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An assessment of plankton diversity as a water
quality
indicator in small man-made reservoirs in
the Mzingwane Catchment, Limpopo
basin,
Zimbabwe
B y
Lefranc BUSANE Basima
A thesis submitted in partial fulfillment of the requirements for
the degree of Masters in Integrated Water Resources Management
University of Zimbabwe Department of Civil Engineering
AN ASSESSMENT OF PLANKTON DIVERSITY AS A WATER QUALITY
INDICATOR IN SMALL MAN-MADE RESERVOIRS IN THE MZINGWANE CATCHMENT, LIMPOPO
BASIN, ZIMBABWE
By
Lefranc BUSANE Basima
A thesis submitted in partial
fulfillment of the requirements for the
degree of Masters in Integrated
Water Resources Management
Supervisor: Prof. B. Marshall
Co-supervisor: Dr. A.
Senzanje
Department of Civil Engineering
University of Zimbabwe
ABSTRACT
Land use changes are believed to have considerable impacts on
water quality of reservoirs, which is at present a global issue considering its
implications to humanity. This thesis reports on a study carried out in the
southern part of Zimbabwe in the Mzingwane catchment, Limpopo basin to
investigate the impacts of land and water use on the water quality and
ecosystem health of eight small man-made reservoirs. Four reservoirs were
located in communal lands while the remaining four were located in a National
Park (Matopos) considered pristine. Plankton community structure was identified
in terms of abundance and diversity as an indirect assessment of water quality
and ecosystem health. In addition, phosphorus, nitrogen, pH, transparency,
electroconductivity and hardness were analysed. The results obtained indicate
that the communal lands' areas have not gone through major land and water use
changes that impact on the quality of reservoirs since no significant
difference was obtained between communal lands and the National Park in terms
of plankton community (P>0.05). Though the highest phytoplankton abundance
was observed in April, February showed the highest number of taxa (highest
diversity). Chlorophytes was the major group in both periods with 29 genera in
February and 20 in April followed by Diatoms with 17 genera in February and 12
in April. The zooplankton community was less diverse and less abundant and did
not show any seasonality pattern. Normal levels of phosphorus (0.022#177;0.037
mg/l) and nitrogen (0.101#177;0.027 mg/l) were obtained and comply with the
natural levels in fresh water and WHO guidelines for drinking water. The
transparency of water was very low (ca. 27 cm secchi depth) in 75% of the
reservoirs with some having a whitish (milky) colour with a likely effect of
reducing light penetration and therefore photosynthesis in addition to low
nutrient levels. The thesis concludes by acknowledging an acceptable status of
the communal lands vis-à-vis the water quality and ecosystem health of
reservoirs but urges water managers to continuously monitor these multipurpose
reservoirs in order to be assured of their quality as well as to prevent
possible detrimental land and water uses.
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