摘要:

SUMMARY.1. Reduced total phosphorus concentrations in the summer which followed the addition of iron aluminium sulphate to White Lough failed to reduce significantly the phytoplankton. which continued to be dominated byOscitlatoria agardhiivar.isothrixSkuja.This species was present throughout the 4 years studied, forming over 50% of the algal volume in 80% of samples. In contrast, species which occurred principally in the summer months were found to be severely curtailed when sediment release of phosphorus was suppressed.2. The phosphorus: carotenoid ratio was used to assess the extent of phosphorus limitation because laboratory studies on O.agardhiivar.isothrixshowed that this ratio was a much beter indicator of cell phosphorus content than the phosphorus: chlorophyll a ratio. Reduced summer phosphorus concentrations in White Lough caused a transition from intermittent to continuous phosphorus limitation rather than a proportional reduction in the summer phytoplankton.3. Reduced autumn grazing pressure byDaphnia hyatinaLeydig allowed large algal populations to develop in the winters following phosphorus reduction despite a 50% decline in total phosphorus. The combination of increased winter phytoplankton and lower total phosphorus reduced soluble reactive phosphorus concentrations to less than 5,μg P l−1which in turn curtailed the spring diatom pul

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01024.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. The organic geochemistry of Coniston Water, a low productivity lake, has been investigated.2. The relative inputs of the various known sources to different compound classes suggest terrestrial higher plants as the major source of sedimentary organic matter.3. Early lipid diagenesis, proceeding in the bottom sediments as a result of microbial activity, produces relatively rapid changes, with shorter chain and unsaturated compounds being preferentially degraded.4. Free and bound (acid liberated) lipids exhibit significant differences in composition, related to their respective sources and stability towards degradation.5. The lipid composition of an aquatic higher plant, growing in the margins of the lake, has been determined; comparison with the sedimentary lipids reveal it not to be a significant source.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01025.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. The duration of egg incubation (Y) inDinocras cephalotesandSiphonoperla burmeisteriwas related to constant temperatures from 4 to 24°C, by the regression equations Y=2382T−1, 402(r2=0.992, P<0.001) and y= 2683T−1.667(r2=0.994,P<0.001), respectively. No diapause was observed in either species.2. Egg incubation inD. cephaloleswas slow and took 784.9±92.7 (mean ± SD) degree days between 12 and 20°C. significantly more than inS. burmeisteri(445±76.17 degree days:t= 7.44. d.f.=13,P<0.001).3. ForD. cephaloteshatching occurred at temperatures between 12 and 24°C, and for S. burmeisteribetween 8 and 20°C. The mean volume of the eggs ofD. cephaloteswas about 5 times greater than that ofS. burmeisteriand the mean body lengths of the newly‐hatched nymphs were 1.13 mm and 0.95 mm respectively.4. This study shows that the freshwater fauna of northern Fennoscan‐ dia also contains species with warm stenotherm eggs. D.cephalotes.which is of a Mediterranean origin (Zwick, 1981a), may exist at the limit of its distribution in norther

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01026.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. A procedure has been developed which uses environmental data to predict the probabilities of macro‐invertebrate taxa occurring at running‐water sites in Great Britain.2. Biological, physical and chemical data were collected from twenty‐ one sites on three river systems in order to evaluate the procedure.3. For most sites the number and type of taxa recorded, using a standard sampling programme, were very close to those predicted using twenty‐eight environmental variables.4. Comparison with other studies at the same sites showed that most taxa whose probability of occurrence was ≥0.5 could be found with more intensive sampling.5. Reducing the number of variables used in making the predictions from twenty‐eight to five resulted in only a slight loss of predictive accuracy.6. Combinations of chemical and physical variables gave better predictions than equivalent numbers of physical variables only but the latter may be more appropriate where chemical pollution is known, or suspected to occur.7. The procedure is of practical value in the detection and assessment of pollution.8. It may also be used to explore patterns in the structure and functioning of stream

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01027.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. In the River Frome, Dorset, this small cyprinid spawned from mid‐April to early August and consequently some 0 group minnows did not develop scales until the following spring.2. Most I group fish formed a summer hyaline band on their otoliths in a edition to the normal winter band.3. Life‐span was short with a winter age‐structure of 67% 0 group, 32% I group and 1% II group fish with mean fork lengths of 29, 55 and 73 mm respectively.4. In June, substantial numbers of I group fish reached reproductive size (50mm) and thereafter progressively replaced II group fish in the spawning shoals. Few II group males survived beyond June, few females beyond August.5. Only half of I group minnows reached matutity. These were usually fish which had reached 30mm by the previous winter. Very few of these large I group fish survived to spawn the following year.6. This differential mortality, together with the loss of condition and disappearance of II group fish during spawning, may indicate the cost of an extended high level of reproductive effort.7. In this productive environment the life history of the minnow more closely resembles that of the small sympatric speciesCottus gobioandNoemacheilus harhatulusthan it does that of sympatric cypr

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01028.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Prior to 1975Dugesia tigrina, an Americati immigrant triclad, was known from only a few flowing water sites in Great Britain. Since then it has been found in a large number of lowland rivers and canals in England and Wales, and in 1985 it was reported from the lower reaches of the River Tweed in Scotland.2. This note gives the recorded distribution ofD. tigrinaup to the end of 1985 (115 10 km squares now occupied) and summarizes the environmental conditions at a subset of twenty‐five sites whereD. tigrinaoccurs.3. Information on the native triclads at sites recently colonized byD. tigrinais used as a basis for speculating on the rivers most vulnerable to the future spread of this species.4. Possible methods of dispersal ofD. tigrinaand the features which make it a successful colonist are discusse

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01029.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. The abundance of pianktivorous juvenile yellow perch,Perca flavescens, was manipulated in three 750 m3enclosures 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 inef

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01030.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Invertebrate drift was sampled at both a rockface and a deep pebble riffle site in streams draining both a clearcut and a forested catchment.2. A sampler was designed to separate the bottom 2 cm of flow, encompassing the effective range of caddisfly (Hydropsychidae: Trichoptera) catchnets. from upper flow.3. No significant difference in drift density (numbers per cubie metre) was seen between sites within each stream. However, numbers per square centimetre intake area per day at the rockface sites were 4 times higher in the clearcut and 10 times higher in the forested stream than at the pebble‐riffle site.4. Rockface habitat which had highest drift availability was also the site of maximum secondary production of the predaceous collector‐ filtererParapsyche cardisin both streams studied.5. Increased sediment load in the clearcut stream may influence the efficiency of utilization of invertebrate drift by collector‐filt

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01031.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. In 1981–84 limnocorral (LC) experiments were performed in Lake Lucerne. Switzerland, to manipulate the planktonic community by varying P fertilization and by removing large zooplankton (with a 95 μm screen).2. The C:P ratios in both suspended and entrapped seston exceeded the ‘ideal’ C:P ratio of 106 proposed by Redfield, Ketchum&Richards (1963) when P was limiting algal growth.3. P fertilization could decrease the sestonic C:P ratio to 106 only when P did not limit algal growth; P additions far exceeding the P loading of eutrophic lakes were necessary to obtain this situation.4. Changes in epilimnetic C:P ratios were usually related to short‐ term changes in primary production, caused by variable insitulight conditions and turbulence, and subsequent variation in POC concentrations.5. Entrapped seston in the 95 μm‐filtered LCs showed C:P ratios slightly higher than those of suspended seston, indicating fast P release and slower C mineralization in the epilimnetic nutrient cycle.6. Removing large crustacean zooplankton enhanced epilimnetic P mineralization, and C:P ratios of entrapped seston in the 95 μm‐filtered LCs were increased.7 Detritus formed a relatively high proportion of the seston and amounted to more than two‐thirds of the measured POC concentration.8. Calculations of algal P uptake using information on sestonic C:P ratios and14C uptake rates are questionable, as long as detritus cannot be separated from algae and net carbon uptake cannot be acc

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01032.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Spatial and temporal variation in the diet of the univoltine predatory stonefly,Kogotus nonus, was studied over 3 years in a small Alberta stream to determine whether the relative abundance of prey types in the diet ofKogotusreflected relative prey densities in the stream and whether the variation in absolute feeding rate was related to either prey or predator density.2. The seasonal shift from sole utilization of Orthocladiinae to inclusion ofBaetisin the diet could not be attributed to seasonal changes in prey density, but was probably related to predator size and ability to handle very active prey. Most of the spatial variation in diet could be related to differences in background prey densities, but very high densities of Baetis caused the predator to specialize on this prey.3. Feeding rate onBaetis. as assessed by per capita gut contents, showed a seasonal shift from a positive correlation withBaetisdensity in winter to a negative relationship with predator density in spring. This suggested that feeding by smallKogotusis a function of prey density. while feeding by later instars is influenced by between predator interactions such as interference.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01033.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY