Remote sensing for monitoring of water hyacinth infestation at the Source Lakes of the Nile

The two major tributaries of the Nile, Blue Nile originating in Lake Tana (Ethiopia) and the White Nile originating in Lake Victoria (Uganda, Tanzania, Kenya). Besides serving as sources for the Nile water, these lakes play fundamental roles in contributing to socio-economic as well as water and aquatic biota resources. Both of these lakes have been severely affected by water hyacinth (Eichhornia crassipes), an invasive plant species that modifies ecosystem functioning in aquatic environments. In this study, we take a closer look at the rate of expansion and seasonal dynamics of water hyacinth in the Lake Tana, a UNESCO biosphere reserve, using satellite imagery and remote sensing techniques. We computed Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) using 30-meter resolution multispectral satellite data derived from Landsat 7. Using these indices, we investigated changes in vegetation and water dynamics from 2010 - 2020 with ground-truthing data identifying locations of water hyacinth infestations. Using the drivers, pressures, state, impact, and response (DPSIR) assessment framework, we then identified various social, economic, and environmental pressures and impacts of water hyacinth on the Lake ecosystem. Preliminary results show that, despite some seasonal shrinking of water hyacinth during the study period, either due to manual removal or due to the lake water dynamics, the overall areal coverage expanded, covering about 0.5% of the total lake area in 2020. The water hyacinth infestation is also observed to increasingly expand to newer corridors of the Lake environment. In search of causes and potential solutions, we identify major socio-environmental and biophysical drivers including land-use and land cover change, land degradation, soil erosion, and urbanization. Here, we also present the utilization of state-of-the-art remote sensing techniques and satellite products for detecting and monitoring invasive aquatic weeds particularly in remote and data scarce regions. Furthermore, we argue that the long-term solution essentially requires an integrated catchment management approach which combines land and water managements for an effective water hyacinth control in the Lake Tana biosphere.