摘要:

SUMMARY.Surveys of the physico‐chemical status of the River Zambezi in Moçambique were conducted between April 1973 and May 1974, to characterize the river prior to the closure of the Cabora Bassa Dam and to provide baseline data from which future changes in the river ecosystem can be followed.The temperature of the river water increases by about 3°C from Lake Kariba to the sea, and with an average pH of 7.8 the water is slightly more alkaline than Kariba Dam water. The river is well oxygenated with no sign of hydrogen sulphide. Transparency is generally very low and changes are mainly determined by the floods of local tributaries. The overall average total alkalinity is 55 mg 1−1CaCO3, with no regular seasonal variation, average concentrations of chloride and sulphate are respectively, 5.4 mg 1−1Cl−and 5.3 mg 1−1SO2‐4. They increase under both the influence of the ionically rich Shire River and the sea; the latter due to vertical mixing. Total hardness and calcium hardness behave in a similar way, while conductivity and silica concentrations increase slightly until the Zambezi—Shire confluence, at which point, conductivity increases by 25% to an average peak value of 153 μS cm−1, and silica decreases by 15% to a minimum average value of 15.5 mg 1−1SiO2. Ammonia and nitrate concentrations show a clear seasonal variation, with respectively, minimum dry season and maximum wet season average values of about 0.05 mg 1−1and 0.3 mg 1−1. The overall average concentration of nitrite is 0.004 mg 1−1. Orthophosphate in the river is mostly affected by Lake Kariba, though other sources are also of some importance. Maximum average concentrations of about 0.4 mg 1−1PO3‐4were recorded during the dry season after the overturn of Lake Kariba. The concentration of dissolved metals is mainly determined by the outflow of Kariba and by the Shire River, with only K and Mg apparently affected by the outflow from Lake Kafue.It is concluded that the water quality of the Middle Zambezi is mainly determined by the Kariba Dam, with the Kafue Dam playing a minor role. At the time of the pre‐impoundment survey, the main impact on water quality of the Lower Zambezi came from the Shire River. With the addition of yet another large reservoir on the Zambezi, in the form of Cabora Bassa, together with the appreciable effect of tributary rivers on the lake, and the likely increased impact of the Shire River on the now more regulated river, the quality of the Lower Zambezi is expected to alter considerably, wit

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01668.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.The zooplankton of the Blue Nile overcomes the adverse conditions of the flood by entering into a state of diapause. Resting stages were found in the river bottom, flowing water and rain pools. They were blown to different localities by wind and can withstand long periods of desiccation. Some species of zooplankton go into diapause more than once a year, notably during their seasonal peaks of abundance. Release from diapause occurred in the temperature range 20–30°C and was facilitated by longer photoperiods and decreased concentrations of suspended silt. Various species of zooplankton were induced in facultative diapause when stored in complete darkne

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01669.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Barton Broad, Norfolk is a shallow, eutrophic lake. During the last 30 years submerged macrophytes have declined and phytoplankton numbers have increased. This change is traced through the stratigraphy of a 60‐cm mud core. Diatom frustule counts of 1‐cm sections of the core showed that an epiphyte‐dominated diatom community was replaced by a planktonic community. From chemical analysis and radio‐isotope dating of the core, sedimentation rates and past phosphorus and iron loadings are estimated. Sedimentation rates were between 1.2 mm and 3.1 mm year−1during the early part of the core but doubled in the 1950s to 5 mm year−1, doubled again in the 1960s and have increased to 12 mm year−1in the 1970s. Retention of phosphorus in the sediment increased from 0.5 g m−2year−1to 18–21 g m−2year−1in two steps. A similar trend is shown for iron. The diatom species composition and chemistry of the core sections are correlated with increased nutrient loading and the decline of macrophytes. Contemporary phosphorus and iron budgets are calculated from inflow–outflow data and balanced using sediment retentions estimated from the core data. It is believed a large proportion of phosphorus and iron enters the Broad by movement of sediment along the river bed. A reduction of 25% of the 1975 phosphorus loadings would probably permit re‐establishment of some macrophytes. The present chemistry and algal communities of Barton Broad and

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01670.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Asellus meridianusfrom sites on the rivers Hayle and Gannel accumulates both copper and lead from experimental solutions: tolerant animals also accumulate copper and lead from metal‐enriched food. Copper‐tolerant animals accumulated up to 6.8 μg mg−1copper after feeding on a copper‐enriched diet for 12 days whereas non‐tolerant animals showed no evidence of copper accumulation from food and no survivors remained after 8 days. Lead‐tolerant animals accumulated up to 28 μg mg−1lead during a 14‐day exposure to a lead diet: non‐tolerant animals showed no accumulation of lead from food and no live animals remained after 10 days.A marked difference in the storage forms of copper is observed in the hepatopancreas of copper‐tolerant isopods, as compared with non‐tolerant animals, when samples are taken f

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01671.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.The ecology of three commonly occurring cyprinodonts,Aphanius dispar(Ruppell),A. sophiae(Heckel) andA. mento(Heckel) was studied in the Lower Mesopotamian Plain of Iraq. These fishes are chiefly herbivorous, live in the same habitat and generally take the same food, although the dentition of the jaw and pharynx inA. dispardiffers from that ofA. mentoandA. sophiae. The gut contents were mostly filamentous algae. In laboratory experiments all three species ateGambusiaembryos.A. disparandA. sophiaeate mosquito larvae whereasA. mentodid not. All three species were infected with a cestode parasite which prevented development of female ovaries. The behaviour of the three species was different. BothA. disparandA. sophiaeform schools, swimming and feeding together. In their natural habitat, males and females ofA. disparwere in separate schools.A. mentodid not form schools; the males of this species displayed aggressive behaviour. Some observations were also made onGambusia affinis(Baird&Girard).

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01672.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Increased sensitivity in the determination of ATP in fresh water and sediment samples was achieved by incorporating protein, EDTA and extra luciferin in the reconstruction of the firefly lantern preparation. Maximum recovery was only obtained when samples were extracted in actively boiling Tris buffer. The method was sufficiently sensitive for the determination of ATP in 1 ml water samples injected directly into the boiling buffer. Concentration of water samples on membrane filters, even volumes as small as 1 ml, caused a significant drop in the ATP recovered. This was thought to be due, at least in part, to cell lysis and the concentration of interfering detrital material on the membrane. Further interference was observed when sediment samples were analysed. This was only partly overcome by dilution of the sample and the importance of the inclusion of internal standards (bacterial cultures) is emphasized.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01673.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Population and production dynamics ofCeraclea ancylus(Vorhies), a leptocerid caddisfly with a univoltine life cycle, five larval instars, and a single cohort population, were examined in Brashears Creek, Kentucky. A systematic sampling approach that included analysis in riffle, pool, and waterwillow bed habitats was used and fourteen sampling transects were taken across Brashears Creek between May 1971 and July 1972. For each of the 70 m2samples taken along a transect, the depth, habitat, and substrate type were recorded. The number ofC. ancyluscases and numbers and dry weights of each larval instar were determined.The majority of theC. ancyluspopulation was in the second larval instar in July, the third larval instar in August, the fourth larval instar in September, and the fifth larval instar from October through May. The spring population was 30% of the early instar maximum estimated the previous August. The spatial distribution ofC. ancylusreflects a logarithmic pattern with early instar larvae more highly clumped than the late larval instar and pupal populations. Initial standing stock estimates were less than 1% of the standing stock biomass. A production estimate of 9.9 mg/m2·year (dry weight) was determined using the instantaneous growth method, Allen's Curve method, and the Hynes method of estimating secondary production. Turnover ratios (7.0 annual TR, 5.7 cohort TR) were higher than estimates reported as typical for benthic macroinvertebrates because of the low initial to final mean individual weight of theC. ancyluslarvae (0.4%).Production estimates calculated forC. ancyluspopulations in waterwillow bed (4.4 mg/m2·year) and pool (13.7 mg/m2·year) habitats were less than calculated for the riffle population (19.9 mg/m2·year). The annual turnover ratio (10.2) was higher in the pool population than in other habitats because of spring larval migration into the pool from other habitats. A trend of higher production estimates with larger sized substrate particles and increased numbers of particles may reflect the increase in available food sources or attachment sites. The accuracy of production estimates and their applicability to water resource management may be limited by a failure to consider the spatial distributions of the population being sampled and the tendency for sampling procedures to be confined to single habit

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01674.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Twenty‐three species of unionid mussels were sampled during the summer of 1975 from a 76‐mile reach of the Upper Mississippi River; this represented eight species fewer than were recorded in a 1930–31 survey for the same section of the river. Of the 244 sites sampled in 1975, mussels were found at 116 sites and the ten most productive sites accounted for 40.8% of the 1205 mussels collected. There were as many as thirteen different mussel species taken from one sampling site. The two most abundant species (Amblema peruvianaandMegalonaias gigantea) constituted 54.5% of the mussels sampled in 1975; these two species made up only 8.3% of the 1930–31 survey. Individuals of the twelve most abundant mussel species were aged, and shell‐length growth equations were determined. In addition, shell‐free dry weight growth rate and shell weight growth rate was determined forAmblema peruviana. The calculated annual production forA. peruviana(assuming a mean density of 1 per m2) was 482 mg/m2shell‐free dry weight, and 14.471 g/m

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01675.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Gammarus pulexL. was studied at three sites in a Danish spring. Breeding took place during the summer and therefore cohorts could be followed. Sexual maturity was not reached until the next summer and maximum age appeared to be two years.Changes in population size differed between stations and was tentatively related to differences in drift and numbers of predators. Generally the drift was non‐selective between cohorts and within cohorts.Yearly production estimated from production curves was 2.6 g dry weight m−2(the young cohort) and 1.2 g dry weight (the old cohort) at Station 1. The respectiveP/B̄ ratios were 3.35 and 1.22. Production of the youngest cohort at the three stations in the period September‐May was 0.9–1.3 g m−2andP/B̄ ratios were 2.14–2.31. Total yearly production at the three stations was estimated at 4–7 g

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01676.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

DEPTH CHARTS OF THE CUMBRIAN LAKES. By A. E. Ramsbottom.THE ALGAE (set nos. S7199, S7200, S7201). Educational Productions Ltd.WEST AFRICAN FRESHWATER FISH. By M . Holden and W. Reed (1972).TEXTBOOK OF FISH CULTURE: BREEDING AND CULTIVATION OF FISH. By M. Huet (1973).THE INLAND WATERS OF TROPICAL AFRICA: AN INTRODUCTION TO TROPICAL LIMNOLOGY. By L. C. Beadle (1974).TURBULENCE IN LAKES AND RIVERS. By I. R. Smith (1975).

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01677.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY