Approche discriminante de contributions de différents échelons microplanctoniques aux mesures globales d'ETS dans des échantillons de mer. b. Bacteria

Discriminating approach of various microplanktonic-stage contributions to whole electron transport system (ETS) measurements in sea-water sampless. b. Bacateria Data obtained from cultures of natural bacterial populations were applied to various water samples in order to determine both the phytoplanktonic and bacterial contributions to whole ETS water-sample measurements. The bacterial part was estimated both by cell enumerations and HPLC muramic-acid measurements and the phytoplankton contribution by enumeration and chlorophyll levels. An appropriate first-order equation is adequate to low carbon content samples but must be corrested for highly organic loaded samples in order to obtain a better adjustment between the sum of the “estimated” phytoplanktonic and bacterial ETS and the really-measured ETS concentrations in the water samples.     

Standing crop densities and distribution of Spirulina and benthic diatoms in East African alkaline saline lakes

SUMMARY. The diversity of Eastern Rift Valley alkaline saline lakes is illustrated and their temporal fluctuations in ionic concentration are emphasized.
The standing crop densities of phytoplanktonic blue-green algae of the genus Spirulina and benthic diatoms were measured. Spirulina abundance was measured as dry mass density and the validity of the gravimatric estimates was checked by chlorophyll analysis and microscopic counting. Benthic diatom standing crops were assessed by chlorophyll determinations. Spirulina density is extremely variable in time and may fluctuate over more than an order of magnitude. High density blooms of Spirulina are not a common characteristic feature of these lakes. The causes of changes in Spirulina standing crop and the associated alterations in the structure of the primary producer community are discussed and three qualitative states which may occur are described.
Similar standing crops of benthic diatoms (mean 45 mg m⁻² of chlorophyll-α) were found at all lakes wherever the water depth was shallow enough to allow light penetration to the sediment surface.     

Eutrophication impacts on a river macrophyte

The postulated relationship between eutrophication, enhanced standing macrophyte crop and flow impedance was assessed in 14 rivers across the UK. We sampled the July standing crop of Ranunculus subgenus Batrachium at 14 rivers across England and southern Scotland, at sites where there is a known relationship between standing crop and flow impedance. We relate standing crop to variation in carbon concentrations and to elevated phosphorus concentrations, using regression analysis. Standing crop increased significantly with P availability as soluble reactive phosphorus (filtered SRP) and total phosphorus (TP). Best subsets multiple regression analysis suggests that, based on this sample of sites, there is evidence that macrophyte biomass increases with SRP concentrations and also increases with the amount of carbon as HCO₃ for a given concentration of SRP in the water. Thus eutrophication is found to increase the standing crop of a submerged aquatic plant in UK rivers. Current targets for P reduction may not be sufficient and managers should now also recognise that eutrophication can exacerbate flood risk by elevating macrophyte standing crop.     

Influence de la spéciation du cuivre sur les populations phytoplanctoniques naturelles de la rivière du Saguenay,Québec,Canada Influence of Copper in Various Forms on Natural Phytoplanktonic Populations from the Saguenay River,Quebec, Canada

In 1981, experiments to study the toxicity of copper in its ionic, complexed (to humic acid) and adsorbed (on cellulose fibers from a local paper mill) forms on species composition, standing crop, and photosynthesis of phytoplankton were conducted in chemostats with natural aggregations composed mainly of either green algae or of diatoms from the Saguenay River. In the aggregations of green algae, the rates of primary production were more strongly inhibited by copper than were the chlorophyll a concentrations, whereas the cell numbers, standing crop and rates of primary production of the diatoms were all strongly inhibited by copper.     

Struttura e biomassa dei popolamenti fitoplanctonici del Lago Omodeo (Sardegna centrale)

Abstract

Composition and biomass of phytoplanktonic communities of Lago Omodeo (Central Sardinia).—A qualitative and quantitative study has been made on the phytoplankton of Lago Omodeo. The algal associations are typical of eutrophic waters. The dominant blue-green algae in summer and autumn were: Chroococcus dispersus, Microcystis flos-aquae, Aphanizomenon flos-aquae, Anabaena flos-aquae, Anabaena planctonica; dominant in winter and spring the diatom Melosira distans. The mean standing crop of algae for the trophogenic zone was 9.2 mm³/l; a maximum crop of 53 mm³/l was recorded in August during a Microcystis bloom.     

A study of spatial and temporal variability in the adenine nucleotides of lake phytoplankton during a diel cycle (Lac Pavin — France)

A study of diel variations in the adenine nucleotide concentrations of natural phytoplanktonic populations led to the following conclusions:There are significant diel variations in cellular ATP concentrations. However, this temporal variability is not as great as the spatial variability between the various sampling depths, characterized by different phytoplankton populations. Within a globally stable pool of adenine nucleotides, diel variations inside the algal cell mainly take place at the expense of ATP and AMP, while ADP concentrations remain relatively stable.The statistical relationship between algal biomass obtained from cell counts and from adenine nucleotides also confirms maximum stability for ADP and (ATP + ADP + AMP). The diel variations in adenine nucleotide cell concentrations gradually become smaller with depth. This probably reflects the importance of light in causing such variability.     

Dynamic of phytoplankton size-class and photosynthetic activity in a tropical hypereutrophic lake: the Yaounde municipal lake (Cameroon)

This study carried out within the framework of a multi-disciplinary project, aimed at highlighting the fundamental processes governing the functioning of the hypertrophic Yaoundé Municipal Lake. It was based on the hypothesis that, even within a small range of lake trophic status, important variations can occur in the species composition, biomass and photosynthetic activity of the phytoplankton size-fractions. For this purpose, samples were taken at weekly intervals from November 1996 to December 1997 at a fixed set of depths in the water column. Spatial-temporal fluctuations of some physical–chemical variables, associated with biological variables such as phytoplankton size-class species composition, phytoplankton size-class biomass, phytoplankton primary production and chlorophyll-a were analysed. The water transparency was low and rarely exceeded 100 cm. Conductivity values relatively higher increased generally from the top to the lake bottom. The oxygen deficiency, and sometimes anoxia, recorded from 2.5 m depth resulted in high quantities of ammonium nitrogen. Total phosphorus and total Kjeldahl nitrogen concentrations were characteristics of hypertrophic lakes. The fertility of this biotope favoured the development of a high phytoplanktonic community with remarkable physiological adaptations to the variations of the nutritive potentials of the lake, characterized by the size-structure of these organisms. Cells of small size (<12 μm) contributed up to 11.42% of the total phytoplanktonic biomass. Species with average size (12–45 μm), dominated by Chlamydomonas spp., represented a more significant contribution reaching up to 69.85%, whereas the cells of big size (>45 μm), mainly Euglenophyta, maintained the relatively most important biomass, accounting for up to 89.85% of the total phytoplanktonic biomass. Chlorophyll-a concentrations are among the highest reported for both fresh water and sea water, being a consequence of high proportions of Chlorophyta and Euglenophyta. This led to intense phytoplanktonic photosynthetic activity which continued throughout the year, even though it was confined to the upmost first meter of the water column. Analyses pointed out the allogenic nature of the functioning of this urban lake ecosystem, due to a poor waste management on the surrounding landscape. Handling editor: J. Padisak     

Variations circadiennes des acides aminés libres de l'hemolymphe de Penaeus japonicus

The non-essential free amino acids of Peneaus japonicus hemolymph (asp, ser, glu, pro, gly, tyr, arg, ala, cys, tau) are more common than the essential ones: 750 pmol μl^?1 of hemolymph vs 330 pmol. Under a light-dark (L-D); 12-12 photoperiod, tricircadian variations of males or tetracircadian variations of females are more pronounced for non-essential amino acids then for essential ones. In the first case, free amino acid concentrations of hemolymph can be multiplied by a factor of three, and in the second case by a factor of six; but circadian variations of females are greater than those of males. Differences between the maximum and minimum of essential free amino acid concentrations of male and female hemolymph are more frequent than for non-essential amino acids. A differences of 2 h between the minimum of essential and non-essential amino acid concentrations in males only appeared during the afternoon. The more concentrated free amino acids in P. japnicus hemolymph are glycine, proline, histidine, and alanine; the less concentrated are lysine, cysteine and glutamic acid while others, like leucine, isoleucine, phenylalanine and tyrosine can only be estimated at 10.00 and 24.00 h.     

青藏高原高寒草原根系动态对氮添加的响应及其调控因素

本研究于2015—2016年进行野外控制试验,分析了不同施氮(N)水平(0、1、2、4、8、16 g N·m^-2·a^-1)对青藏高原高寒草原根系生产、周转速率和现存量的影响及其调控因素。结果表明: 随着施N量的增加,根系生产量和现存量呈线性或指数下降的趋势。与对照相比,16 g N·m^-2·a^-1处理根系生产量和现存量2年平均下降43.0%和45.7%。根系周转速率呈先上升后下降的趋势,2015年和2016年分别在2和4 g N·m^-2·a^-1处理达到峰值。线性混合模型结果显示,根系淀粉含量是调控根系生产量和周转速率的主要因素,分别解释二者变异的21.7%和25.4%;而根系现存量则受根系蛋白含量的影响,其解释率为20.8%。N富集对根系生产和现存量表现出抑制作用,低N促进而高N抑制根系周转速率,根系碳氮代谢指标是调控根系动态对N添加响应的主要因素。     

Contribution a l'etude limnologique du lac pavin (France) I: Facteurs abiotiques et phytoplancton

Located at 1197 m in the Massif Central Français, lake Pavin has a volcanic origin. It is a dimictic and meromictic lake of 44 ha of area and 92 m depth. Samples were collected bimonthly at 8 depth (0 to 40 m) from May 1973 to April 1974. Physicochemical parameters (light energy, temperature, pH, conductivity, Oxygen, Nitrogen, Phosphorus, Silice, Carbon) and dynamics of phytoplanktonic populations (cells counts, standing crop, primary production, photosynthetic pigments) were studied.The waters of this lake are clear, with low conductivity and high concentrations of oxygen in the first 40 meters. In a water column, 0–40 meters, the means of nitrogen concentrations are between 45 and 279 µg/l and between 0 and 161 µg/l for phosphorus. Phytoplankton is caracterised by an important development of Diatoms (Melosira italica subsp. subarctica and Asterionella formosa) in winter and spring, opposed to low standing crops of Chlorophycea (Coenococcus, Sphaerocystis, Chlamydomonas) in summer. The annual mean of primary production is about 360 mg C ass./m².J. The highes values of the activity coefficient (P/B) are found during the development of Chlorophycea, but photosynthetic efficiency is maximum in winter for Diatom populations.To summarize physico-chemical parameters and phytoplankton relationships, a synthetical mathematical model was made by Principal Components Analysis.

     

Ammonium formation in cape timiris (Mauritania) upwelling

Ammonium formation was studied in two consecutive years by following a newly upwelled ammonium-free ‘parcel’ of water with a drogue. High concentrations (> 2 μg-at. NH₄-N l^?1) were found at the end of each study. The relative importance of WP-2 net mesozooplankton excretion on the ammonium values is greater before the phytoplanktonic bloom (35–48%) than during it (10–16%). From carbon grazing estimates, it is shown that other herbivore excretion does not take the place of WP-2 mesozooplankton and because of synchronous variations of chlorophyll with dissolved organic nitrogen, and bacterial activity with ammonium, it is suggested that much of the ammonium is produced from phytoplankton decay or nitrogen excretion during the bloom.     

CARBON,NITROGEN, AND PHOSPHORUS AND THE EUTROPHICATION OF FRESHWATER LAKES1

The question of nutrients responsible for eutrophication of freshwater lakes is reviewed, and recent additions to the literature on nutrient limitation are discussed. The paper by Lange is criticized on several grounds, including the facts that utilization of HCO₃^? by phytoplankton and the invasion of lake waters by atmospheric CO₂ are ignored as sources of photosynthetic carbon. The phosphorus and nitrogen concentrations used in Lange's experiments are far higher than values published by others for Lakes Erie and Ontario. Preliminary results of fertilizing a small oligotrophic lake with nitrogen and phosphorus are described. The standing crop of phytoplankton increased by 30–50 ×, while the P:N:C ratio in seston did not change from ratios found in unfertilized lakes. Other experiments done in water columns isolated with polyethylene film showed that addition of carbon did not increase the phytoplankton standing crop. Since the fertilized lake was initially lower in total CO₂ than any other recorded in the literature, it is concluded that carbon is unlikely to limit the standing crop of phytoplankton in almost any situation. Measurements of invasion of atmospheric gases to the fertilized lake by the Rn²²² technique were compared with phytoplankton production measurements, revealing that atmospheric invasion of CO₂ is sufficient to support the high phytoplankton standing crop in the epilimnion of the lake. Possible errors in interpretation of culture and bottle-bioassay experiments with respect to eutrophication are discussed.     

Distribution and faunal associations of benthic invertebrates at Lake Turkana,Kenya

The benthic environment and fauna of Lake Turkana were studied during 1978–1979 to determine distribution patterns and associations of benthic invertebrates. Lake Turkana is a large, closed-basin, alkaline lake, located in northern Kenya.Detailed environmental information is currently only available for substrate variations throughout Lake Turkana. Water chemistry and other data are currently inadequate to evaluate their effects on the distribution of Lake Turkana benthic invertebrates. Three weak faunal-substrate associations were discovered at Turkana. A littoral, soft bottom association (large standing crop) is dominated by the corixid Micronecta sp. and the ostracod Hemicypris kliei. A littoral, rocky bottom association, also with a large standing crop, is dominated by various gastropods and insects. A profundal, muddy bottom association, with a very small standing crop, is dominated by the ostracods Hemicypris intermedia and Sclerocypris cf. clavularis and several gastropod and chironomid species.     

Feedback regulation of constant leaf standing crop in Sasa tsuboiana grasslands

The standing crop of current leaves of Sasa tsuboiana was measured on the upper slopes of Mount Horai, Shiga prefecture, central Japan. Upper one-year-old branches in the canopy produced greater mass of current leaves than lower ones. Furthermore, culms in artificially thinned plots produced larger leaf mass per culm than those in control plots. These results reveal that leaf production is positively correlated with light intensity. Therefore, when the leaf standing crop in a given year is somewhat smaller than usual, it may increase in the following year because the branches will receive stronger light. This feedback regulation causes uniformity in the horizontal distribution of the leaf standing crop. The constancy of the leaf standing crop throughout dense stands of different heights indicates that a common equilibrium value of the leaf standing crop exists. This uniform distribution leads to an almost-uniform weak light intensity under the canopy of S. tsuboiana, and can consequently exclude other plant species.     

Approche discriminante de la contribution de différents échelons microplanctoniques aux mesures globales d'ETS dans des échantillons d'eau de mer. a. Phytoplancton

Discriminating Approach of Various Microplanktonic-stage Contributions to Whole ETS Measurements in Sea-water Samples. a. Phytoplankton Data obtained from algal cell cultures were applied to various sea water samples in order to estimate the specific contribution of phytoplanktonic organisms to whole ETS (electron transport system) measurements of these samples which have been collected at eleven stations in the northwest Mediterranean Sea. When the phytoplankton ETS contributions were quantified by cell enumerations or by other indirect-biomass-indicator measurements, the results are in good accordance to the recorded ETS measurement values of the sample. More specific of the phytoplankton stage is the index used for such an estimation (as chlorophyll a), and better is the relationship between both estimated and measured ETS values.     

An alternative method of flax retting during dry weather

During exceptionally dry and hot weather undesiccated flax (Linum usitatissi-murri) and flax desiccated with glyphosate that was pulled and laid on the ground to dew-ret, retted 1–2 wk before flax that was desiccated and left as a standing crop. This was because dew-retted flax was colonised by fungi faster than that left standing. Cladosporium herbarum, Epicocum nigrum and yeast, including Aureoba-sidium pullulans, appeared first; they were followed by Alternaria alternata, Fusarium culmorum and Phoma, Mucor and Rhizopus species. The standing crop retted more slowly despite the presence of greater concentrations of cell-wall degrading enzymes. However, the fibres of flax retted as a standing crop retained more of their strength than those of flax retted on the ground. Thus dew-retting provides means of retting when the weather is dry and hot.     

HIGH-RESOLUTION AIRBORNE REMOTE SENSING OF BLOOM-FORMING PHYTOPLANKTON1

Remote sensing of highly turbid finfish aquaculture impoundments using the Calibrated Airborne Multispectral Scanner (CAMS) mounted on a Lear jet flown at 900 m was conducted in central Mississippi on 16 May 1990. Concurrent in situ data consisted of phytoplankton pigment concentrations and standing crop, water color, turbidity, and surface-water temperature. Surface and near-surface assemblages of cyanophytes and chlorophytes varied dramatically among impoundments; total chlorophyll concentrations and standing crop values ranged from 8 to 483 mg·m^?3 and 8.0 × 10² to 2.2 × 10⁶ cells-mL^?1, respectively. Regression models fit to CAMS data provided reliable estimates for and produced accurate digital cartographs of total chlorophyll and carotenoid concentrations, phytoplankton standing crop, and turbidity. Although a model to effectively estimate in situ c-phycocyanin concentrations was not identified, the lack of a suitable model may have resulted from variability of pigment extraction during quantification rather than failure of remotely sensed imagery to detect c-phycocyanin. Models derived from imagery of impoundments directly beneath the aircraft sufficiently described in situ parameters in imagery of adjacent series of impoundments not directly below the aircraft. High-resolution airborne remote sensing provides a means for monitoring local phytoplankton dynamics in temporal and spatial scales analogous to biotic and abiotic processes affecting such dynamics and necessary for applications to ecological research and fisheries or aquacultural management.     

Long-term Dynamics of Benthic Invertebrate Standing crop Palos Verdes Shelf,Southern California

Wet weight standing crop of macrobenthic invertebrates from the Palos Verdes Shelf, California showed several major fluctuations from 1972 to 1986, mainly due to the bivalve Parvilucina tenuisculpta and the echiuroid Listriolobus pelodes. From 1972 to 1986 mean biomass was 285 g/m². When this value was compared with standing crop from other shelves, Palos Verdesstanding crop fell within the range documented for the tropics to higher latitudes. There was a small decline with increased effects of El Nino in 1983. When Palos Verdes standing crop was compared to the biomass portion of the Pearson-Rosenberg SAB curve, it was concluded that their model is probably not applicable on this portion of the shelf. Finally, the long-term data base provided the opportunity to propose several hypotheses. These concerned the potential effect of L. pelodes on species diversity and hydrogen sulfide in the sediment and the influence of L. pelodes on excess standing crop.     

Litter standing crop of shrubland ecosystems in southern China

Aims Litter is an important component of terrestrial ecosystems, which plays significant roles in carbon and nutrient cycles. Quantifying regional-scale pattern of litter standing crop would improve our understanding in the mechanism of the terrestrial ecosystem carbon cycle, also with help in predicting the responses of carbon cycle of terrestrial ecosystems to future climate change. Our objective was to examine variation in litter standing crop of shrublands along the environmental gradients in southern China.
Methods During 2011-2014, we investigated the litter standing crop at 453 shrublands sites by the stratified random sampling, reflecting climatic and soil attributes across southern China.
Important findings We found that the mean value of litter standing crop in these shrubland ecosystems across southern China was 0.32 kg·m^-2. It was 68% of forest litter standing crop (0.47 kg·m^-2) and was five times higher than that in grasslands (0.06 kg·m^-2) in China. Litter standing crop increased with latitude. Our results showed that litter standing crop was negatively correlated with mean annual temperature, soil total P and soil pH, but not significantly correlated with other environmental variables, including mean annual precipitation, soil carbon, nitrogen and soil organic matter. The conversion coefficient of carbon in litter standing crop was 0.41, which is significantly lower than that of vegetation in shrublands (0.50), resulting in an overestimate in carbon storage of litter standing crop in shrubland up to 22% by applying wrong conversion coefficient. We concluded that litter standing crop of shrublands is an important component in terrestrial ecosystems. Mean annual temperature was the most important environmental variable, accounting for the variation in litter standing crop of shrublands in southern China. To our best of knowledge, this is the first study to quantify variation in litter standing crop of shrublands at the regional scale. Therefore, our study will have important implications for assessing the carbon budget of terrestrial ecosystems in China.     

Spatial variation in epilithic algae in a stony stream (Wilfin Beck) with particular reference to Cocconeis placentula

SUMMARY. Epilithic algae in a small softwater stream in the English Lake District were studied using a direct counting epifluorescence technique. A small trickling filter sewage treatment plant discharged into the stream and cattle grazed in fields adjoining the upper reaches. Both increased the inorganic nitrogen and phosphorus concentrations in the stream but the effect of the cattle was of a more intermittent nature. Cocconeis placentula was the dominant diatom but large numbers of encrusting green, blue-green and red algae also occurred in samples from the middle reach, which was heavily shaded by trees in summer. Although it was possible to demonstrate the effect of the sewage effluent on the rate of colonization of clean surfaces placed in the stream, it was only during periods of stable water flow that this was reflected in the standing crop of algae on the stones. The Cocconeis counts below the sewage outfall tended to be highest in the autumn whereas those of the other diatoms were highest in the spring. The results were, however, extremely variable and apart from the effect of the nutrient inputs, the Cocconeis standing crops were largely related to the rate of water flow. Counts decreased and the variability between and within stones increased as higher rainfall and flow caused instability and scouring of the stones. A similar decrease in standing crop and high variability occurred in conditions of very low water flow but this could not be explained.