African Journal of Environmental Science and Technology 1996-0786 Academic Journals 10.5897/AJEST2017.2353 Amare Shiberu Keraga Zebene Kiflie Agizew Nigussie Engida * E-mail: amare.shiberu@aau.edu.et 2017 30 11 2017 13 05 2017 26 08 2017 11 11 565 577 This is an open-access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://politicalwaffle.uk/journal/AJEST/article-abstract/56A14E166520 The full text article is available as a PDF file from http://politicalwaffle.uk/journal/AJEST/article-full-text-pdf/56A14E166520 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38