bluuebunny/crossref_metadata_2025_split huggingface dataset:
Release of extracellular organic carbon during a diatom bloom in Lake Mossö: molecular weight fractionation
Authors: SöNDERGAARD MORTEN , SCHIERUP HANS‐HENRIK 
Published: May 2006

SUMMARY. Carbon fixation and release of extracellular organic carbon (EOC) during a diatom bloom were measured by the 14C—technique. Release in light was always a small fraction (1.5‐6.0%) of total carbon fixation. Maximum values were found during the stationary phase of growth. A larger (15–50%) fraction of the inorganic carbon assimilated in the dark was released, although the absolute values were lower than in the light.Gel permeation chromatography showed that low molecular weight products (<700 daltons) dominated EOC released in the light. A shift toward more complex molecules (> 10,000 daltons) was found in the stationary phase. EOC released in the dark had almost equal amounts of low (< 700 daltons), intermediate (˜5,000 daltons) and high (< 10,000 daltons) molecular weight products.It is shown that with time the molecular weight composition of EOC shifted towards a predominance of larger molecules.
Photosynthetic activity and respiration in an equatorial African soda lake
Authors: MELACK JOHN M. 
Published: May 2006

SUMMARY. Photosynthetic activity and respiration in Lake Sonachi (Kenya), a meromictic soda lake lying in a volcanic crater, were measured through diel cycles during a 15‐month period. A pattern of thermal stratification in the morning and mixing in the afternoon and night occurred in the mixolimnion. Diel variations in dissolved oxygen at 50 cm were 2.2–7.5 mgO2 1‐11% of the incident photosynthetically available irradiance (PAR) reached a depth of 1.3–2.4 m and, as a consequence, the steepest thermal gradients and highest oxygen concentrations occurred in the top 1–2 m.Vertical profiles of dissolved oxygen were used in three ways to estimate photosynthetic and respiration rates. Changes in dissolved oxygen at the depth of maximal photosynthesis (c. 50 cm) during mid‐morning were corrected for vertical diffusion to determine net free water oxygen increases of 70‐1800 mg O2 m‐3 h‐1 Variations in areal oxygen content at successive intervals throughout the day and night were corrected for air‐water oxygen exchange to calculate net free water oxygen change per h. Maximal rates of increase (550–4850 mg O2 m‐2 h‐1) usually occurred in late morning or early afternoon; maximal rates of decrease (440–2600 mg O2 m‐2 h‐1) were common at sunset. The correction for air‐water exchange was usually small because of the low wind speeds and the nearness to saturation of the surface water. Summation of daytime and night‐time rates of oxygen change provide estimates of net (‐3.4–12 gO2 m ‐2) and gross (‐0.7‐18.7 g O2 m‐2) daily photosynthesis and respiration (0.8‐7.2 gO2 m‐2).Photosynthetic rates of bottled samples ranged from 150 to 870 mgO2m ‐2h ‐1 and 1.4 to 6.8 g O2, m‐2 day ‐1The efficiency of utilization of PAR incident on the lake surface varied from 1.0 to 7.2 mmol O2E‐1 periods with higher irradiance typically had lower efficiencies.Free water estimates of photosynthesis usually exceeded the rates measured in bottles. For example, net, free water changes per hour were 1.2–10 times higher than gross areal rates per hour in bottles.Photosynthetic activity in Lake Sonachi in 1973 and 1974 was modest when compared to other tropical African soda lakes.
Behavioural responses of Biomphalaria glabrata(Say) to chemical factors from aquatic macrophytes including decaying Lemna paucicostata(Hegelm ex Engelm)
Authors: STERRY P. R. , THOMAS J. D. , PATIENCE R. L. 
Published: May 2006

SUMMARY. 1. The behavioural responses of the freshwater pulmonate snail Biomphalaria glabrata to homogenates of various aquatic macrophytes were investigated with the aid of diffusion olfactometers.2. Of the eleven species studied, three lacked any attractants or arrestants, two contained weak arrestants, and three induced strong repellent effects. Only two, Apium nodiflorum and Lemna paucicostata, induced significant attractant and arrestant effects comparable to those obtained with lettuce (Lactuca sativa) controls.3. Decaying Lemna paucicostata homogenate proved to be a significantly stronger attractant and arrestant than fresh homogenate. Evidence is given that these effects are mainly due to low molecular weight compounds (<1000 mol. wt) of which the major end products of microbial decomposition, short chain carboxylic acids (C2‐C5), are likely to be the most important. However, as carboxylic acids account for only a fraction of the total response, other low and high molecular weight compounds are also implicated.4. The ecological relevance of these results is discussed with particular reference to the hypothesis that the relationship between the snails and macrophytes is essentially mutualistic.
Evidence for the production of extracellular herbivore deterrents by Anabaena flos‐aquae
Authors: OSTROFSKY M. L. , JACOBS F. G. , ROWAN J. 
Published: May 2006

SUMMARY. 1. Daphnia pulex grown in the cell‐free filtrate of a log phase culture of Anabaena flos‐aquae showed lower fitness as measured by filtering rate, survivorship and reproduction than did individuals in a control treatment. This suggests that the extracellular metabolites of some algae may have considerable adaptive value as a herbivore deterrent.2. Heating of the cell‐free filtrate neutralized the inhibitory effect on filtering rate, but increased the depression of reproduetive rate. This suggests the presence of a variety of bioactive compounds which may inhibit specific herbivore functions.
The colonization of ball‐clay ponds by macroinvertebrates and macrophytes
Authors: BARNES LAURIE ELIZABETH 
Published: May 2006

SUMMARY.1. The rate and nature of colonization of ball‐clay ponds by aquatic macrophytes and macroinvertebrates were studied by comparing communities present in a scries of ten ponds of similar dimensions, but of different ages, ranging from 6 months to 15 years.2. Multivariate analyses of the biotic data distinguished between‘neutral’and‘acid’ponds; further analyses concentrated on the former type.3. Initial colonization of neutral ponds was rapid with a predictable sequence of species arrival, probably reflecting short dispersal distances. Variations in macroinvertebrate invasion times were related to dispersal strategy and ability. As the pond aged, successional changes, linked with macrophyte colonization, produced a shift in dominance from algivores and predators towards epiphyton grazers and detritivores. Some evidence of succession of species within invertebrate orders was found.4. Low pH affected colonization principally by preventing the establishment of acid‐intolerant immigrant species, but also by retarding succession.5. It is concluded that non‐interactive models of insular colonization, with constant immigration and extinction rates, are of limited applicability to pond colonization in temperate areas.
Diel aspects of the thermal structure and energy budget of a small English lake
Authors: FREMPONG E 
Published: May 2006

SUMMARY. The did response of the thermal structure of Esthwaite Water to prevailing meteorological conditions was analysed for seven selected days, covering different phases of stratification. Meteorological measurements were combined with published empirical relations to compute 24‐h thermal energy budgets for 2 days. Amplitudes of diel changes were controlled by the seasonal phase of stratification and the magnitude of incident solar radiation. Heat storage usually followed a sinusoidal curve with a minimum during the night and early morning and a maximum during the late afternoon. Wind‐induced turbulent mixing, and vertical circulation induced by nocturnal cooling of the surface water through evaporative and conductive processes, also modified depth‐time trends in thermal structure.The budget accounted for almost all the thermal energy exchanges of the lake. Possible sources of a slight imbalance are considered. Although there was a positive daily surplus of net radiation, it may not always imply heat gain by the lake as it may be counter‐balanced by heat losses through fluxes of latent and sensible heat, Net back‐radiation was a major component of daily heat loss. The combined latent and sensible heat fluxes also accounted fora high proportion of heat loss to the atmosphere. Net flow of sensible heat to the lake was small but not always inappreciable. Net daily heat storage represented 26% (9 May) and 13% (17 June) of solar radiation Input. Advected energy due to lake inflow and outflow was negligible. Qualitative comparisons are made with long‐term (seasonal and annual) energy budgets and heat fluxes.
A laboratory simulation of diel changes affecting cellular composition of the dinoflagellate Ceratium hirundinella
Authors: FREMPONG E. 
Published: May 2006

SUMMARY. Changes of cellular composition of a planktonic dinoflageilate, Ceratium hirundinella, were studied over 2–1–48‐h periods in the laboratory on three separate occasions. Samples from a lake population in the stationary phase of the population cycle were incubated at lake temperature under continuous illumination and in a light‐dark (LD) regime of LD 14:10.The magnitudes of diel variability in ratios of carbohydrate:chlorophyll‐a, carbohydrate:carbon. carbon:nitrogen and carotenoids:chlorophyll‐a for samples incubated at LD 14:10, were similar to those observed in situ at a similar phase of the population growth cycle. The ratios involving carbohydrate showed the most diel variation, which was not reduced under continuous illumination.By appearance ‘dark’ and ‘pale’ cells of Ceratium were distinguished in the fixed samples; a persistent periodicity for the interconversion of dark and pale cells is described. The periodicity and amplitude of inter‐conversions were not always in phase with those of chlorophyll‐a synthesis and decomposition. The observed changes were almost certainly independent of the light‐dark cycle: they were apparently induced by nutrient deficiency.
Optimal reproductive strategies in age‐structured populations of zooplankton
Authors: DORAZIO ROBERT M. , LEHMAN JOHN T. 
Published: May 2006

SUMMARY. We describe a model of zooplankton population dynamics that accounts for differences in mortality and physiology among animals of different ages or sizes. The model follows changes in numbers of individuals and changes in individual and egg biomass through time and it expresses mortality and net assimilation as functions of animal size.We investigated the effect of egg size, age at first reproduction, and size at first reproduction on the per capita growth rates of populations growing under different conditions. In the absence of predation or when exposed to vertebrate predators that prefer large prey, populations achieve maximum growth rates when animals hatch from small eggs and reach maturity quickly at small sizes. Populations exposed to invertebrate predators that concentrate on small animals may increase r in two different ways. One way is for animals to increase juvenile survivorship by hatching from large eggs and by shortening the juvenile period. An alternative strategy is for animals to hatch from small eggs and to postpone maturity until they grow beyond the range of sizes available to their predators. Certain life history strategies maximize r if animals continue to grow after they reach maturity. By growing larger, non‐primiparous females are able to hatch larger clutches and thereby increase the overall rate of population growth.The model analysis shows how to assess age‐dependent mortality rates from field data. The net rate of population increase and the age distribution of eggs together provide specific, quantitative information about mortality.
Continuous ammonium enrichment of a woodland stream: uptake kinetics, leaf decomposition, and nitrification
Authors: NEWBOLD J. DENIS , ELWOOD JERRY W. , SCHULZE MEL S. , STARK ROBERT W. , BARMEIER JUDY C. 
Published: May 2006

In order to test for nitrogen limitation and examine ammonium uptake by stream sediments, ammonium hydroxide was added continuously at concentrations averaging 100 μg1‐1 for 70 days to a second‐ order reach of Walker Branch, an undisturbed woodland stream in Tennessee.
Ammonium uptake during the first 4h of addition corresponded to adsorption kinetics rather than to first‐order uptake or to Michaelis‐ Menten kinetics. However, the calculated adsorption partition coefficient was two to four orders of magnitude greater than values reported for physical adsorption of ammonium, suggesting that the uptake was largely biotic.
Mass balance indicated that the uptake of ammonium from the water could be accounted for by increased nitrogen content in benthic organic detritus. Nitrification, inferred from longitudinal gradients in NO3, began soon after enrichment and increased dramatically near the end of the experiment.
Both ammonium and nitrate concentrations dropped quickly to near background levels when input ceased, indicating little desorption or nitrification of excess nitrogen stored in the reach.
There was no evidence of nitrogen limitation as measured by weight loss, oxygen consumption, phosphorus content, and macroinvertebrate density of red oak leaf packs, or by chlorophyll content and aufwuchs biomass on plexiglass slides. A continuous phosphorus enrichment 1 year earlier had demonstrated phosphorus limitation in Walker Branch.
The macroinvertebrate fauna of the drainage channels of the Gwent Levels, South Wales
Authors: CLARE P. , EDWARDS R. W. 
Published: May 2006

SUMMARY. From a survey of the fauna at sixty sites in permanent drainage channels of the Gwent Levels during the spring of 1976 and at some of these sites (thirty‐three) during the autumn, speeies and site associations were identified using classification and ordination techniques. Sites in some groups had identifiahly similar environmental characteristics and grouping seemed particularly related to the vegetational stage in the hydrosere, water How and the incidence of salt contamination from the Severn Estuary. Characteristics which were common within particular species groups and whieh, in part, explained their distributions were: adaptation to low oxygen concentrations, food preferences and dispersal mechanisms.Whilst there was some temporal stability in site groups between the spring and autumn surveys, such associations were not idenlical. The oxygen status of channels appeared a major factor determining faunal distribution.Twelve sites, representing a range of channel types, were sampled six times in a 12‐month period. Far more species were colleeled within the water column and on plants than in the benthos. Several oligochaetes, e.g. Aulodrilus pluriseta, Dero digitata, Limnodrilus claparedeanus, were not recorded at most sites during the summer probably because of the SUStained lack of oxygen at these sites.Three contiguous reaches of channel were maintained during the period March—October 1977 with different plant cover (no Lemnu; complete Lemna cover: control with partial Lemna cover). The oxygen status of the reaches was different, that with complete Lemna cover being continuously anaerobic near the channel bed for several months, the control reach which had partial Lemna cover being anaerobic for a shorter period and that with no Lemna being only anaerobic at night. Whilst the distribution of macroinvertebrate species was prineipally related to this oxygen status, the control reach whieh was strueturally the most complex, having both submerged and floating plants, contained about twiee as many species as the other reaches during the summer (colleeted in the water column and on plants): benthic samples in this and the reach with complete Lemna cover contained only between zero and two species during the period May‐ September.
Effects of concentrating phytoplankton on the acetylene‐reduction assay for nitrogenase activity
Authors: LEONARDSON LARS 
Published: May 2006

SUMMARY.

The consequences of concentrating freshwater phytoplankton communities prior to measurement of nitrogenase activity using the acetylene‐reduction assay were investigated.
Retention of heterocystous blue‐green algae by 10 and 45 öm plankton nets was usually much less than 100% and the percent retention differed among blue‐green algal species and varied for the same species both on different sampling dates and in different lakes. Retention of heterocyst numbers and helerocyst volume during concentration differed from that of total cell volume of heterocystous blue‐green algae.
Effects of concentration on specific nitrogcnase activity varied among the lakes studied. In Lake Bysjön activity decreased on all sampling occasions, in Lake Trummen there was no apparent effect, and in Lake Vaxjosjon both results were found.
Effects on nitrogenase activity of mechanical disturbance during concentration and of increased pH. reduced carbon availability. light inhibition and subsaturation. photorespiration and oxygen supersaturation in concentrated samples are discussed. Interactions between these factors are suggested to explain the varying responses in the three lakes.
It is concluded that phytoplankton should not be concentrated in the acetylene‐reduction assay for nitrogenase activity, since both volumetric and cell concentration factors are inadequate and effects of concentration on specific nitrogenase activity are not predictable.
Microbial heterotrophic utilization of dissolved organic matter in a piedmont stream
Authors: KAPLAN LOUISA. , BOTT THOMAS L. 
Published: May 2006

SUMMARY.

The microbial heterotrophic utilization of dissolved organic matter (DOM) was determined experimentally in microcosms using stream water and stream‐bed sediments from a third order reach of White Clay Creek (Pennsylvania, U.S.A.).
Sources of DOM for the experiments included White Clay Creek water at baseflow and stormflow and cold water extracts of jewel weed (Impatiens capensis L.) and spicebush (Linderu henzoin (L.) Blume).
The heterotrophic activity of the sediments was measured as uptake of the following: dissolved organic carbon (DOC), molecular weight fractions within the DOC pool, carbohydrates, amino acids and peptides, phenolics, and dissolved oxygen (DO), all in the overlying water.
Concentrations of adenosine triphosphate (ATP), and direct microscopic counts of bacteria were used to estimate bacterial biomass in the surface sediments.
The microcosm experiments showed that specific DOC molecular size classes and DOM functional groups were selectively removed from solution, exposure to one DOM source affected responses to a different DOM source and certain DOM sources were more readily utilized than others.
Continued exposure to a DOM source increased microbial heterotrophic activity (a condition which persisted even after removal of the DOM source for several days).
Rates of biotic DOC uptake ranged from 3.6 to 242.8 mg Cm‐2h‐1.
Indirect estimates of biosynthesis calculated from DOC and DO data ranged from 1.6 at baseflow and 2.6–61.2 at stormflow to as high as 192.6 mg C m‐2 h‐1 when the community was repeatedly exposed to enriched DOM sources.
The mean generation times of bacteria in sediments, determined from direct microscopy data, ranged from 12.5 to 46.2 h at 15°C.
Production of a stream shredder, Peltoperla maria (Plecoptera: Peltoperlidae) in disturbed and undisturbed hardwood catchments
Authors: O'HOP JOE , WALLACE J. BRUCE , HAEFNER JOHN D. 
Published: May 2006

SUMMARY. (1) The average benthic density of Peltoperla maria in an undisturbed southern Appalachian stream was more than twice that of a nearby stream draining a previously clear‐cul catchment in its tenth year of natural secondary succession.(2) Peltoperla production estimates, using three methods, do not show a significant difference in production between streams draining the two catchments. We attribute these results to quicker growth and slightly higher densities of larger nymphs in the disturbed stream. Production estimates for the disturbed stream ranged from 498 to 560 mg (ash free dry weight) m−2y−1 while those for the undisturbed stream were 41–4–515 mg m−2 y−1.(3) Our results reinforce the view that conclusions based solely upon numerical densities may lead to erroneus interpretations about the roles organisms play in ecosystems.(4) Annual frass production by this shredder is about 20 times (10 g m−2 y−1) the secondary production of P. maria.
Macroinvertebrate–habitat relationships in the River Teifi catchment and the significance to conservation
Authors: JENKINS R. A. , WADE K. R. , PUGH E. 
Published: May 2006

SUMMARY. 1. A macroinvertebrale survey of various habitats (e.g. riffles, pools, tree roots) at sixteen sites in the Teifi catchment in September 1981 yielded 217 taxa excluding Hydracarina and Chironomidae.2. Sites with the greatest number of habitats were generally rich in taxa and supported the highest number of ‘rare’ species, the latter generally being associated with vegetation. However, species were not generally restricted to particular habitats although ecdyonurid mayflies predominated in riffles and one leptocerid caddisfly was principally collected from tree roots.3. Four groups of taxa which characterized three habitat groups were established using classification procedures and it was concluded that three habitat types (eroding, depositing and vegetation) should be sampled to describe adequately the macroinvertebrate fauna at each site.4. Three attributes (species richness, species rarity and site uniqueness) were used to establish the conservational value of each site; in general, the main river and one lowland tributary were of highest conservational significance.5. Multiple regression analyses were used to establish significant relationships between the three attributes and environmental features such as number of habitats, altitude, river width, pH and total hardness. Such relationships may facilitate a rapid assessment of resource value without expensive biological survey.
Changes in sediment nutrient content in a subarctic lake subjected to lake fertilization
Authors: BJÖRK‐RAMBERG SUSANNA 
Published: May 2006

SUMMARY. 1. Phosphorus and nitrogen concentration in the surface sediment was analysed before, during and after fertilization of a small, stratified, subarctic lake. During stratification most (70%) of the added nutrients were deposited in the epilimnion sediment.2. After 2 years of fertilization there was a significant increase of both nutrients at all water depths, although values were 30–50% higher per square metre in the shallow areas.3. Nutrient budget calculations based on the sediment analyses showed that 75% of the added phosphorus and 45% of the nitrogen were accumulated in the sediment after fertilization.
Sexual dimorphism in Gammarus pulex: the effect of current flow on pre‐copula pair formation
Authors: GREENWOOD PAUL J. , ADAMS JONATHAN 
Published: May 2006

SUMMARY. 1. Male Gammarus pulex (L.) are typically twice as heavy as females in field caught pre‐copula pairs and mating is positively size assortative. Earlier work had shown that relatively large males can swim in pre‐copula at higher current speeds than males that are relatively small compared with their mates. We describe experiments on pair formation in the laboratory, in static water and in an artificial stream.2. Pairs formed in the artificial stream had a significantly higher weight ratio than either those formed in static water or those caught in the field. In both experimental conditions, males in pairs were significantly larger than singles. In the stream, the weight ratio of pairs increased with formation sequence due to a significant decrease in the size of selected females.3. It is concluded that these results are consistent with the hypothesis that the relatively large size of paired male G. pulex is a product of mechanical constraints rather than male–male competition.