Conserving rivers

Chiredzi and Runde Rivers

The Chiredzi River forms the western boundary of Malilangwe, with the HVGS on the opposite bank. Of the 38 vegetation types at Malilangwe, the riparian and aquatic habitats of the Chiredzi River are arguably the most important in terms of the biodiversity and density of wildlife they support. The riparian forest found along both banks provides nesting sites for Pel’s fishing owl, black sparrow hawk, African hawk eagle, African goshawk, crowned eagle, white backed vulture, hooded vulture and Verreaux’s eagle owl. A number of these species are of high conservation importance. In addition, this habitat offers suitable nesting opportunities for lappet-faced and white-headed vulture, both of which are becoming increasingly rare in southern Africa.

Parrots, especially brown-headed parrots, are becoming a conservation priority in southern Africa because of harvesting for the pet trade. Their presence at Malilangwe and in the HVGS is owed almost exclusively to the riparian habitat along the Chiredzi River, which is used for both foraging and nesting. Consequences of degradation of the riparian forest for this species are therefore obvious. The shallow pools and reed beds provide habitat for high profile conservation species such as saddle-billed, woolly-necked, and yellow-billed storks. The riparian and aquatic habitats support at least 12 species of mammal. In particular, the riparian habitat provides a very important source of grazing for elephant bulls during the wet season and, in so doing, helps to buffer the woody vegetation of the other habitat types from damage by elephants. In addition, the Chiredzi River is the most important source of drinking water for wildlife both at Malilangwe and within the HVGS. This is especially true for large herds of buffalo and elephant because their water requirements are not satisfied by the small artificially supplied pans found away from the river.

Shallow pools and flanking reed beds of the Chiredzi River Given the above, any changes that negatively impact the Chiredzi River and its associated habitats will greatly reduce the diversity of wildlife supported by the area. Unfortunately, the ecological integrity of the river is threatened by polluted irrigation return flows from nearby sugar cane fields. To determine the extent of this problem, seasonal changes in water quality and the abundance and diversity of macroinvertebrates were studied in the Chiredzi and Runde Rivers between November 2009 and February 2010 (Nhiwatiwa et al. 2017). The quality of the water in the rivers was significantly impacted by irrigation return flows, and this had lowered the abundance and diversity of macroinvertebrates in the system. Macroinvertebrates are a primary source of food for many of the higher order animals living in aquatic environments, and a reduction in their diversity has a negative cascading effect on overall ecological health. The volume of polluted water entering the rivers could be reduced by improving the efficiency of the flood system that is currently used to irrigate the sugar cane fields.