摘要:

SUMMARYAnin situgrazing chamber is described which facilitates the handling of radioactive materials, improves the capture of zooplank‐ ton, and optimizes the mixing of labelled food particles into the food suspensio

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01291.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1, The seasonal changes in filament dimensions and the occurrence of separation valves in a population ofMelosira granulata(Ehrenb.) Ralfs were investigated in a eutrophic lake in southern England. Experiments were carried out in culture to study the effects of various environmental factors on the diatom's morphology.2. Major blooms ofM. granulataoccurred from September to October, coinciding with an increase in mean filament length brought about by the high growth rate of the diatom. This increase was controlled by a reduction in the frequency of separation valve production. A similar increase in filament length occurred in rapidly growing cultures.3. The population was lost from the epilimnion when thermal stratification occurred. Immediately prior to this the population consisted of short filaments.4. The mean filament length was greatest during occasional summer blooms and was again controlled by a reduction in the frequency of separation valve production. This appeared to be a response to the reduced nutrient concentration in the lake. This is supported by similar morphological changes in low nutrient cultures.5. Increases in the filament length of the diatom were accompanied by increases in the diatom's sinking velocity. The length increase thus ensured its rapid return to the sediment, after summer growth periods, where the cells could be replenished with nutrients.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01292.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

1. Experiments simulating spring acidic snowmelt episodes were conducted to determine the effects of short‐term inputs of H+and Al on the chemistry and biology of a poorly buffered mountain stream. HC1 and A1C13were added in separate experiments to first‐ to third‐order reaches of a New Hampshire stream.2. Cation exchange and Aln+dissolution reactions neutralized experimentally added H+, whereas groundwater dilution was insignificant. Mobilized Ca++, Mg++and Aln+concentrations progressively increased from third‐ to first‐order reaches during HC1 additions. Mobilization of Ca++and Mg++was greater during A1C13than HC1 addition.3. Total phosphorus was mobilized from stream sediments during both HCI and A1C13addition. Dissolved organic carbon (DOC) decreased during A1C13addition in the second‐order but not in the third‐order reach. DOC concentration decreased during HCI addition only when Aln +mobilized from the stream bottom was>0.28 mg AI 11.4. Production of foam at the water surface during AlCl3addition to a second‐order and HCl addition to a first‐order reach indicated a reduction in surface tension of the streamwater and may be related to complexation reactions between Al and DOC at low pH (4–5).5. Mayfly nymphs and blackfly and chironomid larvae drifted at greater rates from HCl‐ and AlCl3treated sections of first‐ and second‐order streams than from corresponding reference areas.6. When stream pH was lowered to 5.25–5.5 by HCI alone (15 μg monomeric inorganic Al l−1), the behaviour of aquatic invertebrates did not change, but pH reduced to the same range during Al additions (280μg Al 1−1) did affect it. Therefore, fluctuating aluminium concentrations in low‐order streams at a pH range of 4.5–5.5 may alter the biology and g

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01293.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

1. To find if fish affect leaf breakdown, sugar maple leaves (Acer sacchrumMarch) were placed in a soft‐water, farm pond at a depth of 1 m for up to 3 months in four treatment groups: (1) enclosure with sunfish (Lepomis macrochirus Rafinesque) (SUNFISH treatment); (2) enclosure with catfish (Ictalurus punctatusRafinesque) (CATFISH treatment); (3) enclosure without fish (NO FISH treatment); and (4) no enclosure (OPEN treatment). The study was conducted in spring and autumn.2. The leaf breakdown rates,k±95% CL, for SUNFISH (0.0082± 0.00059 and 0.0111±0.00162 d−1) and CATFISH (0.0072±0.00096 and 0.0103±0.00077 d−1) were greater in spring and summer, respectively, than in the OPEN treatments (0.0065 ±0.00048 and 0.0105± 0.00141 d−1) and NO FISH (0.0067±0.00039 and 0.0088±0.00099 d−1). However, onlykfor SUNFISH was significantly different from NO FISH and OPEN treatments.3. Fish in the pond did not appear to affect breakdown rates of OPEN leaf packs in the first replicate but k approached that of the fish treatments in the second replicate.4. Fish may have promoted leaf breakdown directly by fragmentation of leaves while foraging for food and, indirectly, by agitation of leaves, leading to increased

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01294.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. Colonization and ecological development of postglacial freshwater communities was investigated in Glacier Bay National Park, south‐eastern Alaska, following the rapid recession of a Neo‐glacial ice sheet within the last 250 years.2. Environmental variables shown to be most significant in stream development were temperature, flow regime and sedimentation.3. The Chironomidae (Diptera) were the pioneer invertebrate colonizers of newly emergent streams arising as meltwater from receding ice sheets and displayed a distinct pattern of succession with stream maturity.4. Ephemeroptera and Plecoptera colonized warmer clearwater streams, but Trichoptera had a minimal role in invertebrate community development.5. Establishment and production of salmonid fish populations in the new streams related principally to stream flow and sediment characteristics.6. Future pathways along which the streams may develop is probably dependent on the degree of large organic debris input.7. Stream development, structure and function are summarized including reference to theories of ecosystem development, ecological succession and community stabil

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01295.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. Computer methods for mapping and calculating morphometric characteristics are described and applied to seventeen previously unsurveyed South Uist lochs.2. Deposited sea salt is shown to have a major effect on water quality and the effect varies according to distance from the west coast. Calcium concentrations appear to be determined by dissolution of locally abundant shell debris. Sulphate and particularly nitrate concentrations are influenced significantly by catchment sources.3. Surface sediment diatom assemblages from all seventeen sites are analysed using multi‐variate methods (Hill, 1979). Assemblages are shown to be clearly distributed along DECORANA axis 1 and are clustered into five groups by TWINSPAN.4. Correlation analysis of water quality, morphometric characteristics, and DECORANA axes scores indicates that conductivity has the strongest influence on surface sediment diatom assemblage composition whereas morphometric characteristics have no demonstrable effec

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01296.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. The range of factors which may influence the wide variation in the structure of pond communities is reviewed.2. Factors explaining the variation in numbers of macro invertebrate and macrophyte taxa are investigated, using multiple regression analysis, for a group of ponds in which biogeographical effects are likely to be minimal.3. Numbers of macro invertebrate taxa in these ponds are highly correlated with pH and probably, therefore, with other associated aspects of water chemistry,4. Many invertebrate taxa, from species to entire phyla, were not found below pH 5.5, but few characteristically‘acidophilic’taxa were apparent.5. Details of species composition of the macro invertebrate fauna differ widely even between ponds of similar pH.6. The diversity and composition of macrophyte communities are not adequately predicted by any of the factors investiga

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01297.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. A water column sampler is described for obtaining absolute population estimates of nektonic insects in shallow waters.2. Relative population estimates were obtained for Corixidae (Hemip‐tera) andBuenoa(Hemiptera: Notonectidae) using a standardized sweep net procedure and compared to absolute estimates from column samples. These two types of estimates were highly correlated among lakes.3. Simultaneous prediction and tolerance intervals for predictions from linear regressions indicated that reliable absolute population estimates generally cannot be expected from relative estimat

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01298.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. Experiments using implanted substrata were conducted in Yuccabine Creek, a n upland stream in north‐eastern Australia which exhibits a strong seasonal pattern of discharge and temperature. The implanted substrata were either set in the stream bed or were raised in the water column. Three experiments were run, at different times of the year.2. Colonization rate was dependent on benthic abundance, mobility of the fauna and distribution of resources. The rates on embedded trays were similar in the late wet season and mid dry season, but colonization rate in the late dry season was greater.3. Drift alone could have accounted for all colonization in the late wet season, 63% of colonization in the mid dry season and less (unmeasured) in the late dry season. Drift acts to disperse early instars to patches of suitable habitat after the summer wet‐season peak in reproduction.4. Following the wet season, stream discharge decreases, benthic abundance increases, resources become more concentrated, and movements of animals in contact with the substratum play an increasingly important role in colonizat

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01299.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. Seasonal change in the respiration of the dobsonfly larva,Protohermes grandis,was studied by measuring the oxygen consumption rate (resting metabolism) bimonthly for 2 years. The respiratory rate of the larva was significantly lower during the summer season when the stream temperature rose to 30°C.2. Summer depression of respiration was confirmed by measuring the rate of carbon dioxide evolution. The mean value of the respiratory quotient was estimated to be 0.76 ± 0.05 SE. The larva is believed to conserve energy by this reduction in respiratory rate,3. In other seasons, however, the larva maintained a higher respiratory rate and remained active even in the winter when the stream temperature decreased near to 0°C. In fact, significant growth in weight occurred from mid‐October to late March.4. This acclimation to temperature may enable the efficient allocation of energy during the long larval period (3 years) in streams which have large annual fluctuations in tempera

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01300.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY