摘要:

SUMMARY.The growth and recession of macrophytes on a shaded section of the R. Lambourn were documented by a mapping procedure. With the exception ofRanunculusspp., the changes in total cover did not indicate directly the pattern of growth and recession of the macrophyles. Analysis of gross changes, expressed as gains and losses on cover, indicated that colonization of gravel and silt by the dominant macrophyte,Berula erecta, did not vary seasonally. Colonization was at a constant rate of about 8% of the site each month throughout the year and this accounted for 50% of the total number of gains byBerula.Gains ofBerulafromRanunculusshowed an annual cycle with a maximum during the summer whenRanunculuswas in recession. Gains ofBerulafromCallitrichespp. also varied annually but the maximum was during the autumn. Total losses ofBerulawere at a constant rate throughout the year but were to gravel and silt during the winter, toRanunculusin spring and early summer and toCallitrichein late summer and autumn. Analysis of loss ofBerulawith time indicated that the position of theBerulacarpet was constantly changing. The growth and recession ofBerulacould not be linked in a meaningful way to environmental variables.CallitricheandRanunculusboth showed an annual pattern of growth and recession. There was temporal separation of the two macrophytes withRanunculusgrowing mainly in spring and early summer andCallitricheshowing maximum growth in late summer and autumn, and some evidence of spatial separation. The observed differences between years in the growth ofCallitrichecould not be attributed to any of the environmental variables measured.Discharge was thought to be an important variable controlling the growth ofRanunculussince increase ofRanunculusin the spring was positively correlated with the mean discharge at that time. In years when discharge was low, the growth ofRununculusappeared to be restricted by shading from epiphytic algae which accumulated on the plant surfaces under these conditions.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00600.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.The algal flora of the Rivers Hayle and Gannel. whieh drain copper and lead mining regions of Cornwall, are described and compared. Although fluctuations in the rarer members of the algal communities were observed, the dominant filamentous algae at most sites did not change over the year of study. Both the total algal abundance and the number of species were depressed at high metal sites. Associations of species that were evident in field samples were confirmed and correlated with water metal levels by principal component analysis. The close similarity between the flora of similar sites on the copper‐polluted River Hayle and the lead‐polluted River Gannei implies that the degree of metal pollution, rather than the polluting metalper se, determines the species present. All mine sites were characterized by aMicrospora‐community whereas a Zygnemales community ofSpirogyraandMougeotiaspecies was typical of low metal pollution. Moderately polluted sites downsteam of the mines had an intermediate flora of Zygnemaies, Microsporales. Ulotrichales and gelatinous Volvocales and Tetrasporales species. No species could be said to invariably indicate metal pollution; the most abundant species at highly contaminated sites were also those with the widest distributions.Field samples of filamentous algae (mainlySpirogyra, Zygogonium, MougeotiaandMicrosporaspecies) contained metal concentrations several orders of magnitude greater than ambient levels. For copper and iron, both algal metal contents and concentration ratios (μg g‐1 algae/μg ml‐1 water) were positive functions of water metal levels, although algal iron appeared to plateau at water concentrations of about 1 mg ml‐1. Algal lead concentrations, but not the concentration ratios, also were positively correlated with water lead levels. Thus, for these three metals, the algal metal contents were indicative of ambient conditions. In contrast, algal zinc concentrations were nearly constant and consequently the concentration ratios for this metal were inversely related to water levels. This result suggests that unlike the uptake of other metals, uptake of zinc by these aigae may be stric

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00601.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.Two‐hundred isolates, comprising 87 species of Chlorophyta, were obtained from sites along the Rivers Hayle and Gannel. which drain the ancient mining region of Cornwall. All isolates were tested for sensitivity to copper, lead, zinc and cadmium. In general, isolates were resistant to the metals normally present in their habitats. However, the distribution of metal sensitivities of the algae from a given site was broad; the effect of metal pollution was to shift the median response of a population toward higher metal resistance. Resistant algae of two general classes were identified: some normally sensitive species were metal‐tolerant, presumably through genetic adaptation; other species were metal‐resistant even when isolated from a non‐polluted habitat. Many isolates of both types displayed multiple‐resistances or co‐tolerances. For example, copper tolerant isolates from high copper sites tended to be also lead resistant; however, algae from high lead sites were usually very copper sensitive. Zinc and cadmium resistances also were correlated among isolates from both zinc‐polluted and non‐polluted sites. General metal‐insensitivity seemed to be common, particularly among gelatinousChlamydomonasandGloeococcusspecies. Thus, several evolutionary strategies appear to coexist among algae from metal poll

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00602.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.Sediment from a precursor of the 2300‐year old Lake Mývatn was traced by diatoms in pseudocrater scoria. This lake (Mývatn I) was deeper than the present Mývatn but similar in size. Tephrochronology confirms an equal age of the Ytrlflói and Sydrifloi basins of the present Mývatn. Diatom succession in the sediment of the Sydriflói basin was divided into four zones, of which the lowest corresponds to inherited and highly disturbed Mývatn I sediment. At 90 cm depth, i.e. around 1600 AD, in the Sydriflói sediment a simultaneous increase occurred inCladophora aegagropila(Chlorophyta),Eurycercus lamellatus(Cladocera) and three diatom species epiphytic onCladophora.The density of Cladocera also followed this trend. The increase in Cladophora was perhaps caused by improved light conditions on the bottom, either because of a decrease in water depth due to sedimentation, or a decrease inAnabaenablooms

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00603.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.Chironomid eggs are the primary food of aduh and nymphalHydrodroma despiciens.Observations on feeding behaviour showed that the palps are well adapted for probing the egg mass jelly. Chironomid egg masses also serve as primary sites for male spermatophore deposition.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00604.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.Aphanius disparwas observed in the field and some simple laboratory studies were undertaken in Oman.A. disparis almost totally ubiquitous in all bodies of fresh water where it occupies a wide range of habitats differing in stream flow, water chemistry, temperature and substrate quality. It often is found in association with one or both of two cyprinid fishes.CyprinionandGarra. Aphaniusis tolerant of wide ranges of salinity up to full marine water and has a wide temperature range.A. disparresemblesCyprinodonspecies in a number of particulars, probably reflecting phylogenetic relationships and a common evolutionary response to desert conditions. It breeds throughout the year with a probable peak in the months of April to June.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00605.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.The flanks of grayling are generally studded with black dots which vary in number. The number and position of these dots are well‐defined for each individual and make it possible to identify each fish, in some cases, as when there are very few dots or none at all, it is necessary to make use of other features such as the general disposition of the scales.The best method for recording these characters is by photographing each fish. When recaptured, a fish can be recognized by comparing photographs. The number and position of dots on their lines can be sorted by a computer. Ultimate confirmation is given by comparing the most likely photographs once they have been selected by the compute

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00606.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY