Seasonality of planktonic ciliated protozoa in 20 subtropical Florida lakes of varying trophic state

The planktonic ciliate populations of 20 Florida lakes ranging from oligotrophic to hypereutrophic were examined monthly for one year. Oligotrophic lakes displayed abundance peaks during fall mixis and biomass peaks in late winter and fall. Mesotrophic systems exhibited a spring-fall bimodality in ciliate abundance with a biomass maxima occurring during fall. Eutrophic/hypereutrophic lakes had pronounced abundance and biomass maxima during summer, with the large ciliates Plagiopyla nasuta and Paramecium trichium often contributing heavily to the midsummer biomass peak. Members of the Oligotrichida numerically dominated abundance and biomass peaks in oligotrophic lakes while the Scuticociliatida dominated the communities of higher trophic states. Total ciliate abundance and biomass were strongly correlated with chlorophyll a concentrations as were various ciliate taxonomic groups. The relationship between ciliate seasonal distribution in these subtropical lakes with lake thermal regimes and trophic state is discussed.     

Analysis of the community structure of planktonic ciliated protozoa relative to trophic state in Florida lakes

The planktonic ciliate populations of 30 Florida lakes constituting a broad trophic gradient were examined to determine the response of protozoan community structure to increasing eutrophication. Both ciliate abundance and biomass were strongly related to lake trophic state. Comparison of the Florida data base with a comparable north temperate lake group indicated that subtropical lakes generally possess higher ciliate abundance and biomass at a given trophic state than temperate lakes. However the equations derived for each data base were not significantly different. Community diversity and species richness increased with increasing lake productivity. Highly acidic lakes displayed significantly reduced diversity and numbers of species when contrasted with nonacidic oligotrophic lakes. Small-bodied (< 30 um) ciliates dominated all lakes but were proportionally less important in oligotrophic lakes. Presence-absence data produced three assemblages: an ubiquitous association of primarily small ciliate taxa, a group of large ciliates mainly restricted to eutrophic-hypereutrophic lakes, and a very large ciliate,Stentor niger, which dominated the protozoan communities of acidic oligotrophic lakes.     

Cladocera and geochemical evidence from sediment cores show trophic changes in Polish dystrophic lakes

Change in the trophic state of lakes is a topic of primary interest for limnologists and paleolimnologists, but also for governments in many countries. These changes can be the result of the natural evolution of lake ecosystems, but nowadays are most often connected with human activity influencing water bodies. In this article, we reconstruct changes in the lake productivity and trophic state in three dystrophic (humic) lakes located in Northern Poland. Sediments from these lakes, which are part of a national park, were submitted to Cladocera and chemical composition analyses. Currently, the trophic state of these lakes has been described based on the water's chemical composition, and they have been classified as undisturbed ecosystems with a stable trophic state. The main objective of this study was to evaluate whether these lakes have been stable and undisturbed ecosystems during the past centuries and therefore whether they can be classified as natural and pristine. The results of subfossil Cladocera analysis and sedimentary geochemical analysis confirmed the specific nature of studied lakes. However, our results were surprising and showed that during the last 200 years two of the three lakes have undergone distinct trophic changes, while one of them has barely changed at all.     

Material transfer from water to sediment in Florida lakes

We describe statistical relationships between chemical aspects of surficial sediments from 34 Florida lakes, and trophic state of the overlying waters. Trophic state is expressed by Carlson's TSI-Chl a. The objectives of the study are two-fold: 1) to understand processes that govern the transfer of material across the mudwater interface, and 2) to develop transfer functions for inferring historical TSI measures in chemically analyzed, ²¹⁰Pb-dated cores. Simple regression of organic matter content or nutrient (C, N, P) concentration in surface sediments vs. TSI yields nonsignificant or weak positive correlations. However, using a novel application of ²¹⁰Pb assay, net accumulation rates of the materials are estimated and show a better correlation with trophic state. Cation (Ca, Mg, Fe, K) and sulfur concentrations in surface muds are poorly related to corresponding TSI's. Net accumulation rates of these elements (Ca, Mg, Fe, K, S) are positively correlated (P < 0.01) with TSI-Chl a. Chemical data from the Florida surficial sediment survey suggest that inferred levels of past trophic state should be based on net accumulation rates of chemical constituents rather than their simple sediment concentrations.     

Species composition and cyanotoxin production in periphyton mats from three lakes of varying trophic status

In lakes, benthic micro-algae and cyanobacteria (periphyton) can contribute significantly to total primary productivity and provide important food sources for benthic invertebrates. Despite recognition of their importance, few studies have explored the diversity of the algal and cyanobacterial composition of periphyton mats in temperate lakes. In this study, we sampled periphyton from three New Zealand lakes: Tikitapu (oligotrophic), ōkāreka (mesotrophic) and Rotoiti (eutrophic). Statistical analysis of morphological data showed a clear delineation in community structure among lakes and highlighted the importance of cyanobacteria. Automated rRNA intergenic spacer analysis (ARISA) and 16S rRNA gene clone libraries were used to investigate cyanobacterial diversity. Despite the close geographic proximity of the lakes, cyanobacterial species differed markedly. The 16S rRNA gene sequence analysis identified eight cyanobacterial OTUs. A comparison with other known cyanobacterial sequences in GenBank showed relatively low similarities (91-97%). Cyanotoxin analysis identified nodularin in all mats from Lake Tikitapu. ndaF gene sequences from these samples had very low (≤ 89%) homology to sequences in other known nodularin producers. To our knowledge, this is the first detection of nodularin in a freshwater environment in the absence of Nodularia. Six cyanobacteria species were isolated from Lake Tikitapu mats. None were found to produce nodularin. Five of the species shared low (< 97%) 16S rRNA gene sequence similarities with other cultured cyanobacteria.     

Differential sensitivity of planktonic trophic levels to extreme summer temperatures in boreal lakes

The stress–size hypothesis predicts that smaller organisms will be less sensitive to stress. Consequently, climate warming is expected to favour smaller taxa from lower trophic levels and smaller individuals within populations. To test these hypotheses, we surveyed zooplankton communities in 20 boreal lakes in Killarney Provincial Park, Canada during 2005 (an anomalously warm summer) and 2006 (a normal summer). Higher trophic levels had larger responses to warm temperatures supporting the stress–size hypothesis; however, rather than imposing negative effects, higher density and biomass were observed under warmer temperatures. As a result, larger taxa from higher trophic levels were disproportionately favoured with warming, precluding an expected shift towards smaller species. Proportionately greater increases in metabolic rates of larger organisms or altered biotic interactions (e.g. predation and competition) are possible explanations for shifts in biomass distribution. Warmer temperatures also favoured smaller individuals of the two most common species, in agreement with the stress–size hypothesis. Despite this, these populations had higher biomass in the warm summer. Therefore, reduced adult survivorship may have triggered these species to invest in reproduction over growth. Hence, warmer epilimnions, higher zooplankton biomass and smaller individuals within zooplankton populations may function as sensitive indicators of climate warming in boreal lakes.     

Comparative study of the planktonic communities of three lakes of contrasting trophic status at Hope Bay (Antarctic Peninsula)

Three water bodies of contrasting trophic status located atHope Bay (Antarctic Peninsula) were studied during the summerof 1999, analysing all of their planktonic communities (zooplankton,phytoplankton and bacterioplankton) and their main limnologicalfeatures. Important differences associated with their trophicconditions were found among lakes. At one extreme of the gradient,in the most oligotrophic lake (Lake Chico), the nektobenthiccopepod Boeckella poppei and the rotifer Philodina gregariawere dominant in the open waters, and copepods presented a singlereproductive event (univoltine life cycle); phytoplankton exhibitedthe lowest densities, dominated by nanoplanktonic Chrysophyceaeand picocyanobacteria. In the meso-eutrophic Lake Boeckella,B. poppei, the dominant zooplankter, exhibited a multivoltinelife cycle; phytoplankton were mainly represented by nanoplanktonicspecies of Volvocales, alternating with flagellate Chrysophyceae,and a great abundance of picocyanobacteria. In the hypertrophicPingüi Pond, zooplankters were exclusively representedby bdelloid rotifers and ciliates; phytoplankton samples includedsome strictly planktonic species (Volvocales), a great proportionof picocyanobacteria and many typically benthic species (oscillatoriansand diatoms) due to the shallowness of the water body. Bacterioplanktondensities did not show important differences among lakes, butfluctuations, probably associated with a top-down control, wereobserved in the hypertrophic pond. This paper constitutes thefirst survey concerning all the planktonic compartments of waterbodies of different trophic status at Hope Bay, describing therelative contributions of autotrophic and heterotrophic componentsto their food webs.     

Relations between trophic state indicators and plant biomass in Florida lakes

We collected quantitative data on macrophyte abundance and water quality in 319 mostly shallow, polymictic, Florida lakes to look for relationships between trophic state indicators and the biomasses of plankton algae, periphyton, and macrophytes. The lakes ranged from oligotrophic to hypereutrophic with total algal chlorophylls ranging from 1 to 241 mg m^–3. There were strong positive correlations between planktonic chlorophylls and total phosphorus and total nitrogen, but there were weak inverse relationships between the densities of periphyton and the trophic state indicators total phosphorus, total nitrogen and algal chlorophyll and a positive relationship with Secchi depth. There was no predictable relationship between the abundance of emergent, floating-leaved, and submersed aquatic vegetation and the trophic state indicators. It was only at the highest levels of nutrient concentrations that submersed macrophytes were predictably absent and the lakes were algal dominated. Below these levels, macrophyte abundance could be high or low. The phosphorus–chlorophyll and phosphorus–Secchi depth relationships were not influenced by the amounts of aquatic vegetation present indicating that the role of macrophytes in clearing lakes may be primarily to reduce nutrient concentrations for a given level of loading. Rather than nutrient concentrations controlling macrophyte abundance, it seems that macrophytes acted to modify nutrient concentrations.     

The change of sediment composition during recovery of two Finnish lakes induced by waste water purification and lake oxygenation

Total oxygen deficit occurred regularly during stagnation periods in the deepest part of Lake Kallavesi in the period 1973–1986. The sediment was black and anaerobic during the first sampling in 1987. After beginning of artificial lake oxygenation and efficient purification of waste waters of a paper board mill in 1986 the oxygen deficit decreased gradually and a light brown oxidized uppermost sediment layer appeared and began to thicken. The following changes in the sediment composition were observed during 1987–1996: loss on ignition, total nitrogen and BOD₇ concentrations decreased in the uppermost sediment layer (0–2 cm) and BOD₇ concentration increased in the next sediment layer beneath (2–10 cm). There were no significant change in phosphorus and iron concentrations.Lake oxygen, total phosphorus and suspended solids concentrations fluctuated in a noticeable degree in Lake Huruslahti depending on waste water input and artificial oxygenation during the years 1980–1993. Oxygen condition was good at times of successful waste water elimination and lake oxygenation while deterioration of either resulted oxygen deficiency as well as increase of total phosphorus and suspended solids concentration. Most of the internal load entered with suspended solids during periods of total oxygen deficiency.An explanation for the findings in Lake Huruslahti could be microbiological. Gas formation inside sediment lift organic material towards top of the sediment and into the water, but after the lake recovery the material retain in the sediment. Also in Lake Kallavesi microbiological gas formation resuspended sediment particles with phosphorus into the overlaying water prior to oxygenation. During oxygenation microbiological processes in uppermost sediment utilize the anaerobic metabolic products, organic acids and methane, and block gas formation. Organic substances remain in the top sediment decomposing gradually in the uppermost layer.     

Relationships between zooplankton abundance and trophic state in seven New Zealand lakes

The zooplankton communities of seven Rotorua, New Zealand, lakes of different trophic status were studied in 1977–78. They were generally dominated by the calanoid copepod, Calamoecia lucasi. Bosmina meridionalis occurred in all the lakes and Ceriodaphnia dubia in most. Only small numbers of Macrocyclops albidus ever occurred. Rotifers were not studied in detail. Community composition was similar to that in other northern New Zealand lakes. No well defined patterns of seasonal change in abundance were found and the timing of changes, which were of low magnitude, was different in each lake. Clutch sizes in all species were small. Calamoecia population parameters were analysed using multivariate methods and shown to be related to lake trophic level. Population densities were higher in more productive lakes whereas breeding levels were inversely related to indices of trophic status and population abundance. It is suggested that the populations, as in other northern New Zealand lakes, are food-limited, probably as a consequence of a lack of marked climatic seasonality and the absence of major predation pressures. Groupings of the lakes based on the Calamoecia data are in general agreement with those derived from parallel studies of water chemistry, phytoplankton and macrobenthos.     

Cladocerans respond to differences in trophic state in deeper nutrient poor lakes from Southern Norway

We investigated the role of trophic state in structuring the cladoceran assemblages in 35 relatively deep lakes of low nutrient levels in Southern Norway. The lakes cover gradients of altitude, latitude, longitude, area and total phosphorus concentration. The environmental control of the cladoceran assemblages was analyzed using canonical correspondence analysis. Total phosphorus was the most important variable in the minimal adequate model. Hence, the cladoceran assemblage changed with trophic state. Typical clear water species were displaced by indicators of eutrofication with increasing trophic levels. Littoral species constituted the majority of the species recorded. Littoral and pelagic species richness showed a unimodal relationship with trophic state. Along with the change in trophic state and shift in cladoceran assemblage, we observed an increase in the ratio of pelagic to littoral species as well as in the ratio of pelagic efficient bacterial feeders to total pelagic filter feeders. The study indicates that zooplankton could provide a valuable indicator of ecosystem’s structure and function in deeper nutrient poor lakes if included in water quality assessments according to the EU Water Framework Directive. Including sampling of the littoral zooplankton would improve diversity estimates and incorporate the response of the littoral zone to eutrophication.     

