摘要:

SummaryThis study covers a 7‐year period from 1965 to 1972, and shows the variation in flow, water chemistry and throughput of nutrients. The annual discharge of the River Frome varied considerably from year to year, ranging from a mean value of 4.48 m3sec−1in 1971 to one of 8.38 m3sec−1in 1966. The mean annual nutrient losses calculated over all 7 years of study from the River Frome catchment were: Nitrate 11.4 kg ha−1, phosphorus 0.49 kg ha−1and potassium 8.4 kg ha−1. There has been an increase in annual throughput (in years of similar flow) of 21% in phosphate and 41% in nitrate from 1

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00152.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryThe results of quantitative sampling of the drifting invertebrates from a riffle area in the upper reaches of the Pawmpawm River in the forest of Ghana are presented. The observations were made once a month during 14 months, April 1970 to May 1971, and also on a daily basis for 3 weeks. Changes in numbers and composition of the animals drifting were examined in relation to the volume of water flowing and the current; there appeared to be two distinct drift phenomena, ‘true’ and ‘background’ drift. The animals belonging to each of these two components are discussed in relation to their response to light, to diurnal fluctuations in total drift and to the phases of the moon. There was a peak drift activity after sunset in those animals which are affected by light, e.g.Centroptilum, Austrocaenis, Chironomidae, Simulium. It is concluded that drift may be simply a function of the activity patterns of the

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00153.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryFactors such as current, light, food, substrate and time of year were found to influence the activity of specimens ofGammarus pseudolimnaeusmaintained in stream tanks in the laboratory. Although there was seasonal variation, levels of diurnal and nocturnal activity were generally much higher when there was no current than when the water was running. Diurnal periodicity occurred but was not as pronounced as had been indicated in the field studies of previous workers. Although there was activity during the day, nocturnal levels were higher especially in specimens collected during the summer. When there was no current, and the lights were left on for 24 h, peak activity occurred at precisely the times when the lights normally would have been off. This strongly suggests that there is an endogenous component in the activity. The nocturnal activity showed a bigeminus pattern, and there was a seasonal change, with the general activity at its highest levels in summer. Activity was significantly greater during daylight both with and without current when there was no substrate present in the tanks. The behaviour ofGammarusappears to be complex and greatly influenced by combinations of the various factors.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00154.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryIn Lake Mahinerangi, a New Zealand hydro‐electric supply reservoir, phytoplankton productivity increased from an annual average of 76 mg earbon m−2day^−1in 1964–66 to 210 mg carbon m−2day−1in 1968–70. It is likely that the increase was due partly to water levels being higher in 1968–70. Results of multiple regression analyses on the annual productivity curves for 1964–66 had suggested that water level, with temperature, was a major factor influencing the productivity at near‐optimal light intensity. In the interval between the two studies the first agricultural land‐development, amounting to 3% of the drainage basin, was carried out, and there is evidence that this development also contributed to the increase in phytoplankton productivity. Streams which drain the developed land were richer in phosphate and nitrate than the unmodified ones. Phosphate concentrations in the lake increased, but other chemical changes were slight. There were no major changes in the species composition of the phyto‐plankton. None of the three dominant species of zooplankton increased, but there were substantial increases in two less abundant taxa,Daphnia carinataKing and Cyclopoida. The relative increase inDaphniais consistent with the hypothesis that large zooplankton enjoy a competitive advantage over smaller species. Similar changes a

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00155.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryAn account is given of the water chemistry and photosynthetic flora of waters in England with a pH value of 3.0 or less. Of the fifteen sites found, thirteen were associated with coal‐mining, one with a barytes mine and one was an industrial effluent. Flowing waters predominated, but in some cases pools in direct contact with the streams were also present. All waters carried high levels of heavy metals and silicate, and most carried moderately high levels of phosphate and combined inorganic nitrogen. The total flora consisted of twenty‐four algae, two mosses and two flowering plants. Of these, three algae and one flowering plant were found in pools only.Euglena mutabiliswas both the most widespread species, and often also the most abundant. The number of species present in a reach showed a positive correlation with pH during late summer, and a negative correlation with total acidity in winter. Only four of the algal species found in England are certainly included in the U.S.A. literature. Some, but not all, the apparent differences between the two floras are very probably due simply to taxonomic probl

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00156.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryAlgal‐iysing bacteria are present in five lochs, two reservoirs, one sewage works and five alkaline soils whieh were examined. Nine out of thirty‐six isolates have been studied in detail and all are gram‐negative non‐fruiting myxobaeteria. All are aero‐philic, require a neutral or alkaline pH (optimum 7.0–9.0) for good growth, have temperature optima of 28–37°C, require contact with the host for lysis to oecur, and are so similar in morphology and host range that they all appear to be strains of a single genus. They lyse all bloom‐forming Cyanophyeeae on whieh they have been tested, including species ofAnabaena, Aphanizomenon, Gloeotrichia, MicrocystisandOscillatoria. Their abundance is usually correlated direetly with the abundance of Cyanophyeeae in eutrophic waters and it is probable that in most ecosystems the algae and the bacteria co‐exist, although if the equilibrium changes markedly as a result of change in environmental conditions situations may arise where the bacteria may play an important role in the lysis of algal blooms. The available evidence suggests, however, that this is likely to be a rare occurrence in

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00157.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY