Comparing microscopic counts and pigment analyses in 46 phytoplankton communities from lakes of different trophic state

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Phytoplankton indicator taxa for reference conditions in Northern and Central European lowland lakes

Phytoplankton data from 606 lakes were used to characterize indicator taxa of near-pristine reference conditions in clearwater and humic lowland lakes of Northern and Central Europe. Reference lakes were selected based on low pressure from catchment land-use, low population density and the absence of point sources. Reference lakes had low phytoplankton biomass and taxa richness compared to non-reference lakes. In low alkalinity lakes of Northern Europe, the reference communities had high biomass proportions of chrysophytes and low proportions of cyanobacteria; in the Central European high alkalinity lakes, the biomass was distributed more evenly among algal groups. Indicator species analysis and similarity analysis listed 5–29 taxa indicating reference conditions. Indicator taxa differed especially between the low alkalinity and the high alkalinity lakes, but there were also country-specific differences. Most common indicator taxa for the northern reference lakes were chrysophytes (e.g. Bitrichia, Dinobryon). In the Central European reference lakes, diatoms (e.g. Cyclotella) were more characteristic. Despite the differences, there was a general finding that taxa present in reference lakes were often also present in non-reference lakes, but typically in lower biomass proportions; another characteristic of the reference communities is the absence of many taxa typically found in non-reference lakes.     

Phytoplankton and physical-chemical features of Tavropos Reservoir,Greece

Phytoplankton biomass values in Tavropos Reservoir, ranging from 92 to 1071 mg m^–3, are within a range characteristic of oligotrophic waters. The seasonal sequence of biomass shows three annual peaks, differing from the monoacmic pattern seen in oligotrophic lakes. This sequence was profoundly affected by changes in water withdrawal and inflow rates. Diatoms, cryptophytes, chrysophytes and dinoflagellates, in that order, were the major constituents of the reservoir phytoplankton. The succession, from diatoms and chrysophytes in late winter-spring, to centric diatoms in late spring-summer and again to diatom-chrysophytes in late autumn was similar to that in oligotrophic lakes.     

Spiniferomonas abrupta, sp. nov. and some rare species of Synurophyceae and Chrysophyceae, not formerly recorded from Denmark

Eight ponds and lakes were examined for scale-bearing chrysophytes (Synurophyceae and Chrysophyceae) and abiotic parameters. Samples were taken monthly, throughout one year. All species of scale-bearing chrysophytes were identified by transmission electron microscopy (TEM). Altogether 74 taxa were found including a new species of Spiniferomonas (S. abrupta sp. nov.). Some rare species, not formerly recorded from Denmark, were also observed: Mallomonas asmundiae, M. corcontica, M. pumitio var. silvicola, Paraphysomonas capreolata, P. elegantissima, P. limbata , and Spiniferomonas silverensis .     

Silica-scaled chrysophytes (Synurophyceae) from some rivers and shallow lakes in Hungary

Silica-scaled chrysophytes are a special group in the phytoplankton of rivers and shallow lakes. They are present the whole year at low density, but sometimes — mainly during autumn and spring — some species can become frequent and very numerous to form real water blooms.In this study, seven species of silica-scaled chrysophytes have been recorded and identified by electron microscopy of phytoplankton samples from some rivers and shallow lakes in Hungary. Most of these silica-scaled chrysophytes have previously been found in eutrophic and hypertrophic localities, and almost all of them are common and widely distributed, even cosmopolitan. Only Synura echinulata Korshikov has not previously been recorded from Hungary. Some of them as Synura curtispina (Petersen & Hansen) Asmund, S. petersenii Korshikov, Mallomonas acaroides Perty emend. Ivanov, M. tonsurata Teiling were frequently found in the phytoplankton samples. Sometimes in autumn and winter Synura petersenii was the most abundant species in the phytoplankton and formed blooms.     

Further observations on the scaled Chrysophycean and Synurophycean flora of the Ocala National Forest, Florida, U.S.A.

The distributions of silica-scaled chrysophytes in 30 freshwater ponds located in the Ocala National Forest, Florida, U.S.A., relative to chemical gradients are described. Phytoplankton, periphyton, and surface sediments from each of the 30 sites were collected in March of 2000 and later analyzed extensively with both scanning electron microscopy (SEM) and light microscopy (LM) for scaled chrysophytes. In addition, water samples were used to measure a suite of chemical characteristics, including specific conductance, pH, alkalinity, total phosphorus, total nitrogen, chlorophyll- a , chloride, sulfate and base cation concentrations. Overall, waterbodies included in this study are oligotrophic, dilute, poorly buffered and low in pH. Including six previously described species which are largely known only from the Ocala National Forest, we have identified forty-nine taxa of silica-scaled Chry-sophyceae and Synurophyceae, 23 of which were present in 5 or more waterbodies, indicating that lakes in this region are quite diverse and abundant in scaled chrysophytes. The most important species included Synura petersenii, S. echinulata and one recently reported new species from this region, Mallomonas wujekii , which was found in 73% of the lakes in this survey. The number of taxa found per lake ranged from 2 to 23 and observations include new records of several rarely reported species. Although the flora includes species commonly found in more northern regions, it also includes a group of taxa that appear to be endemic to the region and others commonly found in more tropical regions. Lastly, a new form found in ten ponds, Mallomonas transsylvanica f. curvata , is described.     

Marked recent increases of colonial scaled chrysophytes in boreal lakes: implications for the management of taste and odour events

1. Lake managers suspect that taste and odour‐causing algal blooms are increasing in frequency and intensity, although long‐term monitoring records are scarce, and a number of critical scientific and management questions remain unanswered. 2. In nutrient‐poor lakes and reservoirs, these events are caused primarily by sporadic outbreaks of some chrysophyte algae, which leave identifiable markers in lake sediments. We examine the siliceous remains of these organisms in more than fifty boreal lakes at broad temporal and spatial scales. 3. Colonial scaled chrysophytes, including the taste and odour‐causing Synura petersenii, have increased markedly in more that 90% of the lakes examined since pre‐industrial times. 4. Detailed stratigraphic analyses of two lakes show a rise in the abundance of colonial taxa in the 1930s to 1950s, with a sharp increase over the past two decades. 5. An examination of biogenic silica and biological ratios in Crosson Lake, Ontario, Canada, indicate that these changes represent true increases in the absolute abundance of colonial chrysophytes. 6. Rapid increases over the past two decades indicate that these trends are the result of one or more anthropogenic stressors that are operating at a broad, regional scale.     

Paleolimnological investigation of three manipulated lakes from Sudbury,Canada

Stratigraphic changes in diatoms and chrysophytes from three manipulated Sudbury lakes were explored in an attempt to examine the influence of fertilization and/or neutralization on algal microfossil assemblages. Both diatom- and chrysophyte-inferred pH profiles indicate that the pH of Labelle Lake has remained fairly stable in the past. The study of Labelle and Middle lakes indicates that the addition of nutrients to acidic and non-acidic oligotrophic lakes did not directly influence diatom and chrysophyte species composition, perhaps because pH remained stable. The diatom and chrysophyte assemblages of Middle Lake only changed when the pH was raised. In Mountaintop Lake the recent shift in chrysophyte species composition and the resulting inferred pH decline is most likely related to a decline in mid-summer epilimnetic pH. Reliable paleolimnological inferences are difficult in lakes such as these because it is difficult to track limnological conditions in the absence of modern analogues.     

Chrysophytes and other protists in High Arctic lakes: molecular gene surveys,pigment signatures and microscopy

Microscopic analysis of the phytoplankton and other protist communities in High Arctic lakes has shown that they often contain taxa in the Chrysophyceae. Such studies have been increasingly supported by pigment analysis using high-performance liquid chromatography (HPLC) to identify the major algal groups. However, the use of 18S rRNA gene surveys in other systems indicates that many protists, especially small heterotrophs, are underreported or missed by microscopy and HPLC. Here, we investigated the late summer protist community structure of three contrasting lakes in High Arctic polar desert catchments (Char Lake at 74°42′ N, Lake A at 83°00′ N and Ward Hunt Lake at 83°05′ N) with a combination of microscopy, pigment analysis and small subunit 18S ribosomal RNA gene surveys. All three methods showed that chrysophytes were well represented, accounting for 50–70% of total protist community biomass and 25–50% of total 18S rRNA gene sequences. HPLC analysis supported these observations by showing the ubiquitous presence of chrysophyte pigments. The clone libraries revealed a greater contribution of heterotrophs to the protist communities than suggested by microscopy. The flagellate Telonema and ciliates were common in all three lakes, and one fungal sequence was recovered from Char Lake. The approaches yielded complementary information about the protist community structure in the three lakes and underscored the importance of chrysophytes, suggesting that they are well adapted to cope with the low nutrient supply and strong seasonality that characterize the High Arctic environment.     

Winter limnology: a comparison of physical,chemical and biological characteristics in two temperate lakes during ice cover

The winter dynamics of several chemical, physical, and biological variables of a shallow, polymictic lake (Opinicon) are compared to those of a deep, nearby dimictic lake (Upper Rock) during ice cover (January to early April) in 1990 and 1991. Both lakes were weakly inversely thermally stratified. Dissolved oxygen concentration was at saturation (11–15 mg l⁻¹) in the top 3 m layer, but declined to near anoxic levels near the sediments. Dissolved oxygen concentrations in the deep lake were at saturation in most of the water column and approached anoxic levels near the sediments only. Nutrient concentrations in both lakes were fairly high, and similar in both lakes during ice cover. Total phosphorus concentrations generally ranged between 10–20 μg l⁻¹, NH₄-N between 16–100 μg l⁻¹, and DSi between 0.9–1.9 mg l⁻¹; these concentrations fell within summer ranges. NO₃-N concentrations were between 51–135 μg l⁻¹ during ice cover, but occurred at trace concentrations (<0.002 μg l⁻¹) during the summer. The winter phytoplankton community of both lakes was dominated by flagellates (cryptophytes, chrysophytes) and occasionally diatoms. Dinoflagellates, Cyanobacteria and green algae were poorly represented. Cryptophytes often occurred in fairly high proportions (20–80%) throughout the water column, whereas chrysophytes were more abundant just beneath the ice. Zooplankton population densities were extremely low during ice cover (compared to maximum densities measured in spring or summer) in both lakes, and were comprised largely of copepods.     

Taxonomy and ecology of the phytoplankton of Lake Fidler and Sulphide Pool,meromictic Tasmanian lakes

A floristic list of 89 freshwater phytoplanktonic algae occurring in two neighbouring, dystrophic, meromictic Tasmanian lakes is given. In both lakes the preponderance of desmids and phytoflagellates, especially chrysophytes, is a characteristic in keeping with their dystrophic nature. All the alga must be adapted to low levels of red light and some habitually inhabit crepuscular depths rather than executing diel vertical migrations such as happens in many dystrophic waters. Floristic differences between the two lakes are related to morphometric differences and the degree of entrainment of tychoplankton. The photosynthetic biomass of both lakes is predominantly monimolimnetic, made up of few species. The floristically-rich mixolimnion contributes little to biomass. The ecology of the dystrophic flora is discussed in relation to the special circumstances of meromixis.     

NEW AND RARE CHRYSOPHYTES FROM WYOMING AND COLORADO LAKES

Colorado and Wyoming lakes with high pH values generally ranging from 8 to 10 are dominated by phytoplankton belonging to the chrysophytes, diatoms and cryptomonads. Our studies on phytoplankton diversity in Dowdy, South Delaney Buttes and Cowdrey Lakes in Colorado and Diamond and Twin Buttes Lakes in Wyoming have yielded several isolates of rare or new chrysophytes. These isolates were examined with light microscopy, SEM, TEM, and novel information regarding their structure is presented. Proposed new species belong to the genera Saccochrysis, Prymnesium and Chrysochromulina. Chrysophytes that were examined for the first time include Monochrysis aphanaster , Uroglenopsis , and a mixotrophic species of Ochromonas , which ingests small diatoms. Probable new species are the following: Saccochrysis sp. nov. differs in chloroplast structure, cell shape and cell number/colony, and absence of a posterior vacuole; Prymnesium sp. nov. is the first freshwater form examined with EM and differs in scale morphology; and Chrysochromulina sp. nov. is similar to Chrysochromulina parva but lacks scales. The ultrastructure of M. aphanaster is unique and appears to be a member of the Chrysophyceae. It has two flagella, one of which is emergent, while the other is hidden within an invagination of the cytoplasm. Diacronema and Sarcinochrysis spp. from these lakes also were isolated and reinvestigated, and some unique cellular features will be discussed.     

Bacterioplankton Community Composition in Five Lakes Differing in Trophic Status and Humic Content

Abstract To investigate the relation between lake type and bacterioplankton community composition, five Swedish lakes, which differed from each other in nutrient content and water color, were studied. Denaturing gradient gel electrophoresis (DGGE) of 16S rDNA was used to examine community composition. The DGGE-patterns of the different samples were analyzed in relation to physical, chemical, and biological data from the lakes by canonical correspondence analysis (CCA). The three variables found to most strongly correlate with the DGGE patterns were biomasses of microzooplankton, cryptophytes, and chrysophytes, suggesting that these biota had an impact on bacterioplankton community structure. Two of the three factors were, in turn, significantly correlated to parameters associated with the trophic status of the lakes, indicating that the nutrient content of the lakes, at least indirectly, influenced the structure of the bacterioplankton community. The relation to water color was less pronounced. Received: 16 February 2000; Accepted: 27 April 2000; Online Publication: 18 July 2000     

Comparison of pelagic food webs in lakes along a trophic gradient and with seasonal aspects: influence of resource and predation

Composition and seasonal dynamics of phytoplankton, bacteria,and zooplankton (including heterotrophic flagellates, ciliates,rotifers and crustaceans) were studied in 55 lakes in NorthernGermany with different trophic status, ranging from mesotrophicto hypertrophic. Mean abundance and biomass of all groups increasedsignificantly with trophic level of the lake, but bacteria andmetazooplankton showed only a weak correlation and a slightincrease with chlorophyll concentration. Composition of phytoplanktonshowed a dominance of cyanobacteria in hypertrophic lakes, whereasthe importance of chrysophytes and dinophytes decreased withan increase in trophic status. Protozoans (heterotrophic flagellatesand ciliates) made up 24% (mesotrophic lakes) to 42% (hypertrophiclakes) of total zooplankton biomass on average, and were dominatedby ciliates (62–80% of protozoan biomass). Seasonally,protozoans can build up to 60% of zooplankton biomass in spring,when heterotrophic flagellates can contribute     

CHRYSOPHYTE POPULATION AND ENCYSTMENT PATTERNS IN TWO CANADIAN LAKES1

The dynamics of chrysophyte populations and the onset of encystment in relation to several physical, chemical, and biological variables were studied in two Canadian lakes, Lake Opinicon (LO) and Upper Rock Lake (URL). LO is shallow and polymictic during the ice-free season, whereas URL is deep and dimictic. Seasonal patterns of many limnological variables, as well as species composition and seasonal dynamics of chrysophyte assemblages, were broadly similar in both lakes. Three groups of chrysophytes were recognized: 1) taxa that were more abundant during ice cover and/or early spring and occasionally in late fall (Dinobryon spp. Ehrenberg and Synura spinosa Korsh), 2) taxa that seemed to prefer moderately warm water proglena americana Calkins and Ochromonas sp. Wyssotzki) and had maximum densities in late summer and occasionally in the fall, and 3) taxa that occurred in low numbers and did not exhibit any discernible seasonality in the two lakes (Mallomonas spp. Perty). Encystment rarely occurred during ice cover in both lakes. Stomatocyst concentrations were highest shortly after ice breakup (late April or early May), declined to trace levels by June, and remained at those levels until the end of the sampling season (late November). Encystment rates (cyst concentrations) were higher in dimictic URL. Encystment in both lakes coincided with concurrent changes in physical and chemical variables and chrysophyte vegetative cell densities, but it was not possible to pinpoint the exact conditions responsible for triggering encystment. Only a small proportion of chrysophytes encysted. Cyst production within a lake may vary from year to year.     

Limnologic consequences of the decline in hemlock 4800 years ago in three Southern Ontario lakes

Four thousand eight hundred years ago hemlock (Tsuga canadensis) populations were decimated throughout eastern North America. We have studied the effects of this loss from the terrestrial community on three Southern Ontario lakes: Little Round Lake, Sunfish Lake, and McKay Lake. This study includes the use of cladocerans, diatoms, chrysophytes, and bacterial pigments to assess the limnologic changes that occurred in these lakes. Each lake experienced a change in trophic status that coincided with the loss of hemlock from its catchment, but the change in the aquatic biota was different in each lake. The lakes' size may have been the most influential factor governing the response to this terrestrial disturbance.     

Responses of epilimnetic phytoplankton to experimental nutrient enrichment in three small seepage lakes

This paper describes the responses of three epilimnetic phytoplanktoncommunities to experimental nitrogen and phosphorus enrichmentas compared to the phytoplankton community in a fourth, unmanipulated,lake. Increased nutrient inputs increased total phytoplanktonbiomass, primary productivity, chlorophytes, cryptomonads andspecies turnover rates in all three enriched lakes; cyanobacteriaincreased in two of the three enriched lakes. However, nutrientaddition also led to declines in previously dominant dinoflagellatesand chrysophytes, and in species diversity. At the species level,there were large changes in community composition from yearto year in both enriched and reference lakes, suggesting thatphytoplankton community composition is highly dynamic even inthe absence of enrichment. Overall, changes in total biomass,productivity and species diversity were consistent among theenriched lakes, while changes in species composition differeddue to variation in the physical, chemical and biotic environmentof each lake. This suggests that aggregated variates are moreuseful for quantitative prediction of nutrient effects, whilespecies responses can be used to signal qualitative differencesin environmental conditions among lakes. ³Present address: Department of Biological Sciences, DartmouthCollege, 6044 Gilman Laboratory, Hanover, NH 03755-3576, USA     

Silica-scaled Chrysophytes from Portugal

Phytoplankton samples from lakes, reservoirs and ponds in Central Portugal were obtained and the scale-bearing chrysophytes investigated by electron microscopy. This is the first study on the occurrence and distribution of these organisms in Portugal and in the Iberian Peninsula as a whole. It reports the presence of 23 species of the genera Chrysosphaerella, Paraphysomonas, Spiniferomonas, Mallomonas and Synura . Most of the species found are of worldwide distribution but a few rare organisms were present in some samples. To conclude, the perspectives of future research in Portugal are briefly outlined.     

Plankton communities of three Central Florida lakes

A study of planktonic primary productivity and community structure was carried out on three lakes of varying morphometric and chemical features, but which were within a single watershed in Central Florida. Primary productivity in these lakes was evaluated by means of in situ light and dark bottle determinations as well as by calculations based upon chlorophyll and light data. Lake Mize, a deep sinkhole lake containing highly colored waters of low pH, proved to be a very unproductive lake, while Biven's Arm, a shallow-basin lake with alkaline waters and Newnan's lake, a shallow-basin like with highly colored waters both showed relatively high productivities. Phytoplankton components of the two productive lakes were quite similar to one another in being composed of bloom-forming blue-green and green algae, while the predominant forms in Lake Mize were chrysophytes, dinoflagellates and a diatom. Zooplanktonic forms were more uniform among the lakes than were the phytoplankton, though population levels reflected relative productivities among the lakes. Rotifers predominated in the Lake Mize plankton while cladocerans were relatively inabundant. This was opposite to the condition in Biven's Arm and Newnan's Lake. It is suggested that the constant presence of larval Chaoborus in the water column in Lake Mize may be partially responsible for the paucity of cladocera.     

Palaeoenvironmental Changes Inferred from Biological Remains in Short Lake Sediment Cores from the Central Alps and Dolomites

In this paper we review research on eutrophication, acidification and climate change based on studies of lake sediments in the Alps. Studies on fossil diatoms, chrysophytes, plant pigments, Cladocera and carbonaceous particles in a number of high altitude lakes in Italy and Switzerland have been used to track environmental changes. We present an original study on fossil Cladocera in sediment cores from 29 lakes that have shown changes in biodiversity from the pre-industrial period (ca. pre AD 1850) to the present. These data show that altitude, ca. 60 years of acidification impacts and fish stocking are the most important factors that affect their distribution and abundance. We review further case studies from two morphometrically and chemically different lakes (Tovel and Paione Superiore). Their lake sediment records span 400 and 150 years, respectively; multi-core, multi-proxy analyses show their pH, trophic and climatic evolution over time.