bluuebunny/crossref_metadata_2025 huggingface dataset:
Laboratory models of diel vertical migration in the dinoflagellate Ceratium hirundinella
Authors: HEANEY S. I. , FURNASS T. I.
Published: May 2006

SUMMARY.
Diel vertical migrations of a dinoflagellate, Ceratium hirundinella, were induced in a laboratory tube (1.63 × 0.15 m) under a light‐dark cycle. The timing of vertical migrations differed between cultures in the exponential and stationary phases of growth; the latter showed a greater coincidence with the light regime.

Migration of cells into the surface layers occurred at low values of surface irradiance (<550 μeinsteins m−2 s−1). At irradiances more closely approaching summer sunshine (> 1300 μE m−2 s−1) there was a marked avoidance of surface waters, and population maxima were found at depths associated with a relative irradiance level of 10% or c. 150 μE m−2 s−1). Thermal stratification restricted downward movement of cells into the cooler layers. The combination of high surface irradiance and thermal stratification resulted in large, stable, sub‐surface maxima of Ceratium, similar to those observed in natural waters under comparable environmental conditions.
The thermal, oxygen and light regimes in isolated columns of water in a turbid impoundment
Authors: TWINCH A. J. , BREEN C. M.
Published: May 2006

SUMMARY.
Temperature, oxygen and secchi disc transparency were measured in 5‐m diameter isolation columns positioned in water approximately 4 m deep. In general the difference in thermal conditions between the adjacent open water and columns was slight. Oxygen levels in bottom waters in the enriched columns were often slightly lower than in the open water but never dropped below 50% saturation. It seems unlikely that sufficient depletion occurred to markedly increase release of phosphorus from the sediment. Light penetration in the columns was more varied than in the open water but was seldom sufficient to permit the development of large stands of benthic algae.
Oxygen consumption in Caridina nilotica (Decapoda: Atyidae) in relation to temperature and size
Authors: HART R. C.
Published: May 2006

SUMMARY.
The oxygen consumption of shrimps ranging from 1 to 30 mg dry mass was determined at 18, 24 and 30°C using a continuous flow recording respirometer based upon a Clark‐type oxygen electrode. Respiration (ascribed to routine metabolism) is described by the power curve: R = a Mb, (R=μg O2 h−1, M= mg dry mass), which gives values of a= 1.632, 2.564 and 4.181, and b= 0.800, 0.898, and 0.793, at 18, 24 and 30°C respectively. The single expression, R= 0.008 T1.829M0.830 provides a reasonable prediction of respiration as a combined function of shrimp size (M) and temperature (T, °C). Using an energy equivalent of 14.14 J mg O2−1 estimates of the energy requirements (E, J h−1 10−3) of routine metabolism are given by the expression: E= 0.115 T1.829M0.830.

Variability in oxygen consumption values between individuals is discussed and the observations on C. nilotica are compared with other crustacean studies.
Toxicity of γ‐hexachlorocyclohexane (Lindane) to Gammarus pulex
Authors: ABEL P. D.
Published: May 2006

SUMMARY.
The acute toxicity of the pesticide γ‐hexachlorocyclohexane (Lindane) to Gammarus pulex was determined by a standard procedure and by a modification of the conventional toxicity test protocol. Animals were exposed to a range of concentrations for various periods of time from 1 to 1000 min and transferred to clean water. Animals continued to die for up to 3 weeks after the initial exposure to the poison. Toxicity curves were obtained expressing the relationships between concentration of poison and median survival time (LT50) and between concentration of poison and median lethal exposure time, i.e., the duration of exposure required to cause the eventual death of half the animals. For a given concentration of pesticide, the duration of exposure which will cause 50% mortality is far less than is indicated by a conventional toxicity test in which animals are continuously exposed to the poison. It is suggested that the results of conventional acute lethal toxicity tests may have limited predictive value even when applied to field situations involving the discharge of lethal levels of pollutants to receiving waters.
Embryonic duration and post‐embryonic growth rates of the tropical freshwater shrimp Caridina nilotica (Decapoda:Atyidae) under laboratory and experimental field conditions
Authors: HART R. C.
Published: May 2006

SUMMARY.
Embryonic durations and post embryonic growth rates of Caridina nilotica were determined under laboratory conditions at constant temperatures near 18, 24 and 30°C. Embryonic durations and intermoult intervals were negative curvilinear functions of temperature. At a given temperature moulting frequency varied inversely with shrimp size and slight sexual differences were apparent. Moulting frequency of berried females was governed by the temperature‐specific embryonic durations.

Growth rates were determined from changes in carapace length (CL) of individual shrimps (laboratory) or batches of shrimps (field enclosures) over 1 month and these data were used to calculate temperature‐specific life‐long growth curves for males and females. Growth in body mass was estimated indirectly from the carapace length‐mass relationship of C. nilotica. On average, males grew marginally faster than females during the first 2 months of life, but growth of males larger than CL= 4 mm was considerably depressed relative to that of females. Inflexions in growth rate, apparently related to the onset of sexual maturity, were apparent in both sexes.

Under laboratory conditions, the growth rate of males increased with temperature, but temperature‐related differences were not as marked in females. Notwithstanding the more rapid moulting rate at 30°C the growth rate of females was slightly slower at 30 than at 24°C as a result of marginally but significantly smaller per moult growth increments observed at 30°C in animals up to CL= 5.5 mm. Possible reasons for this depressed growth are discussed.

Growth rates of animals in field enclosures in Lake Sibaya over 1 month in winter (20 ± 3°C) were generally comparable to those estimated for the 18°C laboratory experiments. Growth rates in enclosures containing tripled standing stocks were almost identical to those containing the naturally occurring biomass of animals, suggesting a non‐limited environment at least during the time of the experiment.
Relationships between body size and biomass of aquatic insects
Authors: SMOCK LEONARD A.
Published: May 2006

SUMMARY.
Predictive equations were developed to estimate dry weight from body length measurements for forty‐three taxa of aquatic insects. The inter‐relationships between dry weight, body length and head capsule width of individuals grouped according to the eight major orders of aquatic insects were also examined. Regression analysis indicated that the relationship between biomass and body size was best expressed by a power equation, Y =aXb, rather than by linear or exponential equations. Changes in body length versus head capsule width were best expressed by linear equations, with three distinct relationships being observed. Body length estimated biomass better than head capsule width. Populations often species of insects collected from two different rivers generally did not differ significantly in their dry weight to body length relationships.
The origin, composition and downstream transport of plant material in a small chalk stream
Authors: DAWSON F. H.
Published: May 2006

SUMMARY.
This study was a large‐scale comparative in situ experiment on the fragmentation and breakdown of typical aquatic and terrestrial inputs of a chalk stream. Two similar lengths of stream were separated by screens of 5‐mm mesh across the entire stream width at their upper and lower limits. The material transported downstream was collected continuously for 3 years. The order of breakdown was: <2 weeks for the emergent herbaceous macrophyte Rorippa nasturtium‐aquaticum; 2–3 months for the dominant submerged macrophyte Ranunculus calcareus and 4–6 months for the terrestrial material, mainly leaves of Salix viminalis and Fraxinus excelsior. The degree of fragmentation of material varied with its structure, composition and time of availability relative to the seasonal changes of discharge. In general, fragmentation of material increased with its time of retention at or near its sites of origin, but this could be greatly modified by the date of the major autumnal increase in discharge. Thus, in a year of early rain, terrestrial leaf material was mainly whole when transported downstream but in a year with late rain, fragments predominated. The breakdown order coincided with an increasing ratio of carbon/nitrogen in the materials. The total annual movement of plant material was between 231 and 426 kg dry weight for both sites but there was considerable variation in the quantities of the individual species present. On an areal basis, with equal inputs of aquatic and terrestrial material, aquatic material was fragmented more than terrestrial material and therefore more of the latter was transported downstream. The aquatic macrophytes in the open section of the stream retarded the progress of terrestrial allochthonous material and resulted in a substantial increase in fragmentation of this material which would have been lost to this part of the stream.
A simple and inexpensive 4π light collector and two designs for a light meter for light attenuation studies
Authors: leB. WILLIAMS P. J. , JENKINSON N. W.
Published: May 2006

