摘要:

SummaryThe Portneuf River (mean monthly discharge near mouth 1.4‐15.4 m3/s) in southeastern Idaho, U.S.A., flows through an area of reduced precipitation (approx. 33 cm/year) and is dependent on underground aquifers and snowmelt runoff from the surrounding mountains for its water. The stream was examined at ten locations, distributed over its 156‐km course, during the period 1967‐1971. The Portneuf River is shown to have undergone a number of changes from its natural state as evidenced by alterations in water quality and the distribution of benthic invertebrates along the stream course. Of particular interest are changes brought about by the use of the stream for irrigation and by runoff from agricultural lands, factors whose effects are magnified by the semiarid conditions of the region and by poor soil‐conservation practices. However, the stream also is affected by wastes from a sewage‐treatment plant, phosphate‐processing operations, and an assortment of scattered urban sources. Benthic invertebrates were collected during all four seasons by means of artificial substratum samplers and during summer and autumn by a qualitative dip‐net technique. In general, the samplers were more effective in obtaining a representative picture ofthe fauna. However, neither procedure alone gave as much information as the combined results. The artificial substratum collections are not believed to be representative of the usual effects of stream devvatering by irrigation withdrawal in as much as the samplers provide refugia for the benthos during the periods of re

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1973.tb00059.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryOrganic and inorganic carbon and nitrogen parameters were sampled simultaneously at 6 h intervals over a diurnal period at seven stations in a small hardwater stream in southern Michigan. Concentrations and budget values (kg/day) varied up to 10‐fold at individual stations and between stations. The most constant parameters were total dissolved organic carbon and nitrogen. The most variable parameter was particulate organic carbon.Significant changes were noted in all parameters as the stream passed through different stream‐side habitats. Budget values facilitated interpretation of these changes over time between stations. High variability in the concentration values was introduced by large allochthonous inputs of dissolved organic matter (DOM) and water alternately adding to or diluting parameters. Distance from upstream terrestrial DOM sources, DOM residence time, the pulsed nature of DOM inputs and biological utilization of DOM have important effects on the quality and quantity of DOM that enters recipient lakes and rivers. The importance of ground‐water flux and DOM content is stressed. The DOM input and turnover within hardwater streams appears t o be in rapid, dynamic equili

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1973.tb00060.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryA new technique for the establishment of a permanent laboratory culture of Chirono‐mus riparius is described. Larvae and pupae were reared in plastic tanks containing tap water, filamentous algae and a commercially prepared fishfood. The tanks were aerated, maintained at a constant temperature of 24°C and subjected to a constant lighting regime of 13 h of light followed by 11 h of darkness. Adults flew freely in a modified handling box, mated, and oviposited on strips of filter paper placed in the plastic tanks containing the aquatic stages. It has proved unnecessary to change the water or medium, which has saved both time and effort. Moreover, larvae established themselves in ail parts ofthe alga, and therefore more could be kept in each tank than when, as in previous methods, they are provided only with a substratum on the floor of the contain

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1973.tb00061.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryPhotosynthetic production by phytoplankton was studied in two Ethiopian soda lakes, alkalinity 51‐67 m‐equiv./l, with abundant blue‐green algae. The deeper lake, L. Aranguadi, contained extremely dense crops composed almost entirely of SpiruUna (Oscillatoria, Arthrospira) platensis. Measurements of the spectral attenuation of light showed that the most penetrating component was displaced to the red spectral region, and estimates of the chlorophyll a content in umt area of the euphotic zone were often similar to the highest values (∼200‐300 mg/m2) expected on theoretical grounds.The vertical distribution of photosynthetic activity per unit water volume was of a typical pattern for phytoplankton, with light‐inhibition often present, although the euphotic zones did not exceed 0.6 m in depth. From these profiles, computed rates of gross photosynthesis per unit area of lake surface reached a magnitude of 1.4–2.4 g O2/m2.h in both lakes. They were obviously severely limited by self‐shading behaviour i n the algal populations. An appreciable inverse relationship between photosynthetic capacity and population density was only found in the densest populations of L. Aranguadi, with chlorophyll a content>2000 mg/m3, where depressed rates might result from experimental artefacts in closed bottles. In this lake, two independent estimates of gross production, based on the analysis of diurnal changes in the open water, were as high as 43 and 57 g O2/m2. day.Diurnal changes of stratification in the two lakes are described and related to the controlling temperature (density) stratification. They include occasionally complete nocturnal deoxygenation in the deeper lake, evidence of heavy respiratory uptake.The high photosynthetic productivity is interpreted as dependent upon the coupling of high algal contents in the euphotic zone (^S) with high values of photosynthetic capacity (^max)‐ It is probably favoured by the tropical situation affecting temperature and illumination, by a surplus of dissolved inorganic phosphate, and especially by the considerable reserves of carbon dioxide in

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1973.tb00062.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryThe life cycle of the cladoceran Simocephalus acutirostratus has been studied in the laboratory with reference to its total life span, duration of instars, egg production and growth. It has four pre‐adult and eighteen adult instars and produces about 248 eggs during a mean life span of 44 days within a temperature range of 28°C‐30°C. Egg production was found to be bimodal, with a sharp decline towards the end of the life cycle. The present results are compared and discussed with those of other tropical and temperate daphnids. It has been shown that while this species resembles most other daphnids (D. middendorffiana, D. pulex, D. carinata) in the growth pattern of pre‐adult instars, it resembles the temperate D. pulex in having a relatively long life span, relatively high egg production and slow rate of growth.While studies on embryonic development of S. acutirostratus resemble the growth stages of the temperate Daphnia magna, there are differences in the total period of development between the two species. In the latter aspect, however, the present species closely resembles other tropical d

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1973.tb00063.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Summary(1) The occurrence of haemoglobin in Phaenocora typhlops (Vejdovsky) is reported.(2) Rhabdocoels were examined spectrophotometrically. The distribution of the pigment was studied by a sodium nitroprusside‐benzidine technique, and the distribution of ferric iron with Perl's technique.(3) Characteristic bands of oxyhaemoglobin were observed at 540 and 580 nm. The oxyhaemoglobin was reduced to haemoglobin by the addition of sodium dithionite and an absorption band appeared at about 560 nm.(4) Haematin was found principally around the pharynx, though a little was found in front of the latter and along the length of the gut. Ferric iron was distributed throughout the worm.(5) The occurrence of haemoglobin in P. typhlops and P. unipunctata is compared. It is suggested that less occurs in the former species. Whether or not this is related to the presence of zoochlorellae is considered. Certainly both species burrow actively in mud where reduced oxygen conditions can occu

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1973.tb00064.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryThe seasonal periodicity of four species of planktonic diatoms in a small eutrophic lake in the Shropshire‐Cheshire Plain, England, is examined. Diatoms typically dominate the spring increase; a second period of growth follows in the summer months. The growth phases are considered in relation to environmental factors in the mere. Of these, light levels appear to be critical in determining the onset of growth and the size of the population maxima, whilst stratification and turbulence play a leading role in the vertical distribution of the algae, and hence, of the growth conditions to which they are exposed. The thermocline is believed to provide a reservoir of diatoms in summer, maintaining them in a position where they are able to gain maximum advantage from increased wind‐induced turbulence. Relative specific differences in growth requirements and in behaviour under varying physical conditions are important in determining which species dominate. Dominance may be modified by the effect of attacks by fungal parasites. It is also shown that, generally, nutrients are present in relative abundance, and only rarely does their availability become a limiting factor. Tt is concluded that diatom growth in this lake is typically subject to physical rather than chemical cont

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1973.tb00065.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY