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

V. Conclusion

The results of an assessment of plankton diversity as a water quality indicator of small reservoirs in communal lands and in the National Park (Matopos) were presented. The study hypothesized that water in small reservoirs in communal lands might be turbid but richer in nutrients as an effect of land and water use. The expected nutrient richness would in turn influence phytoplankton abundance, which would therefore be expected to be greater and less diverse. And a second hypothesis followed by expecting reservoirs in the National Park to have less nutrients but more diverse plankton community than those in communal lands.

This study found that water quality throughout the study area was at acceptable levels, and did not significantly differ between National Park and communal lands. This finding was contrary to expectations, and indicates that water conditions may be better in areas of human influence than currently thought. This pattern is attributed to limited upstream development, a condition that should be maintained to ensure the integrity of the aquatic ecosystems. High levels of vegetative cover were also thought to mitigate the impacts of local conditions on water bodies, and should be preserved to protect these systems from future change.

A third hypothesis expected no seasonal changes in plankton community structure of the studied small reservoirs. Contrary to this expectation, the diversity and abundance of plankton communities in the study area were influenced by an informal sub-seasonal rainfall patterns. Species composition of both phyto- and zooplankton were similar to expectations based on other ponds and lakes. However, species of phytoplankton were found that could potentially develop into toxic algal blooms with changes in water quality. Zooplankton species abundance was at a lower level than expected, possibly due to the presence of planktivorous fish in the reservoirs.

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