bluuebunny/crossref_metadata_2025_split huggingface dataset:
The upper limit of photosynthetic productivity by phytoplankton: evidence from Ethiopian soda lakes
Authors: TALLING J. F. , WOOD R. B. , PROSSER M. V. , BAXTER R. M. 
Published: May 2006

SummaryPhotosynthetic production by phytoplankton was studied in two Ethiopian soda lakes, alkalinity 51‐67 m‐equiv./l, with abundant blue‐green algae. The deeper lake, L. Aranguadi, contained extremely dense crops composed almost entirely of SpiruUna (Oscillatoria, Arthrospira) platensis. Measurements of the spectral attenuation of light showed that the most penetrating component was displaced to the red spectral region, and estimates of the chlorophyll a content in umt area of the euphotic zone were often similar to the highest values (∼200‐300 mg/m2) expected on theoretical grounds.The vertical distribution of photosynthetic activity per unit water volume was of a typical pattern for phytoplankton, with light‐inhibition often present, although the euphotic zones did not exceed 0.6 m in depth. From these profiles, computed rates of gross photosynthesis per unit area of lake surface reached a magnitude of 1.4–2.4 g O2/m2.h in both lakes. They were obviously severely limited by self‐shading behaviour i n the algal populations. An appreciable inverse relationship between photosynthetic capacity and population density was only found in the densest populations of L. Aranguadi, with chlorophyll a content > 2000 mg/m3, where depressed rates might result from experimental artefacts in closed bottles. In this lake, two independent estimates of gross production, based on the analysis of diurnal changes in the open water, were as high as 43 and 57 g O2/m2. day.Diurnal changes of stratification in the two lakes are described and related to the controlling temperature (density) stratification. They include occasionally complete nocturnal deoxygenation in the deeper lake, evidence of heavy respiratory uptake.The high photosynthetic productivity is interpreted as dependent upon the coupling of high algal contents in the euphotic zone (^S) with high values of photosynthetic capacity (^max)‐ It is probably favoured by the tropical situation affecting temperature and illumination, by a surplus of dissolved inorganic phosphate, and especially by the considerable reserves of carbon dioxide in these soda lakes.
Algal nitrogen fixation in Californian streams: diel cycles and nocturnal fixation
Authors: HORNE ALEXANDER J. 
Published: May 2006

SummaryThirty‐six hour diurnal studies of Ng‐fixation by Nostoc in a rocky‐bedded stream were carried out during the peak of the seasonal cycle of growth on clear and cloudy days in 1971 and 1972. On both occasions an unexpected pattern of N2‐fixation occurred with maximum fixation rates in the light but also in the dark portion of the day, with lowest fixation periods in the early evening. I postulate that competition for reductant between nitrogenase and other processes, especially photorespiration, controls this unusual diel cycle rather than variations in the intracellular N‐pool. N2‐fixation rates on a cloudless May day in 1971 ranged from 0.2 to 4.8 nmoles C2H4 cm−2 h−1 and from 0.3 to 3.3 nmoles C2H4 mg−1 h−1 dry weight of Nostoc, depending on time of day and favourableness of site. On the same site on a cloudy, rainy May day in 1972 fixation ranged from 0.5 to 3.1 nmoles C2H4 mg−1 h−1 dry weight, and from 1 to 4.5 nmoles C2H4 mg−1 h−1 ash‐free dry weight of Nostoc. Since Nostoc is most abundant in unshaded areas, and since one‐third of each day's nitrogen i s fixed in the dark, future studies should take dark fixation into account.
A pumping system for collecting horizontal plankton samples and recording continuously sampling depth, water temperature, turbidity and in vivo chlorophyll
Authors: GEORGE D. G. 
Published: May 2006

SummaryThis paper describes a deck‐mounted pumping system developed for collecting discrete, sequential plankton and water samples while also providing a continuous record of sampling depth, water temperature, turbidity and in vivo chlorophyll. It includes some results obtained with the equipment during a study of factors influencing the horizontal distribution of crustacean plankton in the lake Windermere.
The rate of colonization by macro‐invertebrates on artificial substrate samplers
Authors: MEIER PETER G. , PENROSE DAVID L. , POLAK LOREN 
Published: May 2006

