Memoire Online - An Assessment of plankton diversity as an water quality indicator in small man-made reservoirs in the Mzingwane catchment, Limpopo basin, Zimbabwe

This study was carried out in the southern part of Zimbabwe (Fig. 2.2) in the Mzingwane catchment, within the Limpopo basin. The Limpopo basin (Fig.2.1) covers up to 1.3 % of the African continent. The Mzingwane catchment is one of the seven catchment areas that have been demarcated by the new water legislation of 1998. The six other catchments are Gwayi, Sanyati, Manyame, Mazoe, Save and Runde. The Mzingwane catchment is located in a semi arid region that is characterized by highly variable rainfall concentrated in one rainy season, separated by relatively long dry seasons (Lawrence and Hasnip, 2004). The Mzingwane catchment is divided into four sub catchments, which are Upper Mzingwane, Lower Mzingwane, Mwenezi and Shashe (Fig. 2.3). The annual rainfall in the Mzingwane catchment ranges from 300mm in the south to 635mm in the north (Table 2.1). Temporal distribution of rainfall follows the general pattern of southern African region. The coldest month (July) when minimum temperature goes below 0^oC as well as the hottest month (October) are both comprised in the dry months that go from April to October. The hottest areas are found around Beitbridge (Conley, 1996 in Mwenge, 2004). The Mzingwane catchment has three major rivers: the Shashe, Umzingwane and Mwenezi. These rivers flow in the southeastern direction into the Limpopo River carrying and depositing sediments along their courses. There is almost no flow in the dry season and riverbeds are sandy alluvial of considerable thickness providing big storage of water³. One of the major features of aridity of the catchment is that the mean annual potential evapotranspiration rates are higher than the mean annual rainfall (1800mm as compared to 465mm). This status indicates low runoff generation and aquifer recharge (Mwenge, 2004).

					min. max. mean
Botswana	581730	80118	19.9	13.8	290 555	425
Zimbabwe	390760	51467	12.38	13.2	300 635	465
South Africa	11221040	185298	4631	65.2	290 1040	590
Mozambique	801590	84981	21.1	10.6	355 865	535
For Limpopo		401864	100.0		290 1040	530

The Limpopo River in southeastern Africa, rising as the Krokodil River in the mountainous Witwatersrand region of northern South Africa, is a trans-boundary river shared by Botswana, South Africa, Mozambique and Zimbabwe. The Krokodil River then becomes the Limpopo and continues northeast along the border between Botswana and South Africa, then east along the border between Zimbabwe and South Africa. It flows southeast through southern Mozambique before entering the Indian Ocean near Xai-Xai. The Limpopo river is one of the most anthropogenically impacted Rivers in the Southern African region and has vast tracks of its length covered by sand and silt and seasonal flow only during the rainy season which spans from November to April.

The eight selected small reservoirs are located in the Mzingwane catchment, with four in the Matobo (Matopos) National Park and four in the Insiza district around Avoca Business centre (Fig.2.4). The National Park is located 34 km south of Bulawayo, at 28^o Longitude East and 20^o Latitude South. It represents one of the major tourist attractions in Zimbabwe. It contains majestic granite scenery; the landscape has been carved out from an almost flat surface of granite by millions of years of weathering, resulting in great «whalebacks» and domes, and castle-like formations (Tregold, 1996). The vegetation in the park is quite different from that of the surrounding countryside, and supports many species of animals and prolific bird life. The park is comprised of a game reserve and a recreational park, both of which contain a number of small reservoirs. The recreational park (western part) is separated from the game reserve (eastern part) by the main road Bulawayo-Kezi. Mpopoma and Chitampa reservoirs, in the game reserve, are respectively located at 7 and 2 km from the entrance gate. In the recreational park, Mezilume reservoir is located at approximately 5 km from the game park entrance gate while Maleme is at 7 km. Mezilume and Maleme are located in the so-called Central Wild Area while Chitampa and Mpopoma are located in the Whovi Wild Area (Game Park). Fish are abundant in most of these reservoirs. Avoca Business Centre (in Insiza district) is located at 127 km east of Bulawayo and its geographic coordinates are 20^o 47' latitude south and 29^o 31'longitude east. Fig 2.3 and 2.4 show the location of selected small reservoirs.

A summary of the studied reservoirs located in communal lands is presented in Table 2.2. The main users of the reservoir are farmers located mainly downstream of the dam. Sibasa is an old perennial reservoir known to have survived the drought period being recharged by groundwater.

Table 2.2. Some characteristics of small reservoir the studied reservoirs in the communal lands, Insiza district, Zimbabwe.

Characteristics

Reservoirs

Makoshe

Sibasa

Denje

Dewa

Location

Capacity (m³)

Type

Construction period

Nature

Ward 6 926,000 Earthy 1997-98

Ward 11 -

Earthy

1945-50

Perennial

Ward 7

- Earthy

Not perennial

Ward 7

- Earthy

Not perennial

2.1.1 Land and water use in the communal Lands

Makoshe reservoir is located in a relatively flat area and its water occupies a large surface. Many standing trees are still present in the reservoir showing that the area was vegetated before the construction of the reservoir. The substrate is mainly composed of dark grayish sand (Table 3.2) (expansive and slippery since mixed with clay) and the littoral land fairly covered by vegetation. The area may be subject to erosion in time of heavy rainfalls. Big rocks are located mainly along the dam wall and some are scattered in the reservoir. Water from the reservoir is allocated to the following uses: irrigation, domestic, livestock, fishing, garden and drip irrigation. Drip irrigation is pumping water for 18 ha plot for some beneficiaries involved in the construction of the reservoir. Approximately 200 households that belong to two villages, Bambanani-Makoshe and Mbawulo, utilize Makoshe reservoir's water. There are no farms upstream of the reservoir, all the gardens and farms being located downstream of the reservoir. A number of birds were observed belonging to the genus Phalacrocorax, Ceryle, Ceyx, Hirundo and Nectarinia.

The shoreline vegetation of Sibasa reservoir is dominated by Cyperus spp and the Water Clover Marsilea vestita. The water is having a whitish (milky) colour. The reservoir is located at 200 m to the first homestead of Sibasa village that is slightly elevated compared to the reservoir. The reservoir is mainly allocated to livestock use, though it is used as well for domestic purposes and recreation (fishing). No farm is located in the close vicinity of the reservoir. A white granite hill is located upstream of the reservoir. Some trees are found in the surroundings of the reservoir as well as some rocks, which are also part of the substrates in the reservoir. The area has suffered from a shortage of rainfall the whole period except January where 211 mm of rain where recorded (Table 2.3). Few birds belonging to Phalacrocorax sp., and Ceryle rudis were observed actively fishing in the reservoir.

Table 2.3. Rainfall pattern in Filabusi district and Sibasa village area during 2004/2005 (Insiza District)

Area	Oct	Nov	Dec	Jan	Feb	March	April	Total	Mean
Filabusi DA	15.2	0	1.31	112.5	4.5	31	0	164.5	23.5
Sibasa village	0	6	0	211	0	0	0	211	31
Matopos area	-	6.8	163.1	160.9	105.9	55.1	5.5	497.3	82.9

Source: Filabusi District Administration and Meteorological Office in Harare, Zimbabwe

Denje reservoir is mainly located in a rocky and slightly slanted area with a low vegetation cover in its littoral zone (score 2 in Table 3.1). The littoral vegetation includes Cyperus spp, Typha spp. and Phragmites spp. A communal garden is situated about 5 meters away from the reservoir. The garden uses manure as a fertilizer. The littoral soils have a yellowish brown colour and the reservoir water has a whitish brown colour. The highest soil pH value (7.8) of the communal reservoirs studied was recorded at Denje. A small business centre is located upstream of the reservoir at approximately 200 m. This Denje business centre as well as the population of Denje village gets water from the reservoir.

Cyperus spp. is the main constituent of the littoral vegetation at Dewa reservoir with
some areas also covered by Polygonum spp. From previously green during the first
sampling (February), the vegetation at the shore and areas surrounding the reservoir has

decayed. The colour of the waters is gray whitish brown while the colour of dry soils is grayish brown (Table 3.1). The littoral zone is full of dung making reference to the considerable number of cattle (10 heads per 10 m² of littoral area) that is ever grazing in the area. The cattle observed were composed of cows, donkeys, goats and sheep. A small communal garden is located in the littoral zone area at approximately 5m from the water level. Manure is the main, if not the sole, type of fertilizer used in the area. The reservoir' s water is mainly used for cattle and domestic purposes. Some points of cloth washing are also located in the same area. Few fishermen were observed on the reservoir. No bird was observed during the two sampling visits. No human settlement is present upstream of the reservoir that is mostly dominated by rocky hills.

An Assessment of plankton diversity as an water quality indicator in small man-made reservoirs in the Mzingwane catchment, Limpopo basin, Zimbabwe

II. Materials and Methods

2.1 Study area

2.1.1 Land and water use in the communal Lands