Current Trend of Water Hyacinth Expanation and Investigation of Possible Cause for Water Hyacinth Using Remote Sensing in the Case Study of Lake Tana, Ethiopia

Abstract Lake Tana is facing a big problem with water hyacinth invasion since September 2011 of which it is worst for lakes in the world that invades vast area of lakes with in limited period of time if it does not control properly. Water hyacinth is an invasive and free-floating water plant that grows into large dense vegetable mats blocks transportation of boats and sun energy transmission into Lake Bottom. Since its official recognition, GPS have been used in order to delineate the infestation on the lake, but using GPS for infestation mapping is not time and cost effective, and note safe for data collectors. Considering this reason, this study focuses on mapping of water hyacinth infestation coverage area and analyzing its possible cause on Lake Tana by applying satellite imagery and nutrient level of it. In this document, Landsat 7ETM+ and Landsat 8 images were used with the conversion of DN values to TOA reflectance, and TOA were used to evaluate different spectral indices like NDWI and NDVI. These indices with dynamic threshold increasing between class variance were used to map potential water hyacinth infestation area from 2011 to 2018, and NDWI used to discriminate Lake Tana from its surrounding background feature while NDVI was used to separate open water surface from aquatic vegetation coverage areas. In addition to these indices, thermal band of Landsat images were used to discriminate water hyacinth from other features. The accuracy of satellite image classification on this study was evaluated using error matrices and achieved with the best overall accuracy and Kappa coefficient (K). Total nitrogen concentration was increased from dry month to wet month and total phosphorus was increased from wet month to dry month and potential water hyacinth was greatly found where nutrient level was highly available. To reduce infestation rate of its special soil management practice applies to reduce nutrient has to implement. In addition, there has to be buffer zone for the lake and recessional agriculture has to be stopped.