SUMMARY.
The influence of exposure time upon macro‐invertebrate colonization on modified Hester‐Dendy substrate samplers was investigated over a 60‐day period. The duration of exposure affected the number of individuals, taxa and community diversity.The numbers of individuals colonizing the samplers reached a maximum after 39 days and then began to decrease, due to the emergence of adult insects. Coefficients of variation for the four replicate samples retrieved each sampling day fluctuated extensively throughout the study. No tendencies toward increasing or decreasing coefficients of variation were noted with increasing time of sampler exposure.The number of taxa colonizing the samplers increased throughout the study period. The community diversity index was calculated for each sampling day and this function tended to increase throughout the same period. This supports the hypothesis that an exposure period of 6 weeks, as recommended by the United States Environmental Protection Agency, may not always provide adequate opportunity for a truly representative community of macro‐invertebrates to colonize multiplate samplers.Many of the taxa were collected in quite substantial proportions after periods of absence or extreme sparseness. This is attributed to the growth of periphyton and the collection of other materials that created food and new habitats suitable for the colonization of new taxa.Investigation of the relationship between ‘equitability’ and length of exposure revealed that equitability did not vary like diversity with increased time of exposure.
Energetics of a population of Asellus aquaticus (Crustacea, Isopoda): respiration and energy budgets
Authors: ADCOCK J. A. 
Published: May 2006

SUMMARY. Respiration of Asellus aquaticus was determined on tiine occasions throughout the year using a Gilson differential respirometer. On each occasion the determination was made at the lake temperature, which ranged from 2 to 18°C, Linear regressions were derived for log oxygen uptake against log dry weight. There was a significant difference between mean rates of oxygen uptake at the various temperatures but the slopes of the regression lines, which varied from 0,62 to O.85 with a mean of 0,76, were not significantly different.The temperature of the lake was monitored throughout the year. Using the relationship of oxygen uptake against temperature, and estimates of population density obtained previously, the total annual respiration of the population was calculated as 4571 ml O2 m‐2, equivalent to an energy loss of 92.3 kj m‐2 year‐1 from a mean biomassof 752 mg m‐2.Consumption of decayed Alnus glutinosa leaves and faecal production rates, and thus assimilation efficiency, were determined by gravimetric methods in the laboratory at 10°C, close to the mean temperature of the lake (10.rC), In the four size classes investigated, larger animals consumed more food per individual, but less on a weight specific basis. However, it was shown that consumption was greater if the leaf material was more highly decomposed, Assimiliation efficiency was calculated as 23%.Using data for respiration, population density and the assimilation efficiency, the annual population energy budget was estimated as (kJ m‐2year‐1): consumption, 568.9 (100%); production, 38.5 (6.8%); respiration, 92.3 (16.2%); faeces, 438.1 (77%). The significance of these energy values, and the ecological efficiencies calculated from them, are discussed in relation to other published work.
Long‐term and seasonal changes in the chemical composition of precipitation and surface waters of lakes and tarns in the English Lake District
Authors: SUTCLIFFE D. W. , CARRICK T. R. , HERON J. , RIGG E. , TALLING J. F. , WOOF C. , LUND J. W. G. 
Published: May 2006

SUMMARY. The composition of bulk (wet and dry) precipitation in 1975 and 1976 was similar to that found 22 years previously. In 1975, mean values for nine precipitation samplers at one site (Wraymires) ranged from pH 4.3 to 4.5; similar values were obtained in 1976. Samplers covered with fine‐mesh plastic gauze caught substantially more Ca2+ and K+ than open samplers, but pH and SO2‐4+ NO3‐ concentrations were similar in open and covered samplers. In precipitation, c. 50% of H+ was balanced by NO3‐ and c. 50% by SOi; 80% of the SO2‐4 was balanced by Ca2+ and Mg2+.Conccntrations of major cations (H+, Na+, K+,Ca2+, Mg2+) and anions (CI‐, NO3‐ SO2‐4 and alkalinity [Alk—largely HCO3‐]) in upland water‐ bodies were similar to those found in precipitation, but pH levels were generally higher and above 6.0 m some tarns. At lower altitudes, on base‐rich roeks and soils, Ca2+ and Alk become dominant. Results of a survey of lakes and tarns in 1974–78 are compared with a survey in 1953–56 and published data (chiefly for pH and Alk) for 1947–50, 1932 and 1928. Comparisons are also made with other measurements of Alk in three productive lakes (Blelham Tarn, Esthwaite Water and Windermere) for 1936–39 and 1945–80. Winter levels of NO3‐N, PO4‐P and Si are given for these lakes; although the first two have increased during the late 1960s and the 1970s there has been no significant change in the last. NO3‐ and probably some SO2‐4. In productive lakes a substantial (c. 50%) rise in mean Alk occurred during the late 1960s and the 1970s, possibly related to increased winter levels of NO3‐N and PO4‐P derived from sewage and fertilizers. In this period the maximum pH levels reached in summer were notably high, sometimes exceeding pH 10. The rise in Alk, conductivity and pH of surface waters is influenced by climatic factors (a decade of drier years), sewage input and biological productivity within the lakes.Considerable seasonal fluctuations in the concentrations of major ions, a characteristic feature of surface waters in the English Lake District, are illustrated and some implications for cation‐anion balance briefly discussed. Mid‐winter concentrations are usually high forNa+, K+, Cl‐. NO3‐and low for Ca2+, Mg2+, Alk. SO2‐4.Alkalinity. pH and conductivity of Lake District tarns and lakes show no signs of acidification during the period 1928–80. On the contrary, productive lakes have become more alkaline and some unproductive low‐alkalinity (< 100 μ‐equiv. 1‐1) lakes also show signs of alkalization, with increased mean concentrations of Na+. Ca2+ and Mg2+, balanced by Alk.
A model relating the results of low pH bioassay experiments to the fishery status of Norwegian lakes
Authors: SADLER K. 
Published: May 2006

SUMMARY. 1. Data from the literature concerning several Norwegian brown trout (Salmo trutta) populations are used to construct Leslie matrices in order to estimate their capacity to withstand egg and fry mortalities. These estimates are compared with the results of bioassay studies conducted at pH 4.5 and at various calcium concentrations in order to predict the percentage of trout populations which would be able to survive these conditions.2. These predictions are in good agreement with the observed fishery status of Norwegian lakes at calcium concentrations <30 /μeq I−1 but above this concentration the recorded status is worse than predicted.3. Likely causes for this difference are considered to be effects acting on fish older than those used in the bioassay experiments (either mortality or reduction in fecundity possibly due to impaired growth) or the effects of other water quality factors, for example aluminium.4. These effects need only be fairly slow acting as compared with the egg and fry mortalities so far studied in detail. Thus the discrepancy between predicted and observed results at pH 4.5 and 50μeq 1‐−1 calcium could be caused by an additional 80% mortality acting over the 4–8 year period before maturation.5. An additional factor which could result in the observed fishery status being worse than predicted is temporal variation in water chemistry which is not assessed in the survey of Norwegian lakes. In particular, the adverse conditions occurring at time of snowmelt could be critically important.
On the habitats of three species of the genus Hygrotus Stephens (Coleoptera: Dytiscidae)
Authors: CUPPEN J. G. M. 
Published: May 2006

SUMMARY. 1. Adult Hygrotus beetles were collected from about 400 localities out of 621 sampled in the Netherlands. Distribution of the three Dutch species of this genus has been related to different environmental variables, principally by use of the Index of Representation (I.R.).2. Hygrotus decoratus is an acidophilous and haloxenous species. It inhabits small water bodies such as peat‐ditches, reed‐lands and overgrown ditches where emergent plants are abundant. Hygrotus inaequalis occurs in all of the habitats studied and has no clear preferences or aversions with respect to the environmental variables examined. Hygrotus versicolor inhabits permanent water bodies such as clay‐ and sand‐canals which have a rich growth of submerged plants and a weak current. The species has a significant preference for waters with a pH between 7.1 and 8.0 and a chlorinity between 60 and 200 mg 1‐−1.3. H. decoratus and H. versicolor rarely co‐exist because of their different environmental requirements, but both species often co‐exist with H. inaequalis. Structural environmental variables such as water depth and abundance and growth‐form of the aquatic plants play a greater role than chemical factors in habitat selection by Hygrotus spp.
The formation, structure and utilization of stone surface organic layers in two New Zealand streams
Authors: ROUNICK J. S. , WINTERBOURN M. J. 
Published: May 2006

SUMMARY.

The development of stone surface organic layers was investigated in dark and light experimental channels at two field sites. Layer formation was monitored by measuring organic carbon, chlorophyll‐a, ATP and rates of oxygen consumption, and using scanning electron microscopy.
In the darkened forest stream channel an organic layer consisting of slime, fine particles, bacteria and fungi developed and attained maximum biomass (=0.08 mg cm‐2) in about 2 months. At the second site, channels were fed by spring water low in dissolved and particulate organic matter (DOC < 0.5 g m‐3) and no organic layer developed on stones in the dark. Organic layers grown in channels subject to natural light intensities and photoperiods were dominated by diatoms and/or filamentous algae at both sites.
Laboratory experiments carried out in enclosed, recirculating stream channels demonstrated the importance of dissolved organic matter (DOM) as a prerequisite for layer formation. Also. DOM additions in the form of leaf leachates stimulated oxygen consumption by preformed layers. Uptake by microorganisms accounted for most of the reduction in water‐column DOM.
Radiotracer experiments (14C and 144Ce) showed that several common stream invertebrates could feed on ‘heterotrophic’ layers. Calculated assimilation efficiencies ranged from 18% to 74% and imply that nonautotrophic components of stone surface organic layers are likely to play a significant role in carbon transfer to the benthos, particularly in small, shaded streams.
Relationships between metal concentrations and organism size in aquatic insects
Authors: SMOCK LEONARD A. 
Published: May 2006

SUMMARY.

The influence of organism size on whole‐body metal concentrations of eight metals was examined in aquatic insects in field and laboratory studies. Information on the partitioning of metals between adsorbed, absorbed and gut content material was also obtained.
For Co, Cr, Fe, Sb and Sc, an exponential decrease in concentration with increasing organism size was observed, indicating surface adsorption as an important mode of metal accumulation.
No, or only a slight, concentration‐size relationship was found for K, Mn and Na. This is expected for metals with high absorption efficiencies and a low capacity to be adsorbed.
Clearing of the gut of the mayfly Stenonema modestum (Ephemeroptera: Heptageniidae) did not significantly after the concentration size relationship for any of the metals studied.
Studies of Cr uptake with Stenacron interpunctatum (Ephemeroptera: Heptageniidae) indicate that the concentration‐size relationship is not affected by variability in the concentration of available Cr.
About 52% of the whole‐body burden of Cr in S. interpunctatum was associated with gut material while at least 33% was adsorbed to the organism's exoskeleton and at most 15% was internally absorbed.
Habitat exploitation by larvae of Amphipsyche meridiana (Trichoptera: Hydropsychidae) in a Javanese lake outlet
Authors: BOON P. J. 
Published: May 2006

SUMMARY. 1. Trichopteran populations below a dam on the River Tuntang (Central Java) and on intake screens above the dam consisted almost exclusively of Amphipsyche meridiana. Larvae on dam screens were in tightly packed aggregations, with greater densities in deeper water, and were predominantly fourth or fifth instars during the period of observation. Below the dam, 40% of larvae were in the first three instars. Larvae at the dam screens were heavier and yielded larger emerging adults which contained more eggs per female.2. Mean net mesh sizes of fifth instar larvae varied greatly from 34×26 μm to 125×106 μm with larger meshes having progressively thicker strands. It is suggested that larger mesh size may be positively correlated with faster flow rates. The dinoflagellate Peridinium, commonly found in the guts of larvae below the dam, was virtually absent in dam screen larvae, possibly due to mesh size differences.3. The behaviour of larvae in aggregations was observed in a laboratory flow channel. After experimental destruction of feeding nets, larvae immediately ingested silk prior to the construction of a new net. Nets were spun in a‘figure 8’fashion, and took between 11 and 30 min to complete. Stridulation between larvae occurred frequently and may be related to the defence of silk reserves within territories.
Movements of marsh‐dwelling invertebrates
Authors: CORKUM LYNDA D. 
Published: May 2006

SUMMARY. 1. Invertebrate movement was monitored in a parkland marsh in central Alberta, Canada, for 24 h periods every 2 weeks during the ice‐free season. Stationary plankton nets captured organisms moving towards or away from shore.2. Movement occurred throughout the sampling programme, particularly during the warm summer months. Most organisms were night active and exhibited directional movements. Hyalella azteca (Saussure) and Caenis simulans McDunnough constituted most of the catch.3. Although there was a significant positive seasonal relationship between maximum water temperature and total numbers of animals captured. no physical factor appeared to control movement on a daily basis.
Ecology and behaviour of a free‐swimming tube‐dwelling rotifer Cephalodellaforficula
Authors: DODSON STANLEY I. 
Published: May 2006

SUMMARY. 1. Cephalodella for ficula (Ploima, Rotifera) lives in tubes it constructs itself. These tubes are built of mueus in detritus‐rich environments. The tubes are often closed at both ends, arc not used as sieves, and are not eaten directly.2. The rotifer swims back and forth in its tube and apparently lives on bacteria which are shed from the inner walls of the tubes. Because of surface‐to‐volume considerations, this feeding strategy is probably only possible for animals smaller than roughly 1 mm. Under low food conditions, rotifers inside a tube have a distinctly higher fitness than rotifers removed from their tube.3. Given high food conditions, rotifers removed from a tube immediately build another. Grazing on particles outside the tube appears to take place when a tube is being lengthened. Rotifers do not leave the tube for routine feeding, but under conditions of starvation or very low oxygen concentration they will leave the tube and swim about.
Hypolimnetic phosphorus retrieval by diel vertical migrations of lake phytoplankton
Authors: SALONEN K. , JONES R. I. , ARVOLA L. 
Published: May 2006

SUMMARY. I. Movement of 33P from hypolimnion to epilimnion in a small, dystrophic lake was investigated using small‐diameter experimental tubes enclosing thermally stratified water columns. This approach was made possible by the extremely sharp stratification found in such lakes, in which the euphotic zone closely coincides with the epilimnion.2. The vertical distribution of inorganic phosphorus in the lake showed a sharp increase across the thermocline so that enhanced concentrations were available to phytoplankton just below the thermocline. Inorganic nitrogen concentrations did not show such a marked relation to thermal stratification.3. One abundant motile alga (Cryptomonas marssonii) showed striking and regular vertical migrations in the lake, moving below the thermocline at night and returning to the surface waters in early morning. These migrations took cells across a 10°C temperature gradient. Non‐motile phytoplankton showed constant vertical distributions.4. In the experimental tubes an upward movement of phosphorus took place from hypolimnion to epilimnion which was only attributable to transport by phytoplankton cells undertaking active vertical migrations. No equivalent movement of phosphorus occurred in control tubes from which algae were absent.5. The possible significance of such nutrient retrieval is discussed with reference to plankton phosphorus budgets and competition between phytoplankton species.
Major ion and carbonate system chemistry of a navigable freshwater canal
Authors: HOWARD J. R. , SKIRROW G. , HOUSE W. A. 
Published: May 2006

SUMMARY. 1. An examination has been made of the water quality of a 50 km (Wigan to Litherland) length of the Leeds‐Liverpool canal. Regular in situ measurements accompanied by sampling for laboratory analysis were made at seventeen stations over a 15‐month period.2. Three principal contributory water types have been recognized, and the observations have allowed estimates to be made of their relative contributions to the total water flux in the lower reaches of the system. Linear flow rates (c. 0.6 km day−1 near Litherland) are consistent with previous reports.3. The combined field and laboratory measurements have been used to obtain estimates of the partial pressure of CO2 in the water (P co2), the degree of saturation of the water with respect to calcite (Ω) and the major ion speciation in the water. Because of the variable ionic compositions of the waters examined, these estimates were made using a program (WATEQ) which took account of ion‐pairing.4. Diurnal and annual cycles with respect to pH, P co2 and ω occur, these being most marked in the lower parts of the study length when, for a large proportion of the spring and summer, P co2 was below the atmospheric level and noticeable supersaturation with respect to calcite occurred. In contrast, two of the contributory water types, the River Douglas input and the Creek, showed low pH and Ω values and high P co2 values throughout the year.
Laboratory and field experiments on the feeding ecology of the cyclopoid copepod, Mesocyclops edax
Authors: WIUJAMSON CRAIG E. 
Published: May 2006

SUMMARY. 1. Gut contents of Mesocyclops edax consisted of rotifers. cladocerans, copepods and algae, the importance of each varying seasonally.2. Functional response experiments using two soft‐bodied rotifers as prey showed an increase in ingestion rate with increasing prey density up to a threshold, followed by a decline.3. Enclosure experiments with natural assemblages of prey from two lakes indicated that Mesocyclops edax is a selective feeder and may ingest fifty or more prey per predator per day, accounting for up to 17% of the standing crop of its preferred prey species per day in nature.