摘要:

SUMMARY1. Laboratory experiments to test the effects of storage of periphyton samples, at 4°C in the dark, on levels of chlorophyllaand alkaline phosphatase activity (APA) are described. It is concluded that either raw or ethanol extracted samples may be stored for 2–3 days for chlorophyll analyses, but APA should be estimated as soon as possible. 2. Experiments are also described on the efficiency of mechanical blending of periphyton samples in breaking up clumps of periphyton cells to improve subsampling reproducibility. It is concluded that blending is a useful procedure to improve the accuracy of periphyton analyses because the subsampling coefficients of variation decreased for most determinands after blendi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01307.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. Turbellarian predators of the genus Mesostoma prey on the aquatic stages of mosquitoes. In order to evaluate their potential as control agents, a comparison of population parameters has been made on three species from Australia, Africa and Papua New Guinea:M. appinum, M. zariae and M.timbunke.2. The life cycle of these species is relatively short at higher temperature ranges (22–30°C) and varies from 12 to 35 days, depending on the temperature.M. appinumdoes not increase in numbers at 30°C, whiteM. timbunkeis unable to reach sexual maturity at 15°C.M. appinum, but notM. zariae, multiplies slowly at 15°C, although both species survive at this temperature. The fastest population growth was obtained forM. appinumat 22°C, and forM. zariaeandM. timbunkeat 30°C. The doubling time for the population is about 6–7 days in the multivoltine species,M. appinumandM. zariae, and about 18.5 days in univoltineM. timbunke.3. A significant part of the growing population is composed of immature individuals, which corresponds to the high values of the reproductive parameters Roand rm. InM. appinumandM. zariae, individuals rarely produce dormant resting eggs except under deteriorating conditions.M. timbunkeproduces only dormant eggs, and in this respect resembles arctic and subarctic species. A convergence of the reproductive modes between this equatorial species and the high latitude species might be interpreted as adaptation to harsh environments.4. The overall population growth of allMesostomaspp. is several times faster than in Dugesia dorotocephala andD. trigrina, other flatworms studied as potential biological control agents of

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01308.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. Microcosm experiments were carried out to simulate, in the laboratory, the conditions occurring at the water‐sediment interface of a stream draining agricultural land. Constant boundary conditions were attained by passing synthetic 'stream water', saturated with dissolved oxygen and containing 1 mmol NO3−N dm−3(or 1 mmol Cl− dm−3, control), once only over the sediment surface.2. Measurements were made of inorganic‐N (nitrate, nitrite, ammonium), redox potential, potential denitrification and nitrification activities, and readily mineralizable carbon sediment profiles at three incubation times up to 24 days. The peaks in denitrification and nitrification activity moved down the profile with time in the nitrate‐treated sediment, but stayed relatively stationary in the control treatment. Although the zone of nitrification was restricted to the top 2–3 mm of sediment in the control treatment, high fluxes of both dissolved oxygen and NH4−N maintained a high nitrifier activity within this zone for the duration of the experiment.3. Increases in denitrifier activity immediately below the nitrifier activity peak indicated that a coupled nitrification‐denitrification sequence was operating in both the control and nitrate‐treated sediment. The greater depth of nitrification when nitrate was present in the ‘stream water’ was attributed to a feedback mechanism in which enhanced denitrification in the sediment reduced the local demand for oxygen and permitted dissolved oxygen to diffuse further into the sediment. The progressively greater depth to which oxygen penetrated caused the contiguous peaks of potential nitrifier and denitrifier enzyme activity to migrate farther from the interface. However, diffusion rates of the reactants limited the depth to which these coupled reactions could extend.4. The possible effect of this feedback mechanism on the nitrate status of natural sediment‐stream water s

