REMOTE & PROXIMAL SENSING FOR THE STUDY OF ANTHROPOGENIC STRESS ON LAKE ABIJATA

ABSTRACT

Lake Abijata is located some 225 kms south of Addis Ababa. Lake Abijata is one of the quartet lakes which constituted the single macrolake in the pleistocenic period. The lake is an endorheic one with a centripetal drainage. Owing to the introduction of agro-industrial activities in the Ethiopia Rift, the lake has been suffering from chronic anthropogenic stress. In order to overhaul the degree of anthropogenic stress within the lentic environment and at the catchment, a synergy of remote and proximal sensing techniques were applied. To take a diagnosis on vegetation removal from the catchment and the park, the Karhunen-Loeb Transformation, the Hadamard Transformation, Tasseled Cap Transformation and the Normalized Difference Vegetation Index were applied. To treat eutrophication as an ecological problem of the lake's ecosystem, two new proposed techniques were applied, namely the Lacustrine productive index and proximal sensing using Grating spectroradiometer GIS analysis.

Based on the findings of the study, Lake Abijata's catchment has already become bold due to forest clearance. Forest removal is fast encroaching upon the Abernosa Ranch and on the National park. The surface area of Lake Abijata's shrinkage is scaring. The water column is showing a similar response. From 14 mt. in the seventies, it is less than 8 mt. at present. This is mainly attributed to anthropogenic causes i.e., Soda-ash extraction and irrigation work at Ziway. To a certain extent, climatic factors also exacerbate the shrinkage.

Based on the application of the proposed new techniques, Lake Abijata is eutrophic. The expansion of tillage and animal husbandry, the high WL ratio, basin morphometry, nutrient influx via the three rivers were found to be the causal factors of its eutrophication. Eutrophication is one of the most pervasive pollutants of a lentic environment. To reinstate the lake ecosystem to its pristine status, different ameliorative measures were suggested. So long as the PH value of Shalla and Abijata is the same, the soda-ash plant must be transferred to Shalla. This is mainly due to the fact that, Abijata is eurtophic, and pigmented. The soda-ash crystal contains green hue. Secondly, Shalla's water column is 266m which guarantees extraction for centuries. Prohibition of the adjacent land as cattle feedlot and farmland must be enforced. Forest abuse, especially charcoal burning at the catchment and in the National Park must be halted. Abijata may be used as algal culture center for the nation to supplement ailing agriculture in the country. Food tablets produced from edible algae may be effective panacea during spells of drought. Algal food packages are important substitutes for bulky grain. In terms of their preparation, transportation, the amount of calories which can be generated, etc, algal tablets are eye popping solution in the nearest future.

Note: Only a manuscript is available at the Department of Mines, Water and Energy, ESTC. The final technical report has not been submitted yet.

(Report 1999)

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