Assessing the effects of sand mining activities on wetland loss in Lwera wetland system using GIS and remote sensing, Lake Victoria Basin - Central Uganda

Abstract

While many wetlands in the central region are being degraded due to encroachment, Lwera wetland system is facing degradation from over harvesting of natural resources, sand in particular. The main objective of this study was to generate the total wetland change from the year 2010 to 2019. The study utilized three sets of Landsat TM/ETM+/MSS temporal images (30 m) of 2010, 2013 and 2019. The classification procedures were carried out using an arc GIS software version 10.3. The classified images were validated in a ground-truthing exercise using high resolution imagery to improve the classification accuracy. Household interviews in Lukaya and Bukulula sub counties were conducted to generate information on the factors that influence people into sand mining and the observed impacts of sand mining activities on the wetland. The major factors included poverty, high demand for sand, high value of sand, land tenure system, availability of sand deposits and poor law enforcement. Majority (93.3%) of the local people perceived wetlands in the area to have undergone high degradation within the last 19 years, and to have declined in quantity and quality of vegetation, soil fertility and water quality. In the period of 2010 to 2019, the area experienced a decline in the wetland coverage changed by 44.2%, from 102.67 to 58.45km2 and grassland by 14.78%. This was in contrast by an increase in coverage ofsand mining sites by 53.1%, from 1.67km2 to 2.078km2; built-up with 77%, while bushland, mined area, open water and bare ground, by 30%, 0.5%, 2.6% and 43.35% respectively. Fragstats, a spatial analysis tool was used to assess the impact of sand mining on the diversity of the wetland vegetation. The number of patches (np) for sand mines increased from 6, 23 and 104 in 2010, 2013 and 2019 respectively due to increase in sand mining areas. The np for wetlands increased from 860 to 1743 then decreased to 713 for the years 2010, 2013 and 2019 respectively and its, pd increased from 2.8 in 2010 to 5.6 in 2013 and then decreased to 2.3 in 2019. Pland of the wetland also continuously reduced from 33.8 to 32,6 and 18.9 for the years as a result of increasing sand mining. Np for grasslands increased from 1053 to 2122 in 2013 and later decreased to 1453 in 2019. The pd increased for 3.4 in 2010 to 6.9 in 2013 and reduced to 4.3 in 2019. The pland also reduced from 23.5to 19.8 in 2013 and the slightly increased to 20.2 in 2019. The mps reduced from 6.9 in 2010 to 2.9 in 2013 and then increased to 4.3 in 2019. The landscape in 2013 was most fragmented and had the most isolated patches. However, there was a slight regeneration in 2019. The lpi however, continued to reduce from 18.7 to 17.69 and 10.7 in 2010, 2013 and 2019 respectively, implying that the landscapes became more heterogeneous with time.