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01309.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. Water from acid (pH 4.3–5.7), brown water streams was low in alkalinity (0–2.3 g m−3CaCO3) and conductivity (2.5–4.1 mS m−1) but contained relatively high concentrations of dissolved organic carbon (6.6–16.3 gm−3). In contrast, alkaline (pH 6.6–8.0), clearwater streams had high CaCO3(12.6–57.6 g m−3) and conductivity (3.7–22.3 mS m−1) but low dissolved organic carbon concentrations (0.3–4.7 g m−3).2. Total reactive aluminium (Al) concentrations were high in acid streams (123–363 mg m−3) but never exceeded 84 mg m−3in alkaline streams. Acid‐soluble and organic monomeric Al were the major Al species in the acid streams (31–168 and 84–178mg m−3, respectively). Concentrations of toxic inorganic monomeric Al were low in all streams (<50mg m−3).3. Sixty‐four invertebrate taxa were collected from the alkaline streams compared to forty‐seven from the acid sites. Numbers of taxa in specific insect orders were similar at all sites, however. Benthic faunas at most sites were dominated by the mayflyDeleatidiumsp. and chironomids.4. Overall, mean densities of benthic invertebrates were 2.4–4.8 times higher in alkaline streams than acid streams. No seasonal patterns of abundance were evident at any site.5. Temporal variability of invertebrate densities was correlated with stream channel stability such that fluctuations in densities declined as stability increased.6. Sources of dissolved organic carbon and aluminium in acid, brown water streams are discussed. We suggest that changes in the food supply available in acid strea

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01310.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. False crane fly larvae,Ptychoptera townesi(Diptera), occurred in high densities in a flow‐controlled section of stream where fine particulate organic matter (FPOM; 0.45 μm to 1 mm in diameter) had accumulated, but were quite rare both upstream and downstream from the section.2. In laboratory studies,P. townesigrew only on FPOM less than 250 μm. Larvae consistently grew fastest when fed small particles (0.45–53 μm in diameter).3.Ptychoptera townesiconsumed relatively small amounts (0.002 mg per mg animal dry mass day−1) of FPOM (0.45–53 μm). They had long gut content passage times (greater than 19 h) and relatively high efficiencies of conversion of ingested food to body substance (20.7%). Gut content passage times were variable, and depended partially on the nature of the substrate.4. False crane fly larvae compacted FPOM into faecal pellets considerably larger in size than particles ingested. They lost mass when allowed to feed on their own faecal material, as well as on faeces greater than 250 μm in diameter produced by shredders. However, they survived and grew on shredder faeces (53–500 μm in diameter) that contained a mixture of smaller particles and particles too large for ingestion.5. The overall pattern of resource utilization byP. townesinvolved slow handling of relatively small volumes of food, which probably passed once only through a complex a

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01311.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1.Paraleptophlehia gregalisandP. temporaliswere abundant throughout a flow‐controlled section of stream that contained large quantities of fine particulate organic matter (FPOM; 0.45 μm to 1 mm in diameter), and in upstream and downstream areas.2. In laboratory studies,Paraleptophlebiaspp. fed and grew on FPOM and CPOM (coarse particulate organic matter; greater than 1 mm in diameter); growth rate was not related to the particle size of food. In addition, these animals were able to survive and grow on various sizes of faecal material produced by shredders.3.Paraleptopblehiaspp. consumed relatively large amounts (0.16±0.09 mg per mg animal dry mass) of detrital material daily.4. The mayflies had short gut content passage times (2–3 h) and low efficiencies of conversion of ingested food to body substance (0.08±0.07%). They egested relatively small, amorphous faeces,5. The overall pattern exhibited byParaleptophlebiaspp. involved rapid processing and partial recycling, through relatively simple alimentary tracts, of large amounts of detrital material from a wide range of s

