Ceratophyllum demersum hampers phytoplankton development in some small Norwegian lakes over a wide range of phosphorus concentrations and geographical latitude

1. Data on submerged and floating-leafed macrophytes, phytoplankton, nutrients (N, P) and calcium were collected from twenty-four small lakes ( 1 km²) over a wide range of latitudes in Norway. The majority of the investigated lakes were mesotrophic or eutrophic, and most of the lakes were markedly affected by diffuse and point-source runoff from agriculture. According to their macrophyte species composition, the majority of the lakes can be classified as Potamogeton lakes or Chara lakes, or a combination of these.
2. This study is consistent with the 'two alternative stable states' hypothesis. We observed clearwater lakes with dense macrophyte cover over a wider range of total P concentration than has been reported previously: from 30 to more than 700 mg P m^–3. The clearwater state was only observed in lakes with mean depths of less than 1.9 m.
3. Most clear lakes with high cover of submerged vegetation showed indications of N limitation.
4. In this study nearly all the macrophyte-dominated lakes with P concentrations above 30 mg m^–3 had dense stands of Ceratophyllum demersum (L.). This indicates that Ceratophyllum may also play an important role in stabilizing and maintaining a clearwater state at high P concentrations.     

Existence of a macrophyte-dominated clear water state over a very wide range of nutrient concentrations in a small shallow lake

Little Mere, a small shallow lake, has been monitored for four years, since its main source of nutrients (sewage effluent) was diverted. The lake has provided strong evidence for the persistence of a clear water state over a wide range of nutrient concentrations. It had clear water at extremely high nutrient concentrations prior to effluent diversion, associated with high densities of the large body-sized grazer, Daphnia magna, associated with low fish densities and fish predation. Following sewage effluent diversion in 1991, the nutrient concentrations significantly declined, the oxygen concentrations rose, and fish predation increased. The dominance of large body-sized grazers shifted to one of relatively smaller body-sized animals but the clear water state has been maintained. This is probably due to provision of refuges for grazers by large nymphaeid stands (also found prior to diversion). There has been a continued decrease in nutrient concentrations and expansion of the total macrophyte coverage, largely by submerged plants, following effluent diversion. The grazer community of Little Mere has also responded to this latter change with a decline in daphnids and increase in densities of weed-associated grazers. The presence of large densities of such open water grazers was the apparent main buffer mechanisms of the clear water state until 1994. The lake has, so far, maintained its clear water in the absence of such grazers. Thus, new buffer mechanisms appear to operate to stabilize the ecosystem. Little Mere appears to have shifted from previous top-down controlled clear water state to a bottom-up controlled clear water state.     

MD simulation of self-diffusion and structure in some n-alkanes over a wide temperature range at high pressures

Self-diffusion and structural properties of n-alkanes have been studied by molecular dynamics simulation in the temperature range between the melting pressure curve and 600 K at pressures up to 300 MPa. The simulated results of lower n-alkanes are in good agreement with the existing experimental data, and support the reliability of results of the simulations of self-diffusion coefficients obtained at the extreme conditions. We predict the self-diffusion coefficients for methane, ethane, propane and n-butane at the similar reduced temperatures and pressures to draw a comparison between them. Then the correlation between self-diffusion and structural properties are further investigated by calculating the coordination numbers. Moreover, we define four distances and their corresponding relative deviations to characterize the flexibility of long-chain n-alkanes. The simulated results show that the self-diffusion of n-alkane molecules is mainly affected by the close packing, and the flexibility has a strong impact on the self-diffusion of longer n-alkane molecules.

Changes in the concentrations of short-chain carboxylic acids and gases during decomposition of the aquatic macrophytes, Lemna paucicostata and Ceratophyllum demersum

SUMMARY.

• 1 Samples of two species of aquatic macrophytes, Lemna paucicostata and Ceratophyllum demersum, with which snail hosts of schistosomes are commonly associated, were homogenized, together with their epiphytic flora, and allowed to decompose in closed systems for up to 42 days.
• 2 After 10 days of incubation it was found that populations of rod and coccoid shaped bacteria had greatly increased. Fermentation proceeded only to the acid forming stage and no methane was produced.
• 3 Despite the differences in the morphologies, habitats and epiphytic flora of the two species, it was found that the short chain carboxylic acids, acetate, propanoate, butanoate and hydrogen were the major end products of microbial decomposition in both cases. There was also some oxygen production from photosynthetically active zones within the homogenates. Most of the accumulation profiles for the acids conformed to logistic growth curves, whereas the hydrogen values fluctuated.
• 4 The reasons for the biochemical changes, the differences between the patterns of decomposition in Lemna and Ceraiophyllum. and the ecological relevance of the results to the plants, micro-organisms and the snails are discussed.

     

Determination of available phosphorus for phytoplankton populations in lakes and rivers of southeastern Norway

A biotest method with diluted phytoplankton populations was used to determine external concentrations of available phosphorus in water samples with high concentrations of inorganic seston from River Rømua. RP (total molybdate reactive P measured on unfiltered samples) was approximately the P fraction available for Synedra cf. acus, Asterionella formosa and Oscillatoria agardhii. In filtered samples RP_F was the available concentration of P.The ratio RP:RP_F may give valuable information on the ratio between total available P (including available P in seston) and available P in filtered water. Different filter types may give different RP: RP_F ratios. The ratio RP:RP_F was often high during spring and autumn in River Rømua and the lakes studied. During the period June–September RP:RP_F 1 in most of the lakes and periodically in River Rømua.     

Alkaline phosphatase activity and cellular phosphorus as an index of the phosphorus status of phytoplankton in Minnesota lakes

SUMMARY. Total alkaline phosphatase activity is inversely related to cellular phosphorus in the particulate organic matter of waters above and below the thermocline in nine Minnesota lakes. Diagnostic criteria for assessing surplus and limiting levels of phosphorus are proposed. When applied to seasonal changes in phosphorus status in Lake Josephine, they demonstrate severe phosphorus starvation in late summer and autumn.     

Sedimentary losses of phosphorus in some natural and artificial Iowa lakes

Phosphorus sedimentation in four natural and four artificial Iowa lakes was measured by using sediment traps to determine if sedimentary phosphorus losses were greater in artificial lakes than in natural lakes and the limnological factors influencing phosphorus loss rates. Mean phosphorus sedimentation rates ranged from 13.3 to 218 mg · m^–2 day^–1. Although phosphorus sedimentation rates for the natural lakes as a group did not differ significantly from the rates for artificial lakes, there were significant differences among individual lakes. Phosphorus sedimentation rates also varied significantly during different seasons at different locations within a lake and at different depths within a location. Despite the variance, phosphorus sedimentation rates were strongly correlated with inorganic sediment concentrations and inorganic matter sedimentation rates, thus suggesting that inorganic sediments influence phosphorus sedimentation rates. When Iowa data were combined with data from published studies, mean sedimentation rates were directly correlated with mean chlorophyll a concentrations of the lakes. These data strongly suggest that sedimentation rates as measured by sediment traps are strongly influenced by the trophic status of a lake. Though sedimentation rates were higher in the more productive lakes, it is suggested that these rates represent only gross sedimentation rates rather than net sedimentation rates because of resuspension and resedimentation of bottom sediments.     

Correlation between HSP90 induction kinetics in murine leukemia cells and the amount of cisplatin over a wide range of cytostatic concentrations

The induction of HSP90 in murine erythroleukemia cells, clone F4 N, by cisplatin (DDP) was examined using indirect immunofluorescence and avidin-biotin technique, and compared with cisplatin cytotoxicity. A reverse dependence of HSP90 induction time was found on a wide range of cisplatin concentrations (0.5-10 microM), which proved to be cytostatic up to 48 h of continuous treatment. Thus, the observed induction pattern of HSP90 in F4 N cells strictly correlated with their high tolerance toward DDP. This indicates that HSP90 might be responsible, at least in part, for cisplatin resistance of F4 N cells.     

Diversity and succession of the phytoplankton in a small lake over a two-year period

Phytoplankton in the small central Finnish lake, Vasikkalampi, was studied over a two-year period by weekly sampling simultaneously with monitoring of physical and chemical properties of water, solar radiation energy and zooplankton. In the present paper, the fluctuations in phytoplankton diversity were studied in relation to environmental factors. The special aim for the study was to detect a relation between environmental disturbances and phytoplankton diversity.     

Quantification of fipronil and its metabolite fipronil sulfone in rat plasma over a wide range of concentrations by LC/UV/MS

Fipronil is an insecticide extensively used to treat pets, which has been identified as a potential thyroid disruptor in the rat. In this species, fipronil is mainly metabolized to fipronil sulfone and plasma concentrations of fipronil sulfone can be at least 20-fold higher than those of fipronil. Investigations of fipronil and fipronil sulfone exposure in blood remain sparse because of the lack of convenient and suitable analytical methods. We have developed and validated an LC/UV/MS/MS method to quantify both fipronil and fipronil sulfone within a wide range of concentrations in rat plasma. The double detection UV and MS coupled on-line enabled the concentrations to be measured over a 3 Log range (2.5–2500 ng/mL). The volume of sample required for the extraction by solid phase extraction was reduced to 75 μL with a recovery higher than 70%. The two-detection method agreement, evaluated with a Bland–Altman plot, was good for concentrations between 50 and 150 ng/mL. The method was applied to monitor plasma concentrations following a commonly used dosage regimen for the toxicological evaluation of fipronil in rats.     

The causes of change in the diversity and stability of phytoplankton communities in small lakes

SUMMARY. 1. A study of the diversity and stability of phytoplankton communities during one vegetation period (February-October 1984) was carried out in four small lakes in the Pfynwald region of Canton Valais, Switzerland: Kaminsee I, Kaminsee II, Grossee and Rosensee. The diversity was calculated according to Shannon & Weaver (1949). The change in diversity ΔH; and SIMI (similarity index according to Stander. 1970) were used as measures of stability. 2. On average, the diversity was highest in the oligotrophic Rosensee (annual mean 3.19) and least in the hypereutrophic Kaminsee I (annual mean 1.34). In Kaminsee I and Grossee, the diversity corresponded in the main to the relative frequency of Cryptomonas erosa Ehrenberg: i.e. the diversity was low when the relative frequency of C. erosa was high and vice versa (Kaminsee I: max. diversity 2.74; min. 0.13. Grossee: max. 3.62; min. 0.28; annual mean 2.21). Kaminsee II and Rosensee exhibited only slight variations in their phytoplankton community structure (Kaminsee II: max. diversity 2.83; min. 1.26; annual mean 2.10. Rosensee: max. 3.79; min. 2.81). High values of diversity, or increases in diversity, were a result of low nutrient availability and grazing pressure. Lower diversity values. or decreases in diversity, were a result of a plentiful nutrient supply, low grazing pressure and grazer selectivity with respect to food organisms. 3. Because values of the diversity index vary by different amounts during the course of a year depending on the water body, the characterization of a phytoplankton community on the basis of one value alone is unsatisfactory. It is suggested that the mean and either standard deviation or range of the diversity be cited in order to overcome this drawback at least partially. 4. No generally accepted measure exists for the calculation of stability. According to the measure of stability employed, a community may appear to be more or less stable. A statement concerning the stability of a community without mentioning the measure employed is therefore worthless. The factors determining the stability of a phytoplankton community do not have the same effect on all measures of stability. 5. The change in diversity ΔH’was influenced in the main by alterations     

Thermotaxis of human sperm cells in extraordinarily shallow temperature gradients over a wide range

On the basis of the finding that capacitated (ready to fertilize) rabbit and human spermatozoa swim towards warmer temperatures by directing their movement along a temperature gradient, sperm thermotaxis has been proposed to be one of the processes guiding these spermatozoa to the fertilization site. Although the molecular mechanism underlying sperm thermotaxis is gradually being revealed, basic questions related to this process are still open. Here, employing human spermatozoa, we addressed the questions of how wide the temperature range of thermotaxis is, whether this range includes an optimal temperature or whether spermatozoa generally prefer swimming towards warmer temperatures, whether or not they can sense and respond to descending temperature gradients, and what the minimal temperature gradient is to which they can thermotactically respond. We found that human spermatozoa can respond thermotactically within a wide temperature range (at least 29-41°C), that within this range they preferentially accumulate in warmer temperatures rather than at a single specific, preferred temperature, that they can respond to both ascending and descending temperature gradients, and that they can sense and thermotactically respond to temperature gradients as low as <0.014°C/mm. This temperature gradient is astonishingly low because it means that as a spermatozoon swims through its entire body length (46 μm) it can sense and respond to a temperature difference of <0.0006°C. The significance of this surprisingly high temperature sensitivity is discussed.     

Increased risk of cyanobacterial blooms in northern high‐latitude lakes through climate warming and phosphorus enrichment

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Kinetic and thermodynamic study of the bacteriorhodopsin photocycle over a wide pH range.

The photocycle of bacteriorhodopsin and its thermodynamic parameters were studied in the pH range of 4.5-9. Measurements were performed at five different wavelengths (410, 500, 570, 610, and 650 nm), in the time interval 300 ns to 0.5 s, at six temperatures between 5 and 30 degreesC. Data were fitted to different photocycle models. The sequential model with reversible reactions gave a good fit, and the linear character of the Eyring plots was fulfilled. The parallel model with unidirectional reactions gave a poor fit, and the Eyring plot of the rate constants did not follow the expected linear behavior. When a parallel model with reversible reactions, which has twice as many free parameters as the sequential model, was considered, the quality of the fit did not improve and the Eyring plots were not linear. The sequential model was used to determine the thermodynamic activation parameters (activation enthalpy, entropy, and free energy) of the transitions and the free energy levels of the intermediates. pH dependence of the parameters revealed details of the transitions between the intermediates: the transitions M1 to M2 and N to O disclosed a large entropy increase, which could be interpreted as a loosening of the protein structure. The pH dependence of the energy levels explains the disappearance of intermediate O at high pH. A hypothesis is proposed to interpret the relation between the observed pKa of the photocycle energetics and the role of several amino acids in the protein.     

Parasite species richness in carnivores: effects of host body mass, latitude, geographical range and population density

Aim  Comparative studies have revealed strong links between ecological factors and the number of parasite species harboured by different hosts, but studies of different taxonomic host groups have produced inconsistent results. As a step towards understanding the general patterns of parasite species richness, we present results from a new comprehensive data base of over 7000 host–parasite combinations representing 146 species of carnivores (Mammalia: Carnivora) and 980 species of parasites.
Methods  We used both phylogenetic and non-phylogenetic comparative methods while controlling for unequal sampling effort within a multivariate framework to ascertain the main determinants of parasite species richness in carnivores.
Results  We found that body mass, population density, geographical range size and distance from the equator are correlated with overall parasite species richness in fissiped carnivores. When parasites are classified by transmission mode, body mass and home range area are the main determinants of the richness of parasites spread by close contact between hosts, and population density, geographical range size and distance from the equator account for the diversity of parasites that are not dependent on close contact. For generalist parasites, population density, geographical range size and latitude are the primary predictors of parasite species richness. We found no significant ecological correlates for the richness of specialist or vector-borne parasites.
Main conclusions  Although we found that parasite species richness increases instead of decreases with distance from the equator, other comparative patterns in carnivores support previous findings in primates, suggesting that similar ecological factors operate in both these independent evolutionary lineages.     

Seasonal succession and strategies of phytoplankton development in two lakes of different trophic states

This study describes the metabolism and structure of phytoplanktoncommunities during seasonal periodicity and discusses strategiesof development adopted by species during succession. The studywas conducted in two trophically different lakes. Each lakedemonstrates a different degree of the ecological succession,which prescribes an increasingly complex taxocenose. In oligomesotrophicLake Pavin the autogenic succession lasts from spring overturnuntil mid-summer. In eutrophic Lake Aydat the autogenic successionis strictly limited to spring. The seasonal changes of the communityproductivity, turnover rate (P/B) and adenylate energy chargeconfirm the hypothesis of a change of the ‘metabolic orientation’of phytoplankton cells during seasonal succession. The autogenicsuccession represents the progression from a growth-orientedstrategy to an equilibrium-oriented one.     

Prediction of phosphorus and nitrogen concentrations in lakes from both internal and external loading rates

A model predicting phosphorus and nitrogen concentrations from loading rates was tested using data collected from a shallow, nutrient-rich lake where both internal and external loading occurred. Predicted nutrient concentrations agreed closely with obaerved values and it is suggested that the model could be used to predict the reduction in loading rate required to effect lake restoration.     

Genomic compatibility occurs over a wide range of parental genetic similarity in an outcrossing plant

The theory of inbreeding and outbreeding suggests that there is a hump-shaped relationship between the genetic similarity of sexually reproducing parents and the performance of their offspring. Inbreeding depression occurs when genetic similarity is high, whereas hybrid breakdown is expected when genetic similarity is low. Between these extremes, the effect of genetic similarity on fitness is unclear. We studied the shape of this relationship by crossing 65 target genotypes of the clonal, self-incompatible Ranunculus reptans with partner genotypes spanning a broad scale of genetic similarity, ranging from crosses within populations to between-population crosses and hybridisation with a closely related species. Offspring were raised in outdoor tubs. Results revealed a quadratic relationship between parental genetic distance and offspring performance, with the clonal component of fitness more strongly hump-shaped than the sexual component. Optimal genetic similarity encompassed a broad range of within-population and between-population crosses. This pattern of genomic compatibility has important implications for the evolution of mating systems and mate choice.     

淮北采煤塌陷区小型湖泊浮游植物群落结构和季节动态

深入了解煤矿塌陷湖泊生态系统的结构与功能,有助于开展淮北煤矿塌陷水域的生态保护和资源的可持续利用。该文从2005年3月至2007年2月,研究了淮北采煤塌陷区两个小型湖泊(南湖和乾隆湖)浮游植物的群落结构和季节动态。结果表明:乾隆湖中总氮和总磷的浓度均高于南湖。蓝藻和绿藻均为南湖和乾隆湖的优势类群,其总和分别约占两湖泊年平均总浮游植物生物量的69.8%和63.3%,且南湖浮游植物生物量明显低于乾隆湖。另外,南湖夏季出现了以铜绿微囊藻(Microcystis aeruginosa)为主的蓝藻水华,而富营养湖泊中常见的微囊藻属(Microcystis)和水华束丝藻(Aphanizomenon flos-aquae)等蓝藻种类在乾隆湖中没有被观察到。除营养盐、温度外,鱼类和硬度水质可能是影响淮北采煤塌陷区小型湖泊浮游植物群落演替和生物量季节变化的重要原因。     

Seasonal and inter-annual scales of variability in phytoplankton assemblages: comparison of phytoplankton dynamics in three peri-alpine lakes over a period of 28 years

1. A method based on hierarchical clustering and Bayesian probabilities is used to identify phytoplankton assemblages and analyse their pattern of occurrence and temporal coherence in three deep, peri‐alpine lakes. The hierarchical properties of the method allowed ranking by order of importance of the effects of changes related to climate and to human activity on the phytoplankton structure. 2. The three deep, peri‐alpine lakes (the Lower Zurich, Upper Zurich and Walen lakes) investigated in this study have been monitored since 1972. During that period they have undergone oligotrophication as a result of management programmes and they have been subject to similar meteorological effects that have led to higher water temperatures since 1988. 3. The phytoplankton assemblages of the most eutrophic lake (Lower Zurich) differ strongly from those observed in the two meso‐oligotrophic lakes. Local environmental conditions appear to be the main factor responsible for species composition and change in climate characterised by the warmer water temperatures observed since 1988 have had a major impact on the winter composition of the lower basin of Lake Zurich by promoting Planktothrix rubescens. 4. Some phytoplankton assemblages are found in all the lakes. Their patterns of occurrence display strong synchrony at the annual and/or inter‐annual scales. However, temporal coherence between the lakes sometimes also involves different assemblages. 5. The reduction in phosphorus had a great influence on long‐term changes in composition. In all three lakes, decreases in phosphorus are associated with a community characterised by some mixotrophic species or species adapted to low nutrient concentrations or sensitive to transparency. In the Lower Lake Zurich the decrease in phosphorus has also led to the development of species adapted to low light intensities. 6. Seasonal meteorological forcing has also induced synchronous changes, but the same assemblages are not necessarily involved, because the pool of the well‐placed candidate taxa that may develop is determined by the local environmental conditions, and mainly by phosphorus concentrations. In the most eutrophic lake, the seasonal pattern is characterised by a succession of more stages. However, the seasonal assembly dynamics involve the succession of species sharing common selective advantages that make them relatively stronger under these nutrient and light conditions.