SUMMARY.
A simple 4π light collector is described suitable for light attenuation studies. It uses table tennis balls as light collectors and its spherical response is near to ideal. A circuit for a simple meter based on an operational amplifier is given as well as that for a direct‐reading log‐ratio meter. Both circuits are intended for use with selenium photocells. The cost of the materials for detector and simple meter is less than £30.
Anaerobic metabolism of particulate organic matter in the sediments of a hypereutrophic lake*
Authors: MOLONGOSKI JOHN J. , KLUG MICHAEL J.
Published: May 2006

SUMMARY.
The anaerobic decomposition of particulate organic matter (POM) was examined in the anoxic pelagic sediments of hypereutrophic Wintergreen Lake. Degradation of sedimented POM occurred rapidly as shown by increased production and release of ammonia, hydrogen sulphide, volatile fatty acids and methane from the sediments 2–3 weeks after large inputs of organic matter. Maximum concentrations of most metabolites were found at the sediment‐water interface, indicating that the initial anaerobic degradation of freshly deposited POM occurred at this site. The absence of the inorganic electron acceptors, nitrate and sulphate, suggested that fermentation and methanogenesis were the major anaerobic processes involved in the dissimilation of organic matter in these sediments during stratified periods. The amount of carbon input converted to methane in the sediments was determined from May to early November 1976 and 1977. Carbon output as methane was measured by quantifying methane lost from the sediments by ebullition and by estimating soluble methane lost to the water column by diffusion. Total methane release during summer stratification accounted for 34% of the particulate organic carbon input to the sediments in 1976 and 44% in 1977. Methane release was directly related to the rate of sedimentation of POM. However, methane production was temporarily inhibited following high rates of sedimentation in 1976, suggesting that the rate of organic loading may be an important factor controlling anaerobic decomposition in these sediments.
Parasitism of the backswimmer Buenoa scimitra (Hemiptera: Notonectidae) by the water mite Hydrachna virella (Acari: Hydrachnellae)
Authors: LANCIANI CARMINE A.
Published: May 2006

SUMMARY.
The life cycle of Hydrachna virella, a water mite parasitic on the notonectid backswimmer Buenoa scimitra, is described. The mite parasitizes immature instars 2–5 as well as adult males and females of the notonectid. Parasitized immature backswimmers spent longer periods of time between moults than unparasitized immature backswimmers. Initially attaching mites appeared to be generally distributed over the host body surface but previously attached mites that reattached after host ecdysis were found primarily on the dorsum of the thorax. The observed frequency distribution of mite larvae on the host was similar to that predicted by the negative binomial distribution.
Some ecological consequences of fish school volumes
Authors: PITCHER T. J.
Published: May 2006

SUMMARY.
Two consequences of a recently published method of calculating fish school volumes are examined in the light of ecological population data. First, minnow and roach schools occupy only about 0.01% of the volume of water in which they live, graphically illustrating the vagaries of field sampling, and providing reference values for foraging studies. Secondly, I show that roach schools in one river are constantly within attack range of pike predators. If this situation is general, theories which assume that schools function strategically merely to reduce the probability of encountering a predator, break down, whereas my predictions suggest that there is strong selection for direct predator evasion tactics in schools.
A fish‐kill in Heart Lake, Ontario, associated with the collapse of a massive population of Ceratium hirundinella (Dinophyceae)
Authors: NICHOLLS K. H. , KENNEDY W. , HAMMETT C.
Published: May 2006

SUMMARY.
A massive population of the common dinoflagellate Ceratium hirundinella developed in Heart Lake. Ontario, Canada during the summer of 1976 and its sudden collapse and subsequent decomposition depleted dissolved oxygen and resulted in a fish‐kill in the lake. The lake was being artificially mixed at the time by supplying compressed air to the bottom waters and the limnological events contributing to the development of the Ceratium population and its collapse appear to be closely related to the artificial destratification process. Artificial destratification during 1976 precluded the development of blue‐green algue. The process also led to an increase in the density of herbivorous zooplankters which controlled the development of smaller planktonic algae. Ceratium flourished in Heart Lake because there was little competition for nutrients from other algae and because Ceratium cells are too large to be grazed by the zooplankton. The maximum size of the Ceratium population (53 mm3 1−1) is apparently the highest biomass reported in the literature and its collapse may have been related to a depletion of inorganic nitrogen. There is apparently no previously published record of a Ceratium‐induced fish‐kill in a freshwater lake.
The velocity of the River Tweed and its tributaries
Authors: LEDGER D. C.
Published: May 2006

SUMMARY.
Velocity measurements at fourteen hydrometric stations in the Tweed basin are described and analysed. Along‐stream velocity variations are examined and it is shown that at most flow levels the highest velocities occur at the lower, flatter end of the river system. Estimates of the frequency with which velocities of different magnitudes can be expected to occur in the river are also presented. These indicate that the velocity at most stations rarely exceeds 3.0 m s−1 and for most of the time it lies between 0.25 and 1.0 m s−1. The inadequacy of subjective velocity assessment is stressed and a method suggested whereby data similar to those presented could readily be produced for almost any cross‐section along a river like the Tweed.
Photosynthetic capacity measured by DCMU‐induced chlorophyll fluorescence in an oligotrophic lake
Authors: VINCENT WARWICK F.
Published: May 2006

SUMMARY.
Wastwater (English Lake District) was sampled at monthly intervals over 1 year to compare the seasonal and vertical extents of floristic and physiological variation in an oligotrophic phytoplankton assemblage. Cellular photochemical capacity (CPC) was measured by in vivo chlorophyll fluorescence before and after addition of the photosynthetic inhibitor 3(3,4‐dichlorophenyl)‐1,1‐dimethyl urea (DCMU). The CPC index proved useful to define an activity coefficient for the chlorophyll levels measured in boiling methanol extracts. Large variations in CPC over time or depth were generally correlated with major shifts in phytoplankton species composition. Highest CPC values were recorded during autumnal mixing. Both CPC and floristic composition of the community demonstrated as great a variation over depth during a period of stratification as that recorded over time throughout the year. These observations emphasize the multi‐canopy structure of the Wastwater phytoplankton community in summer.
Overwintering of Microcystis in Lake Mendota
Authors: FALLON ROBERT D. , BROCK THOMAS D.
Published: May 2006

SUMMARY.
Microcystis, an important bloom‐forming blue‐green alga in Lake Mendota, Wisconsin, was found to accumulate at the lake bottom and overwinter there. Microcystis collected from winter sediments were photosynthetically active, showing temperature and light optima similar to summer and autumn populations. Sediments incubated under in situ conditions in the laboratory maintained photosynthetic activity for at least four months. Such a maintenance ability may be part of an overall strategy by Microcystis populations to ensure a suitable inoculum for the following growth season.
A bacteriological investigation to elucidate the feeding biology of Nais variabilis (Oligochaeta: Naididae)
Authors: HARPER R. M. , FRY J. C. , LEARNER M. A.
Published: May 2006

SUMMARY.
The estimated average number of bacteria in the gut of laboratory‐cultured Nais variabilis was 100.4 × 104. This compares with values of 6.7 × 104 and 32.8 × 104, respectively, for N. variabilis and N. barbata obtained from a river.

Comparison of the viability of heterotrophic bacteria in the food and gut of N. variabilis indicated a decline in viability of up to 99.6% during the passage of bacteria through the gut. The estimated gut retention time was 39 ± 8 min at 18°C and therefore loss of viability is unlikely to be due to long retention in the gut. Loss of viability is, however, a prerequisite of bacterial digestion by the worm and provides circumstantial evidence that ingested bacteria are used as food.

No conclusive evidence was obtained indicating (a) preferential ingestion of certain kinds of bacteria, (b) that the gut environment was selectively hostile to the particular kinds of bacteria studied or (c) that worms had a specialized gut micro‐flora.
The spatial distribution of nutrients in the South Basin of Windermere
Authors: GEORGE D. G.
Published: May 2006

SUMMARY.
The vertical and horizontal distribution of electrical conductivity, soluble reactive phosphorus (SRP), total phosphorus, ammonia‐nitrogen and nitrate‐nitrogen in the South Basin of Windermere is described and related, where possible, to spatial variations in phytoplankton and zooplankton.

For most variables, the maximum range of horizontal variation on a single day was greater than the maximum range of seasonal variation measured at a single station over a full year. Horizontal variations in SRP and ammonia were particularly high, with coefficients of variation often exceeding 100%. The errors associated with sampling at a single station were most pronounced when local accumulations of zooplankton or phytoplankton occurred in the lake.

Horizontal variations in conductivity were primarily influenced by the discharge of treated sewage effluent into the central region and the mass transport of water from the more oligotrophic North Basin. Occasionally, more widespread variations in conductivity appeared to be related to spatial variations in photosynthetic activity. The major factor influencing the horizontal distribution of SRP was the discharge of treated effluent into the central region. Despite the intensive recycling of phosphorus, SRP concentrations were nearly always 10–30% higher near the sewage works than elsewhere in the basin. On a few occasions, significant horizontal differences in SRP concentration were also detected within downwind accumulations of crustacean zooplankton. Horizontal variations in total phosphorus were produced by spatial differences in SRP concentration or by local accumulations of phytoplankton or zooplankton. Horizontal differences in ammonia concentration appeared to be produced, both by the effluent discharge and by the turbulent transfer of nutrients from sediments in shallow water.

Observations of effluent movement and dispersion demonstrate that wind‐induced water movements tend to recirculate nutrient‐rich water in the central region and limit mixing along the axis of the basin. The statistical implications of nutrient heterogeneity are discussed in relation to sampling strategy and the possible effects of persistent nutrient concentration gradients on phytoplankton patch formation are assessed.
Changes in submersed macrophytes in Chautauqua Lake, 1937–1975
Authors: NICHOLSON STUART A.
Published: May 2006

SUMMARY.
Changes in macrophyte richness, relative abundances, depth distributions and dominant species from 1937 to 1975 were assessed in Chautauqua, a eutrophic lake. Change was greatest in dominant species, with several formerly abundant native Potamogeton species being replaced by the exotics, Potamogeton crispus and Myriophyllum spicatum. Two extensively practiced management techniques, herbicidal poisoning and mechanized cutting, were considered to be primarily responsible for the observed macrophyte changes.
Growth and recession of aquatic macrophytes on a shaded section of the River Lambourn, England, from 1971 to 1980
Authors: HAM STEPHANIE F. , COOLING D. A. , HTLEY P. D. , McLEISH PENELOPE R. , SCORGIE H.R.A. , BERRIE A. D.
Published: May 2006

SUMMARY. The growth and recession of macrophytes on a shaded section of the R. Lambourn were documented by a mapping procedure. With the exception of Ranunculus spp., the changes in total cover did not indicate directly the pattern of growth and recession of the macrophyles. Analysis of gross changes, expressed as gains and losses on cover, indicated that colonization of gravel and silt by the dominant macrophyte, Berula erecta, did not vary seasonally. Colonization was at a constant rate of about 8% of the site each month throughout the year and this accounted for 50% of the total number of gains by Berula. Gains of Berula from Ranunculus showed an annual cycle with a maximum during the summer when Ranunculus was in recession. Gains of Berula from Callitriche spp. also varied annually but the maximum was during the autumn. Total losses of Berula were at a constant rate throughout the year but were to gravel and silt during the winter, to Ranunculus in spring and early summer and to Callitriche in late summer and autumn. Analysis of loss of Berula with time indicated that the position of the Berula carpet was constantly changing. The growth and recession of Berula could not be linked in a meaningful way to environmental variables. Callitriche and Ranunculus both showed an annual pattern of growth and recession. There was temporal separation of the two macrophytes with Ranunculus growing mainly in spring and early summer and Callitriche showing maximum growth in late summer and autumn, and some evidence of spatial separation. The observed differences between years in the growth of Callitriche could not be attributed to any of the environmental variables measured.

Discharge was thought to be an important variable controlling the growth of Ranunculus since increase of Ranunculus in the spring was positively correlated with the mean discharge at that time. In years when discharge was low, the growth of Rununculus appeared to be restricted by shading from epiphytic algae which accumulated on the plant surfaces under these conditions.
Metal resistances of Chlorophyta from rivers polluted by heavy metals
Authors: FOSTER PATRICIA L.
Published: May 2006

SUMMARY. Two‐hundred isolates, comprising 87 species of Chlorophyta, were obtained from sites along the Rivers Hayle and Gannel. which drain the ancient mining region of Cornwall. All isolates were tested for sensitivity to copper, lead, zinc and cadmium. In general, isolates were resistant to the metals normally present in their habitats. However, the distribution of metal sensitivities of the algae from a given site was broad; the effect of metal pollution was to shift the median response of a population toward higher metal resistance. Resistant algae of two general classes were identified: some normally sensitive species were metal‐tolerant, presumably through genetic adaptation; other species were metal‐resistant even when isolated from a non‐polluted habitat. Many isolates of both types displayed multiple‐resistances or co‐tolerances. For example, copper tolerant isolates from high copper sites tended to be also lead resistant; however, algae from high lead sites were usually very copper sensitive. Zinc and cadmium resistances also were correlated among isolates from both zinc‐polluted and non‐polluted sites. General metal‐insensitivity seemed to be common, particularly among gelatinous Chlamydomonas and Gloeococcus species. Thus, several evolutionary strategies appear to coexist among algae from metal polluted environments.
The palaeolimnology of Lake Mývatn, northern Iceland: plant and animal microfossils in the sediment
Authors: EINARSSON ÁRNI
Published: May 2006

SUMMARY. Sediment from a precursor of the 2300‐year old Lake Mývatn was traced by diatoms in pseudocrater scoria. This lake (Mývatn I) was deeper than the present Mývatn but similar in size. Tephrochronology confirms an equal age of the Ytrlflói and Sydrifloi basins of the present Mývatn. Diatom succession in the sediment of the Sydriflói basin was divided into four zones, of which the lowest corresponds to inherited and highly disturbed Mývatn I sediment. At 90 cm depth, i.e. around 1600 AD, in the Sydriflói sediment a simultaneous increase occurred in Cladophora aegagropila (Chlorophyta), Eurycercus lamellatus (Cladocera) and three diatom species epiphytic on Cladophora. The density of Cladocera also followed this trend. The increase in Cladophora was perhaps caused by improved light conditions on the bottom, either because of a decrease in water depth due to sedimentation, or a decrease in Anabaena blooms, or both.
Notes on the ecology of Aphanius dispar (Pisces, Cyprinodontidae) in the Sultanate of Oman
Authors: HAAS R.
Published: May 2006

SUMMARY. Aphanius dispar was observed in the field and some simple laboratory studies were undertaken in Oman. A. dispar is almost totally ubiquitous in all bodies of fresh water where it occupies a wide range of habitats differing in stream flow, water chemistry, temperature and substrate quality. It often is found in association with one or both of two cyprinid fishes. Cyprinion and Garra. Aphanius is tolerant of wide ranges of salinity up to full marine water and has a wide temperature range. A. dispar resembles Cyprinodon species in a number of particulars, probably reflecting phylogenetic relationships and a common evolutionary response to desert conditions. It breeds throughout the year with a probable peak in the months of April to June.
Observations on the growth and production of chub Leuciscus cephalus and dace Leuciscus leuciscus in a small lowland river in southeast England
Authors: HICKLEY P. , BAILEY R.G.
Published: May 2006

SUMMARY. The River Eden (Kent, England) holds a mixed coarse fish population in which minnows (Phoxinus phoxinus), gudgeon (Gobio gobio), chub (Leuciscus cephalus) and dace (Leuciscus leuciscus) are numerically predominant. Chub and dace provide the major interest to anglers and their growth and production were studied. Observed growth rates of both species were marginally below recorded averages from other British habitats. Back‐calculations showed that year‐class strength and relative growth rates varied between years. Instantaneous mortality rate Z was 0.147 for chub aged 1–10, 0.438 for chub aged 10 and over, and 0.172 for dace. Exclusive of the 0‐group, fish numbers, biomass (wet wt) and production were found to be 0.1305 m‐2, 19.12 gm‐2 and 5.38 gm‐2 year‐1, respectively, for chub and 0.0968 m‐2, 4.33 gm‐2 and 1.69 gm‐2 year‐1 for dace. Smoothing of data produced theoretical production figures of 6.69 gm‐2 year‐1 for chub and 1.15 gm‐2 year‐1 for dace.
Distribution of puimonate snails in the New River of Virginia and North Carolina, U.S.A.: interaction between alkalinity and stream drainage area
Authors: Jr ROBERT T. DILLON , BENFIELD ERNEST F.
Published: May 2006

SUMMARY. The distribution and abundance of five species of pulmonate snails over 87 sites in the New River seem to be related to two variables, alkalinity and drainage area of the stream. The snails were generally found in the more alkaline streams regardless of stream drainage area and in the larger streams regardless of alkalinity. Considering only the 26 sites where at least one species of the five pulmonates occurred, rank snail abundance is significantly correlated with rank alkalinity, rank drainage area, and the alkalinity/area interaction. But the correlations between abundance and both alkalinity and drainage area drop to low levels when interaction is partialled out, while the correlation between abundance and interaction remains high upon partialling out alkalinity or area. This suggests that the apparent correlation between puimonate abundance and alkalinity is secondary and that neither alkalinity nor water chemistry variables correlated with it directly limit the distribution and abundance of pulmonates in the New River. Both alkalinity and stream drainage area may influence the abundance of pulmonate food.
Extraction of chlorophylls a and b from phytoplankton using standard extraction techniques *
Authors: RIEMANN BO , ERNST† DTETER
Published: May 2006

SUMMARY. Pigments extracted in methanol, acetone and ethanol from three cultures of green algae and one blue‐green alga revealed different extraction efficiencies depending on the species, the extraction solvent used and the extraction time. Chromatographic identification and quantitative measurements of chlorophylls a and b were made from six green algae. When extraction of pigments was incomplete, chlorophyll‐b was extracted faster than chlorophyll‐a. This effect was more pronounced for acetone extractions, whereas methanol extractions gave the stable ratios of chlorophyll b/a after about 6–10 h. When green algae are frequent, a 6–10 h methanol extraction, without any extra manipulations, is sufficient to ensure reliable ratios of chlorophyll b/a and extraction of the major proportion of the chlorophylls without risk of induced destruction of the chlorophylls.
Seasonal changes in biom ass of macrophytes on shaded and unshaded sections of the River Lambourn, England
Authors: WRIGHT J. F. , CAMERON A. C. , HILEY P. D. , BERRIE A. D.
Published: May 2006

SUMMARY. Monthly changes in the biomass of Ranunculus, Berula and Callitriche were recorded on two 50‐m sites on the River Lambourn at Bagnor between March 1971 and October 1973. On the unshaded site. Ranunculus was the dominant macrophyte and characteristically its biomass changed from 20–40 g dry wt m‐2 in March to around 400 g dry wt m‐2 at the end of the growing season. On the shaded site, where Berula was the dominant macrophyte. the biomass of Ranunculus was lower than on the unshaded site. There was no significant difference between the mean biomasses of Berula on these two sites but Callitriche had a signifieantly higher biomass on the shaded site. Estimates of the total biomass of macrophyte on each site were calculated and the biomass of macrophyte removed during cutting operations each summer was also assessed.
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.
Effects of forest clearcutting on leaf breakdown in a southern Appalachian stream
Authors: WEBSTER JACKSON R. , WAIDE JACK B.
Published: May 2006

SUMMARY. Effects of forest clearcutting on rates of leaf breakdown were studied in Big Hurricane Branch, a second‐order stream located at Coweeta Hydrologic Laboratory in the southern Appalachian Mountains of North Carolina, USA. Breakdown rates of leaves of three tree species were measured in the stream before, during and after the catchment was clearcut. Changes in the stream attributable to logging and associated activities—principally road building—were increased stream flow, increased sediment transport, elevated water temperatures, increased nitrate concentrations and decreased allochthonous organic inputs. Breakdown rates of all three leaf species were slowed during clearcutting and accelerated later. Following logging the breakdown rate of dogwood leaves was equal to the pre‐treatment rate, and white oak and rhododendron leaves broke down faster than prior to treatment. We attribute the slow breakdown during treatment to burial of the leaf packs in sediment. Subsequent acceleration may have been due to a lack of alternative food sources for invertebrate detritivores.
Effect of air temperature upon mean water temperature in streams in the north Pennines and English Lake District
Authors: CRISP D.T. , HOWSON G.
Published: May 2006

SUMMARY. Water temperatures from six north Pennine streams (approximate mean annual discharges 0.04–1.5 m3 s‐1) and two Lake District streams (mean annual discharges c. 0.04 m3 s‐1) were used to examine the possibility of predicting 5‐day or 7‐day mean water temperatures from standard meteorological/hydrological data collected at north Pennine stations. The relationship between mean air temperature (X) and mean water temperature (Y) was approximately linear, except in the Pennine streams for periods when mean air temperature was below 0°C. The calculated regressions of mean water temperature upon mean air temperature accounted for 86–96% of the variance of water temperature even when the air and water temperatures were measured at stations some 50 km apart. A negligible improvement was obtained by the use of multiple regressions incorporating rainfall or stream discharge from a nearby metering weir. Predicted water temperatures were rather lower than observed values during the first half of the calendar year and rather higher during the second half, but these seasonal differences could not be adequately quantified for practical application.
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.
A simple theory of algal deposition
Authors: SMITH I. R.
Published: May 2006

SUMMARY. A model describing the deposition of algae in a turbulent environment is outlined, it being assumed that all algae falling on the bed are trapped there forever. Its main features are that, above a certain threshold of turbulence the rate of deposition is independent of the turbulent intensity, and the rate of algal loss by sedimentation, in such conditions, is described by a first order kinetic equation. The hydraulic conditions under which algae settle at their intrinsic, still‐water rate and those for which the model is applicable, are examined. Some ecological implications of the model are discussed.
Effects of the freshwater gastropod Planorbis carinatus on reed (Phragmites australis) litter microbial activity in an experimental system
Authors: POLUNIN NICHOLAS V. C.
Published: May 2006

SUMMARY. The freshwater gastropod Planorbis carinatus can enhance the aerobic respiration of micro‐organisms on reed (Phragmites australis) litter in laboratory systems. This effect is contributed to by both direct and indirect mechanisms and, at least in the latter case, increased microbial respiration entails accelerated decomposition. Enhanced turnover of dissolved inorganic phosphate in the presence of the snail may play a role in these interactions.
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.
The effect of food availability, female culture‐density and photoperiod on ephippia production in Daphnia magna Straus (Crustacea: Cladocera)
Authors: CARVALHO GARY R. , HUGHES ROGER N.
Published: May 2006

SUMMARY. A method is described whereby ephippia (sexual eggs plus protective membranes) are experimentally induced at low food levels (≤ 0.05 mg spinach D. magna‐1), high female culture‐densities (≤ 0.4 D. magna ml‐1) and in short‐day photoperiods (L:D < 12:12, 12°C). The density‐dependent ephippial response was related to an increased encounter rate between females at the higher densities. External metabolites had no significant effect on ephippia production. Ephippia were formed in the second generation after exposure to short day‐lengths. Five clones from the same population exhibited genetic variation in their critical photoperiods for induction of sexual reproduction (≥= 10% ephippia). There was evidence of a genetic difference in photoresponse between two populations of D. magna. The evolution of timing mechanisms for ephippia production are discussed in relation to the predictability of environmental change.
The A/C (Araphidineae/Centrales) ratio in high and low alkalinity lakes in eastern Minnesota
Authors: BRUGAM RICHARD B. , PATTERSON† CAROL
Published: May 2006

SUMMARY. Diatoms from surface sediment samples from lakes on both sides of a glacial drift border in eastern Minnesota show that Araphidinate diatom genera like Fragilaria, Asterionella and Synedra are more common in lakes in drift with lower CaCO3 whereas Stephanodiscus and Melosira species are more abundant in those with high CaCo3. In a lake sediment core from low carbonate drift Fragilaria crotonensis and Asterionella formosa increased when pioneer farmers arrived. These results confirm speculation that high A/C ratios are associated with low‐alkalinity eutrophic lakes.
A revised key to larvae of the genus Plectrocnemia (Polycentropodidae: Trichoptera) in Britain, with notes on Plectrocnemia brevis McLachlan
Authors: WALLACE I. D. , WALLACE BRENDA
Published: May 2006

SUMMARY. The key distinguishes the previously unknown larva of Plectrocnemia brevis McLachlan from larvae of the other two British Plectrocnemia species, P. conspersa (Curtis) and P. geniculata McLachlan. Notes are given on the larval habitat, life cycle and identification of the adult of P. brevis.
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.