bluuebunny/crossref_metadata_2025_split huggingface dataset:
The light‐climate of Loch Leven, a shallow Scottish lake, in relation to primary production by phytoplankton
Authors: BINDLOSS MARGARET E. 
Published: May 2006

SummarySeasonal changes in incident irradiance and underwater light penetration at Loch Leven from 1968 to 1971 are discussed in relation to the photosynthetic behaviour and crop density of phytoplankton.Light extinction was highest in the blue and lowest in the orange spectral regions, a pattern typical of other turbid waters. Euphotic depth varied between 1·2 and 7·4 m and was on average c. three times the Secchi disc transparency. Underwater light extinction depended chiefly on phytoplankton crop density (estimated as chlorophyll a). Despite the shallowness and wind‐exposed situation of the loch there was no evidence of appreciable light extinction due to sediment disturbance. Possible causes of variability in the relationship between the minimum vertical extinction coefficient (k min) and the concentration of chlorophyll a are discussed.The value of ks, the increment in kmin per unit increment in algal concentration, was estimated from field data as 0·0086 In units per mg chl a/m2 and from laboratory spectroradiometer data as 0·0079 In units per mg chl a/m2. These ks values imply theoretical upper limits for the amount of chlorophyll a in the euphotic zone (Σn max) of 430 and 468 mg chl a/m2, respectively. Observed euphotic chlorophyll a contents (Σn) were sometimes close to these upper limits.Typical photosynthesis/depth profiles are described. Profile area is shown to be related to the logarithm of the ratio between surface‐penetrating irradiance (Io') and the irradiance (Ik) defining the onset of light‐saturation of photosynthesis. Standardized profiles, plotted on a common scale of ‘optical depth’, are used to illustrate the relatively minor influence of variations in Io' and Ik on hourly rates of photosynthesis per unit area.The saturation parameter (Ik) generally increased as photosynthetic capacity (Pmax) increased; the temperature‐dependence of Ik is explained by the temperature‐dependence of the enzyme‐controlled (dark) reactions of photosynthesis, which control Pmax.A spring peak in the ratio between surface penetrating irradiance (Io') and Ik is interpreted as a result of a lag in the seasonal increase in water temperature with increase in surface irradiance.The gradient (K') of the linear light‐limited region of the photosynthesis‐irradiance curve showed little variation and had an average value of 0·31 mg O2/mg chl a.h per 1 W/m2 (PAR).Interactions between mixed depth, underwater light extinction and phytoplankton productivity are discussed; comparisons are made with other shallow, optically deep lakes.
Some observations on the use of the in vivo fluorescence technique to determine chlorophyll‐a in natural populations and cultures of freshwater phytoplankton
Authors: HEANEY S. I. 
Published: May 2006

SUMMARY.
The variation in the ratio (R) between cellular fluorescence of chlorophyll‐a and unit extractable chlorophyll‐a was examined with natural populations of phytoplankton and unialgal cultures. Photo‐inhibition of in vivo fluorescence was observed al high values of irradiance with natural populations and in algal cultures, except with blue‐green algae. If samples were dark‐adapted (< 6 W m−2) before measurements were made, changes of fluorescence due to photo‐inhibition could be minimized. Measurements of in vivo fluorescence with dark‐adapted samples of phytoplankton, dominated by species showing large values of R, gave significant correlations (P< 0.001) with determinations of chlorophyll‐a concentration over periods of several weeks.The values for R for blue‐green algae were appreciably lower than for other algal groups. This, and their lack of photo‐inhibition effects at high irradiance values, are attributed to the association of most of chlorophyll‐a with photosystem I which fluoresces weakly compared to chlorophyll‐a in photosystem II. The significance of these findings for ecological studies is discussed.
Effects of temperature on gut‐loading and gut‐clearing times of the burrowing mayfly, Hexagenia limbata
Authors: ZIMMERMAN MELVIN C. , WISSING THOMAS E. 
Published: May 2006

SUMMARY.
The effect of temperature on gut‐loading times, gut‐clearing times, and the calculated ingestion rates, egestion rates, and consumption indices of the deposit‐feeding burrowing mayfly, Hexagenia limbata, were investigated in laboratory experiments. Rates of movement of two natural sediments of differing colour through the digestive tract were monitored to quantify feeding intensity when ambient water temperatures approached 5, 10, 15, 20, and 25°C.At each temperature, gut‐loading times (GLT) and gut‐clearing times (GCT) increased as nymph length increased. Mean GLT and GCT values decreased as temperature increased from 5 to 20°C but were longer at 25°C than at 20°C. Relationships between GLT, GCT, and length of nymphs and temperature were best described by multiple regression equations. No diel variation in gutclearing times was observed. Low water temperatures resulted in lower ingestion and egestion rates and consumption indices. At most temperatures nymphs ingested over 100% of their dry body weights per day.
Further observations on limnetic zooplankton in a small lake and two enclosures containing fish
Authors: SMYLY W. J. P. 
Published: May 2006

SUMMARY.
In a small lake (Blelham Tarn, English Lake District) two plastic cylinders, each of which extends from the lake surface to the bottom sediments and encloses 18 000 m3 of water, were used to investigate effects of enclosure on the zooplankton. This paper describes observations from March 1973 to October 1974 and is the second part of a report on a project spanning 4 years.Seasonal population densities of the more abundant species were essentially similar to those observed in the first part of the project, despite large changes in algal and predator populations. In the enclosures, fish (mostly Perca fluviatilis) populations are known from observations by divers to have been large in the period under consideration and small in the first part of the project. Populations of Chaoborus larvae in the enclosures were small at all seasons from March 1973 to October 1974.
The fauna of the muddy sediments of Lough Neagh, with particular reference to eutrophication
Authors: CARTER C. E. 
Published: May 2006

SUMMARY.
The main groups of animals found in the muddy sediments of Lough Neagh were Chironomidae (Diptera) and Oligochaeta (mainly Tubificidae). At 8 m depth, the average biomass of the main species in these groups was: Chironomus anthracinus, 2.64gm−2; Procladius, 342.8 mgm−2; tubificids (Tubifex, Potamothrix, Aulodrilus, Limnodrilus), 418.7mgm−2. At 25m depth C. anthracinus and Procladius were less abundant, C. plumosus was present and among the tubificids Limnodrilus had a higher density (up to 50000m−2) often an order of magnitude greater than at 8m. Kinnego Bay, a semi‐enclosed, polluted area of the lough, had fewer chironomids than the open lough, with chiefly C. plumosus and Procladius. Limnodrilus was more abundant than at 8m. Dero obtusa (Naididae) was also present, sometimes in large numbers (31000m−2).The response of this fauna to eutrophication in L. Neagh appears to be a diminution in the number of species present, with C. plumosus gradually replacing C. anthracinus as the dominant Chironomus, and tubificids, particularly Limnodrilus, becoming more abundant, A further stage, shown in Kinnego Bay, has Procladius as the most numerous' chironomid. Average total biomass at the three sites was 3.9gm−2 at 8m, 13.2gm−2 at 25 m in the main lake, 2.8gm−2 in Kinnego Bay. At 8m depth, C. anthracinus contributed 76% of the total biomass, at 25m Limnodrilus contributed 74% and C. anthracinus 15%, and in Kinnego Bay, Limnodrilus contributed 40%, C. plumosus 28% and Procladius 20%.
Heterotrophic activity, glucose uptake and primary productivity in Lake Kinneret*
Authors: CAVARI B. Z. , HADAS O. 
Published: May 2006

SUMMARY.
Chlorophyll, ATP and glucose concentrations as well as glucose uptake rate and primary production were determined every 2–4 h during three 24–h surveys in Lake Kinneret. In spite of the fluctuations in glucose uptake rate, the estimation of the daily glucose uptake rate from a single sampling carried out at 10.00 hours is justified. The same applies also for the primary production.Routine bi‐weekly determinations of primary production and glucose uptake rate were carried out from October 1976 to July 1977. No correlations were found between glucose uptake rates and ambient concentrations of ATP, chlorophyll and glucose.The glucose uptake rate showed two distinct seasonal patterns; the period which was dominated by the Peridinium (January‐April) and the rest of the year. In the former period the percentage of glucose‐carbon utilized out of the carbon formed in the water column by the photosynthetic activity, fluctuated between 1 and 9%, and in the latter period fluctuated between 5 and 37%. The yearly average was 11.1%, SD 9.8.
Temporal and vertical distribution of ciliophoran communities in the benthos of a small eutrophic loch with particular reference to the redox profile
Authors: FINLAY B. J. 
Published: May 2006

SUMMARY.
The ciliate communities occurring at three benthic sites in a small eutrophic loch have heen investigated over a 2‐year period. Two characteristics of the community were studied in detail, the pattern of vertical distribution within the sediment and the temporal distribution of ciliates occurring in the surface sediment. The relationships between ciliate distributions and the environmental factors recorded were analysed by multiple regression. Significant relationships were revealed between vertical distribution of ciliates and the sediment redox (Eh) profile, the larger ciliate communities being associated with regions of higher potential. Other factors such as sediment density, organic matter, temperature and daylength, combined with other indicators of benthic metabolism (sulphide ion activity (Es2−), pH, oxygen flux) were selected in the regression analysis as accounting for much of the variation in the depth distribution of ciliates.In analysing the temporal distribution of ciliates in the surface sediment, numbers were inversely related to Eh, Es2− and oxygen flux, a result of the upwards migration of reducing conditions and greater microbial activity in the sediment surface during the summer. Daylength, temperature, organic carbon and benthic chlorophyll‐a were also selected as accounting for much of the variation in ciliate number. It is proposed that the large increases in number and biomass of surface‐sediment cilates in the summer months resulted from an intolerance of reducing conditions developing immediately beneath the surface and the increased productivity of the benthos as a whole during this period.Methods are also described for the construction, calibration and operation of electrodes used in measuring Eh, Es2− and oxygen flux in the freshwater benthos. Data recorded for these three variables revealed similar seasonal patterns at each site in each of two consecutive years.
Cadmium and calcium interactions in the freshwater amphipod Gammarus pulex
Authors: WRIGHT D. A. 
Published: May 2006

SUMMARY.
The accumulation of cadmium from an experimental medium by the freshwater amphipod Gammarus pulex is described.Much of the uptake is internal as opposed to adsorption on the body surface, and after an apparent saturation of the exoskeleton the hepatopancreas becomes an increasingly important site of cadmium storage. The haemolymph cadmium concentration reaches a high level compared with marine crustaceans, achieving a concentration factor (ratio of internal Cd/ external Cd) of 100 after about 60 h uptake.The cadmium uptake process is severely inhibited after exposure of experimental animals to 0.5 mM 2:4 Dinitrophenol, indicating the mediation of an active process. This fact together with the negative relationship between cadmium uptake rate and the calcium concentration of the animal suggests that cadmium accumulation by this species may be at least partially accounted for by a process of ‘accidental’ active cadmium uptake, with cadmium substituting for calcium on a calcium regulatory mechanism.As yet it has not been possible to establish a true stoichiometric relationship between the two metals. Although calcium influx and cadmium uptake (influx) rates are similar over a wide range of external concentrations, calcium influx is clearly inhibited by a low external ratio of cadmium to calcium. This indicates that the relationship between the two metals is far from an equimolar one and the possibility of non‐competitive inhibition of calcium influx by cadmium cannot be eliminated.
Major ion chemistry in a tropical African lake basin
Authors: GAUDET JOHN J. , MELACK JOHN M. 
Published: May 2006

SUMMARY.
The amount of water lost by seepage from Lake Naivasha, calculated as the residual in the water budget, was 5 (1973), 11 (1974) and 20% (1975) of the total water loss. Direct measurements of seepage in nearshore shallows indicated that water entered the lake via ground‐water seepage in the northern portion and left the lake in the southern portion. Naivasha lies in a topographic closed basin but is hydrologically a seepage lake; it is distinctive among the lakes lying in the endorheic rift valleys of Ethiopia, Kenya and Tanzania because the water is fresh.The mean chemical composition (mg l−1) of bulk precipitation collected on two transects across the rift valley near L. Naivasha and at three stations near Nairobi was: Na, 0.54, K, 0.31; Ca, 0.19; Mg, 0.23; SO4, 0.72 and Cl, 0.41. The major inflow, the Malewa River, was largely a solution of bicarbonate (1.15 m‐equiv, l−1), sodium (9 mg l−1) and calcium (8 mg l−1) and carried a total dissolved solid load (kg ha−1) of 62 (1973) and 120 (1974). Total dissolved solids, sodium, calcium and bicarbonate concentrations were inversely related to discharge.Among the standing waters in the Naivasha basin, sodium and bicarbonate are predominant and the mean total dissolved solute content (mg l−1) increased from a low under the northern papyrus swamp (217) to intermediate values in L. Naivasha (329), the nearshore lagoons (367) and Crescent Island basin (394) to a high in Oloidien Lake (831). Ion ratios and stability field diagrams indicated that calcite is formed in the Crescent Island basin and Oloidien Lake. Calcite was detected in the sediments of the two basins. Ion ratios also indicated that sulphate was retained in the sediments of the northern papyrus swamp.Several factors combine to keep L. Naivasha's water fresh. A large fraction of the water supplied to the lake comes from dilute rivers and rain. The lake does not lie in a closed basin, but loses water and solutes via seepage. Exchanges with sediments both in the pelagic and littoral regions of the lake are the major routes for solute movement and biochemical sedimentation is a major factor in removal of silica. Both geochemical and biochemical sedimentation account for much of the potassium, calcium, magnesium and bicarbonate removal. Only low levels of the conservative ions, sodium and chloride, are taken up by the sediments, while very low levels of sulphate and fluoride are actually released.
Effect of temperature on larval growth of Ecdyonurus dispar (Ephemeroptera: Heptageniidae) from two English lakes
Authors: HUMPESCH U. H. 
Published: May 2006

SUMMARY.
Mature larvae of Ecdyonurus dispar were collected from Ennerdale Water and Windermere (English Lake District) and reared to adult males and females in the laboratory. The females were then fertilized artificially and their progeny were kept at constant temperatures (range 4.2–20.2°C). Larvae collected directly from the two lakes were also reared under the same conditions.The maximum number of instars from egg to subimago was 25, the average body length increment (mm) per moult was proportionately constant at c. 15% and Dyar's rule was applicable. The interval between moults decreased with increasing temperature and the relationship between the two variables within the temperature range 4.2–19.8°C was described by a power law. Larval growth was exponential and variations in mean specific growth rate (range 0.23–5.23% length day−1) were related to mean temperature which was the major factor affecting growth in the laboratory. A few experiments were also performed in the lake to test the adequacy of the estimated values for larval growth at different temperatures in the laboratory. There was agreement between the estimates and the actual growth rates in the lake. Therefore, the regression equations obtained from the laboratory experiments are probably applicable to larval growth in the field.Values for daily production in the laboratory ranged from 0.53 to 9.33 mg dry wt day−1 m−2. The lowest value was obtained at 8.9°C and the highest at 20°C.Information on different life cycles of E. dispar is briefly reviewed and it is concluded that E. dispar from the lakes can only achieve one generation per year.
Photographic identification of individual grayling, Thymallus thymallus, based on the disposition of black dots and scales
Authors: PERSAT H. 
Published: May 2006

SUMMARY. The flanks of grayling are generally studded with black dots which vary in number. The number and position of these dots are well‐defined for each individual and make it possible to identify each fish, in some cases, as when there are very few dots or none at all, it is necessary to make use of other features such as the general disposition of the scales.The best method for recording these characters is by photographing each fish. When recaptured, a fish can be recognized by comparing photographs. The number and position of dots on their lines can be sorted by a computer. Ultimate confirmation is given by comparing the most likely photographs once they have been selected by the computer.
Reactions of singlet oxygen in humic waters
Authors: BAXTER R. M. , CAREY J. H. 
Published: May 2006

SUMMARY. The oxidation of 2, 5‐diniethylfuran (DMF) to cis‐1, 2‐ diacetylethylene (DAE) is a specific test for singlet oxygen (1O2). A method has been developed for the measurement of DAB by direct injection gas chromatography. By the use of this method, the photochemical generation of 1O2 has been demonstrated in samples of two Canadian humic waters.Two other photochemical reactions probably mediated by 1O2generation, the oxidation of histidine and the inactivation of a‐chymotrypsin, have been demonstrated in these waters.The possible ecological and environmental implications of these findings are discussed.
The life history and production of Asellus aquaticus (Crustacea: Isopoda) in the River Ely, South Wales
Authors: MURPHY P. M. , LEARNER M. A. 
Published: May 2006

SUMMARY. A population of the isopod Asellus aquaticus was studied for sixteen months in the organically polluted River Ely. South Wales. There were two complete generations each year. The overwintering population released young (the spring‐brood) over the period April‐June. These animals in turn produced their own offspring (summer‐brood) in late July‐October. Each generation died after breeding and the overwintering population was comprised entirely of animals from the summer‐brood.Seasonal patterns of mortality were related to water flow, temperature and life‐cycle stage. Individual growth rates were affected by both temperature and life‐cycle stage.Annual population production (P) was 195.68 g wet wt m‐2, mean annual biomass (B) was 32.98 g wet wt m‐2 and the annual P/B ratio was 5.93.
Extracellular release of photosynthetic products by freshwater phytoplankton populations, with special reference to the algal species involved
Authors: BLAAUBOER MARIANNE C. I. , VAN KEULEN R. , CAPPENBERG TH. E. 
Published: May 2006

SUMMARY. Over three successive years, depth profiles of C‐fixation and excretion, chlorophyll‐a concentrations, phytoplankton species composition and bacterial numbers were determined in Lake Vechten, a slightly eutrophic lake in The Netherlands. Special attention was given to the method used to measure extracellular release.Excretion of dissolved organic 14C depended largely upon the photo‐synthetic activity of the phytoplankton, ranging from 0–2.5 mg m‐1 h‐1, representing a percentage extracellular release (PER) of 0–25%.During a period in August, however, a subsurface chlorophyll‐a maximum at 5–7 m depth coincided with high excretion rates of up to 10 mg Cm‐3 h‐1 (PER = 55%). Phytoplankton analysis revealed a stratification in numbers of Mallomonas caudata with a maximum at 5–7 m depth.The results suggest that in these water layers bacterial populations grew at the expense of the dissolved organic carbon compounds excreted by Mallomonas caudata. This means that extracellular release can temporarily function as an important nutrient source for the heterotrophie community in addition to the more or less constant dissolved organic carbon pool.
The drift of some chironomid egg masses (Diptera: Chironomidae)
Authors: WILLIAMS C. J. 
Published: May 2006

SUMMARY. The drift of chironomid egg masses was investigated in the River Mole (Devon) and the River Wye (Powys) in 1981. Large numbers of egg masses were found in the drift just after dusk; on one occasion an estimated 50,000 egg masses passed a sampling point in 5 h. Oviposition of free‐floating egg masses appeared to be initiated and synchronized by the onset of darkness. Egg masses of some Pentaneurini (Tanypodinae), Tanytarsini and Chironomini (Chironominae) were found in the drift and adhering to submerged stones.Flotation by means of a gas vacuole within the egg mass was observed in the Polypedilum ‘convictum’ group. The gas vacuole decreased in size over 8–11 h and the egg masses sank after 2–3h.Some chironomid egg masses are capable of drifting large distances after oviposition. The implications of sueh drift are briefly discussed in relation to the distribution of chironomid larvae.
Relationship of macrophyte‐mediated changes in the water column to periphyton composition and abundance
Authors: MORIN JOANNE O'NEILL , KIMBALL KENNETH D. 
Published: May 2006

SUMMARY. 1. Dense growths of Myriophyllum heterophyllum influenced temperature, dissolved oxygen, pH and light levels in the littoral waters of Lake Winnipesaukee, a soft‐water. New England lake. Periphyton species composition and abundance (algal units cm' stem) were related to the macrophyte‐mediated changes in the physicochemical environment.2. Duringearlysummer, M. heterophyllum occupied onlythe lower part of the water column. Limnetic and littoral waters exchanged readily and were chemically similar. Early summer periphyton species composition was dominated by diatoms from the phytoplankton, entangled in the finely dissected leaves of M. heterophyllum.3. By mid‐summer, M. heterophyllum occupied the entire watercolumn of the littoral zone. The metabolic and photosynthetic activity and dense foliage of M. heterophyllum created marked vertical gradients in physicochemical conditions. Mid‐day temperature, dissolved oxygen, pH and light levels were maximal in the surface waters of the M. heterophyllum mat during the summer. Concurrently, periphyton species composition shifted to blue‐green and then to a filamentous green alga on the apex and mid‐stem. On the lower stem, diatoms consistently dominated the periphyton.4. Periphyton abundance on the apex was inversely related to apical elongation. Temporal fluctuations of periphyton abundance on the lower and mid‐stem were small throughout the study. Periphyton abundance was lowest on the lower stem, where the deteriorating leaves provided less surface area for colonization.