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01312.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. A study of the diet ofE. octoculata(L) andH. stagnalis(L) using a serological technique was carried out in a lot ic habitat subject to organic pollution and seasonal sewage fungus growth.2. The results indicate thatE. octoculataconsumed predominantly Chironomidae and Oligochaeta, whileH. stagttalishad a less pronounced prey preference, consuming rather similar proportions of chironomids, oligochaetes,Asellusand gastropod snails.3. At enriched sites,E. ocioculataconsumed relatively more chironomids and fewer oligochaetes, whileH. stagnalistook more gastropods and fewer chironomids.4. Seasonal differences were noted in the diet of both leeches with chironomids predominating chiefly from April to August, and molluscs, oligochaetes andAsellusat other times of the year. Intra‐specific differences (on a weight‐age basis) were only seen forE. octoculata, small forms consuming chiefly oligochaetes and larger ones concentrating on chironom

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01313.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. Mean annual density and biomass (B̄) ofCambarus bartoniiin an Appalachian mountain stream (U.S.A.) was 12 individuals m−2and 1669 mg (ash‐free dry weight) m−2.2. Annual production (P) ofC bartoniiwas 961 mg AFDW m−2. Despite high biomass, low growth rates resulted in low production and a low P/B̄ ratio of 0.58.3. WhileC bartoniiconstituted 61% of the total macroinvertebrate biomass, it contributed only 13% of annual community secondary production.4. Litter processing was positively related to temperature and crayfish size.Cambariis bartotniiwas estimated to comminute 36 g m−2y−1of leaf litter (>1 mm2) to 24 g m−>2y−1fine particulate material (5()% of shredding activity by crayfish occurred from June to September which was also the period of lowest litter standing crops and activity of other shredding macroinvertebrates.5. We speculate that during summer crayfish play an important role in temperate woodland streams by converting slowly processed leaf litter species (e.g.Rhododendron) to fine particles which are then available to collector‐gatherers (e.g. Chirono

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01314.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. The temporal dynamics and demography ofMeta‐diaptomus meridianus(Van Douwe),Lovenula excellensKiefer.Daphnia gibbaMethuen,D. barbataWeltner andMoina brachiataJurine were studied for 2 years in a small bay of Lake le Roux (Orange River, South Africa). Total zooplankton biomass and population density were 1.4–3 times higher during the less turbid conditions of 1982/83 (Secchi depth transparency around 35 cm) than they were at around 25 cm Secchi depth during 1981/82, whenD. barbatawas absent.2. On average, instantaneous birth rates, rates of population change and death rates varied only slightly between years. Birth and death rates were considerably higher above 15°C than below 15°C. These rates correlated with one another and with zooplankton abundance both inter‐ and intra‐specifically suggesting that competitive interactions were important in population regulation. Mortality rates varied more strongly and consistently in a density‐dependent direction than did birth rates. In addition to depressed fecundity, the inferred survival of young was poor and population growth low, possibly because food shortage caused high post‐natal mortality.3. Estimates of annual production derived from finite birth rate values varied consistently with annual differences in biomass, and amounted to between 6 and 10 g m−2y−1dry wt. Annual P/B values varied from around 20 for the daphnids to 55 for the copepods and 75 for Moina. Apart from the latter, whose annual P/B ratio virtually doubled from 45 to 75 following reductions in turbidity, annual differences in P/B

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01315.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

1.Psephenus herricki(DeKay) larvae were observed in aquaria and artificial streams using videomacroscopic techniques. Dye visualization was used to determine flow around the organisms.2. The highly flattened larvae ofPsephenus herrickiare able to withstand and/or avoid the force of flowing water in streams through a number of mechanisms. The legs are vital: if they cannot gain purchase the larvae can be dislodged by the lifting forces acting on the body. At the flow rates tested (up to 50 cm s−1), suction under the carapace is not needed to maintain position.3. Active pumping of water through lateral slots of the carapace and out from under the body posteriorly greatly reduces turbulence around the body and may act to decrease drag at high Reynolds numbers.4. An interpretation of the flattened body‐shape ofPsephenus herrickilarvae as an adaptation to fast currents and/or to prevent the larvae from being removed from the substrate by a predator is of questionable ecological significance because individuals are usually found in crevices and on the undersides of sto

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01316.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY