摘要:

There are two groups of southern African lakes, a southern group made up of the Wilderness lakes and a north-eastern group comprising lakes on the Natal, Zululand and southern Moçambique coastal plain. Bathymetric maps are presented for representative lakes of these two series. There appear to be three types of lakes with respect to origin. Most of the lakes represent drowned valleys associated with river systems. Evidence is presented to show that St Lucia, although 1 to 2 m deep at present, was originally much deeper. The narrow coastal lakes of southern Moçambique are interpreted as low-lying land inundated as a result of rise in sea-level. The third type of lake is typified by Rondevlei at Wilderness; this lake apparently originated as a deflation basin.

ISSN:0035-919X    

DOI:10.1080/00359197509519440

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Lake Nhlange (KwaZulu, South Africa) is connected to the sea through the Kosi estuary and has a salinity between 36%0and 5%0. The benthos of the lake was sampled at approximately six-monthly intervals from July 1965 to January 1969. The substrates are mainly sandy in shallow water and also on steeply sloping profiles even in the deepest water of 30 m. Flat areas are mainly silty. In December 1965, following the closure of the estuary mouth and severe rains, the lake level rose to about 2 m above its normal level. Although the salinity changed little (5%0, to 3%0), quantities of peat-stained water and detritus were brought into the lake. A waning pattern of low oxygen conditions below about 12 m in the hot season, followed by reasonably well-oxygenated conditions in the cold season, was found. Particularly severe oxygen depletions were discovered at the mud water interface, even where well-oxygenated conditions pertained in the open water column at equivalent depths.

ISSN:0035-919X    

DOI:10.1080/00359197509519441

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The limnology of Lagoa Poelela in southern Moçambique was investigated in July 1973. This lake is connected to the sea via a 75 km long channel, the area is 65 km2, it has a mean depth of 13,7m and a maximum depth of 24 m. The water was saline (8%0) and the major ions, with the exception of sodium, were in the proportions expected of diluted sea water. The concentration of sodium was twice as high as expected; this sodium enrichment has been found in other coastal lakes. Temperatures were relatively uniform from the surface to the bottom and the oxygen saturation at 20 m was 80% of the surface value. Light penetration was higher than for other southern African lakes and at 22 m was 3% of surface illumination. Aquatic macrophytes were absent from shallow water in the main lake, only being found deeper than 3 metres wherePotamogeton pectinatusandNaias? marinawere common.Naiaswas found to a depth of 10 m andCharasp. to 12 m. Only 11 species of fish were found. The fish population was dominated by the cichlidsTilapia rendalliandT. mossambicaalthough some estuarine species were also found. It is suggested that the domination of this brackish lake by cichlids reflects a general tendency for cichlids to increase in numbers in estuarine systems which become isolated from the sea.

ISSN:0035-919X    

DOI:10.1080/00359197509519442

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The benthos of Lagoa Poelela (Mozambique) was sampled in July 1973 with a Van Veen grab. The substrates of the lake were sandy between o m and about 3 m. Thereafter sand and silt were common to about 9 m and mainly pure silt below this depth.

ISSN:0035-919X    

DOI:10.1080/00359197509519443

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The Mgobezeleni lake-system in Zululand is described and a checklist of decapod crustacea, molluscs and fish presented. The biota consists of freshwater, estuarine and marine forms. Several uncommon or rare species were found. The effect of various man-made changes on the system is assessed, with particular reference to the mangrove community. Constantly high water levels and excess fresh water have decimated theBruguieria gymnorhizaforest and associated fauna respectively.

ISSN:0035-919X    

DOI:10.1080/00359197509519444

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

St Lucia Lakes (Zululand, South Africa) were sampled with a Van Veen grab in January 1972, July 1972, and January 1973. The system had high salinities at the commencement of the programme (70%0-80%0False Bay, 55%0-60%0North Lake, 45%0-58%0South Lake) which quickly dropped to less than sea-water values in the first six months. The January 1972 samples showed that only a fewPolypedilum(Chironomidae) survived in False Bay, while a very reduced faunal list was shown for North Lake (9 sp.). Nevertheless South Lake showed a fairly complete faunal list (21 sp.). By July 1972 nine species were recovered in False Bay, 18 in North Lake and 23 in South Lake, indicating reinvasion consequent upon dilution of the salts in the water. No great change was shown by the result of the January 1973 samples.

ISSN:0035-919X    

DOI:10.1080/00359197509519445

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

ISSN:0035-919X    

DOI:10.1080/00359197509519446

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor