The Impact Of Communal Land Use On Dambos In Lower Gweru, Zimbabwe

Abstract

The study investigated how the exploitation of dambos changes their vegetation composition, soil properties and how that will in-turn affect the water quality. Species diversity and evenness ware higher in Madikane (H’ = 2.52, E = 0.69) than Dufuya H’ = 2.14, E = 0.63). There was a significant difference in species composition between Madikane dambo, a protected area and Dufuya dambo, an area impacted by communal agriculture and grazing. Species that were present in Madikane indicated a permanent or semi-permanent wetness compared to species tolerant to arid conditions and indicating disturbance that were present in Dufuya. The arid condition in the outer region of Dufuya indicates a shrinking in size of that dambo. Dambo utilization also indicated a change in dominance from perennials to annuals and an increase in exotic species. There was no significant difference in the physical structure of the soil (% clay and % silt, p > 0.05). A significant difference was recorded in the chemical properties of the soil. There was a wide pH range in Madikane (4.98 – 10.15) than Dufuya (5.26 – 7.86). The organic carbon content was positively correlated with moisture content in Madikane (r = 0.74) and Dufuya (r = 0.88). Organic carbon content was significantly different (p < 0.05) Madikane (3.58 %; 17.67 %) than Dufuya (2.38 %; 7.38 %) both in the outer and central zones respectively. There was a significant difference (p < 0.05) in phosphorus and nitrogen concentrations. Nitrate-N and ammonium-N were higher in the surface zone (0 -20 cm) than the subsurface zone (20 -100 cm) for both dambos indicating leaching of nutrients from the surface zone. Nitrate-N and ammonium-N were higher in Madikane than Dufuya which is a characteristic of soils with more organic matter. Higher levels of phosphorus in Dufuya than Madikane indicates additions through fertilizer application. Phosphorus from soil was exported more readily into water in Dufuya (r2 = 0.52) than Madikane (r2 = 0.24). Leaching of soil nutrients was also shown by an increase in calcium ions in the water in Dufuya (2.23 mg L-1) than Madikane (1.21 mg L-1) which in-turn caused a high conductivity in Dufuya (287 µS cm-1) than Madikane (125 µS cm-1).