Bull. Org. mond. Sante' 1964, 30, 389-400 Bull. Wld Hith Org. | Observations on the Distribution of Freshwater Mollusca and Chemistry of the Natural Waters in the South-eastern Transvaal and Adjacent Northern Swaziland* C. H. J. SCHUTTE I & G. H. FRANK' An extensive survey of the molluscan fauna and of the chemistry of the freshwaters of the Eastern Transvaal Lowveld has revealed no simple correlation between the two. The watersfall into fourfairly distinct andgeographically associatedgroups chiefly characterized by their calcium and magnesium content. The frequency of the two intermediate hosts of bilharziasis was found to be roughly proportional to the hardness of the water but as the latter, in this area, is associated with altitude and this again with temperature and stream gradient it is thought highly probable that the distribution of these snails is the result of the interaction of a complex offactors. None of the individual chemical constituents in any of the waters examined is regarded as outside the tolerance range of these snails. It is also concluded that under natural conditions this area would have had few waterbodies suitable for colonization by these snails but that the expansion of irrigation schemes has created ideal conditions for their rapid establishment throughout the area. Primarily, the survey reported here was intended DESCRIPTION OF THE AREA as an attempt, not so much to correlate the presence The area (Fig. 1) is bordered by the Drakensberg of snails and the chemical composition of the waters escarpment in the west, the Lebombo range in the in which they occur, as to compile general ecological east, by the Sabie river in the north and the Komati data essential to further research work on the and Black Umbuluzi rivers in the south. A portion intermediate hosts of bilharziasis. The work was of the game reserve north of the Sabie river and an extension of the programme initiated by de Meil- part of the Komati valley south of the Komati river lon and others (1958), undertaken to form a baseline (west of Diepgezet) are also included. The greater for future hydrobiological research. Although part of the area is known as the Lowveld and Middle- laboratory work (Chernin & Michelson, 1957; veld of the Transvaal and Swaziland. Varying in Wright, 1960) has demonstrated the marked influence altitude from about 500 feet (150 m) in the east to of dissolved salts on snail intermediate hosts, above 6000 feet (1830 m) in the west, the country is attempts to find a simple correlation between local generally broken with steps, basins and deep valleys. snail distribution and chemical properties of natural The vegetation consists mainly of Lowveld tropical waters have been very disappointing (de Meillon bush and savannah and inland tropical forest types. et al., 1958). This is probably due to the very wide All the larger rivers originate on the Highveld west actual or incipient tolerance range of these animals of the Drakensberg and flow eastwards into the (Hunter, 1961) and the fact that local waters show Indian Ocean. few extremes of the sort found by Sioli (1953) in The climate is subtropical with mild winters and South America. hot summers. The mean annual rainfall increases from 500 mm to 1500 mm from east to west respec- * Published with the permission of the South African tively with almost all the rain falling during the six Council for Scientific and Industrial Research. summer months from October to March and with I Research Officers, Bilharzia Research Unit, South African Council for Scientific and Industrial Research, maximum precipitation in January or February. Nelspruit, Eastern Transvaal, Republic of South Africa. Generally temperatures increase eastwards. While 1406 - 389- 390 C. H. J. SCHUTTE & G. H. FRANK the larger waterbodies have a more or less stable Flowing waters temperature, small creeks show large diurnal Perennial streams. The flow in these varies con- temperature fluctuations (up to 13°C). The highest siderably during the year. They have been roughly water temperatures usually occur in January (up divided into four categories according to the volume to 35°C) while the lowest recorded water temperature of water they carry. was in July (10°C). (a) Rivers with a mean annual run-off (expressed Fig. 2 shows that most of the area consists of as even flow) of between 500 and 1500 cubic feet per Old Granite and Gneiss bordered by the more second (ca. 14 160 to 42 500 litres/second). Transvaal on the west and the soluble System 5 Karroo System of volcanics and sediments on the (b) Streams with a flow of between and 100 east. Between these two systems a series of geolo- cusecs (ca. 142 to 2830 litres/second). gical formations, some with a relatively high mineral (c) Creeks with a flow of less than 5 cusecs (ca. content (e.g., Jamestown Igneous Complex), runs 142 litres/second). diagonally from south-west to north-east. (d) Irrigation canals with a flow of up to 25 cusecs For the sake of convenience the area has been (ca. 707 litres/second). They are mostly mud-lined; divided into three topographical regions and further cement-lined canals are the exception. subdivided according to the river systems. Tenmporary streams. These are more directly Western Zone dependent on local rainfall and cease to flow in the This is a very mountainous area. The eastward dry season, leaving separate pools in an otherwise protrusions of the escarpment form watersheds dry river bed. which separate four distinct transverse basins: (a) Interrupted streams are semi-perennial. They (a) Elands-Crocodile river system, may cease flowing only at the end of the dry season (b) Sabie river system, when a string of separate or near-separate pools (c) White-Crocodile river system, remain. (d) Kaap river system. (b) Intermittent streams flow only during the wet season. Residual pools form after the floods have South-Eastern Zone subsided. These streams were sampled as pools This zone is roughly separated from the Western only and as such are more comparable with the Zone by a mountainous watershed between Barber- following section during the dry season. ton and Piggs Peak. It is mainly flat bush country. Except for the mountainous western part near Stagnant waters Piggs Peak, it lies entirely in the Lowveld. Four Seepage pools. Such pools resemble the residual main river systems drain the area: pools found in intermittent streams but have no (a) Eastern Crocodile river system, direct connexion with streams and are filled to (b) Lomati river system, some extent by surface water but mainly by ground water. (c) Komati river system, (d) Umbuluzi river system. Large catchment dams. These are built privately are built across North-Eastern Zone (southern part of Kruger by individual farmers. The walls National Park) an existing river or stream. This is semi-arid bush country lying entirely in Small catchment dams. These, too, are built the Lowveld and separated from the above zones privately by individual farmers. The walls are either by the Nsikazi river in the west and the Crocodile built across streams or are placed so as to receive river in the south. Except for these and the Sabie catchment water. there are no permanent running and Sand rivers, These are used for irriga- waters. Ground storage dams. tion and are filled by canals or pumps from streams CLASSIFICATION OF WATERBODIES or rivers. To simplify the description of waterbodies, Cenment reservoirs. Cement reservoirs are filled Watson's (1958) system has been adapted to local by pumping from boreholes, streams and rivers conditions. and are used similarly to ground storage dams. FIG. 1. SOUTH-EASTERN TRANSVAAL AND NORTHERN SWAZILAND, SHOWING ZONAL DIVISION DESCRIBED IN THE TEXT MAG. NORTH TRUE NORTH Wr I LESS THAN I OOO FEET ca. 305 METRES) -:::-:-:-:BETWEEN 1000 MD 40 FEET ( ca. 305-1220METRES) 40 FEET (ca. 1220 METRES) .AND HIGHER S 10 Km FIG. 2. GEOLOGY OF THE SURVEYED AREA (SIMPLIFIED)a MAGK. NORTH TRUE NORTH :--SEDIMIENTS KAROO SYSTEM . .VOLCANICSI ONVERWACNT I SERIES ISWAZILAND FIG TREE I SYSTEM SERIES I |HOOP OLD GRANITE AND fy -0 W GNEISS 11111MOODIES SYSTEM I JAMESTOWN IGNEOUS COMPLEX TRANSVAAL SYSTEM / I) mile 10 K-- a Adapted from Hall (1918). FIG. 3. DISTRIBUTION OF THE INTERMEDIATE HOSTS OF BILHARZIASIS IN THE SURVEYED AREA a AACH. WORTH TRUE MONTH * BIOMPHALARI* P. PFEIFFERI o BIOMPHULARIA P. BRIDOUXIAM A BULNUS (PH.) AFRICANUS A BULINUS (PH.) GLOBOSUS X NO BIOMIPHALARIA OR B. (PHYSOPSIS) FOUND 10 Miles 10 Km a The numbered areas are those in which either Bulinus (Physopsis) predominated in the running waters (1-4) or Biomphalaria was the most common in ground dams (5-8). See the text and Table 1. FIG. 4. DISTRIBUTION OF SOME SNAIL TYPES FOUND TO BE LIMITED TO PARTICULAR AREAS MACK. NORTH TRUE NORTH < to | ~~~~KOMTIPOOT HA l~~~~~~~~~~~E BUIUSFRSAI 08 LYMNAEA COLUMELLA _f m> _ X / f *~~~~~~~~~BULINUS(B.)TROICUS 9 t < 7 ^~~~~~~~~~~~~~BULINUS(B.)NATALENSIS UNIDENTIFIED / , ni *~~~~~~~~~~~~BULINUS (B.) °~~~~1 BULINU-S FORSKLII S OPERCULATES EXCL. MELAI X MELANOIDES VICTORIAE (A, O *BIVALVES| t 1OMSKm 101Cm~~~~ FIG. 5. DISTRIBUTION OF WATER SAMPLING POINTS WITH INDICATION OF THE WATER CATEGORY .MAGN. RTH TME NOTH O VERY SOFT * SOFT [] HARD * VERY HAD , 10 S" .__A- 10 is MOLLUSCAN FAUNA AND CHEMISTRY OF NATURAL WATERS IN S-E TRANSVAAL 391 METHODS USED IN THE CHEMICAL ANALYSES No. 1 filter-paper were determined by the phen- OF WATERS anthroline method (American Public Health Associ- ation, 1955); expressed as p.p.m. Fe. Samples were taken as recommended by the Ameri- can Public Health Association (1955). For complete Manganese. Determined by the periodate method analysis at least 4 litres were collected in dark- with the Hellige Aquatester; expressed as p.p.m.