摘要:

SUMMARY.1. Egg development and larval growth ofProtonemura intricata(Ris, 1902)(Plecoptera: Nemouridae) were studied in the laboratory and in the Breitenbach, a small stream‐in Germany (F.R.G.).2. The mean number of eggs in batches collected from the field was 627 (S=314).3. Mean batching success in the laboratory was 60–100% at 2–18°C. Cumulative hatch in individual batches could be described by asymmetrically sigmoid curves. The length of the hatching period was positively correlated with the length of the incubation period.4. The incubation period ofI', intricatanormally consists of an initial dormancy followed by subsequent development. The length of embryonic development (Y. days) is strongly inversely temperature (T, °C) dependent and can be described by the equation:5. The length of dormancy is dependent on oviposition dale, and is shorter the later that the eggs are laid. It also depends on temperature during incubation and is increased by rising temperatures. As a consequence, larvae hatch more or less synchronously in the field during autumn. Total incubation period, i.e. dormancy and actual development, exhibits a complex dependence on both incubation temperature and oviposition date. Under constant laboratory temperatures, a late sharp fall in temperature can terminate dormancy earlier.6. Photoperiod probably induces dormancy and may already act on the last larval instars of the parent generation. The dormancy ofP. intricatais classified as an oligopause (Müller. 1970, 1976).7. In the laboratory. P.intricatalarvae from early batches with long dormancy grew faster than larvae from late batches with direct development. Final size was the same in both cases. This acted against the population synchrony induced through egg dormancy. Benthos samples suggest the same in the field.8. Avoidance of the suboptimal summer conditions in streams by the cold stenothermous P. intricata is suggested to partly explain the success of the species, which contributes more to total emergence biomass than do other Plecoptera in the Bre

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01079.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. The River Suså is a small, nutrient‐rich stream situated in an open landscape with clayish subsoil under intensive cultivation. Discharge was variable daily and seasonally due to low groundwater input. Above‐ground development of submerged macrophytes was restricted to late May to November, when water velocity and depth were low. Dominant macrophytes were rootedPotamogeton pectinatusandSparganium emersumand unrootedCladophora. Biomass development was closet) related to light availability.2. Growth rates of macrophytes were linearly related to light availability when self‐shading was accounted for.Potamogeton pectinatusgrew rapidly m May‐June, concentrated the biomass at the water‐surface during July‐August, and then declined exponentially when the shoots became basally senescent.Sparganium emersumhad linear, flexible leaves that were continuously replaced from a basal meristem.Sparganium emersumwas less susceptible to high water velocities thanPotamogeton pectinatusand the biomass declined later and at lower rates during autumn.Sparganium emersumalso regrew after culling that left its meristem intact in the sediment. UnrootedCladophoradeveloped a high biomass during sunny periods and subsequently disappeared at high discharges. The summer biomass of rooted macrophytes was greater in years with high summer discharge, whereas the biomass ofCladophoraand of the epiphytic microbial community was lower due to scouring.3. Submerged macrophytes played a key role in structure and functioning of the ecosystem. They reduced water velocities two to four fold during summer and promoted extensive organic sedimentation. The biomass of benthic diatoms declined parallel to increased macrophyte shading and sedimentation. In addition, submerged macrophytes formed a large substratum for macroinvertebrates and for a microbi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01080.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. Exposure to simulated acid rain resulted in changes in the chemical content of riparian vegetation and terrestrial leaf litter and had significant effects on leaf litter decay rates in a well‐buffered lotic ecosystem.2. Foliar nitrogen and phosphorus decreased with decreasing pH of the simulated acid rain and microbial activity was greater on leaf litter exposed to rain of pi I 5.4 than on leaf litter exposed to pH 3.0 or pH 4.0.3. Detritivore numbers and biomass were significantly higher on leaf litter exposed to pH 5.4, probably due to the greater palatability of the leaf substrate.4. Decay rates of leaf litter processed in the summer months were significantly lower than decay rates of leaf litter processed during the autumn/winter due to reduction in nitrogen content and microbial respiratio

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01081.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. Quantitative variations in downstream movements of benthic macroinvertebrates were studied in a large European river, the Rhône, upstream from Lyon. Artificial substrates were suspended at three depths in the water column, both near a bunk and in mid‐channel, monthly from December 1978 to March 1980. Drift nets were used to determine the diurnal rhythm in drift and to investigate the efficiency of our suspended artificial substrates in capturing the drifting macrofauna.2. Drift densities (number and biomass) reached a maximum during summer, especially near the river bank, and at night. Mean individual weight of organisms was higher close to the bottom and at night.3. Artificial substrates were reliable, but underestimated drift by about a quarter in number and a sixth in biomass. compared with drift nets. Two detailed analyses of the drift distribution across the width of the river revealed similar densities along both banks, and uniformity in the channel as a whole.4. Mean annual drift densities estimated for the section of river were 100 individuals, per 100 m3and 60 mg dry weight per 100 m3. These densities are similar to those obtained from other temperate rive

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01082.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. The contribution of drift to macroinvertebrate colonization was studied over 10 days using pairs of substratum‐filled trays, one suspended above the streambed (and thus able to be colonized by drift only) and one buried flush with the streambed (and thus open to colonization from all directions). Trays were filled with sand, gravel or stones.2. Colonization of sand‐filled trays was rapid, being completed within 24h (i.e. no subsequent change in numbers of individuals per tray); colonization of gravel or stone‐filled trays was not completed by the end of the experiment.3. Drift contributed an average of 86% of the colonizing fauna of the sand‐filled trays, 36% of the fauna of the gravel‐filled trays and 25% of the fauna of the stone‐filled trays. The low contribution of the drift to the gravel and stones is at odds with some studies which, using similar techniques, suggest that drift is the primary source of colonizing individuals.4. Most individual species showed low contributions by drift to colonization, with the majority having contributions under 66%.5. Distinct differences were noted between the fauna colonizing the sand‐filled trays and those colonizing the gravel or stone‐filled trays (which were similar).6. Several species common in the drift were rare in the colonizing fauna and several species which were common colonizers were absent or ra

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01083.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. The eggs of a planktonic, predatory water mile Piona exigua Viets were reared in the laboratory at constant temperatures ranging from 10°C to 280C. Egg development rates increased with increase in temperature.2. Five models describing the effect of temperature on egg development times were fitted to the data.3. The variances of the egg hatching times at each temperature differed widely, but these variances were not made more equal by In‐transformation.4. A simple power curve, fitted to the raw data, accounted for ≥.97% of the variation in the data. Two further models, both of which included a third parameter, provided a better fit at the temperature extremes.5. Close examination of the patterns of variance at difference temperatures may provide information relating to the pattern of emergence of aquatic poikilotherms.6. At temperatures below 230C. eggs ofPiona exiguadeveloped more rapidly than eggs ofPiona constricta, from Heney Lake. Quebec (Riessen,

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01084.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1 During eutrophication of shallow lakes, communities of submerged plants are often replaced by dense phytoplankton populations, but the mechanism by which this occurs is obscure though often assumed to involve shading.2. This paper introduces a series investigating this change and describes a system of experimental ponds which were variously fertilized with nitrogen and phosphorus, had fish added or removed, and had their submerged aquatic plants cleared or left intact.3. Fertilization with phosphate and ammonium nitrate in quantities effectively greater than those in a series of lakes in the adjacent Norfolk Broads, which have lost their submerged plants, did not displace the plant populations.4. Total phosphorus and soluble reactive phosphorus concentrations in the water did not increase much with increasing loading in the presence of submerged plants but did so if the plants were manually cleared. Ammonium and nitrate concentrations were kept low, despite large additions in both plant dominated and manually cleared ponds.5. In the absence of fish there were modest increases in chlorophyllaconcentrations with phosphorus loading in the presence or absence of submerged plants. The concentrations achieved, however, were much lower than anticipated probably because of grazing by large‐bodied Cladocera.6. Ponds dominated by plants continued to have low phytoplankton populations even when fish were stocked. Low fish survival in these ponds permitted grazing zooplankters to flourish. In ponds cleared of plants, however, there were significant relationships between cholorophyllaconcentration withDaphniabiomass (inverse) and log stock of potentially zooplanktivorous fish (positive). There was a significant relationship between chlorophyllaand total phosphorus concentrations in the plant and cleared ponds in 1982 but only in the plant ponds in 1983. In all cases the phytoplankton communities were dominated by small, often flagellated, organism

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01085.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. In 1982 and 1983 sets of experimental ponds were left with their submerged plant communities intact (plant ponds) or were cleared manually of them (cleared ponds). The ponds were all fertilized with ammonium nitrate and with variable amounts of phosphate. In 1982 fish were removed from the ponds. Zooplankton communities were dominated by large Cladocera withDaphniaprominent in the cleared ponds andSimocephalusin the plant ponds. There was no detectable effect of differential phosphorus additions on zooplankton communities or populations.2. In 1983 zooplanktivorous fish (mainly roach) were stocked in the ponds. In the plant ponds the fish did not survive, probably through severe deoxygenation and the zooplankton community again included large‐bodiedSimocephalus.Fish survival was variable in the cleared ponds. Where fish stocks were absent or low (0.5–1 g m−2) aDaphnia‐dominated community persisted; at intermediate fish stocks (18.1 g m−2)Eudiaptomus graciliswas predominant and where fish stock was high (22.8–29.1 g m−2)Bosmina longirostris, and cyclopoid copepods dominated the communities. Mean biomass of the zooplankton community declined with increase in fish stock to between 5.1 and 18.1 g m−2then increased.3. On the basis of results from the experimental ponds and elsewhere, a new hypothesis is put forward to account for the switch from aquatic plant to phytoplankton dominance in eutrophicated shallow lakes. It envisages dominance by either group to be possible as alternative states over a wide range of high nutrient loadings. It suggests that each state is buffered against increased loading by mechanisms involving plant and algal physiology and zooplankton grazer populations. The nature of the buffers and the reasons by which one state may be switched to the other

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01086.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1 Mechanisms which might have caused a switch from submerged plant dominance to phytoplankton dominance in a series of shallow lakes, the Norfolk Broads, during the 1950s and 1960s, are reviewed. It is argued that a likely mechanism was a poisoning of the community of Cladocera which graze on algae and are associated with the plants. This allowed phytoplankton to take advantage of the increased nutrient loadings and to increase. The 1950s and 1960s were periods of liberal organochlorine pesticide use. Cladocera are particularly susceptible to organochlorine toxicity.2. Sediment cores were taken from Hoveton Great Broad, in which the switch to phytoplankton has occurred, and from two Broads (Upton and Martham South Broads) in which submerged plants are still dominant. Analyses were made for cladoceran remains, diatoms and molluscs. Cross dating with previously taken dated cores allowed time‐scales to be applied.3. In Hoveton Great Broad, a switch from clear‐water‐associated chydorids to turbid‐water forms was found to coincide with the loss of aquatic plants in the 1950s. NoDaphniaremains were found. In the other two Broads, clear‐water chydorids, mostly plant‐associated, were found throughout the cores.4. Residues of dieldrin (HEOD), DDD and TDE were found in the Hoveton Great Broad cores, with the DDT derivatives particularly associated with the end of the phase of submerged plant dominance and the beginning of that of phytoplankton dominance.Bosminaremains became more abundant after this point. Pesticide residues were scarce in the cores from the other two Broads and did not form any particular pattern. Residues of polychlorinated biphenyls were widespread in all cores.5. Calculation of DDT concentration in the water at the time the sediments with greatest concentrations of residue were laid down suggests that concentrations above typical LC50values forDaphniaspecies could have b

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01087.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. The filtration rate ofDreissena polymorphaPallas measured in the field in three shallow Dutch lakes shows an inverse exponential relationship with the dry matter content of the water.2. Temperature seems to set only a gross level to the filtration rate in summer and winter season respectively; within a season no clear relation between the filtration rate and temperature exists.3. Under laboratory conditions the risk of measuring abnormal behaviour ofDreissena polymorphais shown to be substantial; hence field‐measurements of the filtration rate are preferable.4. The clearing capacity of theDreissena polymorphapopulations in Lakes IJsselmeer and Markermeer is sufficient to filter both lakes at least once or twice a month. This indicates the potential importance of this species for restoration of turbid, eutrophic lakes by means of biomanipulatio

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01088.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY