Detection of land cover changes around Lake Mutirikwi, Zimbabwe, based on traditional remote sensing image classification techniques

Abstract

Land cover changes around Lake Mutirikwi in 1984–2011 were mapped from Landsat images using traditional image classification methods including the maximum likelihood classifier algorithm. The possibility of mapping the coverage and abundance of surface floating aquatic weeds was also tested. Landsat images from 1984, 1995, 2001 and 2011 were used to compute a normalised difference vegetation index (NDVI), which was then used as a proxy for indicating areas infested by surface floating aquatic weeds. Forest and shrubs covered 310.8 km² in 1984, but had deteriorated by 24.87% to 77.3 km² in 2011, while the area under cultivation increased by 51.44% between 1984 and 2011. Runoff from surrounding farms could be responsible for washing soil nutrients into Lake Mutirikwi, enriching its water. A large aggregation of surface floating aquatic weeds concentrated upstream along tributaries of Lake Mutirikwi, mainly the Mucheke which received sewage from Masvingo town, with less coverage in the central parts of the lake. Vegetation indices such as NDVI proved successful as a proxy for mapping the coverage of surface floating aquatic weeds in Lake Mutirikwi in space and time.

Keywords:

• eutrophication
• land cover classification
• Landsat
• NDVI
• surface floating aquatic weeds