Seasonal variation of Water Hyacinth in Lake Koka, a part of Awash Basin and Lake Ziway (Ethiopia)

Abstract

Water hyacinth is an invasive weed that poses a significant threat to the ecosystem and human well-being in Ethiopia. It has invaded Lake Koka and Lake Ziway, substantially decreasing water availability and sustainable water biodiversity in Ethiopian lakes. Although the threats and effects of this weed are well-documented, its distribution is not well understood. Therefore, the main objective of this study was to predict the coverage areas of the water hyacinth over the surface of the lake using the geographical information system (GIS) - based multi-criteria evaluation technique (Sentinel-2 image). Field collections were conducted in Lake Koka, a part of the Awash Basin, and Lake Ziway during the wet and dry seasons of 2020. During sample collection, the coverage of water bodies was inspected for water hyacinth infestation, and GPS readings were taken at various points while in the water. Multivariate statistical classifier was used to classify various land cover features. This classifier was then used to map the spatial distribution of water hyacinth and determine the accuracy of the classification. The results of the study found that during the dry season, the area of Lake Koka covered by water hyacinth ranged from 1455.39 ha (3.87%) of the lake area to about 4678.06 he (12.44% of the lake area) during the rainy season. Similarly, in Lake Ziway, the area covered by water hyacinth ranged from 6526.30 (10.014%) of the lake area during the dry season to about 7424.05 hectares (11.39% of the lake area) during the rainy season. According to the study, during the rainy season, a considerable portion of Lake Koka and Lake Ziway becomes covered by water hyacinth, which is detrimental to water biodiversity and socioeconomic development. The study revealed that there was a decrease in the area covered by water hyacinths in agricultural land, water, and bare land. To prevent these adverse effects, it is recommended to restore healthy land use and regularly assess the growth of the weeds.