ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00001.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Nyumba ya Mungu reservoir was completed in 1965 in northern Tanzania. By 1970 there was a thriving tilapia fishery but it declined catastrophically in subsequent years. A team of biologists surveyed the lake in 1974, and this paper outlines their hydrological, geographical, and climatic findings.The dam, constructed across a north/south Neogene fault‐trough 80 km south of Mt. Kilimanjaro, has produced a reservoir about 180 km2with a mean depth of 6 m. The catchment area is extensive but the main source of water is from Mt. Kilimanjaro. The lake is situated in an arid area, and over one quarter of the input water evaporates from the lake's surface. The outflow is regulated by a hydro‐electric power station and is practically constant. At full capacity the retention time of the lake is one year but due to abnormally low rainfall, the reservoir was not full, and the retention time was nearer nine months.The lake is polymictic and a deep wind‐driven current is maintained by the Trade Winds for most of the year.The general features of Nyumba ya Mungu are briefly compared with other man‐made and natural lakes in

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00002.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

This publication reports on the chemical and phytoplankton aspects of a three month biological survey of Nyumba ya Mungu reservoir, Tanzania.The lake had a total salt concentration of about 8 meq dm‐3and specific conductivity of 900 μS cm‐1. The main salt in solution was sodium bicarbonate, and when the lake level fell it sometimes formed a crust on the exposed shore. The concentrations of major nutrient ions were probably not limiting to algal growth and good nutrient replenishment was provided by the two inflow rivers.Nyumba ya Mungu supports a rich phytoplanton dominated byMelosiraand blue‐green algae. Acetone extractions gave chlorophyll ‘a’ concentrations ranging from 20–40 mgm‐3in the vertical profiles, and light and dark bottle experiments indicated a maximum gross photosynthesis of about 800 mg O2m‐3h‐1. There was evidence of chemical stratification in the open water and diurnal stratification in the sheltered bays, but discontinuities were short‐lived and the Trade Winds ensured regular mixing of the water. The lake appeared to have a higher primary production than the larger Rift Valley lakes and it was considered that this level of produ

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00003.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

The periphyton communities established in Nyumba ya Mungu were investigated between July and September 1974.One hundred and ninety‐two taxa were identified. One hundred and fifteen taxa were collected in the southern end of the lake, where 97 taxa were non‐selectively distributed in the littorine epiphytic, epilithic, and epixylic environments. The offshore epixylon supported only 53 taxa. The epipelon and epipsammon were poorly developed at the southern end of the lake but were well developed in the northern inflow regions.Diatoms and cyanophytes were the dominant phyla which contributed over 80% of the algal numbers. Chlorophytes were not common. Taxonomic compositions of periphyton on artificial and natural surfaces were similar, but artificial substrata accumulated greater proportional representations of diatoms.The mean net production rates of periphyton on artificial substrata located at depths from 0‐0.65 m for 28 days ranged from 140 mg organic dry weight m‐2day‐1on shoots in the macrophyte zone to 820 mg organic dry weight m‐2day‐1on glass surfaces on a rocky shore. The epiphytic environments produced the least standing crops of less than 250, 000 individuals cm‐2, but maximum densities of over 2,000,000 individuals cm‐2were recorded

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00004.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

A study was made of the aquatic macrophyte ecology of Nyumba ya Mungu; a nine year old man‐made lake in northern Tanzania. The vegetation is described with the aid of percentage cover histograms and standing crop estimates. Concurrent physical, chemical and biological studies helped in ecological interpretations. Distinct vegetation communities were found in the deltaic swamps of the two major inflow rivers and it is concluded that this was due to water chemical differences. The water of the more alkaline River Kikuletwa appeared to influence the greater part of the perimeter swamps as the species composition largely coincided with that reported for higher pH, higher conductivity African lakes.Typha domingensisswamp was predominant and extensive, whilstCyperus alopecuroidesandPaspalidium geminatumwere also common emergent species. Floating and submerged plants were relatively unimportant in the lake with respect to cover. The major zonations of species appeared to be a function of water depth, while chemistry seemed the main factor controlling vegetation pattern. In conclusion the significance of interrelationships between the macrophytes and other aquatic organisms is discusse

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00005.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Eight species of Crustacea and 28 species of Rotifera were identified in zooplankton samples from Nyumba ya Mungu reservoir. In all localities the dominant organism was the copepodThermocyclops hyalinus.Cladocerans and rotifers made a variable contribution. Insects, among which the Chironomidae were pre‐eminent, formed the major component of littoral macroinvertebrate communities. Oligochaetes, crustaceans and gastropods, including vectors of Schistosomiasis, were rare or restricted in distribution. In contrast to the deep end of the lake, where submerged trees were the poorest substrate, those at the shallow end supported a high biomass of invertebrates, since prolonged exposure had accelerated rotting and facilitated colonisation by the burrowing nymphs ofPovilla.The variety of invertebrates on stony and muddy shores was increased when rooted emergent plants were present. The richest benthic community was found in submerged beds ofCeratophyltum.It is suggested that drawdown and the restricted development and movement of floating vegetation, have limited the spread of gastropods in the lake. Zooplankton, chironomid larvae and pupae, and ephemeropteran nymphs were shown to be important in the diet of small carnivorous and omnivorous fish specie

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00006.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Twenty species of fish were found in Nyumba ya Mungu reservoir on the River Pangani which, with two exceptions, were indigenous to the river basin. Their distribution is described and some information on their growth, reproduction and feeding habits is presented. The highest densities of fish were found in the littoral and the broad, shallow, upstream region of the lake. The lacustrine environment has favoured the endemic tilapias,Sarotherodon jipeand S.pangani, which graze periphyton, and the introduced species,S. esculentuswhich feeds on phytoplankton. Males of the endemic forms may grow to a large size, but the introduced species, includingTilapia rendalli, were heavier for a given length. A reduction in tilapia stocks since 1970 is reflected in experimental catches during 1972‐74 and was attributed to the combined effects of heavy commercial exploitation and a loss of spawning grounds. In the same period a striking increase in the populations of small carnivores,Rhabdalestes leleupiandHaplochromisgr.bloyeti, was recorded. Kully plantivorous and piscivorous fish are absent but omnivores are represented byBarbusspecies andSynodontis punctulatus.Tilapias exhibited a high incidence of nematode infection and the available evidence indicates that fish‐eating birds are important predators of cichlids in Nyumba ya Mu

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00007.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Nyumba ya Mungu reservoir is a man‐made lake in the Kilimanjaro region of northern Tanzania. The commercial fisheries are principally based on the cichlids,Sarotherodon panganiLowe,S. jipeLowe,S. esculentusGraham, andTilapia rendalliBoulenger.Examination of gut contents revealed that the dominant species,S. panganiandS. jipe, fed on the epiphyton attached to the vegetation in the littoral zone,S. esculentuswas a phytoplankton filter feeder, andT. rendalliconsumed macrophytes and associated epiphytes.A fish exclosure quantitatively demonstrated that the epiphyton community was appreciably depleted by the grazing of fish. After 35 days the mean epiphyton density on the submerged surfaces ofCyperus articulatusL. within the exclosure was 285 times 103individuals cm‐2shoot, but only 181 times 103individuals cm‐2shoot on grazed surfaces outside the exclosure. The differences were statistically significant, and corresponded to a difference in biomass of about 6.5 g organic dry weight m‐2lake surface. Vertical profiles of periphyton density onCyperusindicated that fish grazed mainly below a depth of 100 mm from the water surface.The littoral epiphyton → commercial fish food chain, which may be unique, is considered to predominate in Nyumba ya Mungu, and is compared with the major food chains of commercial fish in some other African natural and man

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00008.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Hydrobiological events in Nyumba ya Mungu reservoir, a recent man‐made lake in Tanzania, are reviewed in the light of those described for larger impoundments in other parts of Africa. An initial phase of rapid eutrophication and of high fish production has been replaced by a slower stabilization phase. At present the inflowing rivers supply a nutrient rich water and the level of primary production remains high. In spite of the risk of an encroachment ofTypha domingensisacross the shallow end and events associated with overfishing, the lake retains most of the essential requirements to continue as a useful tilapia fishery. The introduction of new fish into the reservoir, to fill gaps in the trophic structure of the fish community is not recommende

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00009.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00001a.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY