bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distribution and quantitative development of aquatic macrophytes in relation to sediment characteristics in oligotrophic Lake Kalgaard, Denmark
Authors: SAND‐JENSEN KAJ , SØNDERGAARD MORTEN 
Published: May 2006

SUMMARY.
The distribution and quantitative development of aquatic macrophytes have been studied in oligotrophic Lake Kalgaard, Denmark. The vegetation is dominated by isoetid species, which are widely distributed (about 40% of the lake bottom) compared to emergent and floating‐leaved macrophytes (about 4%). Littorella uniflora dominates at depths of 0–2 m and Isoetes lacustris from 2.0 to 4.5m. Within the colonization area the mean midsummer biomass of Littorella is 112g organic dry weight m−2 and that of Isoetes, 66 gm−2. The total biomass of these two species constitutes 99% of the biomass of submerged macrophytes.The perennial Littorella shows only small seasonal biomass variations. The vegetational biomass, the above‐ground fraction of the biomass, and the weight of individual plants all increased with the organic content of the sediment at water depths from 0 to 0.75 m. At the same time the interstitial concentrations of carbon dioxide, extractable inorganic nitrogen, and exchangeable inorganic phosphorus increased, thus supporting the hypothesis that an increasing organic content of the sediments at this low level creates a physiologically richer medium for the plants.The isoetid growth form is discussed in relation to the chemical environment of oligotrophic, softwater lakes.
The freshwater littoral meiofauna in a South Carolina reservoir receiving thermal effluents*
Authors: ODEN B. J. 
Published: May 2006

SUMMARY.
The freshwater littoral meiofauna along a temperature gradient in Par Pond (a cooling reservoir receiving thermal effluents from a nuclear reactor) was sampled from September 1975 to October 1976. Monthly samples were taken at three stations; ‘hot‐water’ (15–40°C), ‘warm‐water’ (13–37°C) and ambient or ‘cold‐water’ (8–37°C) sites. Total numbers of individuals at the ambient site ranged from 971 to 3674 per 10 cm2 (mean = 2263), approximating the density reported from productive estuarine environments. Nematodes, rotifers, ostracods, cladocerans and mites comprised 80% of overall density. When compared to the ambient site, thermally affected sites demonstrated reduced faunal density.Contrary to other environmental perturbation studies, the Shannon‐Weaver diversity index (H') did not reflect alteration of structural complexity within the rotifer taxocene when hot‐water, warm‐water and cold‐water sites were compared. Though there was a significant reduction in number of species at the thermally altered sites, high ‘equitability’ among the reduced species resulted in H’ values comparable to those in natural communities. Distinct winter‐spring and summer‐autumn assemblages were evident in the ambient community while no seasonal clustering was apparent at the thermally affected sites. It is hypothesized that the maintenance of temperatures above ambient normals masks environmental cues that normally would elicit seasonal changes in the rotifer fauna at those two sites.
Photosynthetic rates in four tropical African fresh waters
Authors: MELACK JOHN M. 
Published: May 2006

SUMMARY.
Seasonal changes in photosynthetic rates of phytoplankton and underwater light in four Kenyan fresh waters (Lake Naivasha, Crescent Island Crater, Oloidien Lake and Winam Gulf) were measured in 1973 and 1974. Daily variations in water temperature were only slightly less than seasonal changes, and complete vertical mixing usually occurred each day. Well oxygenated water from top to bottom provided evidence for daily mixing.The vertical profiles of photosynthetic rates in the four lakes had the familiar feature of subsurface maxima. Of the photosynthetically available radiation (PAR), 1% coincided with the limit of detection of photosynthesis in Naivasha and Crescent Island Crater. The PAR at the depth of the maximal photosynthetic rate was higher for Naivasha (mean= 1.71 einsteins (E) m−2) than for the Oloidien and Crescent Island Crater (means = 1.23 and 1.20 E m−2 h−1, respectively).The maximal rates of photosynthesis (mg O2 m−3 h−1) were usually higher in Oloidien (260–750) and Winam Gulf (230–640) than in Naivasha (150–240) and were least in Crescent Island Crater (50–180). Chlorophyll‐a concentrations were directly related to photosynthetic rates. Because of the inverse relation between euphotic zone depth and maximal photosynthetic rates, the areal rates varied less among the lakes than the volumetric rates (i.e. 3.0–12.1 g O2 m−2 day−1).The efficiency of utilization of PAR expressed on a molar basis ranged from 6.1 to 1.9 mmol O2 E−1, but was usually 2–4 mmol O2 E−1.The seasonal changes over a 12‐month period in the areal photosynthetic rates ranged from a 3‐fold variation in Oloidien and Crescent Island Crater to a 1.5‐fold variation in Naivasha. In Winam Gulf over a 5‐month period a 2.3‐fold variation occurred.
Further observations on developmental polymorphism and its evolution in the rotifer Brachionus calyciflorus
Authors: GILBERT JOHN J. 
Published: May 2006

SUMMARY.
In laboratory experiments, long, Asplanchna‐induced posterolateral spines of Brachionus calyciflorus were very effective in preventing their capture and subsequent ingestion by the predator Asplanchna sieboldi but provided no protection against predation by Mesocyclops edax. Young, short‐spined B. calyciflorus were always captured after attack by adult A. sieboldi and were ingested in about 12 seconds. Adult, short‐spined forms were captured on c. 35% of occasions when attacked by this predator and were ingested in about 50 s. Young and adult long‐spined forms were captured by this predator on c. 60% of occasions when attacked, but they both almost invariably escaped or were rejected 20–35 s after capture. Short‐ and long‐spined B. calyciflorus adults were always captured when attacked by adult, female M. edax and were completely ingested in about 20 s and 30 s, respectively.Life‐table experiments conducted with B. calyciflorus at several levels of the food organism, Aerobacter aerogenes, showed that neither the possession of long posterolateral spines nor the production of offspring with long posterolateral spines interfered with survivorship, fecundity, or reproductive potential.In the laboratory, the volumes of the amictic parthenogenetic eggs of B. calyciflorus cultured on Euglena or Aerobacter were significantly greater in individuals from populations maintaining long posterolateral spines than in comparable‐sized individuals from populations maintaining short spines. Egg volume was generally independent of adult body length, but it was significantly greater in Brachionus fed on Euglena compared with Aerobacter.Possible reasons why B. calyciflorus does not produce long posterolateral spines in the absence of Asplanchna are discussed. Few organisms other than B. calyciflorus are known to develop novel defensive phenotypes in direct response to the presence of a predator. It is suggested that such developmental responses evolve only when two conditions apply: (1) the defensive structure is primarily effective against a single type of predator, and (2) the prey organism exhibiting the response has a short generation time.
Wind‐induced water movements in the South Basin of Windermere
Authors: GEORGE D. G. 
Published: May 2006

SUMMARY.
The results of direct current measurements in the South Basin of Windermere are presented and related to wind history and horizontal variations in near‐surface water temperature. Currents were measured by Lagrangian methods using drift‐bottles and depth‐specific drogues. Except when sudden calms followed strong winds, internal seiche movements had little effect on horizontal transport in the epilimnion. The most important factor governing mass water movement was direct wind forcing. Variations in wind speed accounted for 93% of the variation in near‐surface current speed.For wind speeds between 100 and 500 cm s−1 the wind factor (current speed/wind speed) decreased linearly with wind speed. At wind speeds above 500 cm s−1 the wind factor remained relatively constant around 1 %.Coriolis effects deflected near‐surface currents 4–38° to the right of the wind. The degree of deflection was strongly correlated with the relative depth DE/D* (where DE was the depth of the epilimnion and D* the depth of frictional resistance). The influence of the Coriolis force also produced pronounced rotations, with depth, of the wind‐driven current. The circulation pattern within the epilimnion was broadly that of a distorted conveyor belt moving at some angle to the wind axis. The strength of the transverse circulation was greatest at low wind speeds with a deep thermocline.Richardson‐number calculations suggest that the thermocline generally acts as a low‐friction boundary between a turbulent epilimnion and a relatively quiescent hypolimnion. Horizontal variations in water temperature, although ranging from only 0.2 to 1.0°C per km, served as a good indirect ‘tracer’ of the circulation pattern.
A comparative study of four dredges used for sampling benthic macroinvertebrates in rivers
Authors: ELLIOTT J. M. , DRAKE C. M. 
Published: May 2006

