摘要:

SUMMARY.1. Annual production was estimated for Trichoptera occurring in each of three distinct habitats of a mountain stream: bedrock‐outcrops, riffles and pools. Production was greatest on bedrock‐outcrops (2608 mg ash‐free dry weight m−2), followed by riffles (1038) and pools (950).2. Annual production in bedrock‐outcrops and pools was dominated by single functional groups, with collector‐filterers and shredders contributing 73% and 75% of the annual production, respectively. Production in riffles was due primarily to shredders (46%), followed by collector‐filterers (27%).3. Taking account of the amount of stream area occupied by each habitat type, total annual production was estimated at 1336 mg AFDW m−2. 53% of this production was attributable to four taxa:Parapsyche cardisRoss (25%),Pycnopsyche gentilis(MacLachlan) (10%),Neophylax mitchelliCarpenter (9%) andRhyacophila nigritaBanks (9%).4. Habitat‐weighted production was distributed among functional groups as follows: collector‐filterers (41%), shredders (29%), engulfing‐predators (15%), scrapers (13%) and collector‐gatherers (2%).5. The distinct taxonomic and functional structures of trichopteran sub‐communities were shaped by the distinct physical characteristics of their principal habitats. Bedrock‐outcrops were characterized by low roughness and high current and were sites of low deposition or organic matter; thus the predominance of collector‐filterers. In contrast, the other habitats of greater roughness (riffles) and/or lower current (pools) were sites of deposition of food (e.g. leaf litter) and greatest shredder production.6. By distinguishing discrete mesoscale habitats, each with a functionally distinct caddisfly sub‐community, we speculate that small mountain streams provided the diverse physical templates essential for the evolution of the major feeding tactics (e.g. scraping, shredding, filt

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00438.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Relations between acidification by atmospheric deposition, water depth and the occurrence of dry summers in this century, as well as their effects on chemistry, macrophytes and diatoms in three moorland pools, are described.2. Direct observations and biological data indicate a decrease of pH byc.0.5 unit over a period of seven decades in a pool where 20% of the bottom desiccates in extremely dry years, and 2 pH units over the same period in a pool where 70% of the bottom is exposed to the atmosphere in such years.3. Acidification promotes the growth ofJuncus bulbosusL.,Sphagnumand the acidobiontic diatomEunotia exigua(Bréb.) Rabenh. and suppresses the growth of isoetids (e.g.Lobelia dortmannaL.) and of acidophilus and circumneutral diatoms. Also the acidobionticFrustulia rhomboidesvar.saxonica(Rabenh.) Toni andNavicula subtilissimaCleve, characteristic of humic waters, decline by acidification.4. In two pools where more than half of the bottom desiccated in 1976, observed concentrations of sulphate were highest in 1977–78 and decreased later on.Juncus bulbosushad a maximum in 1977–80.Eunotia exiguabecame the dominant diatom after 1976 and decreased after 1981 in the pool with the shortest residence time (3 years).5. In desiccating pools the long‐term decrease of pH is apparently much larger than in softwater lakes in Scandinavia and North America. During the last 50 years, pH dropped rapidly after dry summers, probably due to oxidation of sulphur and nitrogen compounds which were originally derived from the atmosphere, reduced and stored in the sediments. Rapid falls in pH were followed by an increase, presumably due to alkalinity production during sulphate reduction and denitrifi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00439.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Life table experiments were carried out in a range of turbidities onD. pulex, representing a ‘clear‐water’, and onD. barbata, representing a ‘turbid‐water’ species.2. In contrast to predictions based on seasonal occurrence patterns,D. pulexhad a higher intrinsic rate of increase (rc)s over most of the turbidity range thanD. barbata.Consistent differences in life history between the two species were found, but life history characteristics were rather insensitive to turbidity levels. Although turbidityper seappears to have little direct effect on life history parameters, it could influence the seasonal succession of these two species by interacting with other factors.3. It is suggested that visual predation by fish rather than turbidityper seprobably influenced the seasonality ofDaphniaspecies. During the warmer months, selective removal ofD. pulexby visually foraging fishes may allowD. barbatato gain dominance. Effects of temperature and nutrition also merit fu

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00440.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Field experiments in a fishless stream were carried out on an abundant caddisfly with a predatory, net‐spinning larva,Plectrocnemia conspersa(Curtis), to assess whether net site availability affects their microdistribution.2. Net sites were supplemented by adding nought, one or four artificial structures to replicated patches on the stream bed. In each of three experiments at different seasons (summer, autumn and late winter), caddis densities increased significantly in patches with extra net sites.3. The response of caddis to supplemented net sites could be affected by the subsidiary effects of food and offish. These potential interactions were assessed in each experiment by varying net site density in two additional treatment stretches in which (1) prey abundance was increased by releasingDaphnia, and (2) brown trout (Salmo truttaL.) were enclosed. The responses of caddis in these two treatments were compared to that in the reference stretch, where only net site density varied.4. Increased food abundance enhanced the response of caddis to net site supplementation in winter, when natural prey was least abundant, but not in summer or autumn. We suggest that extra food affects the mechanism determining net building only when prey availability is below some threshold.5. The presence of fish precluded any effect of extra net sites in summer, but had no effect in autumn (the winter fish treatment was lost). We suggest fish predation reduced the densities of caddis in summer, so that net sites no longer limited local densities. In autumn, fallen leaves provided refugia from fish, which consequently were less effective predators ofP. conspers

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00441.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Lake Goang has a pH of 2.5. Associated with this low pH are high concentrations of sulphate, chloride, iron and aluminium. There are no fish in the lake.2. A single species of Heterococcales was found in the phytoplankton.3. The zooplankton consists of one species of rotifer and a stalked species ofVorticella.4. The shallow water fauna consists of two species of nematodes, at least two larval Diptera, one trichopteran, a zygopteran, a small crab (Sundatelphusa) and a cyclopoid copepod (Paracyclops).5. During January an oily slick appears and is deposited as asphalt around the shore of the lake.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00442.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. The successional patterns of the dominant phytoplankton species in Lake Maarsseveen (The Netherlands) were very similar in 1980 and 1981. In December/January the diatomsStephanodiscus hantzschiiGrun.,Stephanodiscus astraea(Ehr.) Grun. andAsterionella formosaHass. dominated the algal community (A. formosahad several further population increases during the year).Fragilaria crotonensisKitt. came to dominance in March/April, followed by the chrysophyteDinobryon divergensImhof and the diatomCyclotella comta(Ehr.) Kütz in May/June. A second appearance ofD. divergenswas observed in July/August, followed in 1980 byF. crotonensisand a third small increase ofD. divergens.In both yearsS. astraeaandS. hantzschiistarted to grow again in November/December. Cryptophyceae andChlorophytawere present throughout the year, but did not show a distinct succession.2. Natural community bioassays, performed under natural light and temperature conditions in a newly developed outdoor bioassay apparatus, showed that phosphate was the major nutrient limiting the growth rate of the phytoplankton. From January till June, during the decline in phosphorus concentration, the diatoms became successively phosphate limited in the sequence:S. hantzschii, S. astraea, F. crotonensis, A. formosaandC. comta.Light limitation was probably the major cause of the relatively late start ofF. crotonensisin early spring.3.D. divergens, increasing after the diatoms from June till September, was stimulated by the addition of a chelator (EDTA). The chelator might stimulate the formation of trace metal species favouring their uptake (e.g. iron).4. The patterns of succession of the diatoms observed from January till June and from July till December were to a large extent symmetrical. The controlling factors followed opposite trends: declining phosphorus concentrations with increasing irradiance from winter till spring and increasing phosphorus concentrations with decreasing irradiance from summer till late winter

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00443.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Churchill estuary beluga whales displayed their highest densities in freshwater habitat, suggesting preferential use.2. Whale densities in freshwater were as high as 350 animals km−2and represented over one tenth of the estimated Hudson Bay population.3. Future environmental assessments of hydroelectric development in northern Manitoba, Canada, must consider the effects on the beluga whale

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00444.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Published data are used to construct a tentative carbon budget for the ecosystem of the lower river Rhine and its sedimentation areas in The Netherlands.2. It is estimated that 287 × 106kg Cy−1of particulate organic material is transported by the river Rhine, and 100 × 106kgCy−1of this material is deposited in the delta.3. Phytoplankton and nitrifying bacteria seem to contribute significantly to the carbon budget, by producingc.78 × 106kgCy−l.4. The mineralization in the water (estimated from routine determinations of biological oxygen demand and fromin situdiurnal fluctuations of oxygen) and in the bottom (estimated from the denitrification rates in the delta, from the production rate of methane and from overall oxygen consumption) is shown to degradec.50% of the carbon input plus autochthonous production.5. The carbon budget and oxygen regime in the lower Rhine suggest that after decades of severe organic pollution the river has more or less resumed the normal, slightly heterotrophic state of a large lowla

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00445.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Age, growth and reproduction in an Atlantic population of the small fish,Aphanius iberus(Cuv.&Val., 1846), from the estuary of the Guadalquivir river were studied.2. The growth period was from April to September and the annulus on the scales was formed in April.3. The life‐span was short with a winter age‐structure of 95.9% 0+ fish, 3.9% 1+ and 0.2% 2+.4. The fecundity of this stock, before the beginning of reproduction, is represented by the formula: Fec=0.907 TL (cm)4.099. During the reproductive period 1+ females contained more, smaller eggs g−1of gonad than 0+ fish.5. Males matured before females, but females were larger than males. The overall sex ratio did not differ from 1:1 but males dominated significantly during most of the spawning period.6.Aphanius iberusspawned intermittently during the reproductive period. From April to July, 1+ group specimens (7–12 months old) reproduced. Their offspring (0+ group; 3–4 months old) reproduced from July to September. Very few of the 1+ group specimens survived to spawn the following year.7. Mean gonadosomatic indices were much higher in the 1+ group than in the 0+ group and in females compared to males.8. The loss of condition and the disappearance of the 1 + group during spawning, may indicate the cost of a prolonged high level of reproductive effort.9. In this productive environment, the life history ofAphanius iberusis similar to that ofGambusia affinis(Baird&Girard, 1853) andFundulus heteroclitus(Linnaeus) found in the

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00446.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. The flow of water through the sediment layer (underflow) of streams can influence nutrient uptake dynamics and the supply of materials to microbes, meiofauna and macroinvertebrates living within stream sediments. We examined the extent of underflow in Hugh White Creek, a headwater stream in the southern Appalachian Mountains and compared underflow at different depths and at different sites within the stream.2. Initially rhodamine dye was used to trace the flow of water through the sediments; however, the dye was strongly absorbed by the sediments in Hugh White Creek. Thus rhodamine was not suitable as a tracer of water flow. Chloride reacted conservatively in laboratory experiments and was used as a tracer.3. The tracer infiltrated the sediments within 5 min to depths of 10 cm at all six sites. Chloride infiltration tended to decrease with depth of sediments at all sites although there was no consistent statistical pattern in chloride concentration with depth for the different sites. Equilibrium between the water column and sediments was reached rapidly, within minutes for the sites with coarse sediments and within a few hours for sites with finer sediments. Minimum rates of chloride infiltration into the sediments ranged between 1.0 cm min−1for the sites with cobble substrate to 0.2 cm min−1for sites with fine sand sediments associated with debris dams. These data suggest that underflow may be a major component in the functioning of Appalachian mountain stre

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00447.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY