bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

SUMMARY

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.
The spectral absorption and scattering properties of dissolved and particulate components in relation to the underwater light field of some tropical Australian fresh waters
Authors: KIRK J. T. O. , TYLER P. A. 
Published: May 2006

SUMMARY. 1. The inherent optical properties (scattering coefficients and absorption coefficients across the photosynthetic waveband) are presented from diverse tropical water bodies (billabongs) in the Alligator Rivers Region of northern Australia.2. The data are used to interpret observed characteristics of the underwater light field as exemplified by the spectral distribution, and overall rate of attenuation, of photosynthetically available radiation (PAR).3. Attenuation of PAR, especially in the blue waveband, is caused primarily by intense light absorption by the yellow‐brown humic pigments, both soluble and particulate, in the water.4. It was estimated that in six moderately turbid billabongs, light scattering increased attenuation by an average of 58% above that attributable to absorption alone, whereas in a highly turbid billabong the increase was 111%.5. A distinguishing feature of the optical character of these billabongs, compared with previously studied water bodies in southern Australia, is the great contribution to light absorption made by the particulate humic material.
The benthos of a natural West African lake, with emphasis on the diel migrations and lunar and seasonal periodicities of the Chaoborus populations (Diptera, Chaoboridae)
Authors: HARE LANDIS , CARTER JOHN C. H. 
Published: May 2006

SUMMARY. 1. Three Chaoborus species dominated in abundance and biomass the mid‐lake benthic fauna of a small, natural Nigerian lake. Each population showed distinct seasonal varialitions. C. anomalus being most abundant during the early rainy season, while (ceratopogones and C edults were most abundant during the dry season. A fourth species. C. fuscinervis (not reported previously from West Africa), was collected only in the adult stage. Also abundant at mid‐lake were the Chironomidae. Chironomus seydeli, Prodadius brevipetiolatus and Tanypus brevipalpis. all of which showed a seasonal pattern most resembling that of C. anomalus.2. Second. third and fourth instar larvae and pupae of the Clutoborus species underwent a diel vertical migration between the lake sediments (diurnal) and the water column (nocturnal) which was strongly related to prevailing light conditions.3. Lunar periodicities of Chaoborus emergence determined from emergence trap collections are described for the first time. Corresponding lunar periodicities of larval abundance were observed in two of the species. The statistical techniques employed in describing the lunar periodicities permit the estimahon of generation times.4. C. anomalus is believed to be parthenogenetie in the study lake (no males collected). while the other Chaoborus species are bisexual (1:1 sex ratios). The biology of this species is discussed in relation to the parthenogenetie condition.
The impact of planktivorous flsh on the structure of a plankton community
Authors: POST J. R. , McQUEEN D. J. 
Published: May 2006

SUMMARY. 1. The abundance of pianktivorous juvenile yellow perch, Perca flavescens, was manipulated in three 750 m3 enclosures in a eutrophic lake.2. There was a significant negative relationship between fish and zoopiankton biomasses. At high fish densities the zooplankton community was dominated by small filter‐feeding cladocera. primarily bosmi‐ nids. At low fish densities the zooplankton community was dominated by large filter‐feeding cladocera, primarily daphnids.3. There was no significant relationship between zooplankton and phytoplankton biomasses when considered over the whole experiment but there was a trend towards lower phytoplankton biomass in the enclosure dominated by daphnids during mid‐summer.4. We conclude that although planktivorous fish have a strong negative impact on zooplankton community biomass and size structure, the relationship at the next lower trophic level, zooplankton and phytoplankton, is much weaker. Therefore, the biomanipulation of planktivorous fish populations as a management technique to control phytoplankton abundance is largely ineffective.
A numerical model of nitrogen flxation and its application to Lake Valencia, Venezuela*
Authors: LEVINE SUZANNE N. , LEWIS WILLIAM M. 
Published: May 2006

SUMMARY. 1. A numerical model for calculation of daily and annual nitrogen fixation in lakes is presented. The model is based on empirically‐derived equations for the rates of nitrogen fixation by heterocysts (nitrogen‐fixing cells) in relation to light and on functions for the vertical and tetnporal distributions of heterocysts and light in a lake.2. Applications of the model to Lake Valencia, Venezuela, between December 1980 and December 1981 indicated that nitrogen fixation is largely a surface phenomenon in this lake: 80% of diurnal fixation occurred within 1m of the water surface.3. Nitrogen fixation is largely restricted to periods of lake stratification, when the phytoplankton have sufficient light for growth, but dissolved inorganic nitrogen is scarce. Nitrogen fixation was maximal late in the stratification period of 1981: 85 % of fixation occurred within the last 3 months of the 9‐month period.4. The annual nitrogen fixation in Lake Valencia is 26 kg ha−1, which is comparable to the nitrogen fixation in temperate eutrophic lakes with seasonal blue‐green algal blooms. However, nitrogen fixation accounted for only 23% of the total nitrogen supply to Lake Valencia in 1981.
Coldingham Loch, S.E. Scotland. II. Phytoplankton succession and ecology in the year prior to mixer installation
Authors: BAILEY‐WATTS A. E. 
Published: May 2006

SUMMARY. 1. Total phytoplankton biomass in the small (8 ha), intermittently stratifying, eutrophic Coldingham Loch exhibited spring and autumn maxima of about 35 μg chlorophyll a l1. Late winter and early spring assemblages included Chlorococcales (dominated by Coetxochloris pyrenoidosa Korsch. and Dichotomococcus curvatus Korsch.), diatoms (unicellular Centrales and Asterionella formosa Hass.) and desmids (Closterium acutum Brèb. and Staurastrum chaetoceras(Schrod.) G. M. Smith). Small populations of Coetastrum and Oocystis characterized the summer period. The commonest “blue‐green alga”, Aphanizomenon flos‐aquae Morr. ex Born, et Flah. (Cyanobacteria) attained its maximum population density in September just after the loch had permanently de‐stratified. It was replaced by another growth of Closterium acutum which reached its annual peak density of 900 cells ml−1 in October.2. It is likely that nitrogen in summer and silica at various times of the year limited the growth of certain species; it is also possible that phosphorus limited growth in spring.3. When physical conditions and nutrient concentrations are resolved into their basic, simple, seasonal patterns, a number of species preferences for particular environmental requirements become apparent. Of special significance is the competitive advantage over other plankters of Aphanizomenon in being able to resist sinking losses under stratified conditions and thrive at low ambient nitrate levels. Equally, there are some species exhibiting adaptability to a wide range of conditions.4. The observed periodicity is examined in relation to recently published schemes that summarize phytoplankton‐environment interactions.
Fossil diatoms and the paleolimnology of Lake Rukwa, Tanzania
Authors: HABERYAN KURT A. 
Published: May 2006

SUMMARY. 1. A 23.1 m sediment core from Lake Rukwa, southwest Tanzania, records 13,000 years of climatic change in five diatom assemblage zones. Zone E (13,000–12,7000 bp) reflects the transition from the waning late glacial arid phase to pluvial conditions, as indicated by the co‐occurrence of diatoms associated with fresh and relatively saline conditions. Zone D (12,700–4400 bp) represents a moist period with frequent stratification, indicated by the halophobic genera Melosira and Stephanodiscus, whieh also represent alternating silica‐rich and silica‐dcpleled waters. Beginning with Zone C (4400–3900 bp) the lake became much more saline with Thalassiosira predominating. This drying trend was reversed slightly in Zone B (3900–3300 bp). During the last three millennia (Zone A), lake salinity was further reduced, while transitory moist phases were occurring in more northerly lakes such as Victoria and Kivu.2. Lake Rukwa was relatively stable over a time scale of centuries, but on an annual basis is quite variable in salinity depending on the local rainy season.3. These results agree well with the generalized paleoclimatie chronology of East Africa and suggest that the Holocene climatic regime of East Africa extended at least to 8°S.
Solar heating and its influence on mixing in ice‐covered lakes
Authors: MATTHEWS P. C. , HEANEY S. I. 
Published: May 2006

SUMMARY 1. The influence of solar heating on the formation of temperature and density profiles of ice‐covered lakes is considered.2. Mathematical models are derived to quantify the effect of solar heating on vertical stability and its dependence on critical parameters,3. Solar heating is shown to be able to account for the thermal structure and mixing patterns of certain ice‐covered lakes.4. The importance of convective mixing is discussed in relation to the distribution of phytoplankton and nutrients.