SUMMARY.
After considering the large number of dredges described in the literature, four light‐weight dredges were chosen for manual operation from a small boat or the bank: Irish triangular dredge, small Fast dredge, medium‐sized and large Naturalist's dredges. The dredges were tested in a series of trials at three sites in two rivers. A stratified random sample (number of sampling units, n = 5) was taken at each site and the modal particle sizes at sites 1–3 were 1–2 mm (fine gravel), 64–128 mm (larger stones) and 128–256 mm, respectively.The dredges usually took a similar range of stone sizes at each site but the design of the Fast dredge excluded larger stones (>16 mm). The Irish dredge sometimes failed to operate correctly. Variations in the volume of substrata taken with each dredge were large, both between sampling units in the same sample and between samples. The latter differences were partially due to the increase in the modal size of the stones, especially between sites 1 and 2, the different sampling areas of the dredges and the depth of penetration into the substratum. Penetration depth was probably greatest for the two Naturalist's dredges, smaller for the Fast dredge and smallest for the Irish dredge.In field trials, the relative abundances of major taxa were similar for most dredges at each site; major exceptions were the Fast dredge at site 2 and the Irish dredge at site 3. There was a high variability between sampling units in the same sample and therefore a lack of precision in the estimates of the mean number of invertebrates per sample. Therefore, the dredges cannot be used as quantitative samplers for the estimation of population density. Their adequacy as qualitative samplers for the estimation of total number of taxa per sample varied considerably and maximum estimates of their efficiencies for a small sample (n= 5) were <40% for the Irish and Fast dredges, >57% for the medium‐sized Naturalist's dredge and >76% for the large Naturalist's dredge.There was a clear relationship between the number of taxa and the number of invertebrates taken at each site and this relationship was well described by a power law with an exponent within the range 0.18–0.53. The number of sampling units in the sample had no significant effect on the power‐law equations for each site. The power‐law equation was very similar for most of the dredges at each site, the only major exception being the Fast dredge at site 1. The implications of this relationship are discussed.
The seasonal variation in silicon concentration in chalk‐streams in relation to diatom growth
Authors: CASEY H. , CLARKE R. T. , MARKER A. F. H. 
Published: May 2006

SUMMARY.
Changes in silicon concentration were used to investigate the seasonal cycle of diatoms in chalk‐streams. Bore‐hole water shows no significant variation in silicon concentration. Five kilometres downstream there is a significant reduction between March and May. Further downstream the cumulative effect of biological silicon removal shows more complex patterns. There is a considerable variation in the seasonal pattern from year to year but an analysis of the seasonal pattern averaged over thirteen years on the River Frome confirms a later summer silicon reduction in August‐September, in addition to a much larger reduction in the spring.The negative correlation between suspended chlorophyll‐α and silicon concentrations confirms that suspended chlorophyll‐α concentrations respond more closely to changes in the loosely attached diatom flora than to other sources of chlorophyll‐α. However, neither variable is always suitable for monitoring changes in benthic diatoms. In headwaters, for example, transitory changes in diatoms do not have a significant impact on silicon concentration, while further downstream the suspended solids are affected by many other factors.Estimates of diatom production, based on changes in silicon concentration, gave rates of 1–2 g Si m‐2 day‐1 in a small headwater chalkstream during the spring.
Standing crop densities and distribution of Spirulina and benthic diatoms in East African alkaline saline lakes
Authors: TUITE C. H. 
Published: May 2006

SUMMARY.The diversity of Eastern Rift Valley alkaline saline lakes is illustrated and their temporal fluctuations in ionic concentration are emphasized.The standing crop densities of phytoplanktonic blue‐green algae of the genusSpirulinaand benthic diatoms were measured.Spirulinaabundance was measured as dry mass density and the validity of the gravimatric estimates was checked by chlorophyll analysis and microscopic counting. Benthic diatom standing crops were assessed by chlorophyll determinations.Spirulinadensity is extremely variable in time and may fluctuate over more than an order of magnitude. High density blooms ofSpirulinaare not a common characteristic feature of these lakes. The causes of changes inSpirulinastanding crop and the associated alterations in the structure of the primary producer community are discussed and three qualitative states which may occur are described.Similar standing crops of benthic diatoms (mean 45 mg m−2of chlorophyll‐α) were found at all lakes wherever the water depth was shallow enough to allow light penetration to the sediment surface.
Species associations and metal contents of algae from rivers polluted by heavy metals
Authors: FOSTER PATRICIA L. 
Published: May 2006

SUMMARY. The algal flora of the Rivers Hayle and Gannel. whieh drain copper and lead mining regions of Cornwall, are described and compared. Although fluctuations in the rarer members of the algal communities were observed, the dominant filamentous algae at most sites did not change over the year of study. Both the total algal abundance and the number of species were depressed at high metal sites. Associations of species that were evident in field samples were confirmed and correlated with water metal levels by principal component analysis. The close similarity between the flora of similar sites on the copper‐polluted River Hayle and the lead‐polluted River Gannei implies that the degree of metal pollution, rather than the polluting metal per se, determines the species present. All mine sites were characterized by a Microspora ‐community whereas a Zygnemales community of Spirogyra and Mougeotia species was typical of low metal pollution. Moderately polluted sites downsteam of the mines had an intermediate flora of Zygnemaies, Microsporales. Ulotrichales and gelatinous Volvocales and Tetrasporales species. No species could be said to invariably indicate metal pollution; the most abundant species at highly contaminated sites were also those with the widest distributions.Field samples of filamentous algae (mainly Spirogyra, Zygogonium, Mougeotia and Microspora species) contained metal concentrations several orders of magnitude greater than ambient levels. For copper and iron, both algal metal contents and concentration ratios (μg g‐1 algae/μg ml‐1 water) were positive functions of water metal levels, although algal iron appeared to plateau at water concentrations of about 1 mg ml‐1. Algal lead concentrations, but not the concentration ratios, also were positively correlated with water lead levels. Thus, for these three metals, the algal metal contents were indicative of ambient conditions. In contrast, algal zinc concentrations were nearly constant and consequently the concentration ratios for this metal were inversely related to water levels. This result suggests that unlike the uptake of other metals, uptake of zinc by these aigae may be strictly regulated.
Some aspects of the host:parasite relationships between adult blackflies (Diptera; Simuliidae) and larvae of the water‐mite Sperchon setiger(Acari; Hydrachnellae) in a small chalk stream in southern England
Authors: GLEDHILL T. , COWLEY JUDITH , GUNN R. J. M. 
Published: May 2006

SUMMARY. In Bere Stream three species of adult simuliids, S. ornatum, S. equinum and S. angustipes were parasitized by Sperchon setiger larvae. Trapped adult S. ornatum were more often parasitized than corresponding adults of S. equinum. The lower 95% confidence limits were used as an indication of the relative importance of the statistically significant differences and were high (10.4–33.6%). Laboratory experiments on the occupation of host pupae by pre‐parasitic Sperchon setiger larvae also indicated that pupae of S. ornatum were more often occupied than S. equinum. This was confirmed by tests on the difference in percentage occupation of more than 4000 held‐collected host pupae. In tests that indicated a significant difference in percentage parasitization between the sexes of the three host species, females were more often parasitized. However, the lower 95% confidence limits for the increase in percentage parasitization of females compared to males were low (0.9–10.2%). The majority of adult simuliids carried only one parasite. The mean number of larvae per trapped parasitized host was significantly greater for S. ornatum (2.69) than for S. equinum (1.77). There was no significant difference between the mean number of parasites carried by the sexes of S. ornatum for each year from 1975 through 1978 but females were significantly more heavily parasitized than males during 1979. The ventral neck region of all three host species is the main attachment site for Sperchon setiger larvae.The morphology of the pupae of S. ornatum and S. equinum is related to differences in levels of percentage parasitization between these two species. It is suggested that pupal morphology may be the most important factor in the selection of host simuliids by Sperchon setiger larvae.
Relationships between chloride and major cations in precipitation and streamwaters in the Windermere catchment (English Lake District)
Authors: SUTCLIFFE D. W. , CARRICK T. R. 
Published: May 2006

SUMMARY. 1. The ranges of concentrations for pH, CV. Na+. K+Ca2+, Mg2+ are given for streams draining igneous rocks (Borrowdale Volcanics) and sedimentary muds, silts and shales (Silurian Slates) in the catchment of Windermere (230 km2). Impacts on the biota are briefly discussed. Relative contributions of inputs from various sources are examined: precipitation, rocks and soils, sewage, deicing salt used on highways./2. In bulk precipitation, ratios of Na+/CV (as μequiv. I−1) ranged from 0.41 to 1.83 over a 2‐year period. The overall volume‐weighted mean ratio was 0.86, as in seawater, hut 2′4%(1975) and 5.7% (1976) of Cl− was non‐marine in origin, being balanced by H + (in winter), K and Ca2+ (in summer). In moorland headwater streams, CI− is largely derived from precipitation: there is a pronounced annual cycle of midwinter high and midsummer low concentrations unrelated to stream discharge. Na* and K+ display similar cycles but Na+, Ca2+ and Mg2+ (and pH) are discharge‐related due to leaching from rocks and soils: 10–20% Na+, 15–17% Mg2+ and 65–75% Ca2+ are so‐derived whereas K+ comes from precipitation. Na+/Cl+ ratios in streams on Borrowdale Volcanics alter seasonally, with midsummer values >1. Lower values occur in streams on Silurian Slates where some CI− is apparently derived from rocks.3. Seasonal changes in streamwater concentrations of Cl, Na4 andK+are exponentially related to time. Instantaneous rates of change i day‐11) are compared in relation to position in the catchment and inputs from anthropogenic sources. Deicing salt has raised (10–100‐fold) the concentrations of Na* and Cl− in streams on mountain passes; the effects persist throughout the year.
A test for the production of sexual pheromones by Daphnia magna (Crustacea: Cladocera)
Authors: CREASE TERESA J. , HEBERT PAUL D. N. 
Published: May 2006

SUMMARY. (1) Swarming in the Cladocera has often been associated with periods of sexual reproduction and this has led to the suggestion that members of opposite sex are attracted to one another. The most plausible mechanism by which this could occur is through the production of pheromones. The present experiments aimed to determine if Daphnia magna Straus produce such chemicals.(2) No evidence was found for the presence of sexual pheromones. The behaviour of both males and females was unaffected by the presence of sexually receptive animals of the opposite sex.(3) It is suggested that the cited relationship between sexual reproduction and swarming may be due to the fact that sexual reproduction occurs during periods of high population density. It is during such periods that swarming behaviour would be most apparent.
The fresh waters of Shetland: Physical and morphometric characteristics of lochs
Authors: GEORGE D. G. , MAITLAND P. S. 
Published: May 2006

SUMMARY. 1. Basic physical and morphometric data are presented for sixty‐five lochs on the Shetland Islands. The interrelations between loch dimensions are comparable to those recorded elsewhere in Scotland, but the smaller lochs on Shetland tend to be somewhat shallower, and the large lochs somewhat deeper than usual.2. The results of a multivariate analysis show that most of the physical variables measured in the field are closely correlated with easily measured map attributes.
Phytoplankton periodicity: the interactions of form, function and environmental variability
Authors: REYNOLDS C. S. 
Published: May 2006

SUMMARY. 1. This review considers the periodic cycles of species dominance in a wide selection of temperate lakes. By ascribing individual species to assemblages, a high incidence of similarity among periodic cycles is demonstrated. Reference to lakes at high and low latitudes, as well as to rivers, shows conformity to parts of the same broad patterns.2. The role of population dynamics in shaping community structure is emphasized. Two types of change are recognized: autogenic, undirectional subsequences (successions), regulated by specific responses to critically changing resource‐ratio gradients; and allogenic changes, regulated by variability in the physical environment.3. Analysis of the responses of representative species to allogenic change permits further grouping of the assemblages. These groupings coincide with clear morphological distinctions among the same phytoplankton species according to their unit sizes and surface area/volume ratios.4. It is argued that these properties condition the physiological responses of algae to seasonal variations in temperature, mixing and exposure to the underwater light field. The responses are compounded by relative resistances to loss processes (sinking, grazing), by short‐term photosynthetic adaptation and vertical migratory behaviour.5. Graphical summaries are presented that relate the morphologically‐, physiologically‐ and behaviourally‐mediated responses to a hierarchy of physical, chemical and biotic environmental variables. Phytoplankton periodicity is the outcome of these interactions.