bluuebunny/crossref_metadata_2025 huggingface dataset:
Radionuclide dating of the recent sediments of Blelham Tarn
Authors: PENNINGTON W. , CAMBRAY R. S. , EAKINS J. D. , HARKNESS D. D.
Published: May 2006

Lake sediments of the last 1000 years provide a unique record of environmental changes. Methods of dating this record are reviewed and discussed. Sediments of the last 20 years, which are of particular biological significance because of their record of man‐made changes in lakes (including enrichment and pollution) have been dated successfully by the distribution within them of the fallout product 137Cs, present in the atmosphere since 1954 and reaching a peak of supply in 1963. The structured pattern shown by the curve for 137Cs concentration in most sediments investigated indicates that faunal mixing of the surface muds does not destroy the vertical stratification of the sediment profile.

Sediments up to 120 years old have been dated by a lead isotope technique, and the results of this proved consistent with both 137Cs dating and with palaeomagnetic dating where this was possible.

Theoretical considerations of the application of radiocarbon dating to organic material of 18th and 19th century date are reviewed.

Results of application of these radionuclide techniques to the sediments of a small lake, Blelham Tarn, near Windermere, are presented. Evidence from 137Cs and 210Pb dating of profiles from several different positions within the lake shows that the depth of the annual increment to the sediments varies by a factor of × 2 from place to place. The concentration within the sediment of chemical and biological variables shows no significant variation from one position to another; therefore calculated values for amounts of each variable included within unit area of the annual increment depend primarily on the thickness of this at the site chosen, and so cannot be directly related to the rates of supply of, for example, pollen grains or total organic matter, and so to rates of productivity.

Results from nine 14C dates on material 400–1000 years old, when correlated with analyses for pollen and sediment composition, demonstrate the profound effects of agricultural practices in the catchment (assumed to be deforestation and ploughing) in disturbing the orderly transfer to lake sediments of material eroded from the catchment.
Dissolved organic matter of a low‐coloured stream
Authors: LARSON R. A.
Published: May 2006

SUMMARY.
The dissolved organic matter (DOM) of White Clay Creek (Pennsylvania, U.S.A.), a low‐coloured stream, was characterized by gel permeation chromatography, humic acid determination, compound classification analysis and gas chromatography.

Large polymers (approximate mol.wt above 5000) were virtually absent. The majority of the DOM consisted of fulvic acid‐like material, of probable mol.wt less than 3000. Highly coloured material represented only a small portion of the total. Substances classifiable as phenols, carbohydrates, lipids, amino acids or proteins made up only a small fraction of the DOM. Sixteen low mol. wt compounds (carboxylic acids, amino acids, carbohydrates and an amide) were tentatively identified.

DOM concentration had a mean value of 6.4 mgC/l and showed annual fluctuations, with maxima in autumn and in late winter.
The biology of an Antarctic aquatic moss community
Authors: PRIDDLE J. , DARTNALL H. J. G.
Published: May 2006

SUMMARY.
Two species of aquatic moss (Calliergon sarmentosum and Drepanocladus sp.) occur in deep water in Moss Lake, Signy Island (60° 43′S, 45° 38′W). Their elongate stems support a structurally complex community of epiphytic algae and associated invertebrates which has a greater diversity than the surrounding benthic algal communities.

Qualitative differences in the distribution and abundance of the epiphytic algae are described. Two groups of algae present on both mosses are distinguished–‘habitual’ and ‘casual’ epiphytes. On Calliergun, algae are most abundant in the leaf axil. The succession of epiphytes down the stem and the progressive deterioration of the moss plant are used to characterize six stem zones.

The invertebrates are benthic and most move actively among the moss. Six species of rotifers are more or less permanently attached and show a preference for the middle stem zones where epiphyte cover is highest. Four species favour the leaf axil, the other two colonize the bare underside of the leaf.

A settlement experiment has shown the importance of wind‐induced mixing in summer for the transport of some epiphytic species from shallow parts of the lake. The settlement of sessile rotifers is effected by their larvae.

Photosynthesis declines from the stem apex to the dead old stem. Much of the primary production of the community is algal. The respiration maximum occurs where the highest concentration of epiphytic algae and invertebrates is found.

