摘要:

SUMMARY.1. Dense growths ofMyriophyllum heterophylluminfluenced temperature, dissolved oxygen, pH and light levels in the littoral waters of Lake Winnipesaukee, a soft‐water. New England lake. Periphyton species composition and abundance (algal units cm' stem) were related to the macrophyte‐mediated changes in the physicochemical environment.2. Duringearlysummer,M. heterophyllumoccupied onlythe lower part of the water column. Limnetic and littoral waters exchanged readily and were chemically similar. Early summer periphyton species composition was dominated by diatoms from the phytoplankton, entangled in the finely dissected leaves ofM. heterophyllum.3. By mid‐summer,M. heterophyllumoccupied the entire watercolumn of the littoral zone. The metabolic and photosynthetic activity and dense foliage ofM. heterophyllumcreated marked vertical gradients in physicochemical conditions. Mid‐day temperature, dissolved oxygen, pH and light levels were maximal in the surface waters of theM. heterophyllummat during the summer. Concurrently, periphyton species composition shifted to blue‐green and then to a filamentous green alga on the apex and mid‐stem. On the lower stem, diatoms consistently dominated the periphyton.4. Periphyton abundance on the apex was inversely related to apical elongation. Temporal fluctuations of periphyton abundance on the lower and mid‐stem were small throughout the study. Periphyton abundance was lowest on the lower stem, where the deteriorating leaves provided less surface area for

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00001.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SUMMARY.1. The ranges of concentrations for pH, CV. Na+. K+Ca2+, Mg2+are given for streams draining igneous rocks (Borrowdale Volcanics) and sedimentary muds, silts and shales (Silurian Slates) in the catchment of Windermere (230 km2). Impacts on the biota are briefly discussed. Relative contributions of inputs from various sources are examined: precipitation, rocks and soils, sewage, deicing salt used on highways./2. In bulk precipitation, ratios of Na+/CV (as μequiv. I−1) ranged from 0.41 to 1.83 over a 2‐year period. The overall volume‐weighted mean ratio was 0.86, as in seawater, hut 2′4%(1975) and 5.7% (1976) of Cl−was non‐marine in origin, being balanced by H+(in winter), K and Ca2+(in summer). In moorland headwater streams, CI−is largely derived from precipitation: there is a pronounced annual cycle of midwinter high and midsummer low concentrations unrelated to stream discharge. Na* and K+display similar cycles but Na+, Ca2+and Mg2+(and pH) are discharge‐related due to leaching from rocks and soils: 10–20% Na+, 15–17% Mg2+and 65–75% Ca2+are so‐derived whereas K+ comes from precipitation. Na+/Cl+ratios in streams on Borrowdale Volcanics alter seasonally, with midsummer values>1. Lower values occur in streams on Silurian Slates where some CI−is apparently derived from rocks.3. Seasonal changes in streamwater concentrations of Cl, Na4andK+are exponentially related to time. Instantaneous rates of change i day‐11) are compared in relation to position in the catchment and inputs from anthropogenic sources. Deicing salt has raised (10–100‐fold) the concentrations of Na*and Cl−in streams on mountain passes; the e

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00002.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SUMMARY.1. Population size, survival and recruitment were estimated from mark—recapture data at frequent intervals.2. Two types of mortality were identified: (1) moult‐associated—an intense but short duration mortality, and (2) overwinter mortality, which operated at a lower estimated weekly rate but over some 30 weeks.3. Population size reached a mid‐summer peak as recruitment into the catchable size classes occurred. Thereafter numbers declined slowly to the end of the growth season, followed by an overwinter decline of some 50% of total.4. Annual production was estimated at 196.5 kg wet wt ha−1in 1977, 116.8 kg wet wt ha−1in 1978 and 87.79 kg wet wt

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00003.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

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−1but 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‐−1calcium 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

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00004.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SUMMARY.1. The behavioural responses of the freshwater pulmonate snailBiomphalaria glabratato homogenates of various aquatic macrophytes were investigated with the aid of diffusion olfactometers.2. Of the eleven species studied, three lacked any attractants or arrestants, two contained weak arrestants, and three induced strong repellent effects. Only two,Apium nodiflorumandLemna paucicostata, induced significant attractant and arrestant effects comparable to those obtained with lettuce(Lactuca sativa)controls.3. DecayingLemna paucicostatahomogenate proved to be a significantly stronger attractant and arrestant than fresh homogenate. Evidence is given that these effects are mainly due to low molecular weight compounds (<1000 mol. wt) of which the major end products of microbial decomposition, short chain carboxylic acids (C2‐C5), are likely to be the most important. However, as carboxylic acids account for only a fraction of the total response, other low and high molecular weight compounds are also implicated.4. The ecological relevance of these results is discussed with particular reference to the hypothesis that the relationship between the snails and macrophytes is essentially mutualisti

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00005.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SUMMARY.1. Phytoplankton density (organisms ml−1), standing crop (chlorophyllamg m−2) and primary productivity (mg C m−2d−1) were measured during years 2 (1976) to 5 (1979) after impoundment on West Point Lake.2. West Point waters had low alkalinity (<0.4 meq 1–1) and low conductivity (<75 μs cm−1at 20°C) but N and P concentrations typically exceeded those considered apt to cause nuisance blooms of algae. Abiogenic turbidity was normally higher in the upstream areas of the reservoir than in the downstream areas and was several times higher in winter‐spring than in summer‐autumn due to increased rains and runoff.3. Primary productivity varied greatly both temporally and spatially. A mean value of 684 mg C m−2d−1was well within the mesotrophic range and did not approach the highly eutrophic state predicted. Productivity increased from a low of 550 mg C m−2d−1in 1976 to high of 763 mg Cm−2d−1in 1979.4. Observed variation in both chlorophyllaand primary productivity was more predictable in the cool (December‐March) than in the warm (June‐September) season and with plant nutrient data than without it. With plant nutrient data in the cool season 84% and 86% of the variation (R2) in chlorophyllaand productivity, respectively, were accounted for by the regression equations. During the warm season, with plant nutrient data, regression equations accounted for 44% and 68% of the variation in chlorophyllaand productivity, respectively. HigherR2values in cool seasons resulted from the overriding influence of abiogenic turbi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00006.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SUMMARY.(1) Swarming in the Cladocera has often been associated with periods of sexual reproduction and this has led to the suggestion that members of opposite sex are attracted to one another. The most plausible mechanism by which this could occur is through the production of pheromones. The present experiments aimed to determine ifDaphnia magnaStraus produce such chemicals.(2) No evidence was found for the presence of sexual pheromones. The behaviour of both males and females was unaffected by the presence of sexually receptive animals of the opposite sex.(3) It is suggested that the cited relationship between sexual reproduction and swarming may be due to the fact that sexual reproduction occurs during periods of high population density. It is during such periods that swarming behaviour would be most apparent.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00007.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Book reviewed in this article:Hey, R.D., Bathurst, J.C.&Thome, C.R.(Eds.) (1982)Gravel‐Bed Rivers—Fluvial Processes, Engineering and Management.Fryer, G.(1982)The Parasitic Copepoda and Branchiura of British Freshwater Fishes: a Handbook and Key.Barnes, R.S.K.&Hughes, R.N.(1982)An Introduction to Marine Ecol

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00008.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY