplankton to changes in flushing rate and water temperature

The phytoplankton lake community model PROTECH (Phytoplankton RespOnses To Environmental CHange) was applied to the eutrophic lake, Esthwaite Water (United Kingdom). It was validated against monitoring data from 2003 and simulated well the seasonal pattern of total chlorophyll, diatom chlorophyll and Cyanobacteria chlorophyll with respective R²‐values calculated between observed and simulated of 0.68, 0.72 and 0.77 (all P<0.01). This simulation was then rerun through various combinations of factorized changes covering a range of half to double the flushing rate and from ?1 to +4 °C changes in water temperature. Their effect on the phytoplankton was measured as annual, spring, summer and autumn means of the total and species chlorophyll concentrations. In addition, Cyanobacteria mean percentage abundance (%Cb) and maximum percentage abundance (Max %Cb) was recorded, as were the number of days that Cyanobacteria chlorophyll concentration exceed two World Health Organization (WHO) derived risk thresholds (10 and 50 mg m^?3). The phytoplankton community was dominated in the year by three of the eight phytoplankton simulated. The vernal bloom of the diatom Asterionella showed little annual or seasonal response to the changing drivers but this was not the case for the two Cyanobacteria that also dominated, Anabaena and Aphanizomenon . These Cyanobacteria showed enhanced abundance, community dominance and increased duration above the highest WHO risk threshold with increasing water temperature and decreasing flushing rate: this effect was greatest in the summer period. However, the response was ultimately controlled by the availability of nutrients, particularly phosphorus and nitrogen, with occasional declines in the latter's concentration helping the dominance of these nitrogen‐fixing phytoplankton.     

Studies on marine algae of the British Isles. 8. Cystoseira tamariscifolia (hudson) papenfuss

The fine structure of the zoospores of Urospora penicilliformis (Roth) Aresch. (Chlorophyceae) is described. Of special interest is the flagellar apparatus. The proximal part of each of the 4 flagella is ribbon-shaped and contains nine wings attached to the peripheral double tubules. The flagellar root system originates from the flagellar bases and includes striated fibrous roots, passing close to the nucleus, and cruciate nine-stranded microtubular roots along the four corners of the cell. The Golgi bodies produce numerous vesicles, concentrating apically in the cell; they are presumed to be of importance for the attachment of the zoospore.     

The relationship between Trichocerca pusilla (Jennings), Aulacoseira spp. and water temperature in Loch Leven,Scotland, U.K.

Loch Leven is a shallow, eutrophic lake in the Scottish lowlands that is famous for its brown trout (Salmo trutta L.) fishery. Studies of planktonic rotifer populations began here in January 1977. Since then, samples have been collected and analysed at more or less weekly intervals. Additional information on the composition and abundance of phytoplankton and crustacean zooplankton species, and on a variety of physical and chemical determinants, has been recorded on each sampling occasion.Long-term datasets, such as that described above, are invaluable for identifying interactions between components of the plankton that only appear for short periods each year, as these interactions would probably be overlooked in data spanning a shorter period of time. This study uses the long-term data from Loch Leven to examine the food and temperature requirements of the summer rotifer species Trichocerca pusilla (Lauterborn). The results suggest that T. pusilla prefers water temperatures above 12 °C and that it feeds, primarily, on the filamentous diatom Aulacoseira spp. During the summer months, its abundance was closely related to the availability of this diatom. When filaments of Aulacoseira spp. were abundant, rotifer densities reached 1000–3000 ind. l^–1 and when they were scarce (e.g. 1980, 1997 and 1998) T. pusilla densities also remained low (i.e. less than 100 ind. l^–1). The reason for the success or failure of Aulacoseira during the summer months each year is unclear but, in general, its abundance was related to the availability of dissolved silica in the water.     

Modelling the response of phytoplankton in a shallow lake (Loch Leven,UK) to changes in lake retention time and water temperature

The phytoplankton community of Loch Leven in 2005 was modelled and subjected to a combination of different flushing rates and water temperatures in order to assess the lake’s sensitivity to these two climatic drivers. Whilst the simulated annual mean total chlorophyll a proved relatively insensitive to these changes, at the species level marked changes were recorded. Some species responded positively to increased temperature (e.g. Aulacoseira), some negatively (e.g. Asterionella), whilst others were negatively affected by increased flow (e.g. Aphanocapsa) and others enhanced (e.g. Stephanodiscus). However, this relationship with flow was season dependent with, for example, a simulated increase in summer inflows actually benefiting some species through increased nutrient supply, whereas an equivalent increase in flow in wetter seasons would have negatively affected those species (i.e. through flushing loss). Overall, the simulations showed that the range of species types simulated in the community was sufficient for one species to always benefit from the changing niches created by the multiple climatic drivers applied in this study. The level of exploitation by such a species was only constrained by the nutrient carrying capacity of the system, which led to the overall dampened response in the total chlorophyll a measure, both at the annual and season scale. Thus, whilst overall biomass showed relatively little reaction to the two climatic drivers tested, the phytoplankton community composition responded markedly.     

Effects of lake mixing with an axial flow pump on water chemistry and phytoplankton

This paper describes the effect of total lake mixing with an axial flow (Garton) pump on the limnology and phytoplankton of two Oklahoma lakes.The Garton pump destratified Ham's Lake (40 ha) in 3 days. Except for one small isolated basin, Ham's Lake remained completely destratified for the rest of the summer. Algal biomass declined, numbers of species of green algae increased, but numbers of species of blue-green algae did not decrease as expected. After destratification, pH remained high (> 8), carbonate alkalinity was observed and reactive phosphate was undetectable.An axial flow pump increased the heat content of Arbuckle Lake (951 ha) and caused the lake to destratify about one month earlier than usual. Increasing the heat content of the lake did not affect the concentration of most water quality parameters or the biomass of algae.     

Seasonal changes in temperature and nutrient control of photosynthesis, respiration and growth of natural phytoplankton communities

1. To investigate the influence of elevated temperatures and nutrients on photosynthesis, respiration and growth of natural phytoplankton assemblages, water was collected from a eutrophic lake in spring, summer, autumn, winter and the following spring and exposed to ambient temperature and ambient +2, +4 and +6 °C for 2 weeks with and without addition of extra inorganic nutrients. 2. Rates of photosynthesis, respiration and growth generally increased with temperature, but this effect was strongly enhanced by high nutrient availability, and therefore was most evident for nutrient amended cultures in seasons of low ambient nutrient availability. 3. Temperature stimulation of growth and metabolism was higher at low than high ambient temperature showing that long‐term temperature acclimation of the phytoplankton community before the experiments was of great importance for the measured rates. 4. Although we found distinct responses to relatively small temperature increases, the interaction between nutrient availability, time of the year and, thus, ambient temperature was responsible for most of the observed variability in phytoplankton growth, photosynthesis and respiration. 5. Although an increase in global temperature will influence production and degradation of organic material in lakes, the documented importance of ambient temperatures and nutrient conditions suggests that effects will be most pronounced during winter and early spring, while the remaining part of the growth season will be practically unaffected by increasing temperatures.     

A comparison of phytoplankton responses to nutrient additions in acidic and circumneutral pH lakewater

An in situ bag experiment was conducted at circumneutral, mesotrophic Lake O'Woods. West Virginia, during summer 1984. Four bags were untreated controls, while four others were gradually acidified to pH 4.5. After 35 days, the algal community in the acid bags closely resembled that of precipitation-acidified lakes in North America. On day 39, two acid and one control bag were fertilized with phosphorus (P) and nitrogen (N). In both cases, algal biomass increased. However, the maximal level reached was 350% higher in the acid plus PN treatment, where the herbivorous zooplankton density had become very low. In the control plus PN treatment, Ulothrix sp. replaced Gymnodinium sp. as the most important alga. However, in the acid plus PN treatment, Peridinium inconspicuum continued to account for ca. 50% of algal biomass until the end of the experiment, as it did in the unfertilized acid treatment. The results suggest that fertilization-induced changes in algal community structure are less pronounced in acid waters than in circumneutral ones. Differential sensitivity to the harsh environmental conditions may strongly control dominance in the acid lake phytoplankton community, regardless of nutrient status.     

Modelling the effects on phytoplankton communities of changing mixed depth and background extinction coefficient on three contrasting lakes in the English Lake District

1. The process‐based phytoplankton community model, PROTECH, was used to model the response of algal biomass to a range of mixed layer depths and extinction coefficients for three contrasting lakes: Blelham Tarn (eutrophic), Bassenthwaite Lake (mesotrophic) and Ullswater (oligotrophic). 2. As expected, in most cases biomass and diversity decreased with decreasing light availability caused by increasing the mixed depth and background extinction coefficient. The communities were generally dominated by phytoplankton tolerant of low light. Further, more novel, factors were identified, however. 3. In Blelham Tarn in the second half of the year, biomass and diversity did not generally decline with deeper mixing and the community was dominated by nitrogen‐fixing phytoplankton because that nutrient was limiting to growth. 4. In Bassenthwaite Lake, changing mixed depth influenced the retention time so that, as the mixed depth declined, the flushing rate in the mixed layer increased to the point that only fast‐growing phytoplankton could dominate. 5. In the oligotrophic Ullswater, changing the mixed depth had a greater effect through nutrient supply rather than light availability. This effect was observed when the mixed layer was relatively shallow (<5.5 m) and the driver for this was that the inflowing nutrients were added to a smaller volume of water, thus increasing nutrient concentrations and algal growth. 6. Therefore, whilst changes in mixed depth generally affect the phytoplankton via commonly recognized factors (light availability, sedimentation rate), it also affected phytoplankton growth and community composition through other important factors such as retention time and nutrient supply.     

Community persistence in Broadstone Stream (U.K.) over three decades

1. Few detailed long-term data sets exist for fresh waters with which to examine large-scale temporal changes in community composition. Consequently, insight into community persistence has been restricted to a few, contingent case studies. We collated and analysed data for the aquatic macroinvertebrate community of Broadstone Stream in south-east England, spanning three decades. The pH of this naturally acid stream has risen progressively since the 1970s, and we sought to examine the potential effects of this environmental change upon the community.
2. Persistence within Broadstone was high when compared with other systems that have been analysed using similar methods. The stream was characterised by a `core' community of eight taxa that were always present, and contributed 75–97% of total invertebrate abundance, with a trailing limb of progressively rarer and more acid-sensitive taxa. There was little species turnover, although the time-series exceeded 20 generations for most species.
3. Despite this high persistence, a long-term response to rising pH was detected: species indicating profound acidity (identified a priori from independent studies) have declined since the 1970s, whereas indicators of moderate acidity increased. The structure of the community food web has also changed since the 1970s, with increased predator diversity and abundance, and a lengthening of food chains following the invasion of a new top predator.
4. These changes in the community appeared to be driven by an interaction between pH and climate. The unusually hot, dry summers characteristic of the 1990s may have raised pH during the more sensitive (i.e. early) stages of the life-cycle, and thus provided a window of opportunity for less acid-tolerant taxa to colonise and become established. Changes in pH appeared to set the boundaries of the available local species pool, within which biotic interactions ultimately shaped the community.     

The response of planktonic and microbenthic algal assemblages to nutrient enrichment in shallow coastal waters,southwest Sweden

Field and laboratory nutrient (nitrogen and phosphorus) enrichment experiments were performed using natural phytoplankton and microphytobenthic assemblages from the brackish water Öresund, S.W. Sweden. The response of algae from a low-nutrient area (Falsterbo Canal) was compared to that of algae from a polluted, nutrient-rich area (Lomma Bay).The biomass (measured as chlorophyll a) of both phytoplankton and microphytobenthos from the Falsterbo Canal increased after the addition of nitrogen. Phytoplankton growth was stimulated by the addition of phosphorus to the nitrogen-rich water of the polluted Lomma Bay. Sediment chlorophyll a showed no significant increase after the addition of nutrients in the Lomma Bay. In containers without sediment, phytoplankton uptake was calculated to account for ≈ 90% of the disappearance of inorganic fixed nitrogen from the water. In the sediment containers the microphytobenthos was estimated to account for ≈20% of the nitrogen uptake. The rest was presumably lost mainly through denitrification.When containers with microphytobenthos from Lomma Bay were kept in the dark, phosphorus was released at a rate of up to ≈ 180 μM · m^?2 · day^?1. We suggest that by producing oxygen microbenthic algae keep the sediment surface oxygenated thereby decreasing phosphorus transport from the sediment to the overlying water.     

Note on the survival of algal resting cells during long-term maintenance in darkness and minimum lake bottom temperature. Comparison of Anabaena (cyanobacteria) and Haematococcus (volvocales)

Resting cell formation in algae and cyanobacteria is one of the strategies developed for withstanding adverse environmental conditions. This note informs about the different capacities of such resting cells to germinate after long-term dark preservation at 4 °C in Anabaena variabilis (Cyanobacteria, Cyanophyta) and Haematococcus lacustris (Chlorophyta, Volvocales).     

Long‐term phytoplankton community changes in a deep subalpine lake: responses to nutrient availability and climatic fluctuations

1. In natural lakes, modifications in the species composition and abundance of phytoplankton communities may ultimately be responses to changes in nutrient availability and climatic fluctuations. Phytoplankton and associated environmental factors were collected at monthly intervals from the beginning of the 1990s to 2007 in the large subalpine Lake Garda (z_max = 350 m, V = 49 × 10⁹ m³). In this study period, the lake showed a slight and continuous increase of total phosphorus (TP) in the water column, up to concentrations of 18–20 μg P L^?1. This increase represented the last stage of a long‐term process of enrichment documented since the 1970s, when concentrations of TP were below or around 10 μg P L^?1. 2. At the community level, annual phytoplankton cycles underwent a unidirectional and slow shift mainly due to changes in the species more affected by the nutrient enrichment of the lake. After a first and long period of dominance by conjugatophytes (Mougeotia) and diatoms (Fragilaria), phytoplankton biomass in recent years was sustained by cyanobacteria (Planktothrix). Other important modifications in the development of phytoplankton were superimposed on this pattern due to the effects of annual climate fluctuations principally mediated by the deep mixing events at spring overturn and, secondarily, by temperature and thermal stability of the water column during the growing season. 3. Interannual variations in the stability and temperature of the water column appeared to influence the development of a few subdominant flagellates (dinophytes and cryptophytes). Nevertheless, the major impact of climate on phytoplankton was indirect, and mediated through the effects of winter climatic conditions on deep mixing dynamics. Winter climatic fluctuations proved to be a key element in a linked chain of causal factors including cooling of hypolimnetic waters, deep vertical mixing and epilimnetic nutrient replenishment. The process of fertilisation was measurable both for TP and dissolved inorganic nitrogen, although only the first had a large effect, reinforcing the seasonal growth of a few dominant groups. The degree of nutrient replenishment further increased the spring development of large diatoms and the increase of Planktothrix in summer and autumn. 4. Currently, changes in nutrient concentrations have the greatest effect on the phytoplankton community, while direct effects due to the interannual variations in the thermal regime are of secondary importance compared with the indirect effects mediated through deep water mixing and spring fertilisation. Overall, the results demonstrate that the consequences of climatic fluctuations and climate warming on phytoplankton communities need to be studied at different levels of complexity and integration, from the direct effects of temperature and thermal regime, to the indirect effects mediated by the physiographic characteristics of water bodies.     

Isolation and verification of anatoxin-a producing clones of Anabaena flos-aquae (Lyngb.) de Breb. from a eutrophic lake

Abstract We present a technique to isolate and confirm anatoxin-a producing clones (single trichome-isolates) of Anabaena flos-aquae (Lyngb.) de Breb. from blooms of this cyanobacterium. A single trichome is isolated from a field sample and grown in ASM medium. Single trichomes are then isolated from this culture and grown in ASM medium to produce single clone cultures. Mouse bioassay, and thin-layer chromatography (TLC) using purified anatoxin-a as reference is then used to confirm the anatoxin-a producing clones. Using this methodology, Anabaena flos-aquae samples collected during July 1991 from Hebgen Lake, Montana, were found to contain only 8.7% anatoxin-a producing clones. This minor proportion of anatoxin-a producing clones apparently accounts for the anatoxin-a produced by the entire population of A. flos-aquae . Our technique is simple and reproducible. A selected clone of A. flos-aquae that produces anatoxin-a and one that does not produce anatoxin-a were deposited in the UTEX culture collection, University of Texas at Austin.     

Seasonal changes in production and nutrient content ofCynodon dactylon (L.) Pers. subjected to water deficits

Seasonal changes in water relations, production and mineral composition were studied in a sward ofCynodon dactylon (L). Pers. subjected to water deficits during a dry summer, and at recovery in autumn. The experiment was carried out under Mediterranean field conditions. Water deficits during summer reduced total dry matter production by 60%, but in autumn there were no differences between treatments. Compared to well-watered sward, the sward grown under drought showed an increase in potassium, calcium and nitrogen of 55, 10 and 10% respectively. These differences decreased with the arrival of autumn rains. Leaf osmotic potential (Ψ_Π) fell during the dry summer to −2.8 MPa in well-watered plants and to −4.2 MPa in stressed plants. In autumn there were no differences between treatments. Nevertheless, relative water content (RWC) only decreased to 0.86 in droughted plants. In summer potassium contributed to the osmotic adjustment. In contrast, under water deficits a decrease of 71% in sodium and, to a lesser but significant extent decreases in phosphorus, magnesium and chlorine was observed. Nitrogen, phosphorus and sulphur showed low concentrations during summer and increased in autumn.     

Light absorption by phytoplankton and chromophoric dissolved organic matter in the drainage basin and estuary of the Neuse River, North Carolina (U.S.A.)

1. We examined the absorption of solar radiation by phytoplankton and chromophoric dissolved organic matter (CDOM) taking into account riparian shading in the rivers, reservoirs, swamps of the Neuse River Estuary and its drainage basin. 2. In the streams, CDOM typically absorbed 55 and 64% of photons in the spectral range of 400–700 nm (photosynthetically active radiation, PAR) and 500–600 nm, respectively. The large proportion of photons absorbed by CDOM indicates high potential for abiotic photochemial reactions in the 500–600 nm region. 3. Despite the high concentration of nutrients, phytoplankton contributed little (2%) to the total absorption of PAR in the streams. Small (<30 m wide) streams typically received only 7% of incident PAR that impinged onto the more exposed reservoirs and estuary. Riparian shading and the low contribution of phytoplankton to the total absorption resulted in conditions where phytoplankton absorbed nearly two orders of magnitude less PAR in the streams than in the estuary and reservoirs. 4. The results indicated that riparian shading and non‐algal absorbing components can significantly restrict phytoplankton production in nutrient‐rich streams with a high concentration of CDOM flowing throughout forested catchments.     

The use of spectral fluorescence methods to detect changes in the phytoplankton community

In vivo fluorescence methods are efficient toolsfor studying the seasonal and spatial dynamics ofphytoplankton. Traditionally the measurements are madeusing single excitation-emission wavelengthcombination. During a cruise in the Gulf of Riga(Baltic Sea) we supplemented this technique bymeasuring the spectral fluorescence signal (SFS) andfixed wavelength fluorescence intensities at theexcitation maxima of main accessory pigments. Thesemethods allowed the rapid collection of quantitativefluorescence data and chemotaxonomic diagnostics ofthe phytoplankton community. The chlorophylla-specific fluorescence intensities (R) and thespectral fluorescence fingerprints were analysedtogether with concentrations of chlorophyll a indifferent algal size-groups, phytoplankton biomass andtaxonomic position. The lower level of R in thesouthern gulf was related to the higher proportion ofcyanobacteria relative to total biomass and the lowerabundance of small algae. The phycoerythrinfluorescence signal was obviously due to the largecyanobacteria. The basin-wide shift in the shape ofchlorophyll a excitation spectra was caused bythe variable proportions of differently pigmentedcyanobacteria, diatoms and cryptomonads. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interactions of temperature and nutrient changes: effects on phytoplankton in the Piburger See (Tyrol,Austria)

1. Contemporary limnological and palaeolimnological data from Piburger See (Eastern Alps, Austria) allowed the reconstruction of its trophic state since the late 19th century and the assessment of changes in phytoplankton biomass and species composition in relation to selected environmental parameters. 2. A radiometrically dated sediment core from Piburger See was analysed for geochemical parameters, spheroidal carbonaceous particles (SCPs), bacterial and algal pigments, and diatoms. The low SCP sediment inventory assigns Piburger See to the ‘cleaner’ sites in Europe with respect to fossil‐fuel related air pollution. The sedimentary pigment and diatom record reveals moderate eutrophication during the 20th century, followed by a slow re‐oligotrophication since the mid‐1980s because of lake restoration starting in 1970. 3. Epilimnetic temperature for Piburger See was reconstructed using air temperature records. A pronounced temperature increase has been recorded during the mid‐1940s and since the late‐20th century, both promoting algal growth and changes in species composition (e.g. increase in centric diatoms and recent bloom of Asterionella formosa). 4. Climate scenarios project additional substantial warming for this mountain lake by the end of the 21st century which will be most pronounced during the growing season. The predicted change in lake water temperature and thermal dynamics represents a key driver for the trophic and ecological status of Piburger See in the future.