Seasonal variations of phytoplankton photosynthate partitioning in two lakes of different trophic level

The aim of this study was to compare vertical and seasonal variationsof inorganic carbon allocation into macromolecules by the phytoplanktonpopulation in a eutrophic lake (Lake Aydat) and an oligo-mesotrophiclake (Lake Pavin). Biochemical fractionation was conducted byconsecu tive differential extractions in order to separate proteins,polysaccharides, lipids, and low molecular weight compounds(LMW). The ratio of light absorption at480 and 665 nm by acetoneextracts of phytoplankton pigments was used as an indicatorof the nutritional statusof natural phytoplankton populations.Our results show that in Lake Aydat, the main photosyntheticend productswere poly saccharides, whereas in Lake Pavin, radioactivitywas predominantly incorporated into the protein fraction. Moreover,the seasonal cycles of mixing and stratification in these twolakes affected the pattern of ¹⁴C incorporation into LMW andmacromolecules. An increase in the relative synthesis of proteinsoccurred during stratification periods. It was linked to anincrease in temperature and nutrient limitation further complicatedby the shift in species composition of the populations. Differences recorded both between the two lakes of different trophicstatus and between seasons confirm that the proportion of carbonincorporated into proteins might be a useful indicator of thephysio logical status of phvtoplankton communities.     

Preliminary data on size composition and settlement ofDreissena polymorpha (Pallas) (Mollusca: Bivalvia) in lakes differing in trophic state

Size composition of colonies and settlement of larvae on nylon substrates as function of depth inDreissena polymorpha demonstrated differences in three lakes of different trophic state. In one lake, the data on size distribution in the colony and of the settled larvae also differed. The explanation requires further research.     

Factors controlling hydrochemical and trophic state variables in 86 shallow lakes in Europe

The total nitrogen mass balance was studied over a two-year period in two reservoirs located in south-eastern Poland. Theobserved nitrogen retention (N_ret) inthe reservoirs ranged from 0.18 to 2.12g m^-2d^-1 (mean 0.83g m^-2d^-1) in case of theRzeszów Reservoir and from -0.02 to0.41 g m^-2d^-1 (mean 0.13g m^-2d^-1) in case of the SolinaReservoir, while the percentage retention(N_ret) ranged from 7 to 42% (mean22%) and -15 to 73% (mean 35%),respectively. A good relationship betweenN_ret and nitrogen loads was observedfor the Solina Reservoir. The data obtainedby the author and collected from theresearches of 6 other reservoirs located insouthern Poland were used to develop anempirical model suitable to predict thenitrogen seasonal dynamics in a reservoir.The model allows for the determination ofboth the annual mean N_ret value andits seasonal variation in a reservoir.     

Melosira distans var. tenella and Eunotia zasuminensis, two poorly known planktonic diatoms in Finnish lakes

The occurrence and ecology of two poorly known planktonic diatoms, Melosira distans var. tenella (Nyg.) M.-B. Florin and Eunotia zasuminensis (Cabejsz.) Körner in central Finland is discussed. Both species have their maximum in late summer when water temperature is > 15°C and they prefer slightly acid water (pH < 7), low conductivity (less than 4 mS/m) and a moderate degree of dystrophy with C.O.D. 10–20 mg O₂/l and water colour 60–120 mg Pt/1. Melosira distans var. tenella was found in ca. 80% of the central Finnish lakes studied, but it is not reported in previously published papers. Eunotia zasuminensis is rarer, but is, however, recorded in at least 22 lakes in central Finland.     

Rotifer occurrence in relation to age,depth and trophic state of quarry lakes

An effect of age of quarry lakes on rotifer abundance and species composition has been evaluated. Rotifers occurred in all lakes under study. They were even found in the youngest (2 years of age) one, Rogonica 4, but both rotifer density and species richness were low there. Rotifer communities of much higher density and species diversity were noted in lakes only 4–6 years older. Lakes of over 30 years of age were strongly differentiated in rotifer numbers and species structure. In general, age of quarry lakes has an impact on rotifer communities only at the very beginning of the process of colonization. Several years later other factors become more important, e.g., depth or trophic state of the lakes.     

Morphometry and trophic state modify the thermal response of lakes to meteorological forcing

We hypothesised that (i) a summer heat wave would increase the thermal stability of lakes and (ii) the size and trophic state differences would modify the lakes’ responses to heating. Within 2 years, 2008 and 2009, we studied the thermal and optical regimes of two adjacent stratified lakes in northern Italy, the oligo-mesotrophic Lake Monate (2.5 km², max. depth 34 m) and the eutrophic Lake Varese (14.8 km², 26 m). After the cold winter 2008–2009, a heat wave starting in May turned the whole year 2009 the second hottest after 2003. The particular sequence of meteorological events resulted in extreme vertical temperature gradients and unusually high thermal stability of both lakes. All calculated thermal parameters showed the highest values in 2009 while also the values for 2008 exceeded considerably those published for these lakes in the past. Due to the large wind exposed surface, wind mixing was supposedly the dominating mechanism of heat transfer in the shallower eutrophic Lake Varese where, due to low water transparency, large amount of solar energy trapped in the upper layers markedly increased the thermal stability. In the deeper and more transparent Lake Monate, the deeper penetrating solar irradiance contributed to better energy dissipation within the water column and smaller interannual differences in thermal stability.     

Comparative investigation of chemical and biological characteristics in waters and trophic state of Mongolian lakes

The objective of this study is to describe the biogeochemical characteristics in the waters of Mongolian lakes, particularly those related to parameters limiting phytoplankton growth and the trophic state. Investigations into the distribution of chemical and biological parameters were carried out in the following 18 lakes: Har Us, Har, Hovsgol, Achit, Dalai, Bayan, Tolbo, Holboo, Bust, Sangiyn Dalai, Tunamal, Dorgon, Uureg, Telmen, Hyargas, Uvs, Erkhel and Oygon, all of which showed a wide range of salinity between 0.16 and 24.9 g l⁻¹. Lake water was classified into four types: six fresh (less than 0.5 g l⁻¹ salinity), three subsaline (0.5–3 g l⁻¹), seven hyposaline (3–20 g l⁻¹) and two mesosaline (20–50 g l⁻¹) lakes. Predominant cations and anions in the order of dominance were Ca, Mg > Na > K and HCO₃ > SO₄, Cl in freshwater lakes, Na > Mg > Ca, K and HCO₃, Cl > SO₄ in subsaline lakes, and Na > Mg > K, Ca and Cl, SO₄ > HCO₃ in hyposaline and mesosaline lakes. Nitrogenous and phosphorus nutrients in the waters were low, seemingly caused by the low loads from their watersheds, where the ground was free of vegetation with an extremely low level of human activity. The present investigations revealed some 234 taxa of phytoplankton and 38 of zooplankton. The PC:PN:PP stoichiometric ratio by weight was (22–202):(3–27):1. Phosphorus was assessed as the potential limiting parameter in eight lakes, nitrogen in six and both nutrients in four others. Twelve lakes showed an oligotrophic character, while six were mesotrophic type. The six oligotrophic lakes seemed to be subject to phosphorus limiting phytoplankton growth, four to nitrogen and two to both limitations. In the mesotrophic lakes, on the other hand, phosphorus limitation was verified in two lakes, nitrogen in two others and both in two lakes.     

Population responses of perch (Perca fluviatilis) and roach (Rutilus rutilus) to recovery from acidification in small Finnish lakes

Decreasing trends in atmospheric emissions and acidic deposition during the 1990s have resulted in chemical recovery from acidification in the sensitive surface water systems of southern Finland. Responses of perch and roach populations to the improved water quality were studied in 30 small lakes with the aid of water chemistry monitoring data gathered in 1987–2002 and the data collected from two consecutive periods of gillnet test fishing, 1985–1988 and 2001–2002. In the most acidified lakes, alkalinity and ANC have increased and sulphate and labile aluminium concentrations decreasæed markedly. The response of perch populations to the improved water quality is seen in improved reproduction success, indicated by a higher CPUE in numbers and a lower mean weight. The growth rate of perch has declined as the population density has increased. Roach populations have not recovered in the same way as perch, there being no major changes in NPUE or mean weight. Lower growth rates were, however, observed in the roach populations of all study lakes. The increased perch population density as an obstacle to the recovery of roach populations is discussed. Despite the chemical and biological recovery of the study lakes, the buffer capacity of many headwater lakes is low and the lakes will be sensitive to any increases in acidic deposition in the future.