Interrelationships between the invertebrates and the epiphytic algae are suggested and a comparison is made between these data and other studies.
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.
Mobilization of sediment phosphorus by submersed freshwater macrophytes
Authors: BARKO JOHN W. , SMART R. MICHAEL
Published: May 2006

SUMMARY.
The mobilization of sediment phosphorus (P) by three submersed freshwater macrophyte species was investigated on five different sediments. The study was conducted under controlled environmental conditions in lucite columns that enabled the separation of sediment and plant roots from the overlying P‐free ‘complete’ nutrient solution. The species investigated (Egeria densa, Hydrilla verticillata, and Myriophyllum spicatum) had minor root systems (on a biomass basis), but were demonstrated to be fully capable of deriving their P nutrition exclusively from the sediments. Phosphorus absorption and translocation into shoots (i.e., mobilization) was substantial, and in some cases suggested a greater than 1000‐fold turnover of interstitial water PO4‐P over a 3‐month period. Sediment P mobilization, a function of both plant growth and tissue P concentration, differed considerably among plant species and sediments. Phosphorus release from the species investigated appears to be primarily dependent upon tissue decay rather than excretory processes. The mobilization of sediment P by submersed macrophytes represents an important aspect of the P cycle, and may affect the overall metabolism of lacustrine systems.
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.
Methods for the isolation, sterilization and cultivation of Lemnaceae
Authors: BOWKER DAVID W. , DUFFIELD ANTHONY N. , DENNY ṔARICK
Published: May 2006

SUMMARY.
A method is described for isolating and sterilizing fronds of Lemnà gibba, L. minor, L. trisulca, L. polyrrhiza and Wolffia arrhiza, employing enrichment followed by sodium hypochlorite treatment. The method enables about 4% of the total number of treated fronds to be used as initiators of clonal cultures in which bacteria responding to organic enrichment and algae are excluded. Appropriate growth media, culture vessels and culture conditions are detailed.
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.
A desk study of the relationship between temperature and hatching time for the eggs of five species of salmonid fishes
Authors: CRISP D. T.
Published: May 2006

SUMMARY.
Information on temperature (T°C) and time from fertilization to 50% hatch (D days) for five species of salmonid fishes has been used to assess several mathematical models relating D and T. No single equation gave the best fit to all five data sets. The power law with temperature correction (α), log101D= log10a+b log10 (T‐ α) and the quadratic, log10D= log10a+bT+b1T2 (where a, b, b1, and α are constants), each accounted for over 97 % of the variance of D and were good fits to the observed data points for all five species. There was little difference between the predictions obtained from these two equations within the range of observed temperatures. Therefore, the simpler power‐law model is preferred. However, there were substantial within‐species differences between values of D predicted from extrapolations of the two models from 2 or 3°C down to 0°C. When more data for low temperatures become available it will be possible to make a more objective choice of model.
Epilimnetic and hypolimnetic symptoms of eutrophication in Great Mazurian Lakes, Poland
Authors: GLIWICZ Z. MACIEJ , KOWALCZEWSKI ANDRZEJ
Published: May 2006

SUMMARY.
An increase in the trophic state and productivity of a lake is not necessarily accompanied by a decrease in epilimnetic Secchi disc transparency. In smaller lakes with sharp thermoclines the symptoms of eutrophication may be more evident as a decrease in transparency in the epilimnion but, in larger lakes with poorly defined thermoclines, symptoms of eutrophication may be more evident in the hypolimnion as shown by an increase in the rate of hypolimnetic oxygen consumption.
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.
Comparison of three wet‐alkaline methods of digestion of biogenic silica in water
Authors: KRAUSSE GERALD L. , SCHELSKE CLAIRE L. , DAVIS CURTISS O.
Published: May 2006

SUMMARY. Methods for determination of low levels of biogenic silica (0.2–0.4 mg SiO2) in aqueous samples after digestion with three wetalkaline extraction procedures compared favourably in both precision of replicates and recovery of silica utilized by diatoms in budgeted cultures. Leaching samples with 0.2 M NaOH for 10–15 min at 100°C was the least time consuming procedure. Also interference from silicate minerals was lower for this method than leaching with either 0.5 or 5% Na2CO3 for 2 h at 85°C. The use of filters to concentrate samples enables detection of low levels of biogenic silica with colorimetric procedures. Polycarbonate filters are recommended in preference to cellulose acetate or polyvinyl chloride filters for sample collection. Time‐course experiments are recommended for establishing digestion times and determining the presence of mineral silicate interference. Wet‐alkaline digestion methods are recommended for routine analysis of biogenic silica in suspended matter in preference to infra‐red analysis, alkaline fusion and hydrofluoric acid/nitric acid methods.
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.
Lough Ennell: laboratory studies on sediment phosphorus release under varying mixing, aerobic and anaerobic conditions
Authors: LENNOX L. J.
Published: May 2006

SUMMARY. 1. The exchange of phosphorus between the epilimnetic (shallow zone) sediment and water column in Lough Ennell was investigated in laboratory experiments using five intact cores.

2. Variations in water mixing, sediment suspension and aerobic–anaerobic oxygen status in the water column and its effects on sediment phosphorus release rates were determined.

3. Experimental results indicated that phosphorus release is possible under both aerobic and anaerobic conditions. Aerobic release (0.025 mg P l−1 over 5 days) was possible up to the point when mass resuspension of sediment occurred. Anaerobic release for the same period and mixing conditions was 0.183 mg Pl−1.

4. The release rate under aerobic conditions at 10°C equates to an internal areal loading of 0.134 g P m−2 yr−1, which is approximately 17% and 30% of the average total phosphorus and orthophosphate loadings respectively for the period 1974–79.

5. The results clearly implicate aerobic inorganic phosphorus release from the epilimnetic sediments as a significant source of this nutrient to the overlying water column and is likely a major factor in the continuing eutrophic status in the lake.
Temporal patterns in diet and rate of food consumption of the three‐spined stickleback (Gasterosteus aculeatus L.) in Llyn Frongoch, an upland Welsh lake
Authors: ALLEN J. R. M. , WOOTTON R. J.
Published: May 2006

SUMMARY. 1. Monthly and diel patterns of food consumption by the three‐spined stickleback, Gasterosteus aculeatus L., were studied in Llyn Frongoch, a small reservoir in upland mid‐Wales.

2. Copepods were particularly prominent in the diet in spring and autumn, with ephemeropteran nymphs prominent in summer. Chironomid pupae and stickleback eggs were also elements of the diet in summer, whereas algae, plant material and debris were more important in autumn and winter. Chironomid larvae and ostracods were present throughout the year, but there was some doubt as to the importance of ostracods as digestible food items.

3. Stomach contents were heaviest in spring and late summer and lightest in late autumn and winter.

4. Samples for the diel samples were taken four times, once in each season. These diel samples largely reflected the seasonal changes in diet noted in the monthly samples. There were few cases of a clear switch in the composition of the diet during a 24 h period. Feeding occurred during daylight, the weight of the stomach contents declined during darkness.

3. Several methods provided estimates of the daily rate of food consumption which ranged from 3.5 mg in December (4°C), to 19.0 mg in May (15°C). These estimates and others obtained independently suggest that the annual rate of food consumption for a stickleback in Llyn Frongoch is between 2000 and 5000 mg wet weight.
A palaeolimnological record of human disturbance from Harvey's Lake, Vermont: geochemistry, pigments and diatoms
Authors: ENGSTROM D. R. , SWAIN E. B. , KINGSTON J. C.
Published: May 2006

Stratigraphic analyses of inorganic geochemistry, pigments and fossil diatoms in a 0.7 m core of profundal sediments are used to reconstruct the limnological history of Harvey's Lake, Vermont, over the last 1000 years. The lake is moderately productive, deep (44 m) and clear, and the phytoplankton today is dominated by the blue‐green alga, Oscillatoria rubescens. Sedimentary pigments unique to blue‐green algae, oscillaxanthin and myxoxanthophyll, provide a detailed history of changes in the O. rubescens population. Accurate sediment chronology is derived from 210Pb, 137Cs and 14C dating and from the stratigraphy of pollen and sawmill wastes.

Primary production increased in Harvey's Lake in 1780 following European settlement and again after 1945, as shown by greater accumulation of sedimentary pigments and diatom frustules, and changes in fossil algal assemblages. Blue‐green algae first appeared in abundance about 1945, indicating nutrient enrichment from dairy wastes and shoreline development. Increased deposition of elements associated with classic minerals also suggests greater soil erosion during both of these intervals.

Two episodes of increased sedimentary anoxia (1820–1920 and 1945–present) are marked in the sedimentary record by enhanced pigment preservation, changes in authigenic Fe and Mn stratigraphy,’and the development of laminated sediments. The earlier episode of oxygens depletion is correlated with the discharge of sawmill wastes into the lake, and the later episode is associated with increased primary production.

Based on these data a new model for Fe and Mn sediment stratigraphy is proposed for lakes that do not undergo complete hypolimnetic anoxia.

Fine‐scale resolution of recent diatom and oscillaxanthin stratigraphy provides historical evidence for a long‐term negative interaction between diatom and blue‐green algal populations in Harvey's Lake.
Aspects of nitrogen fixation in Lough Neagh. I. Acetylene reduction and the frequency of Aphanizomenon flos‐aquae heterocysts
Authors: RIDDOLLS ANTHEA
Published: May 2006

SUMMARY.

An investigation was made of the relationships between rates of nitrogen fixation (acetylene reduction), Aphanizomenon flosaquae heterocysts, NO3‐N concentration and other environmental factors which occurred in Lough Neagh between 1969 and 1972.

The maxima of cells differentiated as heterocysts (approximately 5% (1970), and approximately 7% (1971 and 1972) occurred when NO3‐N concentration was very low or undetectable.

Acetylene reduction was detectable between 16 May and 8 September 1972 but was not measured in the other years. Rates were greatest in the euphotic zone and it appeared that the nitrogenase activity was closely linked to a light dependent system.

Areal rates of acetylene reduction were highly correlated with Aphanizomenon heterocyst concentration (r=0.92). There was some indication that a release of phosphorus from the sediments might have stimulated Aphanizomenon nitrogen fixation on one occasion at the end of a calm period. Results show that the most likely conditions for the development of large crops of heterocystous species in Lough Neagh include a scarcity of NO3‐N and a plentiful supply of phosphorus.
Crustacean diversity in relation to the size of water bodies: some facts and problems
Authors: FRYER GEOFFREY
Published: May 2006

SUMMARY.

Data on the crustacean faunas of 207 lowland water bodies in Yorkshire, involving 125 species, are discussed in relation to site area. Not unexpectedly, large water bodies generally have the most diverse faunas, but the relationship is not a simple one so far as individual species are concerned. While many show a progressive increase in percentage occurrence from small to large water bodies, the reverse is true for others.

Chydorid cladocerans, of which twenty‐one species were recorded, show an unambiguous preference for large water bodies. While differences in habitat diversity appear insufficient to explain the almost seven‐fold difference in chydorid representation between ponds and large water bodies, there are also difficulties in attributing the situation to ease, or difficulty, of dispersal. The strategy of firmly attaching resting eggs to substrata employed by some chydorids is more likely to frustrate than to promote dispersal.

General habits, ecological preferences and feeding habits of the commonest species are analysed in an attempt to clarify the relation of number of species to size of water body and some paradoxical features of dispersal are noted.

Extrapolation from the data to very large lakes is shown to be misleading. Numerical data, even for a large number of water bodies, are no substitute for knowledge of the ecological requirements and tolerances of individual species.

Examples are given of the rapid colonization of newly formed ponds by small crustaceans. The relevance of such observations to the theory of island biogeography and to various ecological problems, and the possibility of experimental work using small crustaceans and small ponds are noted.
Measurement and interpretation of sedimentary pigments
Authors: SWAIN EDWARD B.
Published: May 2006

SUMMARY.

The factors that control the concentrations of pigments in lake sediments are examined using data from (i) transects across lake basins, (ii) surface samples from logographic and atrophic lakes, and (iii) two 210Pb‐dated short cores. Methods for the rapid non‐chromatographic analysis of percent native chlorophyll and the blue‐green algal pigments oscillaxanthin and myxoxanthophyll are described.

The concentrations of chlorophyll derivatives, total arytenoids, oscillaxanthin and myxoxanthophyll, and percent native chlorophyll, are higher under conditions along the transects favorable for preservation. Chlorophyll degrades at about the same rate as total carotenoids, and oscillaxanthin degrades at about the same rate as myxoxanthophyll. Therefore, both the ratio of chlorophyll to arytenoids (CD/TC) and the ratio of oscillaxanthin to myxoxanthophyll (OSC/MYX) are mostly determined by the quality of autochthonous production rather than by preservation conditions.

CD/TC values are higher in logographic lakes than in atrophic lakes, apparently as a result of differences in production of the two pigment types. Calculations show that CD/TC shifts in these two cores cannot be a record of the allochthonous‐autochthonous Baltic in the systems. Instead, the CD/TC values shift with large changes in the kinds of plants dominating primary production.

The stratigraphy of percent native chlorophyll appears to record the hypohmnetic oxygen concentrations at the time of deposition.

No obvious reason exists why a eutrophic lake should produce more pigment per gram organic matter than should an oligotrophic lake. However, several correlated mechanisms tend to produce higher sedimentary pigment concentrations in eutrophic lakes. Most of these mechanisms, such as hypolimnetic oxygen consumption, indirectly translate greater primary productivity into greater sedimentary pigment concentration. Therefore, pigment concentrations are sometimes misleading, and pigment accumulation rate may be a better indicator of past primary production.
The effect of tadpoles on algal growth in temporary, rain‐filled rock pools
Authors: OSBORNE P. L. , McLACHLAN A. J.
Published: May 2006

SUMMARY.

Small, temporary, rain‐filled rock pools in Malawi, Central Africa, are colonized by algae, insect larvae and tadpoles. Algal growth in these pools is largely controlled by nutrient supply, flushing rate and the presence of tadpoles.

Dissolved nitrogen and phosphorus concentrations were usually high following filling but subsequently declined. Nitrogen supply may limit algal growth at times. The flushing rate of the pools is an over‐riding factor in determining the population size of floating algae.

Experiments and field observations showed that tadpoles apparently, paradoxically, promoted the growth of the epineustic and phytoplanktonic algae on which they grazed. The explanation of this paradox probably has in the transfer, by the tadpoles, of nutrients from the sediments to the overlying water. This nutrient enrichment stimulates the growth of the epineuston and phytoplankton.
Movements of self‐marked caddisfly larvae, Chyrnda centralis (Trichoptera: Limnephilidae), in a Sierran spring stream, California, U.S.A.
Authors: ERMAN NANCY A.
Published: May 2006

SUMMARY. 1. The tendency of larvae of Chyranda centralis to mark themselves by adding coloured plastic segments to their cases was used to study instream movements of the species. Plastic strips of different colours were placed at measured distances down a small spring stream and larvae cut pieces and incorporated them in their cases.

2. Over 50% of the marked population moved upstream into cooler water prior to pupation in an exceptionally dry year. The greatest distance moved upstream by a single larva was 56.9m, In a wet year, when daytime stream temperatures were cooler, 11–28% of the marked population moved upstream. Downstream movement occurred in both years late in the fifth instar.

3. Larvae selected yellow in preference to other colours in laboratory tests and they preferred heavy, textured plastic to light, smooth plastic as they neared pupation.

4. Upstream movements, found also in Desmana bethula (Trichoptera: Limnephilidae) in the same spring stream, may be an adaptation for avoiding pupation in areas of high temperature, low oxygen concentration, or intermittent flow.
The distribution of breeding dippers (Cinclus cinclus (L.); Aves) in relation to stream acidity in upland Wales
Authors: ORMEROD S. J. , ALLENSON N. , HUDSON D. , TYLER STEPHANIE J.
Published: May 2006

SUMMARY. 1. The distribution of breeding dippers was assessed in 1984 over seventy‐four sites on soft‐water streams throughout mid and north Wales.

2. Sites without breeding dippers had significantly higher mean concentrations of filterable aluminium, lower mean pH, fewer trichopteran larvae and ephemeropteran nymphs, and were on rivers with more conifer afforestation on their catchments, than sites where dippers were present.

3. We speculate that influences which increase the acidity of soft‐water streams could be detrimental to their populations of dippers, although further data are required on causative mechanisms.
Are the lake‐dwelling leeches, Glossiphonia complanata (L.) and Helobdella stagnalis (L.), opportunistic predators on molluscs and do they partition this food resource?
Authors: YOUNG J. O. , PROCTER R. M.
Published: May 2006

SUMMARY. 1. Predation on the mollusc genera Potamopyrgus, Bithynia, Valvata, Lymnaea, Physa, Planorbis and Pisidium by the leeches Glossiphonia complanata (L.) and Helobdella stagnalis (L.) was examined in five eutrophic lakes at monthly intervals over one year using a serological technique.

2. Feeding intensity varied seasonally, being lowest in winter and highest in summer. Small, medium and large leeches preyed to the same extent on the several mollusc genera; this was true for both leech species. Qualitatively, the diet of both glossiphoniids was similar throughout the year. Snail genera were consumed in proportion to their relative abundance in the field. Quantitatively, Glossiphonia preyed more heavily on snails than did Helobdella.

3. It is concluded that both leech species are opportunistic predators.